Incomplete oculomotor palsy with pupil sparing caused by compression of the oculomotor nerve by a posterior communicating posterior cerebral aneurysm

Purpose: To report a patient with agenesis of both internal carotid canals who presented with incomplete oculomotor palsy with pupil sparing. Methods: The incomplete oculomotor palsy was followed clinically, and the precise anatomical relation of the aneurysm to the subarachnoid oculomotor nerve was investigated during clipping surgery for the aneurysm. Results: A 39-year-old woman with agenesis of both internal carotid arteries was admitted because of diplopia and left blepharoptosis. The left superior palpebral and the superior rectus muscles were severely palsied. The paralysis of the medial rectus muscle was milder than that of the former two muscles, and the inferior rectus was the least affected muscle. The papillary reflexes were normal. Examination during clipping surgery showed that the aneurysm was located below the oculomotor nerve in the subarachnoid space about 6.5 mm from its exit from the midbrain. The differences in severity and resolution time of the palsies of the extraocular muscles suggested that the fibers destined for the superior levator and the superior rectus were concentrated on the caudomedial portion of the subarachnoid oculomotor nerve. The fibers innervating the medial rectus muscle were located within the core of the nerve, and the fibers innervating the pupils and the inferior rectus muscle occupied a more rostral part. Conclusions: The functional distribution of fibers within the subarachnoid oculomotor nerve about 6.5 mm from its exit from the midbrain succeeds to that of the intraparenchymal oculomotor nerve. Jpn J Ophthalmol 2007;51: 470-473 (c) Japanese Ophthalmological Society 2007.