Since the description by Fee1 of perilymphatic fistula (PLF) to the middle ear space, there has been an explosion in the number of reports describing PLF. It is likely that PLF has been used to explain clinical cases of unexplained sensorineural hearing or vertigo, or both. The diagnostic criteria of PLF are not clearly defined and surgical exploration has been used as the principal approach to diagnosis as well as management. A major impediment to recognition of perilymph in the oval or round window niches (RWN) is the presence of tissue fluid produced by middle ear mucosa that reaccumulates when aspirated. An additional misconception responsible for reported round window membrane fistulae is the assumption that a fenestrated membrane, which often covers the entrance to the RWN, represents the RWM. Removal of the bony overhang of the RWN is necessary for exposure of the RWM. It is not surprising that PLF is overdiagnosed and overtreated. This has formed the basis for controversy regarding the issue of diagnosis, recognition, and treatment of PLF.

A perilymphatic fistula (PLF) may be defined as a communication of the perilymphatic space to the middle ear space. The volume of perilymph in the labyrinth is normally small, as it is derived as a transudate of the vasculature in the spiral ligament and, to a limited degree, the cerebrospinal fluid (CSF) space through the cochlear aqueduct. Therefore, perilymph loss in a PLF is small and reaccumulates slowly. A large volume of fluid from a fistula in the oval or round windows (surgical or traumatic) represents the flow of CSF through a congenital defect in the labyrinth that allows the subarachnoid space to communicate with the perilymphatic space. This form of CSF otorrhea will not be considered in this discussion of PLF, as its presence is easily recognized by its copious flow, and treatment is non-controversial. The PLF, which has attracted considerable controversy, is represented by a defect either in the ligamentous or bony structures of the oval or round windows in a normal labyrinth. It should also be pointed out that fistulization of the bony labyrinth (cochlea and semicircular canals) from chronic middle ear inflammation, particularly cholesteatoma, does not include communication into the perilymphatic compartment. The inflammatory response to bone erosion from cholesteatoma creates fibrosis of the endosteal membrane and variable degrees of labyrinthitis rather than a defect permitting perilymph loss. Issues of diagnosis and recognition of PLF at surgery form the main areas of disagreement.

Vast clinical experience is based on the signs and symptoms that result from a humanmade fistula in the oval window. This derives from the stapedectomy or stapedotomy procedure where either a large or small fenestra is fashioned in a fixed footplate and sealed with a tissue prosthesis to reconstruct a sound transmission mechanism. Although the fenestra with PLF in this procedure is of short duration, as it is sealed with tissue and the healing response of the labyrinth and the middle ear, poststapedectomy symptoms reflect a controlled PLF. Both vestibular and auditory symptoms follow stapedectomy with the vestibular symptoms consisting of dizziness and dysequilibrium, occasionally accompanied by spontaneous nystagmus being the most troublesome. Auditory system effects appear as elevated bone conduction thresholds with some decrease in speech discrimination, which may require one or several weeks to return to normal levels. It is for this reason that the usual post stapedectomy auditory examination is obtained at 4 to 5 weeks. Animal research² has demonstrated rapid healing of a defect in the oval window by regeneration of the endosteal membrane within 24 to 48 h, followed by regeneration of middle ear mucous membrane. This reparative response is more rapid with a small fenestra than with a large (total stapedectomy) fistula.

Clinical experience with the end result of an unhealed PLF comes from our experience with direct trauma to the tympanic membrane and ossicular chain as a result of the introduction of an instrument (toothpick, hairpin) into the external ear canal. When such an injury is accompanied by vestibular symptoms, it is axiomatic that immediate surgical exploration and removal of a subluxed or fractured stapes footplate with soft tissue seal of the PLF be performed.^{3, 4} If such repair is not performed the PLF leads to irreversible sensorineural hearing loss with eventual resolution of vestibular symptoms as a result of central vestibular compensation. Early surgical repair of the oval window fistula insures recovery of auditory and vestibular deficits. Thus, surgical repair of PLF is capable of reversing the labyrinthine deficits caused by PLF.

Round window membrane ruptures can be produced in the laboratory animal (cat) by increasing subarachnoid pressure.⁵ However, the cochlear aqueduct is short and wide in the cat but is long, narrow, and filled with periotic duct tissue in humans. Therefore, this pathway usually will not permit transmitted CSF pressure in humans as in the laboratory animal, at least in the majority of temporal bones. Furthermore, the RWM is very thin with a reduced lamina propria in the laboratory animal (cat, guinea pig, chinchilla),⁶ whereas the human RWM has a thick lamina propria that will resist disruption by increased pressure.⁷

Animal research has demonstrated that cochlear potentials do not change^{8, 9}

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