Glomus tympanicum

Findings

There is a 2 mm mass arising from the right cochlear promontory without bony erosion.

Differential diagnosis of a vascular middle ear mass:
- Glomus tympanicum
- Congenital cholesteatoma
- Aberrant internal carotid artery
- Dehiscent jugular bulb
- Hemangioma


Diagnosis: Glomus tympanicum


Key points

Glomus tympanicum is a benign hypervascular tumor that arises from glomus bodies (neural crest tissue).
Glomus bodies in the middle ear are situated along Jacobson's nerve (a branch of CN IX) which forms the tympanic plexus. Branches of the tympanic plexus (and potential locations for glomus tympanicum tumors) occur on the cochlear promontory, near the round window, eustachian tube egress, tensor tympani tendon and along the inferior tympanic canaliculus. The classic location is the cochlear promontory.
On CT, the tumors are typically small, do not erode the bone (as opposed to cholesteatomas). On MR they demonstrate marked enhancement. Larger tumors may have a 'salt and pepper' appearance caused by flow voids in the mass.
Glomus tumors occur (in order of frequency) at the jugular foramen, branches of the vagus nerve (Arnold's nerve), carotid bulb or hypotympanum.
Overall glomus tumors are multiple in 15% of patients.