Petrous Apex Masses, Cysts, Cholesterol granulomas, Etc.

Overview

The petrous apex is located in the center of the head approximately 2-3 inches from the outside of your ear. It is one of the most inaccessible areas to reach in the skull. The petrous apex can have lesions and tumors within it. The most common type of lesion is a petrous apex fluid filled cyst. This petrous apex cyst may take the form of a petrous apex cholesterol granuloma, cholesteatoma (epidermoid), or other type of lesion.

You may reference the Anatomy of the Ear page for better understanding of the anatomy.

Presenting Symptoms of Petrous Apex Cysts

Petrous apex lesions can be silent. But, they can commonly present with problems they cause due to expansion. The expansion can cause problems by putting pressure against adjacent structures such as the inner ear, the nerves of the inner ear, the facial nerve, the nerves that move the eyes (most commonly abducens nerve), or the nerve that supplies the sensation of the face.

Causes

The cause of these lesions are unknown. There are various theories for petrous apex cholesterol granulomas including eustachian tube dysfunction and invasion of bone marrow by air cells. Petrous apex cholesterol granulomas appear to occur when there is bleeding into the air pockets in the petrous apex and a cyst forms around it.

Petrous apex cholesteatomas can be congenital or acquired. In congenital petrous apex cholesteatomas, most commonly, a few skin cells are left behind in the embryonic stage and these cells form a skin cyst (cholesteatoma) in that area. The cyst will grow over time and will invade various structures.

Acquired petrous apex cholesteatomas occur due to eustachian tube dysfunction and can extend from the ear drum all the way into the petrous apex.