Hemangioma of the geniculate fossa

Clinical History

A middle-aged woman presented to our ENT-departement with a slowly progressive left-sided facial nerve paresis lasting as long as 2 years now. In her medical history there was a mastoidectomy for a cholesteatoma on the same side as the paresis.

Imaging Findings

High resolution CT and MRI of the temporal bone was performed to depict the facial nerve from the pons to the parotid gland. MRI of the temporal bone revealed an ill-defined lesion centered at the geniculate fossa which was hypointense on T1, hyperintense on T2. After administration of gadolineum there was marked enhancement. High resolution CT of the temporal bone confirmed an osteolysis located at the geniculate fossa in close proximity to the labyrinthine and proximal tympanic segment of the facial nerve. The osteolytic area showed irregular margins and internal bony spicules resulting in a 'honeycomb' appearance suggesting a partly calcified tumoral matrix. This is a characteristic feature for an intratemporal hemangioma. Schwannomas which are more frequently seen at the geniculate ganglion compared to hemangiomas usually present as a well-marginated osteolysis without interior spicules or calcifications on CT and as a homogeneously enhancing nodule on T1 with gadolinium.

Discussion

Intratemporal hemangiomas are rare extra-neural lesions which can secondarily grow into the nerve and cause neural palsy. Histologically hemangiomas are vascular tumors consisting of large irregular spaces lined by endothelium and with broad intervening bands of fibrous connective tissue and bony spicules. The fibrous tissue and bony spicules are responsible for the inhomogeneous aspect of the lesion on CT and T1 with gadolinium. Most hemangiomas of the facial nerve originate in the geniculate fossa but any segment of the facial nerve can be affected. Cases with hemangiomas in the internal auditory and mastoid canal have been reported in the literature. Multi-segmental involvement is also possible. Differential diagnosis of a geniculate fossa lesion is a schwannoma, a hemangioma and a supra-labyrinthine cholesteatoma in which schwannomas are the most frequently seen. Cholesteatomas do not enhance which allows distinguishing them from schwannoma and hemangioma. Distinguishing a small hemangioma from a schwannoma can be very difficult, in larger lesions hemangiomas usually have unsharp margins and exhibit intra-tumoral calcifications. Bony spicules resulting in a honey comb appearance is a well-known feature of (ossifying) hemangiomas. High resolution CT and MRI with gadolinium are complementary and imperative for early diagnosis which is extremely important to preserve anatomic integrity of the nerve and to avoid facial nerve reconstruction. However small lesions can be easily overlooked.

Differential Diagnosis List

Final Diagnosis

hemangioma of the facial nerve/geniculate ganglion

URL:	https://eurorad.org/case/4265
DOI:	10.1594/EURORAD/CASE.4265
ISSN:	1563-4086