Pneumolabyrinth: A late complication of stapes surgery.

Abstract

As temporal bone imaging techniques continue to improve, it is likely that we will see an increase in the detection of pneumolabyrinth. Several mechanisms have been proposed to explain how air enters the labyrinth. A small number of authors has reported an association between pneumolabyrinth and temporal bone fractures, perilymphaticfistulae, and displaced stapes prostheses. In this article, we describe a new case of pneumolabyrinth that was seen as a late complication of stapes surgery, and we summarize what is known about this rare condition.

Introduction

Only six reports of pneumolabyrinth have been previously published in the literature. [1-6] These cases were associated with longitudinal and transverse fractures of the temporal bone, perilymphatic fistulae, and a fracture of the stapes footplate. In this article, we describe a new case of pneumolabyrinth that was seen as a late complication of prosthesis dislocation in a patient who had undergone stapes surgery more than a decade earlier.

Case report

A 56-year-old woman came to us for evaluation of disequilibrium, aural fullness, and intermittent tinnitus. She denied true vertigo, hearing change, rhinorrhea, postnasal drip, and antecedent trauma. Her history was significant for bilateral otosclerosis, for which she had undergone stapedectomy in both ears (22 years earlier on the right and 16 years earlier on the left).

Otoscopic examination revealed that her tympanic membranes were intact and mobile and that her middle ear space was free of fluid. A Rinne's test was positive bilaterally, and a Weber's s test lateralized to the left. Anterior rhinoscopy revealed normal nasal passages without congestion or discharge. Nystagmus could not be elicited. Findings on the remainder of her head and neck examination were normal.

Pure-tone audiometry revealed a mixed hearing loss on the left (air-bone gap: [greater than]20 dB) and a downward-sloping sensorineural hearing loss on the right (figure 1). Tympanograms were type A bilaterally, and acoustic reflexes were absent bilaterally.

We obtained noncontrast high-resolution axial and coronal computed tomography (CT) of the temporal bones in 1-nun sections (figure 2). Evidence of a complication of the patient's previous stapedectomy on the left was visible on CT. The stapes prosthesis had partly migrated into the vestibule, and air was present adjacent to the horizontal semicircular canal. CT on the right showed that the stapes prosthesis was in its proper position. In both ears, no fluid had collected outside the oval window, in the middle ear, or in the mastoid air cells.

The patient was given two treatment options: surgery or observation. The surgical recommendation was to explore the middle ear and repair the defect caused by the dislodged prosthesis with a piece of the tragal perichondrium. The observational option was to perform repeat CTs at regular intervals and to resort to surgery only if her hearing or disequilibrium worsened. The patient opted for observation and did not experience any worsening of symptoms.

Discussion

A small number of investigators has attempted to discover the mechanisms of pneumolabyrinth and its effects on hearing. Experiments on guinea pigs by Yanagihara and Nishioka showed that these animals experienced a sensorineural hearing loss only as long as there were air bubbles in the labyrinthine system; once the bubbles were removed, hearing returned to baseline levels. [5] It has been proposed that these bubbles disturb the propagation of the traveling wave of the basilar membrane.

Several causes of pneumolabyrinth have been proposed. [3,6] One is a disruption of the otic capsule and membranous labyrinth by a temporal bone fracture. Another cause appears to be a rupture of the round window by an implosive force. Others include fracture of the stapes footplate (which can allow air to enter the vestibule from the oval window) and perilymphatic fistulae (which might form a spontaneous connection between the inner and middle ear). A perilymphatic fistula from an explosive force, combined with an increase in middle ear pressure as a result of weightlifting or straining, might push air into the vestibular system and cause a sensorineural hearing loss. Some experiments have shown that a mere puncture of the round window membrane that does not allow air to enter the labyrinth does not result in a hearing loss. [5]

Kobayashi et al set out to determine which part of the cochlea is affected by pneumolabyrinth. [7,8] They found that perfusion of air into the scala tympani resulted in a drastic decrease in the cochlear microphonics and in the amplitude of the compound action potential. [7] The endocochlear DC potential, however, seemed to be highly resistant to air and was not affected until the duration of the perfusion exceeded 30 minutes. This indicates that the sudden hearing loss was likely the result of interference in the generation mechanisms of the cochlear microphonics and the action potential rather than by strial dysfunction. Once the perfusion was stopped, there was a gradual return in the amplitude of the cochlear microphonics and the action potential.

This led Kobayashi et alto compare these findings with those observed after instillation of air into the scala vestibuli. [8] They discovered that even a small amount of air in the scala vestibuli resulted in a decrease in the cochlear microphonics, the action potential, and the endocochlear potential. Moreover, hearing did not return to baseline levels in some cases after the air was removed. The greater impact that air in the scala vestibuli had on hearing might have been the result of a collapse of Reissner's membrane. Kobayashi et al concluded that pneumolabyrinth involving the oval window might be more severe and perhaps cause irreversible hearing loss.

With regard to stapes surgery, complications are grouped into three categories: intraoperative, postoperative, and delayed. Delayed complications can occur weeks to months after surgery. Among the common delayed complications are a slipped prosthesis, a necrotic incus, a perilymphatic leak, and recurrent otosclerosis. Dislocation of the prosthesis can be caused by trauma, inaccurate sizing, or adhesion formation. In our patient, the prosthesis had slipped into the vestibule and allowed air to enter the labyrinth. A displaced prosthesis is the most common cause of stapes failure that requires revision surgery; dislocation has been reported to account for 41 to 82% of all such failures. [9]

Because of the small number of cases of pneumolabyrinth reported in the literature, there is no consensus on management. Several authors have reported performing a middle ear exploration and repairing the involved windows with fascia and muscle obliteration. [2] Others report sealing the oval window with tragal perichondrium to prevent a further influx of air into the vestibule. [5] Surgical exploration is probably indicated for patients with progressive sensorineural or fluctuating hearing loss and persistent vertigo, especially if symptoms are acute. Exploration of the labyrinth carries risks and benefits similar to those of stapedectomy. When pneumolabyrinth occurs as a result of a subluxed stapes prosthesis, the patient should be made aware that removal of the prosthesis and replacement in the proper position might not improve hearing, but it might alleviate vestibular symptoms.

References

(1.) Issaacson JE, Laine F, Williams GH. Pneumolabyrinth as a computed tomographic finding in poststapedectomy vertigo. Ann Otol Rhinol Laryngol 1995;104:974-6.

(2.) Lyos AT, Marsh MA, Jenkins HA, Coker NJ. Progressive hearing loss after transverse temporal bone fracture. Arch Otolaryngol Head Neck Surg 1995;121:795-9.

(3.) Mafee MF, Valvassori GE, Kumar A, et al. Pneumolabyrinth: A new radiologic sign for fracture of the supes footplate. Am J Otol 1984;5:374-5.

(4.) Nurre JW, Miller GW, Ball JB, Jr. Pneumolabyrinth as a late sequela of temporal bone fracture. Am J Otol 1988;9:489-93.

(5.) Yanagihara N, Nishioka I. Pneumolabyrinth in perilymphatic fistula: Report of three cases. Am J Otol 1987;8:313-8.

(6.) Weissman JL, Curtin HD. Pneumolabyrinth: A computed tomographic sign of temporal bone fracture. Am J Otolazyngol 1992:13:113-4.

(7.) Kobayashi T, Itoh Z, Sakurada T, et al. Effect of perilymphatic air perfusion on cochlear potentials. Acta Otolaryngol 1990;110:209-16.

(8.) Kobayashi T, Sakurada T, Ohyama K, Takasaka T. Inner ear injury caused by air intrusion to the scala vestibuli of the cochlea. Acta Otolaryngol 1993;l13:725-30.

(9.) Wiet RJ, Harvey SA, Bauer GP. Complications in stapes surgery. Options for prevention and management. Otolaryngol Clin North Am 1993;26:471-90.

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