Cerebral aneurysms presenting with visual field defects.

ANEURYSMS occur more frequently within the cranium than elsewhere in the body, and most-75 to 85 per cent. according to Walsh (1964)-are situated on the anterior part of the circle of Willis. In this region they are closely related to the primary visual pathways and motor nerves to the eye. Extra-ocular muscle palsies are well recognized by ophthalmologists as indicative of such lesions, particularly if accompanied by pain in and around the eye. Green, Hackett, and Schlezinger (1964), in their evaluation of oculomotor nerve paralysis, reported that almost 30 per cent. of all isolated third nerve palsies could be attributed to aneurysms. It is less well recognized that patients harbouring these abnormalities can present initially with signs of compression of the visual pathways, thus exhibiting sensory rather than the more common ophthalmoplegic or motor involvement. Such sensory defects have been reported by Dailey, Holloway, Murto, and Schlezinger (1964), as occurring alone in 12 per cent. of cases of verified cerebral aneurysm, and combined with motor nerve involvement in a further 10 per cent. Walsh (1964), in a series of 117 proven cases, recorded visual field defect due to aneurysm in 13 per cent. This paper reports two cases of cerebral aneurysm presenting with signs of compression of the visual pathway. In one, sudden ipsilateral blindness was the presenting symptom and in the other, the ocular defect was on the side opposite to that on which the aneurysm originated.