What are the structural causes of intermittent unilateral tinnitus?

Structural Causes of Intermittent Unilateral Tinnitus

The most important structural causes of intermittent unilateral tinnitus include vascular abnormalities (sigmoid sinus diverticulum/dehiscence, high jugular bulb, arteriovenous malformations), retrocochlear masses (vestibular schwannoma, meningioma), middle ear pathology (glomus tumors, cholesteatoma, otosclerosis), and temporomandibular joint dysfunction. 1, 2, 3

Vascular Structural Abnormalities

Vascular causes are particularly important when tinnitus is pulsatile or changes with position/movement:

• Sigmoid sinus abnormalities including diverticulum or dehiscence are common structural causes that produce pulsatile tinnitus exacerbated by positional changes 2, 3, 4
• High jugular bulb or jugular bulb dehiscence creates vascular proximity to the inner ear structures, producing audible blood flow 2, 3
• Persistent petrosquamosal sinus represents an anatomical variant that can cause pulsatile symptoms 3
• Arteriovenous malformations or fistulas produce abnormal vascular flow patterns detectable on imaging 3, 5, 6
• Carotid artery abnormalities including atherosclerosis or dissection can generate audible turbulent flow 3, 5, 6

Retrocochlear Structural Lesions

Mass lesions in the internal auditory canal and cerebellopontine angle require imaging evaluation:

• Vestibular schwannomas (acoustic neuromas) occur in 63-75% of patients presenting with unilateral tinnitus and are the most common retrocochlear cause 1, 6
• Intralabyrinthine schwannomas represent a less common variant that can be missed on non-contrast imaging 1
• Meningiomas in or around the internal auditory canal and cerebellopontine angle cistern can cause unilateral tinnitus 1
• Endolymphatic sac tumors are rare posterior fossa masses readily diagnosed by MRI 1

Middle Ear Structural Pathology

Direct examination may reveal visible structural abnormalities:

• Glomus tumors (paragangliomas) appear as retrotympanic vascular masses on otoscopy and show contrast enhancement without vascular blush on angiography 1, 3, 4, 5
• Cholesteatoma represents chronic inflammatory middle ear pathology requiring CT differentiation from simple otitis media 1
• Otosclerosis causes conductive hearing loss with associated tinnitus through ossicular fixation 1, 5
• Tympanic membrane perforation or ossicular abnormalities impair sound transmission and may produce tinnitus 1

Temporal Bone Structural Abnormalities

Bony abnormalities of the temporal bone create mechanical causes:

• Superior semicircular canal dehiscence produces sound-induced or pressure-induced tinnitus that varies with Valsalva or position changes 3, 4
• Cochlear nerve aperture stenosis associated with cochlear nerve hypoplasia presents with sensorineural hearing loss and tinnitus 1
• Vestibular aqueduct abnormalities can be identified on CT temporal bone 1
• Temporal bone fracture from recent head trauma may cause delayed or immediate tinnitus 1

Temporomandibular Joint Dysfunction

TMJ pathology has anatomical proximity to ear structures:

• TMJ derangement or dysfunction causes unilateral tinnitus that worsens with jaw movements like yawning due to close anatomical relationship between the TMJ and ear structures 3
• Dedicated MRI of the temporomandibular joint should be considered when TMJ pathology is suspected based on history of jaw symptoms 1

Critical Diagnostic Approach

Imaging is mandatory for unilateral tinnitus to exclude dangerous structural causes:

• MRI head and internal auditory canal without and with IV contrast is the most appropriate first-line imaging for non-pulsatile unilateral tinnitus to exclude vestibular schwannoma 1, 2
• CT temporal bone without contrast plus CTA head and neck with contrast is first-line for pulsatile tinnitus to identify vascular abnormalities and bony dehiscences 1, 2, 4
• Unilateral tinnitus has higher risk of underlying structural pathology compared to bilateral tinnitus and should never be dismissed without imaging 1, 2, 3

Important Clinical Pitfalls

• Do not assume intermittent symptoms exclude serious structural pathology—vestibular schwannomas and vascular abnormalities can produce intermittent tinnitus 1, 2
• Bilateral sudden sensorineural hearing loss is rare and should prompt consideration of non-idiopathic causes including autoimmune disease, infection, or ototoxicity 1
• Tinnitus that changes with body position or maneuvers (like yawning) strongly suggests mechanical or vascular etiology rather than sensorineural causes 3