CNS Tumors

CNS TUMORS

CNS tumors account for 20% of all pediatric tumors. Most pediatric tumors mainly arise in the posterior fossa, while adult tumors arise in the supratentorial region. Factors determining prognosis and response to therapy include the following:

•         Age

•         Tumor location

•         Grade

•         Extent of surgical resection

•         Molecular subgroupings

The World Health Organization (WHO) grading system assigns grades I–IV, with grade IV tumors the most aggressive. While grade IV glioblastoma patients usually succumb to disease within a year, other patients with treatable grade IV tumors may survive 5 years. Metastasis of CNS tumors is rare.

Tumors of Neuroepithelial Tissue

Tumors of neuroepithelial tissue are categorized as astrocytic tumors, oligoden-droglial tumors, ependymal tumors, and embryonal tumors (further broken down as medulloblastoma or CNS primitive neuroectodermal tumor).

Astrocytoma originates from astrocytes and exhibits fibrillary background, immu-noreactivity for glial fibrillary acidic protein (GFAP), and diffuse (ill-demarcated) pattern of growth.

•         Pilocytic astrocytoma is a well-differentiated, benign astrocytic tumor that arises throughout the neuraxis; it is common in children and young adults. It is the most common benign CNS tumor in children.

•         Sites of involvement include posterior fossa (cerebellum) and diencephalon

Radiographically, most show cystic lesion with a mural nodule

Histology shows spindly neoplastic astrocytes with long bipolar pro-cesses

Rosenthal fibers are thick, corkscrew-like eosinophilic structures that derive from hypertrophic processes of astrocytes

Posterior fossa tumors have favorable prognosis

Activating mutations in BRAF are common

•         Fibrillary (diffuse) astrocytoma is a low-grade tumor that arises in the cerebral hemisphere of young to middle-aged adults and the brainstem of children.

IDH1 (immunostain) is positive.

•         Anaplastic astrocytoma is cellular, pleomorphic and mitotically active.

•         Glioblastoma is the most common CNS primary malignancy in adults.

Histology shows necrosis and/or vascular proliferation in addition to features seen in anaplastic astrocytoma.

The prognosis of astrocytomas varies.

•         Well-differentiated astrocytomas grow slowly; affect younger patients.

•         Anaplastic astrocytomas and glioblastoma are aggressive; affect older patients; median survival for glioblastoma is 15 months.

Oligodendroglioma occurs more often in adults than in children. Its cortical location may cause seizures. Histologically, perinuclear halos are a fixation artifact that is not seen on frozen section. This tumor is slow-growing. Tumors with deletions of 1p and 19q respond well to therapy.

Ependymoma is typically located in the fourth ventricle in children, where it presents with obstructive hydrocephalus. In adults the spinal cord is the most common site. Pseudorosettes are a helpful diagnostic feature on microscopic study. Multifocality in the spinal cord is associated with NF2. The prognosis depends on tumor location and adequacy of resection.

Embryonal (primitive) tumors are a group of small round cell tumors that occur predominantly in children. In the cerebellum, they are called medulloblastoma.

•         Medulloblastoma is the most common malignant brain tumor in children.

•         Molecular subgroupings are proving useful for prognosis; Wnt subgroup has the best prognosis.

Tumors of Cranial and Paraspinal Nerves

Schwannoma originates from Schwann cells of cranial or spinal nerves. The most frequent location is on CN 8 at the cerebellopontine angle (CPA). Schwannoma manifests characteristically with unilateral loss of hearing and tinnitus. The prog-nosis is good after surgical resection.

•         Has spindly cells arranged in hypercellular Antoni A areas; alternating hypocellular Antoni B areas; and Verocay bodies, parallel rows of neoplastic Schwann cells.

•         Neoplastic cells are immunoreactive for S-100.

Tumors of the Meninges

Meningioma is a tumor that originates from meningothelial cells of the arachnoid. It is common in adults (women > men) and rare in children. It is a dura-based mass that can recur if the brain has been invaded, but invasion is unusual. It has varied clinical features but commonly presents with headache, seizures, and neurological deficits.

•         Histology shows cellular whorls and psammoma bodies. Many patterns are seen; the syncytial pattern is common.

•         Abnormalities of chromosome 22 are sometimes present.

•         Multiple meningiomas occur in NF2 patients.

The prognosis of meningioma is good, though tumors in some locations may not be amenable to complete resection.

Tumors of the Sellar Region

Craniopharyngioma arises from rests of odontogenic epithelium within the suprasel-lar/diencephalic region. It most commonly affects children and young adults. The most common presenting symptoms are headache, hypopituitarism, and visual field disturbances.

•         Contains deposits of calcium, evident on x-ray

•         Histology shows squamous cells and resembles adamantinoma, a bone tumor of unknown histological origin that is the most common tumor of the tooth

•         Is benign but tends to recur after resection

•         Beta-catenin (CTNNB1) gene mutations have been reported

Other Neoplasms

•         Lymphomas are the most common CNS tumors in the immunosuppressed. Primary CNS lymphomas may be multiple, unlike other histologic types. They do not respond well to chemotherapy.

•         Germ cell tumors are more common in children than adults. The germinoma is the most common histologic type. It resembles the seminoma of the testis and the dysgerminoma of the ovary; the cells are large with a prominent nucleolus. These tumors are radiosensitive.

Metastatic Tumors

About 25–50% of all CNS tumors are metastatic tumors from sources outside the CNS. Carcinomas are the most common.