Unilateral pupil sparing oculomotor nerve paresis with an anterior communicating artery aneurysm: A case report with literature review

Objective

An anterior communicating artery (ACoA) aneurysm causing unilateral pupil sparing oculomotor nerve paresis is highly unusual. This is, to the best of our knowledge, the second case report of its sort. Compression, ischemia, or haemorrhage affecting the anterior visual pathway are common neuro-ophthalmic manifestations of ACoA aneurysm but when there is partial paresis it only affects the superior division of the third cranial nerve's fibres which is an extremely rare occurrence.

Case presentation

A 45-year-old man came in as an outpatient with complaints of severe headache and right eyelid drooping for the previous 6 days. He had GCS 15 (E4,V5,M6), and right eyelid partial ptosis with normal reactive pupils. The other cranial nerves and neurological examination came out normal. A non-contrast enhanced computed tomography (CT) scan of the brain revealed a hyperdense area around the ACoA region and SAH. During CT angiography, an ACoA aneurysm was found. The patient was clipped on the 24th post-bleeding day. On the three-week follow-up appointment, the ptosis had improved somewhat.

Conclusions

Although unilateral pupil sparing oculomotor nerve paresis has little localising utility, it does help to comprehend acute microvascular spasm, which may have therapeutic implications.