Venous vascular malformation of the facial nerve

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

Terminology

As they do not appear to have clinical course, or histological features of haemangiomas, 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 rapid onset mimicking a Bell palsy. Sensory neural hearing loss (SNHL) 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 IAC), compared to schwannomas which can occur anywhere along the nerve. 

Morphology

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

Both capillary and cavernous sub types are identified histologically and both types can be seen within the one tumour.

Variants

A variant is the ossifying haemangioma 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

MRI

Reported signal characteristics of the region includes:

• T1: iso or slightly hypo intense
• T2: hyper intense
• T1 C+ (Gd): intense contrast enhancement

Treatment and prognosis

• content pending

Differential diagnosis

Imaging differential considerations include

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