Chapter 510. Disorders Causing Airway Obstruction

It is important to recognize the differences between the pediatric and adult upper airway to fully understand why even a relatively minor obstruction can cause significant airway compromise in children (Fig. 510-1). The pediatric airway is shorter and narrower and the larynx is placed more anterior than in adults.1 The narrowest portion of the pediatric airway is the subglottis, which is below the vocal cords. Therefore, mild edema in this region can result in a large reduction in the cross-sectional area of the airway. The resistance is inversely proportional to the fourth power of the radius of the airway (see Chapter 503). Therefore, even a small decrease in airway diameter leads to a much larger increase in resistance. Young children, and infants especially, have a large tongue in relation to the small oropharynx.1 They also have a larger epiglottis.1 Signs of partial inspiratory obstruction include stridor (a high-pitched sound heard on inhalation), hoarseness, and increased work of breathing (suprasternal and intercostal retractions).2 Stridor can be inspiratory or expiratory, depending on whether the obstruction is supraglottic or subglottic respectively. If the obstruction is severe or near-complete, worsening agitation, cyanosis, and respiratory failure will likely occur. Although acute stridor is usually infectious in etiology, other disorders may be present, especially when symptoms are severe or persistent. This chapter discusses inspiratory airway obstruction of infectious or noninfectious origin.

Noninfectious Causes of Upper Airway Obstruction

Laryngeal Anomalies

Disorders of the upper airway are also discussed in Chapter 371.

Laryngomalacia is the most common cause of noninfectious, persistent stridor in infants. It is characterized by a long, curved epiglottis that folds into an omega shape, with varying degrees of prolapse of the arytenoids during inspiration.3The flaccid supraglottic structures prolapse into the airway, leading to obstruction while breathing in. The inspiratory noise can begin in the first 2 months after birth, and it commonly presents as stridor that worsens with crying and activity; improvement occurs when the infant is placed in the prone position. Diagnosis is usually based on the history and physical examination; however, airway endoscopy is also helpful. The condition usually resolves spontaneously by 12 to 24 months. In more severe cases, surgery (supraglottoplasty) may be necessary.4 Gastroesophageal reflux disease (GERD), has been linked to laryngomalacia, and the possibility of concurrent reflux should be considered and treated.5 GERD can worsen the symptoms of laryngomalacia by contributing to further inflammation and edema of the larynx.

Laryngeal cysts, webs, laryngoceles, and saccular cysts are much less common conditions that can cause airway obstruction.4 Depending on the degree of obstruction, they can present soon after birth. Laryngeal cysts can present with hoarseness and stridor. Saccular cysts are caused by obstruction of the laryngeal saccule opening.4 The saccule is a mucus membrane pouch located between the false vocal cords and the inside of the thyroid cartilage.2 Its function is to moisten the vocal cord surfaces with mucus. The saccular cyst is full of mucus secretions and therefore causes airway obstruction at the level of the vocal cords. Diagnosis is made via airway endoscopy, and treatment requires marsupialization or surgical excision. Laryngoceles are another abnormality of the laryngeal saccule. In this condition, the saccule is filled with air and can compress the laryngeal airway.4 This can cause a weak cry as well as other symptoms of airway obstruction. Evaluation and treatment is similar to that of saccular cysts. Laryngeal webs are rare congenital anomalies that can present in the newborn period if the web is large and cause significant respiratory distress and stridor. The most severe entity along the spectrum of laryngeal webs is laryngeal atresia, which presents at birth and requires immediate intervention with tracheotomyl.4 Treatment includes surgical approaches such as laryngotracheal reconstruction. Infants with congenital laryngeal anomalies should have a genetic and cardiovascular evaluation to screen for other syndromes that may occur in conjunction.2

Thyroglossal duct cysts (originating from the thyroglossal duct) usually present early in the neonatal period. They are most commonly found in the neck but can also be seen at the base of the tongue in the vallecula.4 Stridor, cough, and changes in voice quality can occur. Laryngoscopy confirms the diagnosis, and treatment is surgical.2

Subglottic Lesions

Congenital subglottic stenosis consists of narrowing of the airway lumen at the cricoid region, not thought to be secondary to intubation, trauma, or other acquired causes.4 Depending on the severity, it is commonly diagnosed in the first few months of life. Common presentations include inspiratory or biphasic stridor (stridor that is both inspiratory and expiratory) and recurrent croup. If the stenosis is mild, it may cause symptoms only during times of upper respiratory tract infection.4 Differential diagnosis includes hemangiomas or cysts in the subglottic region. Airway endoscopy is necessary to evaluate the severity of the stenosis and confirm the diagnosis. Surgical intervention such as laser excision of scar tissue and laryngotracheal reconstruction,2 may be necessary for extremely severe cases, but in most children, the symptoms improve as the larynx grows.4 The milder cases are therefore managed conservatively with observation and follow-up.

Subglottic hemangiomas (congenital vascular lesions) are rare but can be life threatening because of their location and size. Symptoms can include recurrent croup, stridor, hoarseness, and cough. Half of these children will also have hemangiomas on their skin.4 Infants will often present prior to 6 months of age, and females are more commonly affected. Diagnosis is confirmed by rigid airway endoscopy.2 Characteristically, hemangiomas enlarge rapidly in the first few months of life, have stable growth from 1 to 2 years of age, and involute by the time the child is school age.2 Corticosteroids are helpful in some, but not all, to hasten regression of the lesion; however, they are not without several side effects. Some patients require tracheotomy to adequately control the airway if the lesion is large, obstructing, and growing.2 Surgical resection may be required for large lesions.4

Tumors of the Upper Airway

Mass lesions and tumors of the upper airway are rare in childhood. Malignancies that affect the head and neck (including the oropharynx) include non-Hodgkin lymphoma, rhabdomyosarcoma, neuroblastoma, and teratoma.2 Airway obstruction may result from external compression or by seeding the oropharynx from another primary site in the head or neck. Management is specific to the tumor type and may include a combination of surgery, chemotherapy, and/or radiation therapy.2

Gastroesophageal Reflux Disease

GERD is associated with or can exacerbate several upper respiratory conditions, including apnea, laryngospasm, spasmodic croup, hoarseness, throat clearing, chronic cough, and stridor.5 Reflux of gastric contents into the laryngopharyngeal region can lead to chronic inflammation and edema. Respiratory symptoms from reflux can occur without the classic regurgitation and irritability during feeds. Parents report that the infant appears happier and has less stridor when in the prone position. GERD often occurs in conjunction with laryngomalacia, and stridor may improve with antireflux medication.5 Apneic episodes in infants should be investigated for the possibility that reflux has a role.5 Animal models have shown that GERD, along with trauma and infection, can lead to subglottic stenosis, and studies in children suggest at least an association between GERD and subglottic stenosis.5 No studies have proven a response to aggressive acid inhibitory therapy but this is often prescribed. Diagnostic testing for GERD may include a pH probe, gastric scintiscan, and esophageal biopsy6 as well as management, are discussed in Chapters 394 and 511.

Vocal Cord Abnormalities

Vocal Cord Dysfunction

Vocal cord dysfunction (VCD), also known as paradoxical vocal fold motion (PVFM), has gained recognition recently as a cause of upper airway obstruction as a result of paradoxical closure of the true vocal folds during inspiration.7 It is most commonly seen in females and historically was thought to be related only to psychiatric or psychogenic disorders.7 This has since been shown not to be the case. VCD can occur over wide range of ages from childhood to adulthood; however, in children, it usually presents in early adolescence.8 A wide spectrum of symptoms can occur, including throat tightness, chest tightness and pain, hoarseness, difficulty getting air “in,” cough, inspiratory stridor, dysphonia, dyspnea, and air hunger.7,8 Patients may experience anxiety and panic during these acute episodes. Triggers are numerous, including emotional stressors, reflux, and exercise.7 Asthma and GERD exist as comorbid conditions with VCD and should be considered and treated if necessary. VCD may be mismanaged, with a false diagnosis of asthma, and patients are placed on unnecessary medications such as corticosteroids. Exposure to irritants, such as cleaning solutions, perfumes, or chlorine in swimming pools has also been associated with VCD.7 Careful history and physical examination, spirometry with inspiratory loops, and documentation of normal oxygen saturation during episodes are the keys to diagnosis of VCD.7,8 Spirometry may reveal attenuation of inspiratory flow, indicating extrathoracic airway obstruction, whereas asthma causes intrathoracic airway obstruction. Laryngoscopy after exercise challenge can also document paradoxical vocal cord motion in those patients whose symptoms are related to activity. Treatment of VCD is best carried out via a multidisciplinary approach. It involves the patient’s physician as well as a speech therapist who can focus on breathing exercises.8 Patient education and their understanding of the condition are also extremely important.

Vocal Cord Paralysis

Causes of vocal fold paralysis are further discussed in Chapter 371 and are shown in Table 371-5. Neonates can present with stridor caused by unilateral (often with a hoarse cry) or bilateral (often with a normal or high-pitched cry) vocal cord paralysis. This can be secondary to birth trauma, neurological disease, or following heart or thoracic surgery (eg, patent ductus arteriosus surgery), and it can also be idiopathic.2 Congenital vocal cord paralysis usually presents in the first month of life, and the possibility of other congenital anomalies should be investigated. Central neurologic disease, such as brainstem compression with an Arnold-Chiari malformation, can cause bilateral vocal cord paralysis.2 Airway obstruction, apnea, and cyanosis are more severe with bilateral paralysis, and many of these infants need tracheotomy. Diagnosis is confirmed with airway endoscopy to observe the motion and position of the vocal cords. Over time, paralysis may resolve spontaneously, but until then, the infant is at risk for aspiration with feeding.2 A modified barium swallow with a feeding evaluation is helpful in assessing aspiration and swallowing problems in these patients. Surgical intervention, such as arytenoidectomy, may also be necessary.

Recurrent Respiratory Papillomatosis

Recurrent respiratory papillomatosis (RRP), caused by human papilloma virus (HPV), commonly affects the vocal folds. HPV types 6 and 11 may cause these lesions, but HPV type 11 causes more aggressive disease in children.9 Patients can present with hoarseness, dysphagia, a weak or hoarse cry, and with advanced lesions, stridor, and shortness of breath. The virus can be transmitted to the infant from the mother with genital HPV infection during vaginal delivery. Risk factors for the juvenile onset of RRP include being the firstborn child, being born by vaginal delivery, and being born to a teenage mother.9 Evaluation includes history and physical examination, followed by nasopharyngolaryngoscopy or direct laryngoscopy for visualization. The diagnosis is made on gross appearance of the lesions as well as pathology.9 Treatment includes surgical therapies such as carbon dioxide laser ablation, pulsed dye laser ablation, as well as adjuvant treatments such as cidofovir and α-interferon.9 Unfortunately, papillomas commonly recur, and some patients require multiple procedures over their lifetime. There is a very low risk of malignant transformation, but progression to squamous cell carcinoma has been reported.2

Foreign Bodies in the Throat

Foreign body aspiration is discussed in detail in Chapter 118. Foreign bodies may lodge just below the vocal cords or in the upper esophagus and produce symptoms similar to croup or asthma. There is often not a witnessed choking episode or clear history of foreign body aspiration. Physicians should have a high suspicion (of foreign body) in a toddler, for example, who presents with sudden onset of stridor, cough, and hoarseness without other signs of an upper respiratory tract infection (such as fever, rhinorrhea, or other viral prodrome). Common foreign bodies include seeds, bones, coins, and pieces of plastic.10

Upper airway and chest radiography is recommended when there is an abrupt onset of symptoms of upper airway obstruction. Radiography of the neck/upper airway can be helpful if the inhaled object is radiopaque (coins, batteries) but not if the object is radiolucent.11 Endoscopic inspection and removal of the foreign body in the upper airway is performed by otolaryngology.

Burn Injury

Airway management is the first concern in a child who has sustained a burn injury. Scald burns can affect the airway if there is significant face and/or neck involvement. Inhalation injuries should be considered after a child has been exposed to a flame injury, especially in a closed space.12 Clinical signs include singed nasal or facial hairs, stridor, wheezing, respiratory distress, hoarseness, oral blisters, as well as edema and blisters of the tongue.12 Flexible bronchoscopy can be used to evaluate the extent of airway involvement. Smoke inhalation can also lead to acute lung injury, affecting lung parenchyma and also result in carbon monoxide intoxication.12 Endotracheal intubation in the acute setting may be necessary, since worsening airway edema may progress rapidly and complicate airway management.12 Management includes obtaining appropriate control of the airway, fluid resuscitation, and other supportive measures of care.12

Angioedema and Angioneurotic Edema

Angioedema and hereditary angioedema are discussed further in Chapters 189 and 193. Angioedema consists of localized swelling that is distinct from urticaria, which can occur to several triggers, and most commonly is seen in vascular areas of the body such as the face, eyes, mouth, and oropharynx. Angioedema occurs in tissues deeper than the dermis and lasts for 24 to 48 hours, while urticaria occurs in the dermis and usually lasts for shorter periods.13 Both entities can coexist in patients. Angioedema can be allergic and can be seen with anaphylaxis (immunoglobulin E [IgE] mediated to foods, insects, or certain medications). It can also be nonallergic, such as is seen when angiotensin-converting enzyme (ACE) inhibitors and aspirin cause angioedema (non-IgE mediated).13 It can occur in autoimmune and lymphoproliferative diseases as well as in trauma and certain infections. It can affect the upper airway, causing obstruction with symptoms of stridor and respiratory distress. Acute management involves use of subcutaneous epinephrine and airway control as necessary. Antihistamines and steroids may be necessary for long-term management.

Hereditary angioneurotic edema is a disorder secondary to low levels of, or defective, C1 inhibitor,14 a protein that inactivates targets (such as C1 esterase) specifically in the complement system as well as in the clotting and kinin pathways. Unchecked activation of these mediators leads to edema formation (via vascular permeability). It is inherited via an autosomal dominant pattern, although there have been cases of de novo mutations in patients whose parents do not have hereditary angioneurotic edema.14 The clinical manifestations are subcutaneous edema, abdominal/intestinal edema, and laryngeal edema. Episodes of larynx edema are rare but extremely concerning because of its serious consequences. Symptoms include stridor, hoarseness, a feeling that something is stuck in the throat (globus sensation), and respiratory distress.14 Acute management includes control of the airway with intubation if necessary and replacement with intravenous C1-inhibitor concentrate. Prophylactic, long-term treatment involves avoiding known triggers and using antifibrinolytics and attenuated androgens.14

Airway Obstruction in Children with Down Syndrome

Children with Down syndrome are particularly at risk for upper airway obstruction secondary to anatomical abnormalities in addition to hypotonia. They have macroglossia and midface hypoplasia combined with a softer supraglottis.15 As a result, there is a higher prevalence of laryngomalacia in these infants.16 GERD is commonly seen alongside laryngomalacia. Obstructive sleep apnea has been found more frequently in children with Down syndrome than in the general population.15 This is also secondary to hypotonia, mandibular hypoplasia, and large adenoids, which all lead to collapse of the upper airway at inspiration while asleep.

Airway Obstruction in Children with Charge Syndrome

CHARGE syndrome represents the following associated malformations: C, coloboma; H, heart defects; A, atresia of choanae; R, retardation of growth and/or development; G, genital anomalies; and E, ear abnormalities.17 It is extremely common for these infants to suffer from laryngopharyngeal airway obstruction, and some require tracheotomy.17 Studies have shown that contributing factors include laryngomalacia and supraglottic obstruction due to hypotonia of this region. Infants with CHARGE syndrome can also have swallowing problems and general laryngeal dyscoordination due to cranial neuropathies (cranial nerves VII, IX, X).17 There tends to be a high frequency of GERD in these infants.

Infectious Causes of Upper Airway Obstruction

Croup (Laryngotracheobronchitis)

Croup is the most common infectious cause of acute stridor and upper airway obstruction seen in children (see also Chapter 241).18 It is seen in the early fall and winter months, when viral upper respiratory tract infections reach their peak. The age group most frequently affected is between 6 months and 4 years of age, and it is seen in males more than in females.18 Several viruses can cause croup; however, parainfluenza type I is the most common organism. Parainfluenza types II and III, respiratory syncytial virus, adenovirus, and influenza can also cause croup. Mycoplasma pneumoniae has also been implicated in croup.19 Many children have a 1- to 3-day history of viral prodrome consisting of nasal symptoms such as congestion or rhinorrhea and possibly fever.20 Subsequently, there is development of a harsh, barky cough that is often described to be similar to “a barking seal or dog.” They may also have inspiratory stridor as well as respiratory distress indicated by nasal flaring and suprasternal and subcostal retractions. Stridor is often worsened with activity, crying, and increased anxiety or agitation. Typically, the course of illness lasts for no more than 1 week.18 The viral infection causes inflammation and edema of the airway, especially in the subglottic region.20 Croup is diagnosed clinically by history and physical examination.18 An x-ray of the upper airway can be useful to distinguish croup from other entities such as a retropharyngeal abscess or foreign body. In croup, a “steeple sign,” which is the tapering of the subglottic airway, may be seen, but many patients will also have normal x-rays.19 The differential diagnosis of croup includes retropharyngeal abscess, epiglottis, foreign body, angioedema, and structural abnormalities such as laryngomalacia or subglottic stenosis. Obtaining a thorough and careful history greatly helps to differentiate croup from these other conditions. Children who have recurrent croup should be investigated for other problems beyond simply recurring viral infections, such as anatomic abnormalities or GERD.

Most children with croup do not require hospitalization; however, many will need to be evaluated in an acute care setting if they are having worsening stridor and respiratory distress. Some physicians continue to recommend treatments such as mist therapy (air humidification), but current studies available do not show evidence that this is effective.20 Exposing children to steam from hot showers or baths at home can put them at risk for scald injuries.20 Fever reduction and avoidance of agitation are useful, both at home and in the hospital setting. Obtaining blood work such as blood gas measurements is rarely necessary and can certainly lead to further agitation, increasing a child’s stridor and dyspnea. Oxygenation should be monitored by pulse oximetry.

Corticosteroids continue to be one mainstay of therapy, even for more mild cases of croup. Dexamethasone, either oral or intramuscular, is effective in decreasing symptom severity, decreasing hospitalization rates, and increasing symptom resolution.1819 The standard use of dexamethasone is a 1-time dose of 0.6 mg/kg; however, smaller doses have been shown to be effective.20 Prednisolone has also been shown to be efficacious compared with placebo for treatment of croup, as is nebulized budesonide at a dose of 2 mg.1819 Nebulized racemic epinephrine is often used to acutely relieve upper airway obstruction by decreasing edema via vasoconstriction and possibly preventing further progression and need for intubation.18 It will not alter the course of the illness as corticosteroids do. It is classically used in patients with more moderate to severe croup. Heliox, which is a helium and oxygen mixture (eg, 80:20) and therefore a gas of much lower density than air (but similar viscosity to air), can improve air flow in severe croup (as well as in asthma and bronchiolitis).20 It is used when a child is in severe respiratory distress and there is concern of potential respiratory failure.

Spasmodic Croup

Spasmodic croup consists of episodes of inspiratory stridor that occur mostly at night, without the classic viral prodrome.21 The child may have had symptoms of a mild upper respiratory infection, but fever is usually absent. The symptoms present quite suddenly, in a well appearing child. Children are older than those who have viral croup, and their symptoms usually resolve within 24 to 48 hours.20 The child awakens with a barking, harsh cough and inspiratory stridor. Many will have recurrent episodes. The etiology is not completely known, but both viral illness and atopic disease is associated with spasmodic croup.20 Gastroesophageal reflux (GER) has also been associated with recurrent croup.21 Parents can attempt supportive care at home, such as exposure to cool night air to improve symptoms. Treatment with racemic epinephrine and steroids is helpful, as in viral croup. If symptoms are frequent and recurrent, structural abnormalities of the airway should also be considered.

Acute Epiglottitis

Acute epiglottitis (also known as supraglottitis) is an infection leading to inflammation and swelling of the epiglottis, which can progress quickly to becoming a life-threatening emergency (see also Chapters 240, 241). Prior to the standard use of Haemophilus influenzae b (Hib) vaccine, this organism was the most common cause of epiglottitis. Currently, Streptococcus pneumoniae, Staphylococcus aureus, and group A β-hemolytic streptococci are among the most common pathogens that cause this infection.19 It is now rarely seen in childhood but must be considered when an ill-appearing child presents with acute-onset of stridor. There have still been cases of epiglottitis caused by Hib in immunized children, indicating the possibility of vaccination failure.19 Children affected are usually between 2 and 8 years old, although most recently the age appears to be increasing. It presents quite suddenly (over 6–24 hours) with high fever, irritability, throat pain, stridor, and what is known as a “hot potato” or muffled voice.18 Unlike croup, there is usually no preceding viral prodrome or cough, and the child has an extremely ill appearance. The child will prefer to sit in the “tripod” position, leaning forward and extending the neck to open the airway and increase air entry.18 Eventually it becomes hard for the patient to handle secretions and saliva, and therefore drooling will occur.18 Cyanosis, stridor, and drooling all point to advanced, severe airway swelling and impending respiratory failure due to airway obstruction.

Airway management is the first priority if epiglottitis is suspected. Therefore, obtaining blood work and aggressive attempts at visualization of the oropharynx should be avoided. Only in a child who appears stable should a cautious examination of the posterior pharynx (without the use of a tongue depressor) be attempted.18 Manipulating or touching the oropharynx with a tongue depressor can cause complete obstruction. The examination may reveal a grossly swollen, erythematous epiglottis, projecting beyond the base of the tongue.18 A definitive diagnosis of epiglottitis should occur in a controlled situation (such as the operating room) with appropriate personnel (anesthesiologist and otolaryngologist) who are trained to manage difficult airways and are able to secure the airway surgically if necessary. A lateral neck radiograph can be helpful but should not delay treatment. A “thumbprint sign,” which describes a round and thickened epiglottis, can be seen on the x-ray.19 Once the child has a secured airway and is out of danger of progressing to total airway obstruction, a complete blood count (CBC) and blood culture can be done and intravenous antibiotics can be started. Patients will often have positive blood cultures. High-dose, broad-spectrum antibiotics such as ceftriaxone or ampicillin-sulbactam should be used.1819 Complications seen with epiglottitis can include complete airway obstruction, pulmonary edema postintubation, pulmonary infiltrates and pneumonia, and respiratory arrest.18

Bacterial Tracheitis (Pseudomembranous Croup or Bacterial Croup)

Bacterial tracheitis is an uncommon entity but an important cause of severe upper airway obstruction. It is commonly caused by Staphylococcus aureus; however, Moraxella catarrhalis,Streptococcus pneumoniae, and H influenzae are also seen (see also Chapter 240).18 Children present with symptoms similar to epiglottitis and croup. After this initial presentation, they can progress to having respiratory distress with high fever and become very ill appearing. Lateral neck radiographs can show subglottic narrowing (steeple sign, as can be seen in viral croup) and irregularity of the tracheal air column (indicating sloughing of pseudomembranous material from the tracheal wall).18 They can also develop pulmonary infiltrates consistent with pneumonia. Airway endoscopy reveals large amounts of mucopurulent secretions and subglottic edema. These secretions are thick and can occlude the airway. They should be suctioned and sent for Gram stain and culture. Treatment includes appropriate intravenous antibiotics as well as airway management such as endotracheal intubation if necessary.18

Retropharyngeal and Peritonsillar Abscess

The retropharyngeal space refers to the area between the anterior cervical vertebrae and the posterior pharyngeal region.2 A retropharyngeal abscess occurs in this space either by spread of an upper respiratory tract infection (such as pharyngitis) to the retropharyngeal lymph nodes or by a penetrating oropharyngeal injury. Group A Streptococcus, anaerobic organisms, and Staphylococcus aureus commonly cause this disease.18 This infection is not common, but it needs to be diagnosed correctly and treated without delay. It is mostly seen in children under 6 years of age, especially in toddlers. This is explained by the fact that the lymphatics that drain the retropharyngeal space atrophy by this age.19 Clinical presentation includes fever, dysphagia, drooling, neck stiffness, and pain. As the infection progresses and pus collects, forming the abscess, stridor and respiratory distress can develop from compression of the pharynx. The differential diagnosis includes meningitis, epiglottitis, and croup. Physical examination can reveal bulging of the posterior wall of the pharynx. Obtaining a lateral neck radiograph is helpful in these cases in order to specifically examine the retropharyngeal space for soft tissue swelling. Widening of this potential space (> 7 mm at the level of the second cervical vertebrae) may indicate a retropharyngeal abnormality.18 Computed tomography (CT) scan of the neck is necessary to distinguish between a true abscess and cellulitis and is often used in evaluation of this deep neck infection.18 Treatment requires the use of appropriate intravenous antibiotics; however, surgical drainage is performed in those cases in which medical management fails. Complications can include respiratory failure, aspiration pneumonia (from abscess rupture), and spread of infection to other areas in the deep neck.19

Peritonsillar infections and abscesses occur as a result of spread from an infection in the tonsils. They are most common in adolescents who have recurrent tonsillitis.19 Fever, throat pain, decreased oral intake, and drooling are some of the symptoms seen. Both anaerobic and aerobic organisms cause this infection. Physical examination can reveal displacement of the uvula.19 CT scan is often used to aid in the diagnosis of abscess.19 Treatment includes intravenous antibiotics and may include surgical drainage. Airway obstruction is a potential complication of peritonsillar abscess.19

Obstruction of the intrathoracic airways while exhaling generally results in wheezing. Other symptoms that may be associated with obstruction of airways while exhaling are cough and shortness of breath. A vast majority of children who have expiratory obstruction and wheeze have asthma. However, all that wheezes is not asthma: Other entities can cause airway obstruction and symptoms that mimic asthma (Table 510-1). These entities differ from asthma in that they typically do not respond to common asthma therapies. In asthma, airflow obstruction on exhalation is reversible with bronchodilators. This can be noted clinically or by measuring response with lung function testing. Likewise, in asthma, response to corticosteroids is significant in most instances. The diagnosis of asthma must be questioned when an individual with wheeze does not respond to the asthma therapies of bronchodilators and corticosteroids.

Obstruction of lower airways is important to recognize and treat because the consequences can lead to significant complications. Obstruction of an airway may lead to atelectasis as gas is absorbed into the lung and that portion of the lung collapses. This area may fill with mucous, and the likelihood of secondary infection increases. With time, chronic infection can lead to abscess formation and/or bronchiectasis. If the obstruction is not complete, air trapping may occur, leading to hyperinflation of lung tissue that can develop emphysematous or cystic formations. These areas of hyperinflated lung can compromise adjacent healthy lung tissue.

This section focuses on those entities that have signs and symptoms consistent with expiratory obstruction but are not due to asthma. Expiratory obstruction may be intraluminal (something within the airway), extraluminal (something outside the airway causing compression), or intrinsic (the airway itself is injured or unable to maintain its shape during exhalation).

Intraluminal Obstruction

Perhaps the most common cause of expiratory obstruction (other than asthma) is something within the airway either completely or partially impeding airflow. This may result from foreign bodies, aspirated particulate matter or food, gastroesophageal reflux, tumors, vascular malformations, edema, and infection. Intraluminal obstruction in intrathoracic airways can cause expiratory obstruction.

Foreign Body Aspiration

Children, more so than adults, can aspirate foreign material into the lungs. A 10-year retrospective chart review of children who had undergone endoscopic removal of airway foreign bodies at the Children’s Hospital of Boston was published in 2000. Of the 135 cases, 64% were boys and 36% were girls. Of the group, 78% were under 3 years of age with the average age being 38.1 months. A vast majority of children who aspirate foreign bodies have a history of a choking or acute coughing episode. If the foreign body is not discovered early, there may be an asymptomatic period, and complications such as pneumonia, chronic cough, and/or dyspnea eventually occur. On physical examination, findings of a unilateral wheeze or diminished breath sounds should suggest the possibility of foreign body aspiration. Negative radiographic studies (chest x-rays and CT scans) should not exclude the possibility of a foreign body, especially if the history and physical examination are consistent with foreign body aspiration. The Boston group found that x-rays were not helpful in the diagnosis of airway foreign body 26.6% of the time. Most commonly, the aspirated object is food, with nuts being the most common. Often, objects such as food do not appear on plain radiographs. Toys and other household objects are also common because children in their toddler years are exploring and often place objects in their mouths.

The treatment for foreign body aspiration is removal of the object as soon as possible to prevent complications. In most cases, the foreign body can be removed via rigid bronchoscopy (see Chapter 506). Rarely, thoracotomy is necessary to remove the foreign body. The most severe long-term complication of foreign body aspiration is bronchiectasis. This is a consequence of delayed removal of the object, which can obstruct mucous clearance and cause chronic infection and inflammation. Delay in treatment usually results from incorrect diagnosis of symptoms, usually ascribed to asthma.

Chronic Aspiration and Gastroesophageal Reflux

Expiratory obstruction from aspiration can also occur on a less acute basis, as with chronic aspiration of food particles, oral secretions, or stomach contents (GER). Foreign material in the airway not only obstructs airflow but can irritate the airways, causing inflammation and mucous secretion that can further obstruct airflow. In an infant with small airways, it does not take much to cause obstruction and significant symptoms.

Swallowing coordination occurs at around 34 weeks’ gestation, so premature infants are at risk for disorders of swallowing and, consequently, aspiration. Certain conditions predispose infants and children to aspiration from above, including neurocognitive and neuromuscular syndromes, craniofacial abnormalities, and anomalies of the glottis and esophagus. Infants and children without underlying medical conditions may also develop a disorder of swallowing. Fatigue and intercurrent illness can acutely impact swallowing coordination, as can prolonged intubation.

GER can lead to aspiration and symptoms of airway obstruction. The aspirated gastric contents can irritate the airways and lead to inflammation and mucous secretion. GER can lead to airway obstruction as a result of silent aspiration of acidic or nonacidic gastric contents, which can stimulate upper airway receptors and lead to bronchospasm. This is often manifested as a cough, but even as the material is cleared by the cough, the stimulus remains and bronchospasm occurs. GER can also stimulate airway obstruction by reflex initiated in the lower esophagus. Receptors in the lower esophagus, when stimulated by acid or pressure, can cause bronchoconstriction and airway obstruction. Regardless of the mechanism, it is clear that GER can be a significant mimic of or contributor to asthma symptoms.

Children at particular risk for having clinically significant reflux include those with tracheoesophageal fistula (even after repair), congenital diaphragmatic hernia, chronic lung disease of prematurity, cystic fibrosis, asthma, hiatal hernia, and other diseases of the aerodigestive tract. Certain medications, such as caffeine, β-adrenergic agonists, and anticholinergics, as well as fatty foods, chocolate, mint, and alcohol, can exacerbate GER.

The most common signs of aspiration are wheeze and cough, often more pronounced at night; other signs include gagging, stridor, and hoarseness. In severe cases, infants and children may present with failure to thrive, apnea, recurrent pneumonias, and dental erosions (from retained acidic gastric contents in the mouth). An infant with GER may simply have colic. Older children with GER may be able to describe symptoms as “wet burps” or “hot burps,” but sometimes, reflux may be silent. The lipid-laden macrophage index (LLMI) is a tool used to evaluate the presence of chronic aspiration. Lipid-laden macrophages discovered in fluid from bronchoalveolar lavage (BAL) are considered to be an indicator of aspiration of fat-containing material. The LLMI appears to be a sensitive index for aspiration but is poorly specific because other chronic lung conditions may yield high LLMIs. The LLMI may have a role as an indicator supportive of the diagnosis of chronic aspiration syndromes. Treatment is discussed in Chapter 511.

Other Intraluminal Obstructions

Intraluminal tumors are rare in children. Bronchial adenomas, which arise from mucous glands and ducts of the airways, occur in 2 histologic types. The carcinoid type is the most common; it resembles carcinoid tumor of the gastrointestinal tract but does not confer symptoms of carcinoid syndrome. The other, the cylindromatous type, is much less common and resembles mixed tumors of the salivary gland with cuboidal or flattened epithelial cells. The carcinoid adenomas are less likely than the cylindromatous type to become malignant.

Papillomas of the airway may occur in children exposed to human papilloma virus. These are often pedunculated, and numerous papillomas may occur throughout the airway, leading to obstruction. Although nonmalignant, they have the potential to give rise to squamous carcinoma. Furthermore, these papillomas may occur in abundance and return after surgical removal, leading to multiple procedures throughout the child’s lifetime. Other benign tumors that may occur in the airways and cause obstruction include hamartomas and hemangiomas. Malignant airway tumors that occur in adults are rare in children, probably because most of the adult malignancies are secondary to significant and prolonged tobacco smoke exposure.

Extraluminal Obstruction

Obstruction may occur from a compressing lesion outside the lumen of the airway. Most often, these lesions are in the mediastinum and include enlarged lymph nodes, thymus, cysts, tumors, or vascular structures. Bronchogenic cysts develop from bronchial walls or lymphatic tissue. They are most commonly situated in the subcarinal region but can occur anywhere along the bronchial tree. Cysts arising from the gastrointestinal tract can also cause compression. These include esophageal duplication cysts, which can cause compression of the trachea and bronchial tree and are at risk for becoming infected. Such cysts should be removed.

Tumors of the mediastinum include thymic tumors, teratomas, lymphomas, thyroid tumors, and neurogenic tumors. Lymph node enlargement may occur secondary to hematologic malignancies, sarcoidosis, and chronic inflammatory or infectious diseases. Vascular and lymphatic malformations such as hemangiomas and lymphangiomas can also occur outside of the airway lumen and cause compression of tracheal or bronchial airways. Treatment of compressing lesions is usually surgical and is often necessary to prevent future complications of atelectasis, pneumonia, emphysematous changes, and the possibility of malignant conversion.

Intrinsic Airway Wall Abnormalities

Airway obstruction may be due to a defect in the airway itself. The airway may become deformed or narrowed during exhalation because intrathoracic pressures placed upon the airways exceed the ability of the airways to maintain patency.

Tracheomalacia and Bronchomalacia

Malacia, or “softening” of the airway, is a condition in which the intrathoracic airways narrow during exhalation, resulting in obstruction. Tracheomalacia and bronchomalacia are the results of compromised elastic fibers in the airway walls. These elastic fibers are responsible for providing shape and structure. For the purposes of discussion, tracheomalacia or bronchomalacia are referred to as tracheobronchomalacia (TBM) unless specifically noted.

Most infants and children with TBM have an underlying or associated problem. Cardiovascular anomalies may occur in up to 60% of the cases, and half of infants with TBM have bronchopulmonary dysplasia and/or GER. Malacia of the airways can be primary (congenital) or secondary (acquired). Primary TBM is the result of inadequate maturation of cartilage in the trachea or bronchi. A common cause of primary TBM is prematurity, but it may also occur in term infants. Disorders associated with TBM include polychondritis, chondromalacia, Ehlers-Danlos syndrome, mucopolysaccharidoses, CHARGE and VATER anomalies, trisomy 21, DiGeorge syndrome, and 22q11 deletions. Tracheoesophageal fistula is also a cause of primary tracheomalacia that persists long after repair of the fistula. The area of the fistula can cause widening of the membranous (or posterior) portion of the trachea, leading to flattening of the trachea and a focal collapse.

More commonly, TBM occurs secondarily. It most commonly results from injury to the airway, as after prolonged intubation of the premature infant. Tracheostomy can also compromise airway structure and strength, leading to tracheomalacia. External compression due to vasculature, tumors, or vascular malformations may inhibit maturation of the airway structure. Infection can also disrupt maturation of the airway leading to TBM.

Signs and symptoms of TBM are commonly wheeze or stridor. Many infants and children exhibit a harsh, barking cough reminiscent of croup. Recurrent episodes of croup should alert the clinician to the possibility of TBM. These symptoms of wheeze, stridor, or harsh cough are due to the close approximation of the anterior and posterior walls on exhalation. Other signs and symptoms of TBM include cyanotic spells, failure to thrive, chest wall retractions, and recurrent pneumonia.

Plain radiographs of the neck and chest are not helpful for evaluating TBM. Fluoroscopy of the neck and chest provides a cinegraphic view of the airway, allowing for the trachea and bronchi to be visualized during inhalation, exhalation, and other maneuvers such as coughing. Such a view allows the observer to determine if there is dynamic collapse of the airway, especially during expiratory maneuvers. Flexible bronchoscopy allows direct visualization of the airway. Although invasive, bronchoscopy can and should be performed with minimal sedation in order to observe the airway with the child breathing spontaneously. Because of the need for minimal sedation and because it does not “stent” open collapsible airways, flexible bronchoscopy is a better alternative to rigid bronchoscopy when evaluating TBM. Bronchoscopy not only identifies the area of TBM but can determine the etiology. In some cases, the area of TBM appears pulsatile due to vascular compression. If there is external compression of the airway, magnetic resonance imaging with magnetic resonance angiography may help distinguish the cause of the compression.

The best treatment for TBM is supportive care and allowing the child to outgrow the condition. Most children with primary TBM will improve by 2 to 3 years of age, although those with tracheoesophageal fistula may have significant problems into adult years. Chest physiotherapy can be helpful to clear retained secretions trapped by collapsible airways. Devices that produce positive expiratory pressure can stent open collapsible airways during exhalation. Such airway clearance devices can be used to facilitate removal of retained secretions. Along the same lines, continuous positive airway pressure can stent open collapsible airways, promoting oxygenation and ventilation.

In extreme cases of TBM, tracheostomy or other surgical treatment may be needed. Patients who have severe TBM may show with poor growth, frequent and recurrent respiratory exacerbations, or even death spells. Such patients will need an intervention to decrease their work of breathing. A tracheostomy can stent open collapsible airways either by bypassing the level of malacia or providing a conduit for positive airway pressure. Other surgical procedures include aortopexy, external splinting, and airway stent placement. Aortopexy is a procedure in which the anterior portion of the aorta is fixed to the posterior portion of the sternum, allowing the anterior wall of the trachea to move forward. Silicone or metallic airway stents can be placed endoscopically, but their use is fraught with complications due to erosion, obstruction, infection, and, specifically in children, the need for replacement. Because of the invasiveness of aortopexies and external splinting, and the complication of stents, surgical treatments for TBM are reserved for infants and children with severe, life-threatening TBM.

Bronchopulmonary Dysplasia

Infants born prematurely may have airway obstruction for reasons other than TBM. Bronchopulmonary dysplasia (BPD) is a common cause of obstruction during exhalation. See Chapters 59 and 513. The immature airways are smaller, and so compromise of the airway can be quite significant. Furthermore, prematurity or the insult that mechanical ventilation can incur may lead to inflammation and injury of the airways, compounding obstruction. Finally, these insults can lead to scarring and fibrosis of the airways and lung parenchyma. Scarring of the airway causes restriction of airflow. Scarring of the lung parenchyma causes loss of elastic recoil and the lung architecture that helps maintain patent airways.

Infants with BPD demonstrate symptoms similar to other conditions causing obstruction during exhalation. They may wheeze, cough, and have recurrent respiratory infections. Lung function testing performed on infants and children with BPD demonstrates airflow limitation. Even infants and children born prematurely but without evidence of BPD may manifest signs of airflow limitation on lung function testing.

Treatment for the infant and child with BPD and obstruction during exhalation is mostly supportive. Bronchodilators are usually ineffective. Despite the inflammation that can occur in BPD, inhaled corticosteroids are also ineffective. The most important factor in treating BPD is assuring adequate growth, which is closely tied to lung maturation.

Bronchiectasis

Bronchiectasis describes the abnormal dilation of bronchi and bronchioles that has resulted from airway damage. This damage may be the result of a congenital disease, such as cystic fibrosis; or an acquired insult, such as infection, foreign body aspiration, or systemic inflammatory disease that affects the lungs (Table 510-2). Persistent infiltrate or atelectasis of the right middle lobe may occur in individuals with bronchial stenosis, foreign body aspiration, or difficult to control asthma or cystic fibrosis. This so-called right middle lobe syndrome can lead to focal bronchiectasis.

Whatever the cause, the pathophysiology of airway damage is consistent. An insult occurs that incites an inflammatory reaction in the airways. Neutrophil influx damages airway walls by releasing elastases and collagenases. Since the lung parenchyma is spared, the elastic forces of the lung tissue pull these damaged airways open and ectasis (Greek for stretching) of the bronchi (Greek for windpipe) occurs. In these stretched and damaged airways, squamous metaplasia and mucous cell hyperplasia occur in conjunction with impairment of mucous clearance. As a consequence, secretions are retained in distal airways and serve as a nidus for infection. Infection further intensifies the inflammatory response, and a vicious cycle is set up for more airway damage.

Clinically, bronchiectasis presents as chronic cough with purulent sputum production. Examination may include weight loss; lung crackles, wheezes or rhonchi; and digital clubbing. Examination of the sputum may reveal typical pathogens, with Pseudomonas aeruginosa being a common bacterium that causes chronic infection. Figure 510-2 demonstrates the radiographic findings encountered with bronchiectasis. Pulmonary function testing often shows findings consistent with airways obstruction.

Cystic fibrosis is the most common autosomal recessive genetic disorder among Caucasians and the most common congenital cause of bronchiectasis. It occurs as a result of a mutation in the cystic fibrosis transmembrane regulator (CFTR) gene. The final common result of lung disease in cystic fibrosis is bronchiectasis. In cystic fibrosis, infection plays an important role in the pathogenesis of bronchiectasis. However, the chronic inflammation that occurs in cystic fibrosis airways also contributes to the destructive process. The inflammatory process is intense and may begin early in life, even before chronic infection is evident.

Primary Ciliary Dyskinesia

Bronchiectasis is also the end result of primary ciliary dyskinesia (PCD). Also autosomal recessive, PCD has a prevalence of 1 in 15,000 to 30,000, although this prevalence is likely underestimated because individuals with this disease are undiagnosed. Kartagener syndrome is the triad of bronchiectasis, sinusitis, and situs inversus. The underlying defect in PCD is an abnormal ciliary ultrastructure and function. Normally, the cilia that line the upper and lower airways have a beat frequency of 15 to 25 times per second and sweep mucous to proximal, large airways where the mucous that has foreign material can be expectorated or swallowed. In PCD, the cilia demonstrate abnormal beating pattern or no motility at all, leading to stasis of mucous secretions. Retained mucous leads to upper and lower respiratory tract infections, and left unchecked, these infections can cause significant damage. In the lower airways, recurrent and chronic infections can lead to bronchiectasis.

Recently, there has been significant advancement in our understanding of the genetic etiologies of PCD. Mutations in dynein, axonemal, intermediate chain 1 (DNAI1) and in dynein, axonemal, heavy chain 5 (DNAH5), which encode components of the cilia, may account for as much as 10% and 28% of PCD respectively.22

The diagnosis of PCD can be difficult to establish. The diagnosis is not often thought of in children who have frequent, recurrent respiratory tract infections because such infections are commonplace in this age group. Certainly, nasal congestion is a symptom of PCD that can occur in all individuals, but in the child who has nasal congestion from birth, PCD should be considered. Other factors that would alert the clinician to the diagnosis of PCD are chronic wet cough, wheeze, bronchiectasis, and particularly severe recurrent sinusitis and otitis media. Nonrespiratory issues that would raise suspicion of PCD include situs inversus, complex congenital heart disease, polycystic kidney disease, biliary atresia and liver disease, hydrocephalus, ectopic pregnancies, male infertility, and retinal degeneration. Digital clubbing and nasal polyposis, often seen in cystic fibrosis, are not often present in PCD.

The most important factor in diagnosing PCD is considering the diagnosis. Once the diagnosis of PCD is considered, there are screening and diagnostic tests to help establish a diagnosis. Screening for PCD can be performed by measuring nasal and exhaled nitric oxide. In PCD, nasal or exhaled nitric oxide is low, as opposed to the high levels that can occur in asthma. The saccharine test, which involves placing a small amount of saccharine on the inferior turbinate and counting the time elapsed until the patient can taste the saccharine, can screen for ciliary dyskinesia. Diagnostic tests include nuclear medicine radioisotope scans that measure mucociliary clearance from the lower airways and biopsy of the respiratory mucosa to evaluate ultrastructure and function of the cilia. Definitive diagnosis of PCD involves examination of ciliary structure by electron microscopy. Genetic testing is also available for common mutations in DNAI1 and DNAH5.22

Much of the treatment of PCD has been adopted from experience with cystic fibrosis. Enhancing mucociliary clearance with chest physiotherapy remains the mainstay of treatment. Inhaled medications such as bronchodilators (eg, albuterol) and mucolytics (eg, dornase-α) have been employed to aid in mucous clearance. Monitoring for and aggressively treating infections is also a mainstay of treatment in PCD. As with cystic fibrosis, individuals with PCD can become infected with organisms such as Staphylococcus aureus, Haemophilus influenza, and Pseudomonas aeruginosa. Intense monitoring and treatment such as identifying and treating infections are important to stabilizing lung function. Genetic counseling should also be offered to parents of an affected child or who are carriers of known disease-causing mutations.

Bronchiolitis Obliterans

Bronchiolitis obliterans is a disorder that causes obstruction during exhalation. Similar to asthma, it affects small and medium-sized airways, causing expiratory obstruction and wheeze, but unlike asthma, the expiratory obstruction is not reversible with bronchodilators. Bronchiolitis obliterans is mostly seen in individuals with chronic rejection after lung transplantation and in individuals with graft-versus-host disease secondary to allogeneic bone marrow transplantation. It can occur in healthy individuals as well, although this is unusual.

Chronic rejection is quite common in the transplanted lung and manifests as bronchiolitis obliterans. This condition is present in greater than 50% of transplant recipients who survive to 5 years. Bronchiolitis obliterans is a heterogeneous disease that may have an insidious or rapid onset. It rarely occurs in the first 6 months after transplantation. Its median time to diagnosis posttransplant is 16 to 20 months. Risk factors for bronchiolitis obliterans have not been definitively identified; however, certain factors appear to place a lung transplant recipient at considerable risk. Acute rejection is believed to have significant effects on the development of later chronic rejection. Other risk factors responsible include human leukocyte antigen mismatching, cytomegalovirus pneumonitis, other respiratory viruses (influenza, respiratory syncytial virus, parainfluenza virus, adenovirus), donor factors (underlying asthma, smoking, head injury as a cause of death), and gastroesophageal reflux. Also, nonadherence to the medical regimen should be considered. In patients with allogeneic bone marrow transplantation, it is estimated that up to 10% of those with active graft-versus-host disease develop bronchiolitis obliterans.

One of the first clues to the presence of bronchiolitis obliterans is a decrease in small airways function with forced expiratory flow (FEF) of 25% to 75%, and symptoms of cough, mucous production, and dyspnea. The patient’s symptoms may be difficult to distinguish from acute infection. Some have no symptoms and are identified only by screening lung function tests, which display airways obstruction and even air trapping. High-resolution CT scanning with inspiratory and expiratory views can demonstrate air trapping in bronchiolitis obliterans.

In the nontransplant patient, bronchiolitis obliterans may occur as a result of several different insults, with the most common being infection. Adenovirus infection is a common inciting factor for bronchiolitis obliterans. Clinical entities associated with bronchiolitis obliterans are listed in Table 510-3. Bronchiolitis obliterans occurs as infection, or other insult leads to acute and chronic inflammation that causes fibrosis of the airway and subsequent obliteration of the airway lumen.

In some instances, if the process occurs early enough in life that it may lead to arrest of maturation in the lung, resulting in Swyer-James-MacLeod syndrome. First described by Swyer and James in 1953 and MacLeod in 1954, this syndrome occurs as a manifestation of a postinfectious obliterative bronchiolitis. The involved lung does not grow normally because the bronchiolitis leads to diminished blood supply and diminished alveolarization. This results in hyperlucency noted radiographically. It is usually the result of an infectious process and adenovirus, Mycoplasma, Staphylococcus, pertussis, Streptococcus, influenza, and respiratory syncytial virus have been implicated. Noninfectious causes of Swyer-James-MacLeod syndrome include inhalation injuries, foreign body aspiration, radiation therapy, and lung transplantation.

Patients with Swyer-James-MacLeod syndrome are often asymptomatic, and it may be discovered serendipitously on chest radiography. Others develop cough, hemoptysis, dyspnea, and chest pain. Physical examination may reveal unilateral wheezing, diminished airflow in the affected lung, hyperresonance during percussion, and unilateral small chest. In most cases, oxyhemoglobin saturations are normal but may decrease when the patient exercises. Radiographic findings, aside from hyperlucency, include mediastinal shift toward the normal lung on exhalation or decreased diaphragmatic excursion on the affected side. CT scan demonstrates the hyperlucency and is also helpful in excluding the presence of a foreign body or mass. Ventilation-perfusion scanning of the chest can identify air-trapped areas of the lung and will display a matched ventilation and perfusion defect of the affected areas.

Treatment for bronchiolitis obliterans in the nontransplant patient and Swyer-James-MacLeod syndrome consists of monitoring for infection and avoidance of any further injury such as aspiration, reflux, or inhalation injury. Occasionally, the affected lung may develop a chronic infection or bronchiectasis. In this situation, lobectomy or pneumonectomy should be considered. However, in most cases, the prognosis for Swyer-James-MacLeod syndrome is excellent and little, if any, morbidity occurs. Treatment for bronchiolitis obliterans secondary to transplantation involves enhancing immunosuppression and aggressive treatment of infection. Unfortunately, bronchiolitis obliterans secondary to transplantation is unrelenting and very difficult to treat. The morbidity and mortality attributed to bronchiolitis obliterans in the transplanted individual is quite significant. In the individual who has bronchiolitis obliterans due to chronic rejection after lung transplantation, the 3-year survival approximates 50%. Because of its devastating effects, monitoring for bronchiolitis obliterans and its risk factors are of paramount importance in the transplanted individual.23-28