Citation, DOI, disclosures and article data
At the time the article was created Frank Gaillard had no recorded disclosures.View Frank Gaillard's current disclosures
At the time the article was last revised Frank Gaillard had the following disclosures:
- Biogen Australia Pty Ltd, Investigator-Initiated Research Grant for CAD software in multiple sclerosis: finished Oct 2021 (past)
These were assessed during peer review and were determined to not be relevant to the changes that were made.View Frank Gaillard's current disclosures
Cholesterol granulomas, also sometimes called chocolate cysts of the ear or blue-domed cysts, are a special type of middle ear granulation tissue that usually occurs at the petrous apex and represent the most common cystic lesion of the petrous apex.
Cholesterol granulomas typically affect young to middle-aged patients often with a history of chronic otitis media. There is no recognized gender predilection 3.
The presentation will depend on location 5:
conductive hearing loss
cranial nerve dysfunction, e.g. CN VII
blue tympanic membrane on otoscopy 8
Any aerated portion of the temporal bone may develop a cholesterol granuloma.
The pathogenesis is controversial with two major schools of thought 3,5:
obstruction-vacuum theory: where eustachian tube dysfunction is thought to be the underlying abnormality 1,5 and causes mucosal edema with repeated episodes of bleeding
exposed marrow theory: where hyperplastic mucosa invades the underlying bone and exposes bone marrow, which in turn bleeds 3
In either scenario, trapped blood undergoes degeneration and is surrounded by a chronic inflammatory response. There may also be a superimposed infection.
Histologically, cholesterol granulomas are composed of yellowish-brownish fluid which contains 4,5:
cholesterol crystals: accounting for the high T1 and T2 signal
multinucleated giant cells
red blood cells and blood breakdown products
This is surrounded by a fibrous connective tissue capsule with fragile blood vessels which are prone to rupture, thus preventing resolution 3.
Typically, there is an expansile well-marginated lesion with thinned overlying bone. This may be dehiscent when the lesion is large. Faint peripheral enhancement post contrast may be seen.
Appearance is related to location. When a cholesterol granuloma is located in the petrous apex, it may be more aggressive in appearance, e.g. bony erosions and extension to the carotid canal or cerebellopontine angle. However, when they are located in the middle ear, associated erosion is rare 1.
T1: overall high signal due to cholesterol component and methemoglobin +/- low signal rim due to hemosiderin rim, and thinned adjacent bone
central high signal +/- peripheral low signal due to hemosiderin rim
thinned adjacent bone
does not attenuate on FLAIR
fat suppression: remain high signal 7
T1 C+ (Gd): no central enhancement although faint peripheral enhancement may be difficult to see due to intrinsic high T1 signal of lesion which is not saturated (not an adipose tissue)
DWI/ADC: no restricted diffusion 6
Treatment and prognosis
If symptomatic, surgical excision is required, and this must include the cyst wall. A number of surgical approaches exist and are chosen based on both the location of the cholesterol granuloma and the degree of hearing loss 5. In some cases, a mastoidectomy may be necessary 3. However high recurrence rates have been reported.
Given its signal characteristics, a cholesterol granuloma should be easily distinguished from other petrous apex/middle ear lesions, such as 2:
normal asymmetry of fatty marrow/pneumatization - no expansion
effusion of pneumatized petrous apex
base of skull tumors
A few lesions can have similar appearances, including:
hydrated mucocele: rare, but may have identical signal on MRI
high protein = high T1
high water = high T2
thrombosed ICA aneurysm 2
signal is usually more complex because of layered blood products
flow void centrally if not completely thrombosed
white epidermoid cyst: atypical imaging phenotype of an intraosseous epidermoid cyst with high T1 signal due to lipid/protein content or hemorrhage
very bright on DWI with or without ADC diffusion restriction, rare location
- 1. Joel D. Swartz, H. Ric Harnsberger. Imaging of the Temporal Bone. (1998) ISBN: 9780865777002 - Google Books
- 2. Connor S, Leung R, Natas S. Imaging of the Petrous Apex: A Pictorial Review. Br J Radiol. 2008;81(965):427-35. doi:10.1259/bjr/54160649 - Pubmed
- 3. Ellen G. Hoeffner, Suresh Kumar Mukherji, Dheeraj Gandhi. Temporal Bone Imaging. (2008) ISBN: 9781588904010 - Google Books
- 4. Mahmood F. Mafee, Galdino E. Valvassori, Minerva Becker. Imaging of the Head and Neck. (2005) ISBN: 9781588900098 - Google Books
- 5. Richard J. Wiet. Ear and Temporal Bone Surgery. (2006) ISBN: 9781588901217 - Google Books
- 6. Baráth K, Huber A, Stämpfli P, Varga Z, Kollias S. Neuroradiology of Cholesteatomas. AJNR Am J Neuroradiol. 2011;32(2):221-9. doi:10.3174/ajnr.A2052 - Pubmed
- 7. Razek A & Huang B. Lesions of the Petrous Apex: Classification and Findings at CT and MR Imaging. Radiographics. 2012;32(1):151-73. doi:10.1148/rg.321105758 - Pubmed
- 8. Jang C, Kim J, Cho Y. Cholesterol Granuloma of the Tympanic Membrane Presenting as a Blue Eardrum. Yonsei Med J. 2009;50(4):585-7. doi:10.3349/ymj.2009.50.4.585 - Pubmed