A Case of Nonapoplectic Pituitary Adenoma Presenting with Isolated Oculomotor Nerve Palsy

We report a rare case of nonapoplectic pituitary adenoma that did not invade the cavernous sinus and was associated with isolated oculomotor nerve palsy. A 61-year-old male was admitted to our hospital due to diplopia that had gradually worsened from 6 months to presentation. He was diagnosed with right oculomotor nerve palsy, and brain magnetic resonance imaging (MRI) showed a mass lesion within the sella. The tumor was homogeneously enhanced on contrast-enhanced MRI. However, no findings suggestive of pituitary apoplexy were found. Brain computed tomography revealed the tumor to have eroded the right side of the posterior clinoid process by gradual expansion. Endoscopic transsphenoidal surgery was used for complete resection of the tumor. Intraoperative findings showed that the tumor did not invade the cavernous sinus. The histological diagnosis was pituitary adenoma, and symptom improvement was observed from the early postoperative stage onward. Surgical treatment is essential because oculomotor nerve palsy caused by the enlargement of pituitary adenoma is not expected to resolve if treated conservatively, unlike that caused by pituitary apoplexy.