Papillomas of the choroid plexus are about one-fifth as frequent as ependymomas. They arise mainly in the lateral and fourth ventricles, occasionally in the third. Two authoritative studies (Laurence et al; Matson and Crofton) give the ratios of lateral/third/fourth ventricular locations as 50:10:40. The tumor, which takes the form of a giant choroid plexus, has as its cellular element the cuboidal epithelium of the plexus, which is closely related embryologically to the ependyma. An oncogene T (tumor) antigen of the SV40 virus is possibly involved in tumor induction (see Schmidek). Essentially, these are tumors of childhood. Fully 50 percent cause symptoms in the first year of life and 75 percent in the first decade. In the younger patient, hydrocephalus is usually the presenting syndrome, sometimes aggravated acutely by hemorrhage; there may be papilledema, an unusual finding in a hydrocephalic infant with enlarging head. Headaches, lethargy, stupor, spastic weakness of the legs, unsteadiness of gait, and diplopia are more frequent in the older child. Tumors that arise from the choroid plexus and project into the lateral recess of the fourth ventricle may present with a syndrome of the cerebellopontine angle (see in the following text). One consequence of the tumor (rather uncertain or inconsistent) may be increased CSF formation, which contributes to the hydrocephalus. Some of the tumors acquire more malignant attributes (mitoses, atypia of nuclei) and invade surrounding brain. They have the appearance of a carcinoma and may be mistaken for an epithelial metastasis from an extracranial site.
Treatment by surgical excision is usually curative, but palliative ventricular shunting may be needed first if the patient’s condition does not permit surgery. The prognosis of the rare choroid plexus carcinomas is poor.
This term was introduced by Hart and Earle in 1973 to describe tumors that have the histologic features of medulloblastoma but occur supratentorially. Various poorly differentiated or embryonal tumors of infancy and childhood were in the past included in this group: medulloblastoma, neuroblastoma, retinoblastoma, ependymoblastoma, and pineoblastoma (described further on). Subsequent authors have broadened the category of PNETs to include all CNS neoplasms of neuroectodermal origin. With the advent of immunohistochemical techniques, many of these poorly differentiated neoplasms of infancy came to be recognized as small cell gliomas (Friede et al); others, after ultrastructural study, could be classified as other types of primitive neoplasms. To some pathologists, the term primitive neuroectodermal tumors has appeal but has added little to our understanding of their undifferentiated embryonal origin. Current classifications have again grouped these with embyronal tumors, the group containing medulloblastoma. In practical terms, the prognosis and treatment of all these tumors are much the same, regardless of what they are called (see Duffner and Cohen). Certain patterns of gene expression are used to distinguish this group of tumors from histologically similar medulloblastomas.
Hemangioblastoma of the Cerebellum
This tumor is referred to most often in connection with von Hippel-Lindau disease, of which it is the essential element. Dizziness, ataxia of gait or of the limbs on one side, symptoms and signs of increased ICP from compression of the fourth ventricle, and in some instances an associated retinal angioma or hepatic and pancreatic cysts (disclosed by CT or MRI) constitute the von Hippel-Lindau syndrome. There is a tendency later for the development of malignant renal or adrenal tumors. Many patients have polycythemia as a result of elaboration of an erythropoietic factor by the tumor.