PERILYMPHATIC FISTULA

Defn:- a communication of the perilymphatic fluid space, usually with the middle ear cavity.

Inc:

-167 surgeons (Hughes, et al, 1990) most (60%) performed >3 explorations for PLF per year.

-average number of PLF explorations for the total group <5 per year.

Aet: any injury that disrupts bony or soft tissue barriers between perilymph &ME space (Fee, 1968). -common example: subluxation/fracture of stapes foot-plate 2ry to trauma of ossic chain.

Experimental observations

-Round window membrane can be displaced and even ruptured in the experimental animal (cat) by

increasing CSF P after experimental cannulation of subarachnoid space (Harker et al., 1974).

-In primates, RW membrane is a much thicker structure (Kawabata and Paparella, 1971) and resistant to such increased pressure.

-pathway for increase in perilymphatic fluid pressure occurs through the cochlear aqueduct.

- membrane heals spontaneously < 7-10days in experimental animal (Simmons, 1962).

-RW membrane rupture experimentally, Þ no significant permanent change in cochlear potentials.

-If intracochlear membrane ruptures (eg, Reissner's) are associated with RW membrane defects, Þ decreased cochlear potentials and a permanent sensorineural hearing deficit (Oshiro 89).

-Reason for this effect is an increased longitudinal flow of toxic endolymph into perilymphatic

compartment produced by RW membrane rupture + an intracochlear membrane break.

This observation has added support to the theory of double membrane breaks, which are

thought to be responsible for SNHL loss after traumatic insults to labyrinth (Simmons1979).

Clinical observations

-Persistent perilymph to ME fistula Þ serous labyrinthitis, which Þ

-permanent and profound SNHL

-disequilibrium (NB less vestibular symptoms due to vestibular compensation.).

-Ossicular chain trauma:

-Higher incidence of PLF at oval window VS RW (Singleton1978).

-Direct trauma to ossic chain Þ injury in the oval window region VS RW membrane (Shea 80). -Indirect trauma (eg head injury or sudden ME pressure changes) Þ force concentrated at oval

window footplate > that transmitted to RW membrane.

-The "thick" RW memb is more capable of withstanding sudden displacement VS annular lig.

\ likelihood of fistulization is: oval window > round window.

Diagnostic evaluation

-History is most important diagnostic information of PLF (Hughes et al., 1990).

-trauma, (hx of sudden auditory/vestib sympts after trauma Þ strongly suggestive of labth injury)

-typical auditory symptoms are:

-threshold elevation with poor word discrimination scores.

-vestibular symptoms:

-ataxia +/- positional vertigo and nystagmus (Healy, 1976; Simmons, 1982; Singleton,1978). \ presence of audit & vestib sympts Þ serous labyrinthitisdue to PLF or intracoch memb breaks. -Clinical signs associated with PLF vary:

-both sensorineural hearing loss and vestibular symptoms usually occur in varying degrees.

\ selective auditory or vestibular symptoms are not characteristic of PLF.

-usually fluctuating sensorineural hearing loss.

-fistula test (nystagmus in response to pneumatic otoscopy) usually positive.

-spontaneous nystagmus or nystagmus induced by positional testing.

-vestibular response as measured by caloric stimulation may be normal or decreased.

\ clinical test findings are variable and not pathognomonic of PLF (Singleton 1978).

NB: History of trauma followed by auditory & vestib sympts in a previously normally functioning ear, Þ PLF through the oval or round windows must be excluded.

Management

-Conservative Rx:

-bed rest, with ancillary measures eg head elevation and avoidance of physical exertion.

-for 10 to 14 days.

-reason: because considerable clinical and experimental evidence predicts spontaneous healing of defects in the round window membrane or annular ligament, a, should be administered

-Surgical exploration

-Indn: If conservative program fails to bring improvement in auditory or vestibular symptoms.

-Proced:

-General: Approp equipd OT

-Posn: supine with one pillow.

-Anaesth: LA (to reduce amount of bleeding and fluid accumulation in ME,

to enhance an area of perilymph leakage with Valsalva maneuver.

to allow a patient's response with Valsalva maneuver

-Incisn: Trans-canal or Permeatal.

-TMF.

-Exposure:

-Complete control of bleeding is necessary for accurate examination of middle ear space.

-Adequate curettage of post-sup canal wall is requ’d to fully visualize oval & round windows. without manipulating any mucosal folds.

-Inspn & Dx:

-Oval window niche is carefully examined first with a No. 24 aspirator tip.

-If no clear fluid has accumulated, Þ depress (2-3 times) ossicular chain +/- Valsalva. -If no fluid has accumulated, Þ RW niche is examined same way, without instruments.

-Mx:

-If no fluid has accumulated in either oval or round window niches, Þ no surgical repair nb: Some authors have recommend placement of soft tissue in windows believing that a

small unrecognized fistula may be present.

If such repair is performed without visible evidence of PLF, treatment cannot be

assessed objectively.

-If fluid has been detected at oval window:

-preprt’n of area in questn (by elevatn of mucosa around area of leakageÞ bone exposure)

-seal with adipose tissue graft (approx 2-3 mm in diameter).

-gelfoam is used to stabilize the adipose tissue grafts.

-If fluid has been detected in round window niche:

-removal of promontory overhang enhances examination of round window membrane. -elevation of mucosal folds

-seal with adipose tissue graft (approx 2-3 mm in diameter).

-gelfoam is used to stabilize the adipose tissue grafts.

-Postoperatively

-pt's activity should be restricted for 1 week to 10 days to permit fibrous tissue repair of defect. -recovery of hearing, should be evident in approx 4 to 6 weeks;

\ audiology no sooner than 6 to 8 weeks post-operatively.

Bibliography:

Cummings, C. Otolaryngology.  chapter 171

Gates Current Therapeutics

Scott Brown, , Otolaryngology

Schucknect, Pathology of the Ear