FINAL DIAGNOSIS: GIANT CHOLESTEROL GRANULOMA OF THE PETROUS PORTION OF THE TEMPORAL BONE WITH A SMALL COMPONENT OF COEXISTENT CHOLESTEATOMA
Inflammatory lesions often present diagnostic difficulties in the practice of neuropathology. Cholesterol granulomas occur most commonly in the pneumatized petrous apex of the temporal bone but also may be seen in other pneumatized portions of the temporal bone, including mastoid air cells and middle ear space (1). It is not a neoplasm but a descriptive term used for a granulomatous reaction to blood breakdown products, primarily cholesterol. They are thought to arise secondarily following disease states where normally ventilated air-containing bony spaces are obstructed, such as in chronic or acute otitis media, cholesteatoma, or mastoiditis (2). Cholesterol granulomas generally grow silently, with clinical presentation after the lesion has caused bony destruction and compression of cranial nerves V-VIII, structures within the inner ear, or the brainstem (3). Symptoms can include headache, diplopia, vertigo, dizziness, hearing loss, and facial paralysis (1).
Cholesterol granulomas (Table 1) are usually cystic lesions with a thin brown-yellow fibrous capsule and lumenal contents consisting of watery chocolate-colored fluid (3). Histologically, they consist of an extensive granulomatous response with cholesterol crystals that are thought to be the byproducts of blood degradation components (4). The crystals are lost with routine histologic processing leaving classic cholesterol clefts that are surrounded by multinucleated giant cells, hemosiderin-laden and foamy macrophages, lymphocytes, plasma cells, and abnormal blood vessels (5). In extensive lesions, there may be evidence of bone destruction (1).
The primary lesion in the differential diagnosis with cholesterol granuloma is cholesteatoma (Table 1). The term cholesteatoma is actually a misnomer since the lesion is not a neoplasm and does not contain cholesterol (6). Cholesteatomas arise in similar regions as cholesterol granulomas and are usually contained within the tympanomastoid region but aggressive lesions do occur with erosion of bone (7). They tend to remain extradural but can become firmly adherent to the dura with dural attenuation (8). Cholesteatomas are either congenital or acquired and thought to originate from epithelial rests or develop after inflammatory conditions such as otitis media (8). Patients typically present with similar symptoms as those of cholesterol granuloma (3, 9). Grossly, cholesteatomas are circumscribed pearly white cysts (3). The characteristic histologic features are of a hyperkeratotic stratified squamous epithelial-lined cyst containing desquamated keratin (4). Focally, the cyst may be lined by respiratory epithelium (6).
CT scan, in both cholesteatomas and cholesterol granulomas, shows a non-specific, non-enhancing soft tissue mass that has a smooth margin and variable bone erosion (1, 3, 9). By MRI, cholesteatomas are hypointense or isointense on T1-weighted images and hyperintense on T2 images (3). Cholesterol granulomas typically are homogenous and show bright signal intensity on both T1- and T2-weighted images without significant enhancement with gadolinium contrast (1, 3). Lipids, proteinaceous components, and methemoglobin all may contribute to the bright appearance on T1-weighted images (1). When large, however, cholesterol granulomas can exhibit a more heterogeneous MRI pattern (3, 9). Hemosiderin and bone fragments may have contributed to the areas of low T2 signal intensity in the present case.
It is important to make the distinction between cholesterol granuloma and cholesteatoma because of treatment differences. Cholesterol granulomas will resolve after internal drainage into the mastoid cavity or middle ear, relieving the obstruction and restoration of the normal pneumatization of the bone (3). However, there have been reports of large destructive cholesterol granulomas that require complete surgical excision (1). Cholesteatomas, regardless of size, require complete surgical removal, have a recurrence rate of up to 50%, and often result in hearing loss (3).
Cholesterol granulomas and cholesteatomas can also occur together (5, 6, 9). In these cases, it is possible that the original lesion was a cholesteatoma that progressed causing obstruction of the air-space network in the bone leading to concomitant growth of a cholesterol granuloma (9). Given the immense size and chronic bony changes in the present case, it seems likely that the granulomatous process must have slowly developed over a period of many years and that the focus of cholesteatoma formation is a minor secondary development.
In conclusion, cholesterol granulomas and cholesteatomas are not considered neoplasms, although they can be locally aggressive with extensive destruction of adjacent bone, are the two most common lesions arising in the temporal bone, can occasionally be seen together, are usually of small size (<5 cm) with rare giant variants (10, 11), and should be carefully diagnosed due to important clinical management and biological behavior issues.
Table 1. Characteristic Findings in Cholesterol Granulomas and Cholesteatomas
|CT||Soft tissue density with possible bone erosion||Soft tissue density with possiblebone erosion|
|MRI||Hypo- or isointense on T1; hyperintense on T2||Hyperintense on T1 and T2|
|Gross||Partially cystic with a thin fibrous capsule and chocolate-colored fluid||Cyst with pearly-white contents|
|Histology||Granulomatous reaction with abundant cholesterol clefts, multinucleated giant cells, hemosiderin-laden macrophages, lymphocytes, and plasma cells||Keratinized stratified squamous-lined cyst filled with anucleate squamous debris|
|Treatment and Outcome||Drainage with restoration of normal pneumatization; if extensive, surgical excision||Complete surgical excision with 50% recurrence rate and hearing loss|
Contributed by Dean M Havlik, MD, Blaine L Hart, MD and Mark W Becher, MD