Extraneural metastases (cervical lymph nodes, lung, liver, and particularly bone) may occur, but usually only after craniotomy, which may allow tumor cells to reach scalp lymphatics. In rare instances the tumor cells may be spontaneously blood-borne and become metastatic to lung or liver. Decerebrate attacks (“cerebellar fits”) appear in the late stages of the disease.
The radiologic appearance of this tumor is distinctive: high signal intensity on both T1-enhanced and T2-weighted MRIs, heterogeneous enhancement, and, of course, the typical location adjacent to and extending into the fourth ventricle. The tumor frequently fills the fourth ventricle and infiltrates its floor (Fig. 30-12). Seeding of the tumor may occur on the ependymal and meningeal surfaces of the cisterna magna and around the spinal cord. The tumor is solid, gray-pink in color, and fairly well demarcated from the adjacent brain tissue. It is very cellular, and the cells are small and closely packed with hyperchromatic nuclei, little cytoplasm, many mitoses, and a tendency to form clusters and pseudorosettes. The interstitial tissue is sparse.
Treatment Maximal resection of the tumor is currently recommended. The addition of chemotherapy and radiotherapy of the entire neuraxis improves the rate and length of disease-free survival even for those children with the most extensive tumors at the time of diagnosis (Packer). The combination of surgery, radiation of the entire neuraxis, and chemotherapy permits a 5-year survival in more than 80 percent of cases.
Fear of radiation-induced cognitive deficits in the young children most often affected by this tumor has led to exploration of postoperative chemotherapy without radiation as an alternative. Rutkowski and colleagues have reported some promising results, especially after gross total tumor resection, but a large number of children nevertheless acquired a leukoencephalopathy, which was said to be asymptomatic. The presence of desmoplastic features (i.e., connective tissue formations) is associated with a better prognosis independent of the type or treatment. Children who have residual tumor after surgery, and more so those with metastases, have a much poorer prognosis. Any of the features of brainstem invasion, spinal subarachnoid metastases, and very early age of onset (younger than 3 years) greatly reduce the period of survival. Acquired genetic alterations in the tumor cells that have prognostic influence have been summarized earlier. A novel inhibitor of the abnormal hedgehog pathway in medulloblastoma cells had a marked therapeutic effect in one adult patient (Rudin et al).
Neuroblastoma This, the most common solid tumor of childhood, is a different entity from medulloblastoma but of nearly identical histologic appearance, arising in the adrenal medulla and sometimes metastasizing widely. Usually it remains extradural even if it invades the cranial and spinal cavities. The main neurologic interest is a syndrome of polymyoclonus with opsoclonus and ataxia that occurs as a paraneoplastic complication as discussed further on. A rare form of neuroblastic medulloblastoma in adults tends to be more benign (Rubinstein, 1985).
In keeping with the genetic determinants of prognosis in this broad class of tumors, a loss of heterozygosity of certain sites on chromosomes 1 and 11 has been associated with somewhat poorer outcomes by Attiyeh and colleagues. MYCN amplification or overexpression is a poor prognostic factor, as it is in medulloblastoma. Various acquired chromosomal deletions and gains may also have predictive importance. More provocative are findings that suggest the emergence of an aggressive tumor based on polymorphisms in chromosome 6p. Maris has provided a review of the interesting genetic aspects of the tumor.