Asymmetric temporal bone pneumatization: an MR imaging pitfall.

A healthy 44-year-old woman was evaluated neurologically because she had had dizziness without vertigo and right facial pain for several months. The pain was not typical for trigeminal neuralgia, and she had had no loss of hearing. Physical examination showed no abnormalities. Cranial MR imaging was ordered for evaluation of the cerebellopontine angle. Axial MR images showed apparently normal eighth cranial nerves bilaterally (Fig . 1). However, an asymmetric area of increased signal was noted anterior to the origin of the right eighth cranial nerve. Coronal and parasagittal sections showed high signal intensity in the right cerebellopontine angle , but without any mass effect. The MR signal from this area was that of fat, and a possible lipoma or other fatty tumor was considered. Axial CT scanning showed asymmetric pneumatization of the temporal bones, particularly the petrous apex. The left was pneumatized completely, and the right contained marrow. This marrow clearly was the explanation for the high MR signal intenSity in the right cerebellopontine angle.