| Discussion: |
Neuroblastoma is the most common extracranial pediatric neoplasm and the third most common pediatric malignancy after leukemia and CNS tumors. They arise from primitive neural crest cells and can arise from anywhere along the sympathetic chain. About 95% of neuroblastomas secrete catecholamines (vanillylmandelic acid [VMA] and homovanillic acid [HVA]), though patients rarely have symptoms related to catecholamine secretion.
Approximately 500-525 cases of neuroblastoma are diagnosed each year in the US. It accounts for 8-10% of all pediatric malignancies, but it is responsible for 15% of deaths from cancer in the pediatric population. Neuroblastoma is the most common neonatal malignancy, accounting for 30-50% of all neoplastic cases in neonates.
Two thirds of patients with neuroblastoma present with metastases at the time of diagnosis. They often present with constitutional symptoms but can cause symptoms from mass effect. Bone metastases can cause focal pain.
Plain radiographs of the abdomen may show a flank mass. Bone metastases usually occur in the long bones and typically present as irregular lucencies or lytic lesions in the metaphysis or submetaphyseal bone. Lateral views of the spine may show widening of the neuroforamina.
The tumors often appear lobulated and typically have a heterogeneous appearance on contrast-enhanced CT. There are areas of low attenuation in the mass secondary to necrosis and hemorrhage. Bone metastases are better evaluated with MRI than CT.
Neuroblastomas are typically hypointense on T1-weighted images and hyperintense on T2-weighted images. When gadolinium is administered, the tumor exhibits inhomogeneous enhancement.
Neuroblastomas appear as an inhomogeneously echogenic mass on sonograms, and sonography can be used to identify liver metastases. Ultrasonography is used to differentiate adrenal hemorrhage from neuroblastoma. They typically appear echogenic in the newborn, as neuroblastomas do, but they gradually become anechoic and avascular and often become smaller on serial sonograms as they regress.
Iodine-131 metaiodobenzylguanidine (MIBG) and iodine-123 MIBG are used to identify sites of primary neuroblastomas, but this is nonspecific because other tumors containing sympathetic tissue such as neuroblastomas, ganglioneuroblastomas, ganglioneuromas, medullary thyroid carcinomas, pheochromocytomas, and carcinoids, take up MIBG.