Cholesterol Granuloma
Background
Cholesterol granulomas are rare, benign cysts that can occur at the tip of the petrous apex, a part of the skull that lies adjacent to the middle ear. They are expanding masses that contain fluids, lipids, and cholesterol crystals surrounded by a fibrous lining.
Within the skull there are numerous air-containing spaces called air cells.
It is believed that cholesterol granulomas form when the air cells in the petrous apex are obstructed. The obstruction creates a vacuum which causes blood to be drawn into the air cells. As red blood cells break down, cholesterol in the hemoglobin is liberated. The immune system reacts to the cholesterol as a foreign body, producing an inflammatory response. Associated small blood vessels rupture as a result of the inflammation. Recurrent hemorrhaging causes the mass to expand.
Granulomas can occur throughout the body as a reaction to foreign material, in most cases with no symptoms or serious effects. However, cholesterol granulomas of the petrous apex are dangerous because of their proximity to the ear and several craniofacial nerves. If the mass is left untreated and continues to expand, permanent hearing loss and/or nerve damage can result, as well as destruction of bone.
Causes/Risk Factors
Cholesterol granulomas arise secondarily to conditions which cause the obstruction of the air cells. Such conditions may include severe or chronic ear infections, cholesteatomas, or head trauma that produces hemorrhaging in the area of the petrous apex.
Symptoms
- hearing loss in one ear
- tinnitus (ringing in the ears)
- facial twitching
- vertigo
- facial numbness
Diagnosis
Upon examination of the ear with an otoscope, the eardrum may appear blue or a brownish protrusion behind it may be evident. Imaging studies (MRI, CT) aid in differentiating the cholesterol granuloma from other lesions, specifically from cholesteatomas, and in revealing its size and precise location. Audiograms may be used to assess hearing loss.
Treatment
Treatment involves drainage and ventilation of the cholesterol granuloma. In cases where the granuloma is particularly large and destructive, complete removal may also be necessary. Access to the petrous apex is difficult and requires special surgical skills. The approach used depends upon the location of the mass, the skills of the surgeon, and the status of the patient’s hearing.
The translabyrinthine approach, in which the incision is made behind the ear, is generally used for patients who already have severe hearing loss, as it results in complete sensorineural loss of hearing. Hearing can be preserved with the infralabyrinthine or infracochlear approaches.
Cholesterol granulomas of the petrous apex, particularly those with growth in the direction of the clivus, with midial expansion or with inferior expansion under the level of the internal carotid artery, can be directly approached through expanded endonasal approach (EEA). This state-of-the-art, minimally invasive surgical procedure uses the nose as a natural corridor to reach these lesions. There are no incisions in the skin of the face or head. When the location of the cholesterol granuloma permits, a transnasal approach is preferred, as it also preserves hearing and is minimally invasive.
Prevention
There are no guidelines for preventing cholesterol granulomas. However, early diagnosis and treatment may help prevent serious complications, some of which are irreversible.