hydrocortisone 100 mg intravenously every six to eight hours) with careful monitoring of electrolyte balance. Surgical decompression is usually indicated although occasional patients do well with conservative management.

Diagnosis: Pituitary apoplexy

Tip: CT is not adequate for ruling out suspected pituitary apoplexy.

Progressive sixth nerve palsy

Case: A 66-year-old retired businessman initially noticed “fuzzy vision” whenever he looked to the left. Over the next month this fuzzy image split into two distinct images. At first he was able to fuse the two images with effort but over the next three months, this became increasingly difficult and he developed consistent diplopia on left gaze. Eventually he experienced diplopia in primary position as well, initially at distance and then at near. He reported no head or eye pain but described a “tired feeling” in his left eye after prolonged distance viewing, such as driving. His past medical history was positive only for benign prostatic hypertrophy. Afferent visual function, pupillary examination and fundus appearance were normal in each eye. He had a 12 diopter esotropia in primary position that increased on left gaze. There was mild limitation of abduction of the left eye and slowing of left lateral rectus saccades, even with small amplitude movements. An MR scan of brain and orbits was reportedly normal (Figure 4.15).

What aspect of this patient’s presentation provides the most compelling diagnostic clue?

This patient provides a clear history of gradually progressive diplopia and his examination points to a unilateral cranial nerve palsy. This combination of clinical findings strongly indicates a compressive lesion as the cause. Careful inspection of his MRI focusing on the course of the left sixth nerve revealed a very small enhancing mass at the

Figure 4.15 Axial post-contrast T1-weighted MR image of a retired businessman with a progressive left sixth nerve palsy, interpreted as normal.

entrance to Dorello’s canal, a bony space at the tip of the temporal bone which encloses the abducens nerve as it enters the cavernous sinus (Figure 4.16). A second, small extra-axial focus of enhancement was identified along the upper lateral left cerebral convexity. The radiographic appearance of these lesions was sufficiently characteristic that a diagnosis of meningioma was made without histopathologic confirmation. He was managed initially with prism correction but over the next six months his esotropia increased to 25 diopters. He was then treated with external beam radiation consisting of 5580 cGy in twice-daily fractions. His esotropia subsequently stabilized and he eventually underwent extraocular surgery with good post-operative ocular alignment.

Discussion: In a certain sense, diplopia is always sudden in onset regardless of mechanism; the