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Petrous Apex Lesions, Cholesterol Granuloma, Cyst, Cholesteatoma


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.


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.

How is a Diagnosis Made?

The diagnosis is made by examination and imaging studies (such as CT scan (special x-ray) of the temporal bone (ear bone) and/or MRI (special imaging study)).


The treatment of a petrous apex cholesterol granuloma or cyst is drainage. The drainage is performed via one of several routes. The drainage is performed either through an infracochlear (below the hearing part of the inner ear) approach, an infralabyrinthine (below the balance part of the inner ear), through the inner ear (translabyrinthine or transarcuate), zygomatic root (through the front and above the ear), transsphenoid (through the sinuses), or middle cranial fossa (from above the ear and under the brain).

The most common approach is an infracochlear approach (see below video). Please note this is a surgical video and may not be suitable for all viewers.

A petrous apex cholesteatoma requires complete removal. This is generally only possible through a middle fossa (below the brain), combined middle fossa and through the ear (above and through the ear but sparing the inner ear), or through the inner ear (translabyrinthine).

What option is best for you?

A comprehensive evaluation has to be performed by an experienced team of you and your imaging studies.

Who should you have do your surgery?

A subspecialist in the field of ear surgery (neurotologist) generally performs this surgery. If a middle fossa surgery is required, a neurosurgeon will assist in these procedures. Most major medical centers perform very few of these procedures per year.

Why come to UC Irvine for your treatment?

Our team has had extensive experience with petrous apex cholesteatomas, cholesterol granulomas, or cysts. Our center performs surgery for these types of tumors on a routine basis. The UC Irvine skull base team examined and discusses each patient and ensure a safe, individualized plan for every patient and provide the information necessary for the patient to make an informed decision. Dr. Djalilian has published articles on the anatomy of the petrous apex and some of these approaches to the petrous apex. Patients from surrounding states have travelled to us for their treatment.

To Make an Appointment with our ear specialists, Drs. Djalilian or Lin, Please Call 714-456-7017 or click here to request an appointment via the web.