A perilymphatic fistula (PLF) is a phenomenon defined as leakage of perilymph through the oval window or round window [1]. The perilymph is located in the bony labyrinth and the bony labyrinth encloses the membranous labyrinth which contains endolymph. When the two different types of lymphatic fluid are mixed or there is a leakage of lymphatic fluid into the middle ear cavity through an abnormal track, this is also called a PLF. Generally, lymphatic fluid leakage due to superior canal dehiscence or dehiscence of the semicircular canal after cholesteatoma is not considered to be a PLF [2]. As reported in many cases, a PLF can be a result of head trauma or an external impact causing a temporal bone fracture. There are several reports indicating that PLF can occur without trauma, for example, after a Valsalva maneuver. Barotrauma such as forceful sneezing, nose blowing, skydiving or scuba diving causing a sudden pressure change are regarded as other causes of PLF. Leakage of perilymph can occur through the oval or round window membrane, fissula ante fenestram, microfissures, or Hyrtl’s fissure [3-5].

Pneumolabyrinth is a condition where air accumulates in the inner ear space such as the vestibule or cochlea through an abnormal track or passage. Increased pressure in the middle ear cavity, after a certain event, will push air from the middle ear into the inner ear through an abnormal passage which in this case is a PLF and can cause inner ear symptoms such as dizziness and hearing impairment. The usual cause is thought to be temporal bone fracture after trauma followed by pressure change, especially PLF after a fracture violating the otic capsule [6]. However, pneumolabyrinth may occur without trauma [7]. Pressure change in the middle ear or cerebrospinal fluid (CSF) is considered to be another typical cause of pneumolabyrinth, and excessive nose blowing or Valsalva maneuver can increase the middle ear or CSF pressure.

We report three cases of complete recovery of hearing loss caused by a PLF followed by pneumolabyrinth after nose blowing and without trauma. In all cases, the patients’ symptoms resolved spontaneously after conservative treatment. We also review the possible mechanisms of PLF formation.

This study was reviewed and approved by the Institutional Review Board (CUH 2020-02-043).

Middle ear surgery such as stapedectomy, or cholesteatoma removal from the oval and round windows may also cause a PLF. Patients with a PLF may suffer dizziness, nausea, vomiting, tinnitus, or hearing impairment. If patients experiencing these symptoms have a history of head trauma or middle ear surgery, this should increase suspicion for a PLF.

Although the exact mechanism of PLF formation is still uncertain, the most widely accepted route is the “implosive” and “explosive” theory suggested by Goodhill [3]. The “explosive” mechanism occurs when there is an increase in CSF pressure which is transmitted from the internal auditory meatus or by the cochlear aqueduct. This mechanism suggests that an increased force in an abnormally patent cochlear aqueduct could rupture the basilar membrane and Reisner’s membrane into the scala vestibuli, and consequently the transmitted force could injure the utricle, saccule, the semicircular canals, the round window membrane, or the annular ligament of the stapes. On the other hand, the “implosive” mechanism would be caused by a Valsalva maneuver, prolonged coughing or nose blowing resulting in a sudden increase in air pressure through the eustachian tube. This sudden increase in pressure in the middle ear cavity would cause rupture of the round window membrane or the annular ligament of the stapes.

Several studies have tried to determine the pressure change across the cochlear membrane and the middle ear pressure, which may be one of the main causes of spontaneous PLF and pneumolabyrinth. Yanagihara, et al. [3,4] reported a case of pneumolabyrinth induced after air inflation of the eustachian tube, suggesting that air entered the inner ear space through a PLF. The authors reported that the opening pressure of the eustachian tube after a Valsalva maneuver ranged between 250 and 650 mmH2O, which may create a positive middle ear pressure from 200 to 400 mmH2O. Air inflation of the eustachian tube or a Valsalva maneuver would also increase middle ear pressure to such an extent that it may lead to a PLF which consequently caused pneumolabyrinth. This is the “implosive” route of PLF formation. There is also a report focusing on the “explosive” route of PLF and pneumolabyrinth. In three patients with tympanic membrane rupture, Sakikawa, et al. [5] used tympanometry with an earplug in the affected ear to measure the changes in CSF and middle ear pressure after nose blowing. They found that nose blowing increased not only middle ear pressure but also CSF pressure to an even greater extent. The mean value of maximum CSF pressure after nose blowing was 388 mmH2O, and the maximum middle ear pressure was 252 mmH2O. That study indicated that nose blowing may cause an outward pressure of more than 130 mmH2O across the cochlear window.

Although PLF is not easy to identify through radiology, pneumolabyrinth can easily be diagnosed by temporal bone high resoluction temporal bone CT. It is not clear that all PLF is accompanied with pneumolabyrinth, but we can assume in our case 3, the patient was highly suspected of having pneumolabyrinth based on clinical history, even though there was no air pockets in the inner ear. The CT scan was performed several days after the initial symptoms, so the air may have been absorbed and dissipated. So doctors dealing with patients having symptoms of PLF should be aware that air is not always visible in the CT scan, especially if the scan is delayed, so PLF should not be ruled out even with negative findings from radiology [8].

There is no consensus on the management of pneumolabyrinth. The treatment options are observation or explorative tympanotomy [7]. Conservative management of pneumolabyrinth includes bed rest, head elevation, and avoidance of the Valsalva maneuver and physical exertion which raises intraabdominal pressure. Surgical exploration may occasionally be required in the management of displaced stapes, of progressive, fluctuating sensorineural hearing loss, or of persistent vertigo [2,9].

Timing of surgical exploration and repair of PLF has received considerable attention, therefore we suggest treatment guidelines for PLF.

Explorative tympanotomy should be performed to the patients with confirmed severe to profound sensorineural hearing loss over 70 dB, and patients who had no clinical improvement even though 1-3 weeks of conservative treatment [8,10].

In our cases, all patients had hearing loss with mild to moderate degree and conservative management was chosen with injection of systemic steroids, and the symptoms in all patients improved after about a week.

In conclusion, high resoluction temporal bone CT of the temporal bone is useful for diagnosing pneumolabyrinth and PLF. Clinical symptoms are as important as temporal bone CT for diagnosing pneumolabyrinth and PLF when the air bubble or fistula is absorbed due to delayed examination.

Initial management of pneumolabyrinth-associated PLF is conservative treatment including intravenous steroids, absolute bed rest, head elevation. Exploratory tympanotomy should be performed when severe to profound sensorineural hearing was found or when there is no effect of 1-3 weeks of conservative treatment.