A 29-year-old male complained of a four month history of horizontal, spontaneous, and nonprogressive diplopia. On examination he had a mild left sixth nerve palsy. The rest of his general and neurologic examinations were normal.
Computed tomography scanning demonstrated a nonenhancing, well-circumscribed, lesion in the left petrous apex (Figure 1). The opposite apex was well pneumatized. The lesion abutted the medial wall of the horizontal canal of the internal carotid artery and pointed towards the lateral wall of the sphenoid sinus. Unfortunately, CT bone windows were not available for this case but would have been helpful in terms of the differential diagnosis. An MRI demonstrated a predominantly high signal mass on T1 and T2 sequences (Figure 2). The diagnosis was a petrous apex granuloma.