MRI Note: SITE, MASS EFFECT and LESION MULTIPLICITY as for scanning. Of particular value in demonstrating tumours around the skull base, cranio-cervical junction and the brainstem.
Coronal and sagittal scanning provide additional information, showing the exact anatomical relationship of the tumour to the sulci and gyri, the ventricles, the falx and the tentorium cerebelli.
Paramagnetic enhancement: intravenous gadolinium increases sensitivity of detection and clarifies the site of origin, i.e. intrinsic or extrinsic, and may delineate the border between tumour and surrounding oedema.
Single or multiple lesions: MRI appears more sensitive than CT scanning in identifying small tumours and improves the detection of multiple lesions, e.g. metastasis.
Angiography/MRA: although angiography may reveal a tumour 'blush' or vessel displacement, it is only occasionally required to supplement other investigations. In some patients, it provides useful preoperative information, e.g. identifies feeding vessels to a vascular tumour or tumour involvement and constriction of major vessels.
CSF examination: lumbar puncture is contraindicated if the clinician suspects intracranial tumour. If CSF is obtained by another source, e.g. ventricular drainage or during shunt insertion, then cytological examination may reveal tumour cells.
Tumour markers: although useful as an aid to histological diagnosis (see page 296), attempts to find a substance in blood or CSF which reflects growth of a specific tumour have been limited - only the link between elevated alpha fetoprotein and human chorionic gonadotrophins with germinomas of the third ventricle helps diagnosis.
DIFFERENTIAL DIAGNOSIS OF INTRACRANIAL MASS LESIONS (other than tumour)
Vascular - haematoma
- giant aneurysm
- arteriovenous malformation
- infarct with oedema
- venous thrombosis.
Trauma - haematoma
Infection - abscess
Cysts - arachnoid
- parasitic (hydatid).
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