Venous vascular malformation of the facial nerve

Venous vascular malformations of the facial nerve, previously known as facial nerve hemangiomas, are rare benign vascular malformations of the facial nerve usually presenting as a facial nerve palsy, which can be rapid in onset mimicking a Bell palsy. 

Terminology

As they do not appear to have the clinical course or histological features of hemangiomas, the nomenclature was changed ⁵. 

Epidemiology

These lesions typically affect middle aged patients and are very slow growing.

Clinical presentation

At presentation, they are usually ~1 cm in size, and typically cause significant symptoms despite their small size. This is another distinguishing feature from schwannomas which despite larger size often have few symptoms. Typically they present with facial nerve palsy which can be of rapid onset mimicking a Bell palsy. Sensorineural hearing loss and tinnitus can also be presentations.

Pathology

Location

It has a predilection for the region around the geniculate ganglion (although even more rarely seen in the internal auditory canal), compared to schwannomas which can occur anywhere along the nerve. 

Macroscopic appearance

The bony margins are indistinct, as although the malformation is localized it is unencapsulated, enabling them to be distinguished from schwannomas, which like schwannomas elsewhere (think jugular foramen lesions) have well defined remodeled margins.

Both capillary and cavernous subtypes are identified histologically and both types can be seen within the one tumor. A variant is the ossifying hemangioma of the facial nerve, which has a distinctive appearance; radiating outwards from its center is a 'spoke wheel' or 'honeycomb' arrangement of ossification.

Radiographic features

CT

There is an osteolytic lesion centered in the facial nerve canal with irregular and amorphous margins. The presence of internal honeycomb ossific matrix, present in half of cases, is pathognomonic ⁶.

MRI

Reported signal characteristics of the region include:

• T1: iso or slightly hypointense
• T2: hyperintense
• T1 C+ (Gd): intense contrast enhancement

Treatment and prognosis

Definitive treatment requires surgical resection.

Differential diagnosis

Imaging differential considerations include:

• facial nerve schwannoma
• facial nerve malignant schwannoma
• facial nerve perineurioma
• meningioma arising from the geniculate ganglion has been reported
• facial nerve metastases, hematogenous and retrograde spread