Significance of Pseudo-Conductive Hearing Loss and Positional Nystagmus for Perilymphatic Fistula: Are They Related to Third-Window Effects?

OBJECTIVES: Patients’ clinical presentation is critical for identifying suspected perilymphatic fistula (PLF). The involvement of third-window lesions in the pathomechanism of PLF has been hypothesized. This study investigated the clinical features of PLF and the relationship of the third-window effect with PLF. METHODS: Sixty patients underwent surgical exploration for suspected PLF and the oval and round windows were reinforced. Clinical features including demographics, pure-tone audiometry (PTA), and videonystagmography were evaluated preoperatively and 1 month postoperatively. Surgical outcomes were analyzed according to the improvement of hearing and vestibular symptoms and signs. The conductive components of PTA (air-bone gap [ABG]) were measured, and the relationship between ABG closure after surgery and hearing improvement was analyzed. In addition, postoperative subjective dizziness was assessed by clinical interviews. Changes in positional nystagmus were analyzed according to ABG closure and hearing improvement. RESULTS: ABG at lower frequencies (LFABG; 250 Hz, 500 Hz, 1,000 Hz) was present in 27 patients (45%). Postoperatively, PTA significantly improved after surgical repair. Among the patients with preoperative LFABG (n=27), 15 (55.5%) showed postoperative ABG closure and significant improvement in PTA at all frequencies compared with the patients without ABG closure (P=0.012). Subjective dizziness improved in 57 patients (93.3%). Positional nystagmus was found in 45 of 49 patients. Multiple canal involvement was more common than single canal involvement (67% vs. 33%). The horizontal semicircular canal was most commonly involved, followed by the posterior and anterior canals. Postoperatively, positional nystagmus disappeared, or the number of involved canals decreased in 22 of 34 patients (64.7%). CONCLUSION: Pseudo-conductive hearing loss at lower frequencies and positional nystagmus originating from multiple semicircular canals were common findings in PLF. Surgical reinforcement of the oval and round windows improved the hearing threshold accompanied by closure of ABG. A third-window lesion might explain these clinical features of PLF.