Tumour of the optic chiasma.

Tumours arising in the small area at the base of the brain between the optic chiasma and cerebral peduncles are common and include meningiomas, suprasellar and pituitary neoplasms, aneurysm of the circle of Willis, and chiasmal arachnoiditis with cyst formation. Tumours arising in the optic chiasma and nerve sheaths, however, are very uncommon. In all these conditions, visual symptoms may obtrude to a degree that renders clinical differentiation difficult. In the case of chiasmal glioma here reviewed, diagnosis was much simplified by the characteristic radiological features.