A perilymphatic fistula (also known as a perilymph fistula or labyrinthine fistula) is a pathologic communication between the fluid-filled space of the inner ear and the air-filled space of the middle ear, most commonly occurring at either the round or oval window.

Clinical presentation

Although perilymphatic fistulas may be spontaneous, a definite diagnosis is characterized by acute onset preceded by a traumatic event (barotrauma or direct trauma) ¹.

Symptoms of perilymphatic fistula include the following:

• audiological symptoms

  • sensorineural hearing loss

  • tinnitus

• vestibular symptoms

  • vertigo, dizziness, or disequilibrium

  • nausea

• ear fullness

On exam, a positive perilymph fistula test consists of examiner pressure on the tragus and external auditory canal that induces nystagmus ².

Pathology

A perilymphatic fistula can be due traumatic, iatrogenic, or intrinsic processes that affect the otic capsule, oval window, or round window. Examples include the following ^1,2:

• blunt trauma (otic capsule-violating temporal bone fracture)

• penetrating trauma (ear pick or cotton swab)

• barotrauma (explosion, pinched nose Valsalva maneuver, altitude/depth change)

• surgery (stapedotomy, stapedectomy, cochleostomy, cochlear implant)

• middle and inner ear diseases (chronic otitis media with cholesteatoma causing lateral semicircular canal dehiscence)

• idiopathic

Radiographic features

CT

The first-line imaging test for suspected perilymphatic fistula is a dedicated, high-resolution temporal bone CT, which can show the following signs ^1,3:

• pneumolabyrinth (air in the vestibule, semicircular canals, and/or cochlea): specific but not sensitive

• fluid in the oval or round window niches: sensitive but not specific

• bony injuries (disorientation of the stapes footplate relative to the oval window, otic capsule-violating fracture, dehiscence of lateral semicircular canal, etc.)

MRI

• may demonstrate fluid-filling in the round window (especially if >2/3 of the round window niche) or in the oval window niches (considered most common sign ³

• may demonstrate a round window sign, defined as a nodular FLAIR high signal in the round window and the presence of associated saccular hydrops ⁴

Treatment and prognosis

Conservative management may be considered in idiopathic cases, with counseling to avoid activities that increase intracranial or inner ear pressure ¹. Surgical management is indicated if conservative management fails and/or a clear cause is identified. Techniques include blood patch and grafting the injured window (such as with fat, fascia, perichondrium, or gelatin sponge) ¹.