Petrous apex.

The petrous apex is the most medial portion of the temporal bone that cannot be directly examined on clinical examination. The referring physician completely relies on imaging and radiologic interpretation. Unfortunately, the petrous apex displays anatomic variations such as asymmetric pneumatization that might be mistaken for underlying lesions. The location of the petrous apex also typically precludes safe percutaneous biopsy. Knowledge of the petrous apex anatomy, normal anatomic variations, and their differentiating features from pathologic entities is critical for accurate interpretation.