The central nervous system (CNS) is the site of origin for approximately 20% of pediatric cancers. CNS neoplasms are the second most common type of childhood tumors, after leukemia. The overall 5-year survival rate for pediatric CNS malignancies is 70%. The prevalence of brain tumors in children younger than 15 years of age is approximately 2.4 per 100,000. High-grade (World Health Organization [WHO] grade ≥3) CNS neoplasms in children include primitive neuroectodermal tumor (PNET), malignant germ cell tumors, grade III/IV astrocytoma, leukemia/lymphoma, esthesioneuroblastoma, and metastatic disease. Low-grade (WHO grade ≤2) tumors include juvenile pilocytic astrocytoma, grade II astrocytoma, germinoma, craniopharyngioma, meningioma, ganglioglioma, nonanaplastic ependymoma, acoustic neuroma, low-grade oligodendroglioma, and dysembryoplastic neuroepithelial tumor (DNET).1
In infants and toddlers, supratentorial tumors are more common than those of the posterior fossa. The most common supratentorial lesions in this age group are astrocytoma, ependymoma, and PNET. Neonatal brain tumors are rare; the most common types are teratoma, PNET, astrocytoma, and choroid plexus papilloma. Infratentorial tumors predominate in children between the ages of 4 and 11 years. The frequency of supratentorial and posterior fossa neoplasms is approximately equal in children older than 11 years of age.
Potential clinical manifestations of an intracranial neoplasm in a young child include progressive macrocephaly, nausea, vomiting, and lethargy. Nausea and vomiting in these children sometimes lead to a mistaken diagnosis of GI tract pathology. Common findings in older children include headache, nausea and vomiting, dizziness, visual impairment, and focal neurological signs such as cranial nerve palsy, ataxia, and hemiparesis. Seizures occur in 40% to 75% of pediatric patients with cerebral hemispheric tumors. Endocrine dysfunction can occur in association with a hypothalamic or pituitary lesion; potential sequelae include diabetes insipidus, growth failure, and precocious puberty.
MR is the imaging modality of choice for the detection and characterization of most brain neoplasms. CT is a lower cost alternative screening technique for children with nonspecific symptoms. CT is also occasionally useful to demonstrate calcifications in tumors or to evaluate calvarial destruction. The MR evaluation of brain neoplasms should include diffusion-weighted and contrast-enhanced images. MR angiography and MR spectroscopy are important for selected patients. In general, high-grade brain neoplasms tend to exhibit restricted diffusion on diffusion-weighted and apparent diffusion coefficient (ADC) map images, whereas low grade tumors are often isointense on these sequences.2
After surgical resection of a brain tumor, a baseline MR within 72 hours of the procedure is often helpful to detect residual neoplasm. A thin enhancing rim at the margin of the resection cavity is common, particularly during the first 24 hours. This postsurgical breakdown of the blood-brain barrier usually does not represent residual neoplasm. Nodular enhancement at this time is suspicious for residual neoplasm. Imaging at 1 to 2 weeks after surgery is suboptimal, as reactive nodular enhancement often has developed at this point. This nonneoplastic nodular enhancement ...