Petrous Apex Lesions


Learn more about petrous apex lesions and how they are treated.

The petrous apex refers to a portion of the temporal bone situated approximately two to three inches in from the outer portion of the ear. Fluid-filled cysts, cholesteatomas, cholesterol granulomas, and other types of lesions may develop on the petrous apex and require medical intervention.

  • These lesions are often benign
  • However, location of the petrous apex can make surgical treatment complicated

What Causes a Petrous Apex Lesion?

The exact cause of some petrous apex lesions is not clear. It is believed that cholesterol granulomas may develop as the result of air infiltrating the bone marrow and creating pockets that then fill with blood and trigger the formation of a cyst. Cholesterol granulomas may also be linked to dysfunctions involving the Eustachian tube. The purpose of the Eustachian tube, which connects the tympanic cavity to the back of the nose, is to allow air to enter behind the eardrum while also allowing fluid and mucus to drain.

Cholesteatomas involving the petrous apex may be congenital, meaning the condition is present at birth, or it may be acquired during the patient’s lifetime. Congenital cholesteatomas are typically caused by skin cells left behind during embryonic development. The cells form a skin cyst known as a cholesteatoma. Acquired cholesteatomas are normally caused by Eustachian tube dysfunction, or rarely from trauma to or surgery in the ear. Both congenital and acquired cholesteatomas can become quite large and impinge on nerves and other nearby inner ear structures. Some congenital cholesteatomas occur outside the petrous apex between the dura and the temporal bone.

Symptoms of Petrous Apex Lesions

Small petrous apex lesions may not cause any issues or symptoms. Problems may arise when the lesions grow and impinge on other nerves such as the facial movement or sensory nerves, the hearing or balance nerves, or nerves that move the eyes. A lesion impinging on the various nerves may affect sensations or movement in the face or impact eye movement. Other symptoms may include a feeling that the ear is plugged up, foul smelling drainage coming from the ear, decreased hearing, balance issues, and rarely pain behind the ear.


A doctor may arrive at a preliminary diagnosis of a petrous apex lesion based on the patient’s symptoms and the results of an initial evaluation. Computed tomography or magnetic resonance imaging scans are normally used to confirm the diagnosis and to determine the best treatment approach. Most petrous apex lesions are diagnosed incidentally on MRI’s obtained for other reasons such as headaches.

Treating Petrous Apex Lesions

The treatment of petrous apex lesions depends on the type of lesion, the severity of the patient’s symptoms, and the amount of damage that the growth has caused to the surrounding structures of the ear. Cholesterol granulomas affecting the petrous apex are fluid-filled cysts, so the primary treatment involves draining the cyst. There are a number of different approaches that the surgeon may use to access the cyst; however, the most frequently used technique is the infracochlear approach. This technique involves accessing the granuloma from a position just below the cochlea of the inner ear. More recently, we have started observing some cholesterol granulomas since some of these have been found to not grow.

Petrous apex cholesteatomas, on the other hand, are a little more complicated since they must be completely removed. Although it is possible to access the cholesteatoma through the inner ear, it is sometimes also necessary to access it through the middle fossa located below the brain. In some cases, the cholesteatoma can be approached via a transcochlear or transotic approach when the hearing is not salvageable.

What to Expect Following Treatment

It is normal to for the ears to feel full or plugged up for a few weeks following the procedure. Most patients find that their normal hearing returns and that they are able to return to their normal activities free of any symptoms, if the inner ear function is normal prior to surgery.

Avoiding Petrous Apex Lesions

In many cases, such as with congenital cholesteatomas, there is nothing that a person can do to prevent a petrous apex lesion. The key is to seek medical attention as soon as possible after symptoms develop. Individuals should consult their doctor if they experience:

  • Recurrent or chronic ear infections
  • Changes in their hearing
  • Issues maintaining balance
  • Pain in or around their ear
  • Drainage from the ears
  • Trauma to the ears
  • Changes in sensation of the face
  • Facial paralysis that lasts more than 6 months warrants further work up