BRAIN TUMORS

Intracranial tumors are the commonest solid tumors and second commonest neoplasms after leukemia in children, accounting for ~15-25% of all neoplasms in different age

TABLE 18.34: Common CNS tumors in childhood

• Infratentorial tumors

- Cerebellar astrocytoma

- Medulloblastoma

- Gliomas, e.g.

- Others, e.g. dermoids, teratoma, epidermoids

• Supratentorial tumors

- Craniopharyngioma

- Cerebral astrocytoma

- Gliomas, e.g. optic nerve glioma, oligodendroglioma

- Pineal body tumors: Germ cell tumor, pinealomas

- Choroid plexus teratoma

• Secondary leukemic infiltrates (at any location)

groups. Infratentorial tumors are more common (~2#8725;3^rd) except below 2 years of age when supratentorial lesions are equally common.

Classification: As clinical presentation of infratentorial and supratentorial tumors is significantly different, these tumors are best classified according to their location (Table 18.34).

Cerebellar astrocytoma and craniopharyngioma are the commonest infratentorial and supratentorial tumors respectively. Medulloblastoma is the commonest brain tumor in children lt;7 years. Gliomas at any site account for ~50% of all brain tumors and ~70% of malignant brain tumors in children.

Etiology: Like other neoplasms, exact etiology is not known but genetic basis exists for some neoplasms, e.g. glioma and meningioma. 25% of optic glioma are associated with neurofibromatosis or tuberous sclerosis. Cranial radiation for leukemia or other metastasis is also known to produce brain tumors.

Pathology: According to the cells of origin, these tumors may be divided as:

• arising from neuroglial cells, e.g. astrocytoma, epen­dymoma and glioblastoma,

• arising from primitive neuroectodermal cells, e.g. medulloblastoma and pineoblastoma, and

• arising from other embryonic remnants, e.g.

Clinical presentation of brain tumors depends on their location or histological type and includes:

• Raised intracranial pressure (ICP) with headache, vomiting and diplopia, is usually the presenting manifestation in infratentorial lesions. Important clinical signs include—(i) increasing head size with bulging anterior fontanel and widening of sutures, (ii) positive Macewan (crackpot) sign, (iii) papilledema, and (iv) strabismus due to VI nerve palsy (false-localizing sign). Children with extremely raised ICP may develop altered sensorium, coma, bradycardia, hypertension and irregular respiration. Hydrocephalus and raised ICP is a late sign in supratentorial tumors, except choroid plexus papillomas (excessive CSF production) and invasive pineal body tumors.

• Seizures are common presenting features in supratentorial lesions, though these are usually generalized with limited localizing value.

• Altered behavior and sensorium: While behavioral abnormalities, e.g. irritability, lethargy and poor aca­demic performance are common and early indicators of all brain tumors, established coma is uncommon, except in terminal stages.

• Localizing motor signs, provide valuable diagnostic clues, e.g.

- Nystagmus and ataxia indicates cerebellar tumors. While midline tumors of vermis begin with truncal ataxia, lesions of cerebellar hemisphere produce unilateral ataxia.

- Nuchal rigidity and head-tilting indicates herniation of cerebellar tonsils-a bad prognostic sign and contraindication for lumbar puncture.

- Dense hemiplegia in early stages indicates pontine or medullary tumors. Cranial nerve palsies, e.g. facial and pseudobulbar paralysis is also common in them. Cortical tumors often have non-dense or fine motor deficits.

- Cranial nerve involvement is characteristic in some tumors, e.g. facial palsy in cerebellopontine angle tumors, pseudobulbar palsy in ponto-medullary tumors, vision loss in craniopharyngioma or optic gliomas, and external ophthalmoplegia in pineal body tumors (Perinaud syndrome-paralysis of conjugate upward movement of eyes with poorly reactive pupils due to pressure on quadrigeminal plate).

- Endocrinal abnormalities, e.g. short stature, obesity and diabetes insipidus, etc. are common in cranio­pharyngioma due to pituitary/hypothalamic involvement. Involvement of hypothalamus in optic glioma produces Diencephalic syndrome of infancy, i.e. extreme emaciation and anorexia with­out loss of linear growth or mental changes.

Diagnosis: Neuroimaging with MRI or CT scan is essen­tial to diagnose and delineate intracranial tumors. MRI is better to identify posterior fossa tumors, to define the extent of infiltrating tumors and to diagnose spinal cord metastasis. However, intracranial calcification- commonly seen in craniopharyngioma, may be missed on MRI.

Routine CSF examination has no diagnostic value in brain tumors. Sella turcica tumors, e.g. cranio­pharyngioma or optic glioma need endocrinal studies before/after surgery.

D/D of brain tumors includes other intracranial space occupying lesions (Table 18.33), specially tuberculoma

TABLE 18.35: D/D supra- vs infra-tentorial tumors

Abn: Abnormal, ICP: Intracranial pressure

and neurocysticercosis.

Important clinical differences between supratentorial and infratentorial tumors are given in Table 18.35.

Management: Control of seizures and raised ICP (with CSF shunt in most cases) is the first priority in these cases. Specific treatment of brain tumors depends on its type and location, as follows:

• Surgical resection is the treatment of choice in localized, low-grade neoplastic tumors except in optic nerve glioma and pineal body tumor. Pre/post operative radiotherapy may be useful in large tumors.

• Chemotherapy is preferred in optic nerve glioma, pineal body tumor and metastatic tumors from extracranial sites.

• Radiotherapy of whole neuraxis is necessary in medulloblastoma and anaplastic ependymoma, along with surgery and chemotherapy in medulloblastoma. Brachytherapy, i.e. intracranial implantation of radiation seeds has improved the efficacy and reduced the risk of radiation in treatment of brain tumors.

Outcome: Five-year survival following best therapeutic modalities is excellent in cerebellar astrocytoma, medulloblastoma, optic nerve glioma, low-grade astrocytoma and germ cell tumors (70-90%), good in ependymoma and craniopharyngioma (50-60%) and poor in brain stem glioma and invasive astrocytoma (10-20%). However, post-surgery or irradiation complications are common and include—(a) impairment of intellect, speech and vision, (b) seizures, (c) focal neurological defects, (d) endocrinal abnormalities, and (e) second malignancies.

Some important brain tumors in children are as follows: Medulloblastoma are midline cerebellar tumors of primitive neuroectodermal origin (PNET), accounting for gt;40% of posterior fossa tumors in young children, specially boys. Presenting as rapidly growing malignant tumors with cerebellar signs and raised ICP, CSF seeding is present in gt; 40% cases with poor prognosis.

Cerebellar astrocytoma arise from one of the cerebellar hemispheres and present as low-grade slow-growing tumors with ataxia and other cerebellar signs, which are often localized and fully resectable with favorable prognosis.

Craniopharyngioma are benign cystic tumors, arising from Rathke pouch and presenting with growth failure, visual field defects, endocrinal abnormalities, e.g. diabetes insipidus and delayed puberty. X-ray skull may show calcifications and treatment includes cyst aspiration followed by radiotherapy.

Gliomas are commonest CNS tumors across all ages in children, arising from neuronal glial cells. Depending on the site of origin, these tumors are termed as optic nerve glioma, pontine glioma, ependymoma, etc. Juvenile pilocytic astrocytoma is the commonest glioma in children. Some glioma are malignant and not resectable, requiring combination of chemotherapy and radiotherapy for treatment with poor outcome.

18.14