CNS tumours account for 20% of all pediatric tumours.
CNS tumours account for 20% of all pediatric tumours. Most pediatric tumours mainly arise in the posterior fossa, while adult tumours arise in the supratentorial region. Factors determining prognosis and response to therapy include the following:
- Tumour location
- The extent of surgical resection
- Molecular subgroupings
The World Health Organization (WHO) grading system assigns grades I–IV, with grade IV tumours the most aggressive. While grade IV glioblastoma patients usually succumb to the disease within a year, other patients with treatable grade IV tumours may survive 5 years. Metastasis of CNS tumours is rare.
Tumours of Neuroepithelial Tissue
Tumours of neuroepithelial tissue are categorized as astrocytic tumours, oligodendroglial tumours, ependymal tumours, and embryonal tumours (further broken down as medulloblastoma or CNS primitive neuroectodermal tumour).
Astrocytoma originates from astrocytes and exhibits fibrillary background, immunoreactivity for glial fibrillary acidic protein (GFAP), and diffuse (ill-demarcated) pattern of growth.
- Pilocytic astrocytoma is a well-differentiated, benign astrocytic tumour that arises throughout the neuraxis; it is common in children and young adults. It is the most common benign CNS tumour in children.
- Sites of involvement include the 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 fibres are thick, corkscrew-like eosinophilic structures that derive from hypertrophic processes of astrocytes
Posterior fossa tumours have a favourable prognosis
Activating mutations in BRAF are common
- Fibrillary (diffuse) astrocytoma is a low-grade tumour 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; the 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 tumour is slow-growing. Tumours 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 the microscopic study. Multifocality in the spinal cord is associated with NF2. The prognosis depends on tumour location and adequacy of resection.
Embryonal (primitive) tumours are a group of small round cell tumours that occur predominantly in children. In the cerebellum, they are called medulloblastoma.
- Medulloblastoma is the most common malignant brain tumour in children.
- Molecular subgroupings are proving useful for prognosis; the Wnt subgroup has the best prognosis.
Tumours 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 prognosis 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.
Tumours of the Meninges
Meningioma is a tumour that originates from the 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 the 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 tumours in some locations may not be amenable to complete resection.
Tumours of the Sellar Region
Craniopharyngioma arises from the rests of the odontogenic epithelium within the suprasellar/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 tumour of the tooth
- Is benign but tends to recur after resection
- Beta-catenin (CTNNB1) gene mutations have been reported
- 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 isthe 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 tumours are radiosensitive.
About 25–50% of all CNS tumours are metastatic tumours from sources outside the CNS. Carcinomas are the most common.