Timothy C. Hain, MD
Page last modified: April 1, 2017
Cholesterol granulomas of the petrous bone are tumor like growths, made of inflammatory cells. The term is actually a pathological one, but generally it is applied to MRI images (where there is no pathology). So basically it occurs when radiologists guess about the pathology of something they see on MRI. When tissue is obtained, there may be a foreign body, a giant cell reaction to cholesterol, with fibrosis and round cells. They are very similar to congenital Cholesteatomas in both their location as well as management.
The terminology has changed through the years. In the past, these were called "congenital epidermoid cysts". The theory regarding their formation suggests that there is poor ventilation of a normally pneumatized space in the temporal bone. The cholesterol is postulated to be related to local tissue breakdown. Bone destruction can occur.
These lesions are not common in children (Radhakrishnan et al, 2014), who comments that "Differential considerations of petrous apex lesions in children include "leave me alone" lesions, infectious or inflammatory lesions, fibro-osseous lesions, neoplasms and neoplasm-like lesions, as well as a few rare miscellaneous conditions".
Presenting symptoms commonly include headache, diplopia, ear pressure, vertigo or dizziness, and occasionally hearing loss and/or facial weakness. About half of these patients have a history of previous trauma to the ear (e.g. surgery).
Double vision has been reported (Roemer et al, 2017), but is not very common. Gradinego's syndrome (petrous apicitis) has also been reported (Lattanzi et la, 2015)
Damage, if it occurs, is generally due to erosion and expansion. This generally occurs gradually over years.
Dizziness and/or hearing loss may occur if the cholesterol granuloma erodes into the inner ear.
Lesion just below the inner ear diagnosed by radiology as being a cholesterol granuloma of the petrous.
Diagnosis is usually from the MRI and CT scan of the temporal bone (Dinh et al, 2016). Usually it is discovered on the MRI, and a temporal bone CT scan follows.
The classic signs of cholesterol granulomas on CT scan are a smoothly marginated expansile mass that is nonenhancing and isodense with brain. It is not wise to do too many CT scans of the temporal bone, as they involve high radiation.
On MRI they are hyperintense on both T1 and T2, and should not exhibit a change on gadolinium enhancement.
Differentiating cholesterol granulomas from congenital cholesteatoma's can be tricky -- perhaps sometimes impossible. On T1 the granuloma should "light up" from cholesterol, but be lower signal intensity for the congenital cholesteatoma. However, there is overlap in imaging characteristics (Dinh et al, 2016), and ultimately one may find out at the time of surgery.
The main two management options are surgery and watchful waiting (Sweeney et al, 2015) . The goal of surgery is removal of as much as possible and providing it with permanent aeration. Watchful waiting is currently advised when there is no growth.
Considerable literature recently has reported endoscopic approaches to these masses. As they are not truly malignant, this seems somewhat reasonable.