Part 2: Disorders of the Respiratory System

Congenital Disorders of the Lower Airways and Mediastinum

INTRODUCTION

Antenatal ultrasound and, increasingly, fetal magnetic resonance imaging (MRI) diagnose many congenital lung malformations, but we now have to decide what to do for a baby affected by an abnormality that may previously have escaped detection. Many lung lesions disappear or regress from the second trimester to term, and the outcome for such fetuses generally is good. Postnatal regression of lung malformations also has been described. The dilemma in the postnatal period is whether to opt for observation or surgery.

DESCRIPTION OF DISORDERS

The nomenclature of congenital lung disease may be confusing. For example, sequestration and cystic adenomatoid malformation (CCAM) are sometimes assumed to be separate identities, but histologic features of both may be found within the same lesion. There is inconsistent use of nomenclature before and after birth. It is necessary to think in new ways about congenital lung disease. The following principles should be followed:

1. What is actually seen should be described, without embryologic or pathologic speculation, which may later be proved wrong. The same clinical appearance (eg, a multicystic mass) may have 1 of several different histologic appearances when excised. A simple “catch-all” term, congenital thoracic malformation (CTM), is useful for clinical discussions, prior to any pathologic examination.

2. The description should be in everyday language, avoiding ambiguity. For example, hypoplastic lung could mean a lung that is small but otherwise normal, or small and structurally abnormal; congenital small lung (CSL) is clearer and avoids assumptions about structure. Congenital lobar “emphysema” is another source of confusion because in adults it implies lung destruction. What is actually seen is a congenital large hyperlucent lobe (CLHL). Throughout this chapter, established terms will be given in parentheses after the proposed new term. A summary comparison of old and new nomenclature is given in Table 500-1, and relevant investigations are summarized in Table 500-2.

3. The respiratory system should be described systematically. The lung is formed from 6 “trees”: bronchial, systemic and pulmonary arterial, systemic and pulmonary venous, and lymphatic. There are no known abnormalities of bronchial venous drainage, so in practice, only 5 trees need to be considered.

4. Important associated organs (in particular, the heart, great vessels, chest wall, and abdominal contents) should be considered in a systematic manner. Congenital multisystem diseases may affect the lung.