INTRACRANIAL TUMOURS

By Dr. J.B. Adetunji

Introduction

• Intracranial tumours may be primary or secondary, benign or malignant. Benign and malignant tumours of the central nervous system occur in almost equal proportions.
• Primary Brain Tumours
• Glial tumours - 50%
• Meningiomas - 25%
• Schwannomas – 10%
• Others - 15%

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• In general metastasis from other parts of the body occurs more frequently than primary tumours in the central nervous system- 15% of these occur in the brain and 5% in the spinal cord among patients who die of cancer. It is imperative to investigate the central nervous system for metastases in cancer patients especially if they manifest central nervous symptoms.

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Clinical Features

The manifestation of intracranial tumours exhibit 3 main clinical syndromes:

• Progressive focal neurological deficit
• Seizure
• Non-focal neurological disorder- headache, dementia, personality change or disturbance of gait.

In secondary intracranial tumours these are often associated with systemic symptom like weight loss, malaise, anorexia or fevers.

• Progressive focal neurological deficits are due to compression of neurons and white matter tracts by the expanding tumour mass and the associated oedema; Haemorrhage may also contribute to the mechanism of the neurological deficit. Tumours that often have associated bleeding intracranially include choriocarcinomas, metastatic melanoma and high-grade gliomas.

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• Seizures-often arise from intracranial tumours. The mechanisms include:
• Disruption of cortical circuit
• Raised ICP.
• Non-focal neurological deficits are often associated with raised ICP and Hydrocephalus, or diffuse tumours spread.
• Behavioural changes are often associated with frontal lobe tumours and this may be accompanied with dementia and/or depression.

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• Non-focal neurological deficits include headache, vomiting, dementia, depression Headache may be due to focal irritation or displacement of pain sensitive structures or raised ICP. Postural headaches are often encountered in intracranial tumours. These headaches tend to be generalized (holocephalic) and occur in episodes; also tend to be worse at night- during sleep. With sustained elevation of the ICP the headache tends to be continuous. Fundoscopy often shows papilledema in patients with intracranial tumours (especially young people and adults below55years; not often seen in infants)
• Karnofky's Performance Scale- used to assess ability of cancer patient to care for self; rate 0-100.

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Investigation

Neuroimaging:

• Mammogram
• CT scan - skeletal survey and bone scan
• Nuclear medicine forms the mainstay of investigating intracranial tumours. These pick up the tumour mass and surrounding oedema. The use of contrast is possible due to the disruption of the blood-brain barrier.

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PET /SPECT:

• Are mainly of ancillary use to delineate tumour recurrences from tissue necrosis (post radiation PX). Mammogram, bone scan skeletal and abdominal scans are done in search of primary with central nervous system metastases.

Serology:

• Not useful in the investigation of primary brain tumours because they have no serological abnormalities-ESR, tumour-specific antigens. However secondary tumours may have systemic effects depending on the type of primary.

Lumbar Puncture:

• Must be done with care if indicated to avoid precipitating herniation.
• In general rarely contains tumour cells with the exception of leptomeningeal metastases; primary central nervous system lymphoma, primitive neuroectodermal tumour i.e. medulloblastoma.
• LP is however useful in excluding infections and demyelinating diseases.

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Treatment is Mainly Supportive:

• Glucocorticoids- Dexamethasone-reduce oedema surrounding tumours mass and relieves symptoms. Dexamethasone has very little mineralocorticoid activity hence its preference.
• Anticonvulsant therapy-Phenytoin, for associated seizure CBZ, valproic acid, etc.
• Anticoagulant-especially when there is associated limb immobility associated with intracranial tumours-especially gliomas and primary central nervous system lymphoma. These tumours probably secrete pro-coagulant factors.

Specific

• Surgery
• Radiation therapy

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NEUROECTODERMAL SYNDROMES

The neuroectodermal syndromes (phacomatoses) are a group of genetic disorders that cause developmental abnormalities of the skin associated with increased risk of tumours of the nervous system. The pattern of inheritance is autosomal dominant with variable penetrance.

• 1. Neurofibromatosis:
• This is the most common form of neuroectodermal diseases. There are 2 main types (NF1 and NF2)- with NFI being much commoner (Von Recklinghausen's disease)- neurofibromas, pigmented patches on the skin (café-au-lait — Caucasian) or café-au-noir —blacks.
• It is also often characterized by freckling in non sun exposed parts of the body like the axilla. Neurofibromas are benign peripheral nerve tumours composed of proliferating Schwan cells and fibroblasts. They may undergo 20malignant degeneration to sarcomas. The NF1 gene is a tumour suppressor which may mutate to cause the disease.

• Other clinical features of NF1 include compressive radiculopathy or neuropathy when the tumour occurs in enclosed spaces. It could also lead to seizures or/and hydrocephalus from aqueductal stenosis; scoliosis, short stature and mental retardation. NF1 patients may develop other nervous system neoplasms like glioma, astrocytoma and phaeochromocytoma or plexiform neurofibromas.
• NF2-more often (>90%) characterized by the development of bilateral vestibular schwannoma. NF2 patients are also predisposed to developing other nervous system tumours i.e. glioma, meningiomas and schwannomas of cranial and spinal nerves. The characteristic cutaneous tumours and patches of skin discoloration seen in NF1 are rare in NF2.
• The patients often present with progressive deafness (usually unilateral). MRI will usually confirm bilateral vestibular schwannomas. NF2 is caused by mutation of NF2 gene on chromosome 22g.

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Treatment

Excision of tumour is sometimes helpful.

Tuberous sclerosis (Bourneville's disease)

• Characterised by cutaneous lesions, seizures and mental retardation. The skin lesions include facial angio-fibromatosis, hypopigmented macules, and yellowish pigmentation of the skin in the lumbosacral region of the back.
• MRI-shows typical subependymal nodules sometimes calcified. T.S. is associated with increased risk of ependymomas astrocytoma in children (>90% subependymal giant cells).

The occurrence of these benign tumours around the Foramen of Munroe could lead to hydrocephalus from occlusion. Other tumours that may occur include rhabdomyoma of the myocardium and angio-myomas of kidney, liver, adrenals, and pancreas.

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Treatment:

• Symptomatic
• Anticonvulsants for seizure
• Shunting of hydrocephalus
• Behavioural therapies for mental retardation.

Prognosis:

• Severely affected patients die before age 30years.

Gene:

• Mutation of either TSC-I gene at 99, or TSC-2 gene at HP.

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