Reader Response: Pearls & Oy-sters: Isolated Oculomotor Nerve Palsy due to Pituitary Apoplexy Missed on CT Scan

I enjoyed reading this interesting case report by Marzoughi et al.1 As explained by the authors, medial lesions of the cavernous sinus can spare other neighboring cranial nerves and present as isolated oculomotor nerve palsy such as in the reported case. However, the authors do not relate to the innervation of the pupil. Their patient had briskly reactive pupils to light and accommodation, that is, the parasympathetic fibers were spared. Pupillary sparing in third nerve palsy has been described in cavernous sinus lesions that save the superior and lateral aspect of the nerve where pupillary parasympathetic fibers are concentrated. Nevertheless, the right pupil was larger than the left. The anisocoria became worse in bright light vs dim light, which indicates a parasympathetic lesion and is in discrepancy with the finding of brisk reaction to light. Could the mild dilatation of the right pupil be due to an irritative lesion of the sympathetic fibers to the right pupil? If this was the case, signs of lesion of the ophthalmic branch of the trigeminal nerve—which contains sympathetic pupillary fibers—should be present. Finally, a physiologic anisocoria could account for mild pupil differences but should not differ in dim vs bright light. Since this is a teaching article, I would be grateful for an explanation.

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