T1 pre-gad T2 T1 pre-gad

Diagnosis: Bilateral cholesterol granulomas

Cholesterol granulomas, otherwise known as cholesterol cysts are due to obstruction of air cells within the petrous apex. They are usually unilateral and in these cases the contralateral petrous apex is usually very well aerated. As the obstruction progresses, inflammatory tissue accumulates within the obstructed air cell often resulting in a large amount of viscous fluid, cholesterol crystals, and hemorrhagic breakdown products. Bilateral cholesterol granulomas of the petrous apices are extremely unusual. Patients usually present with cholesterol granulomas in young adulthood or middle age with headache or cranial nerve deficits most commonly hearing loss and hemifacial spasm. On imaging, they usually have bright signal on both T1 and T2 with a significant amount of heterogeneity to the signal and may have a small amount of peripheral enhancement. They may reach very large size and expand the petrous apex often resulting in mass effect upon the skull base and the brain stem. There is no calcification within the lesion but adjacent bone may be sclerotic. In the typical case of unilateral cholesterol granuloma, the main differential entity is epidermoid cyst otherwise known as primary cholesteatoma. These are congenital lesions and are much less common than cholesterol granulomas. They are well defined, ovoid expansile masses within the petrous apex. On MR, they have been described as having signal intensity between brain and CSF on T1 which may be helpful in differentiating them from cholesterol granulomas which tend to be bright on T1 due to the large amount hemorrhagic breakdown products . Mucocele of petrous apex is another entity which may be in the differential of unilateral cholesterol granuloma but this is extremely rare.

The differential in this case is complicated by the fact that there are two lesions. Other entities to consider when faced with a large mass which seems to involve the clivus primarily are chordoma and chondrosarcoma although these tend to be off midline where chordomas are in the midline. Other skull base lesions more commonly seen in older patients may include metastases and plasmacytoma. Occasionally craniopharyngiomas attain a huge size obscuring their true origin. In this case, the diagnosis of bilateral cholesterol granulomas is not listed in the differential because of its extreme rarity. It maybe considered in retrospect, however, if you notice that the lesions seem to be centered in each petrous apex and appear to kiss in the middle. This is best appreciated on the coronals. Related Cases

Henick DH, Feghali JG. Bilateral cholesterol granuloma: an unusual presentation as an intradural mass. Journal of Otolaryngology, Feb 1994; 23(1):p15-8.

Thedinger BA, Nadol JB Jr, Montgomery WW, et al. Radiographic diagnosis, surgical treatment, and long-term follow-up of cholesterol granulomas of the petrous apex. Laryngoscope, Sep 1989; 99(9):p896-907.

Smith PG, Leonetti JP, Kletzker GR. Differential clinical and radiographic features of cholesterol granulomas and cholesteatomas of the petrous apex. Ann Otol Rhinol Laryngol, Nov-Dec 1989; 97(6 Pt 1):p599-604.

Greenberg JJ, Oot RF, Wismer GL, et al. Cholesterol granuloma of the petrous apex: MR and CT evaluation. AJNR, Nov-Dec 1988; 9(6):p1205-14.

Gamache FW Jr, McLure T, Deck M, et al. Bilateral cholesterol granuloma of the skull base: case report and review of the literature. Neurosurgery, Jun 1988; 22(6 Pt 1):p1098- 101.

Griffin C, De La Paz R, Enzmann D. MR and CT correlation of cholesterol cysts of the petrous bone. AJNR, Sep-Oct 1987; 8(5):p825-9.















































Chordoma Craniopharyngioma Cholesterol granulomas