bubble_chart Overview

Simmon (1968) first proposed that the rupture of the labyrinthine window membrane is one of the causes of sudden deafness, which was subsequently confirmed by the surgeries performed by Stround (1971) and Goodhill (1973).

bubble_chart Etiology

According to the Goodhill report, injury can occur through two pressure transmission pathways: ① Explosive injury (Explosive route): This is the most common cause, resulting from a sudden increase in cerebrospinal fluid (CSF) pressure transmitted outward to the inner ear, such as during coughing, vomiting, or forceful laughter or crying. The CSF pressure transmission process is as follows: CSF → cochlear aqueduct → scala tympani → basilar membrane → scala media → vestibular membrane → scala vestibuli → stapes footplate ligament → middle ear; or via CSF → internal auditory canal → cribriform plate → saccule and utricle → footplate ligament → middle ear. ② Implosive injury (Implosive route): This occurs when pressure in the tympanic cavity or Eustachian tube suddenly increases, directly pressing on the inner ear through the stapes footplate and round window. Examples include flying, diving, nose-blowing, playing wind instruments, hyperbaric chambers, gunshot wounds, boxing, and sneezing. The pressure transmission process is: nasopharynx → Eustachian tube → footplate → scala vestibuli → CSF; or nasopharynx → Eustachian tube → round window membrane → tympanic membrane → CSF. ③ Direct injury: Such as from surgery or head trauma. ④ Congenital anatomical abnormalities: The cochlear aqueduct typically has an internal diameter of 0.02mm and an external diameter of 2–3mm. If the opening is abnormally wide, the round window's shear resistance loses its protective function. The lack of choroid-like fibrous tissue in the duct means that a sudden increase in perilymph pressure in the scala tympani can cause window membrane rupture. Generally, the left duct is larger than the right, which may explain the higher clinical incidence of left-sided cases. If the stapes footplate is fixed in the oval window and the annular ligament loses its cushioning effect, this can also lead to round window membrane rupture. Animal experiments show that the critical pressure for round window membrane rupture when CSF pressure is elevated is 2.67–4.00 kPa. A simple round window membrane rupture causes only a few decibels of hearing loss, but clinically observed cases involve severe deafness, indicating that the window membrane rupture is often accompanied by vestibular or tegmental membrane rupture due to potassium toxicity from the mixing of endolymph and perilymph. Stewart examined 68 normal temporal bone specimens and found that 55% had a round window niche membrane, which can be perforated, reticulated, or closed. Sando described the round window membrane as consisting of two fan-shaped structures not on the same plane, with the posterior-superior part horizontal and the anterior-inferior part more vertical, covering a total area of 2.29±0.42mm²

. It has three layers (inner, middle, outer), is 50–70 μm thick (thicker at the edges and thinner in the center), and contains elastic fibers, blood vessels, and nerves in the middle layer. The opening of the cochlear canaliculus is located on the medial wall of the scala tympani, 0.3mm inward. In humans, the cochlear canaliculus is very narrow and filled with soft tissue, so intracranial hypertension transmitted to the perilymph is significantly attenuated and unlikely to cause membrane injury, though it may lead to chronic progressive injury. Antagonism, infantile open cochlear canaliculi, and anatomical abnormalities increase susceptibility.

bubble_chart Pathological Changes

Weisskopf et al. completely scraped off the round window membrane of guinea pigs and measured post-operative hearing using microphonic potentials, finding only a 6dB injury. Simmosn speculated that in cases of severe deafness with this condition, there must be concurrent injury to other parts of the cochlea. Flint, using scanning electron microscopy, observed that early damage to hair cells was limited to the apical and basal turns, which did not proportionally correlate with hearing loss. Simmons conducted puncture experiments on the round window membrane of cats, noting that the wounds healed within a week, and hearing returned to normal within 1 to 4 weeks. Animal experiments have yet to fully explain the phenomenon of severe deafness.

bubble_chart Clinical Manifestations

Sudden deafness after injury presents with highly variable symptoms and signs. Many initial symptoms are subtle, sometimes manifesting only as deafness and grade I vertigo. One-third of patients experience positional vertigo accompanied by nausea and vomiting, which typically subsides within a few days but may leave behind ataxia. Mild cases may show unsteadiness while standing or a staggering gait, while severe cases can lead to difficulty walking, though individual limb coordination remains normal. Some cases present with sudden severe tinnitus and deafness, accompanied by intense nausea and vomiting, making it easy to confuse with sudden deafness caused by other diseases. Others may exhibit only vertigo, with deafness appearing one to two years after the onset of illness.

bubble_chart Diagnosis

Otoscopic examination of the tympanic membrane is generally normal, occasionally showing congestion, turbidity, and fluid levels. When the affected ear is positioned downward in lateral decubitus, rotational nystagmus with a latent period occurs, accompanied by a sense of vertigo, presenting as fatigable peripheral vestibular type. According to Singleton's report, positional nystagmus in cases of perilymphatic fistula has a short latent period and is non-fatigable, with 26–60% of cases showing a positive fistula test. Patients with a clear history of barotrauma or trauma to the head, face, or ear, or those who suddenly experience vertigo and deafness after flying, diving, or exertion, along with a positive fistula test, should be suspected of this condition. They should be hospitalized for observation, undergoing intracranial imaging, neurological examinations, and auditory and functional tests. Simmons (1979) proposed checking hearing thresholds in increments of 100 Hz from 400 to 1300 Hz. The presence of a notch suggests possible rupture of the intracochlear membrane. Clinically, this condition should be differentiated from Ménière's disease, benign positional vertigo, and other sudden deafness cases. Acoustic impedance testing has limited diagnostic value and carries the risk of further labyrinthine injury, making it unsuitable for use.

bubble_chart Treatment Measures

(1) Conservative Treatment During the acute phase, absolute bed rest is essential, with the head of the bed elevated to help reduce intracranial pressure and promote the healing of the window membrane. Avoid straining during bowel movements and coughing. Vasodilators such as nicotinic acid or scopolamine may be used, or intravenous drips of 5–7% sodium bicarbonate and lidocaine can be administered. Hormones and energy mixtures may also be given intravenously. If dizziness persists or hearing continues to deteriorate after 7–10 days of observation, exploratory tympanotomy should be performed.

(2) Surgical Treatment Using the stapes surgery approach, an endaural incision is made, and the posterior tympanomeatal flap is reflected forward. Under the microscope, the round window is first examined for any clear fluid leakage. Sometimes, an electric drill or small chisel is used to remove the posterior edge of the round window niche to better visualize the window membrane. A rupture may be observed without fluid movement, or fluid leakage may be seen without visualizing the window membrane. Pressure can be applied to the internal jugular vein to increase intracranial pressure, aiding in examination. The same procedure is then followed to inspect the stapes and oval window. If a rupture is found in the round window membrane, a small dissector is used to remove the surrounding adhesions, and a small piece of temporal fascia or periosteum is inserted into the window. According to Ribari's test, the best materials for repair are fascia, periosteum, or cartilage membrane, while fat or venous wall is unsuitable. If the oval window is ruptured, the stapes should first be removed, and a small piece of fascia or temporalis muscle is inserted into the window before repositioning the stapes. Generally, vestibular symptoms show significant improvement after repair, but hearing recovery is often limited. Strohm's statistics indicate that vertigo improved in 97% of cases, tinnitus improved in 92%, but complete hearing recovery occurred in only 21%. Moreover, the treatment outcome showed no clear correlation with the timing of surgery. However, it is generally believed that earlier surgery yields better results.