1

Introduction

Osteomas and exostoses are benign tumors of bone with an estimated prevalence of 0.42% . When present, they are most commonly found in the calvarium, facial bones, and mandible . Rarely, they are found in the internal auditory canal (IAC). Twenty one cases of osteomas and exostoses of the IAC have been reported with only six cases demonstrating bilaterally . Associated symptoms include hearing loss, vestibular dysfunction, tinnitus, and facial spasms. However, patients may be asymptomatic with the lesions only incidentally discovered on radiograph or upon autopsy.

Radiologically, osteomas may be distinguished from exostoses by the presence of bone marrow as well as an acute protrusion into the IAC space. In contrast, exostoses are smooth and broad-based, and are more likely to be bilateral. Definitive distinction between osteomas and exostoses is by histopathology. These secondary causes of IAC stenosis should be distinguished from primary causes such as hyperostotic thickening of the medial temporal bone from pathologies including Paget’s disease, fibrous dysplasia, or osteopetrosis.

1.1

Case 1

A 38-year-old woman presented with a one-year history of progressive, bilateral sensorineural hearing loss and tinnitus (L > R), otalgia, and vertigo. High-resolution computed tomography of the temporal bone revealed prominent bony osteomas along the cerebellopontine angle cisterns and porus acusticus bilaterally, right greater than left. The right proximal IAC showed significant stenosis to 2 mm in the AP dimension, and the left IAC showed stenosis to 5 mm ( Fig. 1 ).

CT axial sections with demonstration of prominent bony osteomas along the cerebellopontine angle cisterns and porus acusticus bilaterally.

Exploration revealed a large osteoma in the jugular tubercle encroaching upon the internal auditory meatus. Because her symptoms were more severe on the left side, microvascular decompression of the left IAC was performed via a retrosigmoidal approach. The osteoma was reduced in a medial to lateral fashion using an ultrasonic surgical aspirator and diamond burrs to decompress and free the vestibulocochlear and facial nerves ( Fig. 1 ).

At follow-up, the patient reported complete resolution of preoperative vertigo, as well as subjective improvement of hearing and tinnitus in her left ear. A post-operative audiogram demonstrated stable discrimination and hearing levels ( Table 1 ). The patient plans to undergo decompression of the right IAC in a staged fashion.

Table 1

Hearing results reported per AAO guidelines.

Patient	Hearing results	Pre-treatment PTA	Pre-treatment WRS	Post-treatment PTA	Post-treatment WRS
1	Right ear	92	84	78	84
	Left ear	103	76	95	80
2	Right ear	28	88	30	80
	Left ear	50	92	23	92

 

2

Discussion

Our retrospective review of the literature identified 21 unique cases of bony lesions of IAC, including 17 osteomas and 4 exostoses. Three out of 17 cases of osteoma and 3 out of 4 cases of exostoses were bilateral in nature ( Table 2 ) . Symptomatic patients presented at average age of 50 with an average symptom duration of 6.4 years. The most commonly reported symptoms associated with osteomas and exostoses of the IAC have been vertigo (13/21), sensorineural hearing loss (9/21), and tinnitus (9/21) with less common reports of facial paralysis or spasms (2/23). Symptoms are thought to be due to either direct mass compression or by serving as a fulcrum for repetitive trauma with movement . The preponderance of symptoms involving the vestibulocochlear nerve suggests that the facial nerve may be more resistant to compressive effects within the IAC .

Table 2

Reports of bony lesions within the internal auditory canal.

Author	Osteoma or exostosis	Gender	Age	Age at symptom onset	Side of lesion	Symptoms	Treatment	Outcome
Baik et al.	Osteoma	M	70	–	Right	R hearing loss and tinnitus	Corticosteroids	2 year follow-up showed no change in lesion; continued tinnitus
	Exostosis	F	65	47	Bilateral	Vertigo	Retrosigmoid approach	Resolution of vertigo over one year
	Exostosis	F	55	54	Bilateral	Bilateral tinnitus, vertigo	–	–
Beale and Phelps	Osteoma	F	50	49	Right	R hearing loss and tinnitus; vertigo	None	–
Ciorba et al.	Osteoma	M	32	–	Bilateral	No symptoms	None	–
Clerico et al.	Osteoma	F	59	56	Right	Vertigo, tinnitus	Suboccipital approach	Resolution of vertigo; hearing and balance unchanged
Coakley et al.	Osteoma	M	42	22	Right	Vertigo, tinnitus	Retrosigmoid approach	Resolution of vertigo and tinnitus
Davis et al.	Osteoma	F	44	39	Left	Episodic vertigo, L facial paralysis	Suboccipital approach	Significant improvement in symptoms, residual mild vertigo and aural fullness
	Osteoma	M	51	48	Right	Episodic vertigo, R aural fullness	Clinical monitoring	No change in size after 4.5 years
Doan and Powell	Exostosis	M	53	53	Right	R hearing loss	Posterior fossa approach	Improvement of R hearing loss
Estrem et al.	Osteoma	F	56	50	Left	Vertigo, L tinnitus	Suboccipital approach	Resolution of tinnitus, vertigo, motion tolerance, nausea
Gerganov et al.	Osteoma	F	30	29	Bilateral	L hearing loss, vertigo, tinnitus	Retrosigmoid approach	Resolution of vertigo and tinnitus, slightly improved hearing
Schutt CA et al.	Osteoma	F	38	37	Bilateral	Hearing loss, tinnitus, vertigo	Retrosigmoid approach	Resolution of vertigo and tinnitus; improvement of L hearing loss
	Exostosis	F	80	80	Bilateral	Hearing loss (L > R)	Corticosteroids	Improvement of L hearing loss
Liétin et al.	Osteoma	F	79	49	Left	L hemifacial spasms	Clinical monitoring	–
Ramsay and Brackmann	Osteoma	F	30	26	Left	Vertigo, hearing loss, tinnitus	Middle fossa approach	Resolution of tinnitus and vertigo; improvement of hearing loss
Roberto et al.	Osteoma	F	33	18	Right	Hearing loss, tinnitus, vertigo	IAC decompressed	Cure of vertigo and tinnitus; hearing loss not improved
Singh et al.	Osteoma	M	33	31	Right	R hearing loss	Clinical monitoring
Smelt	Exostosis	F	67	–	Bilateral	None	–	–
Vrabec et al.	Osteoma	F	31	–	Bilateral	Incidental finding after head injury	–
	Osteoma	F	61	59	Left	Hearing loss; episodic vertigo	Low-salt diet and diuretics	5 year follow-up showed no change in lesion, free of severe vertigo
	Osteoma	M	59	–	Left	None	Clinical monitoring	No change in size after 18 months
Wright et al.	Osteoma	F	34	32	Right	Hearing loss, tinnitus	Posterior fossa approach	30 dB improvement in pure tone after 6 months

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