Presentation
74 male under radiological surveillance for a presumed facial nerve schwannoma, an incidental finding on imaging investigations following an MVA. Completely asymptomatic with no headache, hearing loss, nor facial weakness. Nil focal neurological deficits to cranial nerve and upper and limb sensorimotor examinations. Audiology testing was similarly unremarkable. Initial CT and MRI imaging (digital images unavailable; reports only) demonstrated a 10mm nodule in the anterio-superior portion of the left internal acoustic canal, with thickening and enhancement of the labyrinthine segment of the left facial nerve and abnormal enhancement in the geniculate ganglion. At his 2 year review, a lobulated mass related to the middle turbinate of the left nasal cavity was also identified.
Patient Data
There is no appreciable change in size or appearance to the enhancing bilobulated mass contained within the left internal acoustic canal and labyrinthine segment of the left facial nerve, not extending beyond the anterior genu. Subtle, thickening and enhancement is also observed in the proximal portion of the greater petrosal nerve. Appearances most likely represent the presence of a facial nerve Schwannoma extending to the geniculate ganglion and proximal greater petrosal nerve.
The enhancing mass adjacent to the lower turbinate in the left nasal cavity in the region of the medial wall of the left maxillary sinus is also noted and not significantly changed in size
The patient underwent biopsy of the left nasal cavity mass.
Histology:
MACROSCOPIC and MICROSCOPIC DESCRIPTION:
A single fragment of cream colored tissue measuring 5mm in maximum dimension. The sections show a polypoid lesion lined by pseudostratified ciliated respiratory type epithelium. The central portions contain benign seromucinous glands surrounded by an edematous stroma which contains a mild infiltrate of inflammatory cells primarily lymphocytes and plasma cells. There is no evidence of malignancy.
DIAGNOSIS: "Left nasal cavity": Benign nasal polyp.
Nil further treatment was initiated for this nasal polyp. The patient recently presented for his annual follow-up at the 8 year juncture, remaining asymptomatic and without focal neurology.
There is a isointense T1, isointense T2 lesion in the left internal acoustic meatus that causes expansion of this osseous canal. The lesion involves the geniculate ganglion with is expanded and extends into the middle cranial fossa, likely via the hiatus for the greater petrosal nerve, pointing towards the foramen lacerum. It is unchanged compared to the previous images. Grossly the internal ear labyrinth has normal appearances. Within the limitations of comparison, there are stable appearances. Polypoid lesion in the medial left maxillary sinus is unchanged in appearance.
Case Discussion
This case illustrates the common MRI radiological features of facial nerve Schwannoma.
Facial nerve schwannomas (FNS) of facial nerve neuromas/neurilemomas, are rare benign neoplastic lesions comprising of Schwann cells 1,2. FNS can arise from anywhere along the course of the facial nerve, from its origin in the cerebellopontine angle to its extracranial ramification within the parotid gland 3. Clinical presentation depends on the extent and location of the lesion, with common presenting symptoms of progressive facial paralysis/weakness, hemifacial spasm, conductive or sensorineural hearing loss, tinnitus and dizziness 3. Other symptoms may include disturbed lacrimation (due to involvement of the greater superficial petrosal nerve), hyperacusis (nerve to stapedius muscle) and/or disturbed taste/salivation (chorda tympani) 2.
Although diagnosis is aided by radiographic studies, the convoluted course of the facial nerve from the pontomedullary junction to the stylomastoid foramen, as well as the variation in its bony confines and surrounding anatomical landscape, makes a “typical” radiological appearance impossible to describe 4.
Bone-algorithm CT, particularly through the temporal bone, shows a mass expanding or remodeling its surrounding bony boundaries 4,5.
Features of FNS on magnetic resonance imaging include 6:
- a mass that is mildly hypointense or isointense relative to brain on non-contrasted T1-weighted images
- heterogeneity and hyperintensity on T2-weighted series
- homogeneous enhancement with larger lesions with cystic degeneration seen as focal intramural low signal intensity on contrast enhanced-T1 images
Case courtesy of Associate Professor Pramit Phal
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