The role of fissula ante fenestram in unilateral sudden hearing loss.

The cause of unilateral sudden sensorineural hearing loss (SNHL) remains unclear in many clinical cases. Perilymphatic leakage through a fissula ante fenestram (FAF) fistula is one possible reason. We present four clinical cases with proven FAF fistula, discovered during surgical exploration. All patients experienced partial hearing recovery after surgical coverage of the fistula. We suggest FAF as a possible site for perilymphatic leakage, representing an anatomical correlate for sudden unilateral SNHL. We recommend early exploratory tympanotomy with special attention to the bony region, anterior to the oval window, in cases of severe sudden SNHL and suspected FAF. INTRODUCTION Pathogenesis of unilateral sudden sensorineural hearing loss (SNHL) can be described as idiopathic or may be based on autoimmune, infectious, or ischemic processes. Moreover, SNHL can be triggered through sudden perilymphatic leakage in the area around the round or oval window. Even though repeatedly discussed in literature, no precise description of any specific location for perilymphatic leakage exists. Fissula ante fenestram (FAF), as first described in 1890 by Siebenmann, is a slit-like space within the bony otic capsule, anterior to the oval window, representing an anatomical variation within the bony labyrinth (Fig. 1). Numerous publications in the late 19th and early 20th centuries have already dealt with its structure and anatomical appearance. If present, an FAF can represent a logical weak point for a fistula with possible perilymphatic leakage. CASE REPORTS We present the clinical cases of four male patients, ages ranging from 19 to 66 years, who attended our department between 2011 and 2014, due to unilateral sudden hearing loss. Each patient showed complete deafness in the affected ear during the first pure-tone audiometry. According to our routine workflow, possible causes for sudden hearing loss were checked with clinical otologic and neurologic examination as well as diagnostic imaging such as a computed tomography (CT) scan of the temporal bone and magnetic resonance imaging (MRI) of the head. In all four patients, none of these examinations indicated an obvious cause for hearing loss, leading to the diagnosis of idiopathic sudden unilateral SNHL. Primary treatment in all cases was intravenous substitution of 500 mg methylprednisolone on day 1 and substitutions of 250 mg on days 2 and 3. For the following 3 days, two patients received intratympanic administration of 4 mg dexamethasone per day on the affected ear, whereas the other patients had further intravenous corticosteroid substitutions with a consecutive dosage each day. None of the four patients experienced a recovery of hearing during corticosteroid therapy. Consequently, due to the unsatisfactory results of the primary treatment, we performed exploratory tympanotomy through an endaural approach on the four patients on day 3, 5, 10, and 28, respectively, after the onset of hearing loss. Tympanotomy was performed under general anesthesia in three of the cases and under local anesthesia in the other. All four tympanotomies were performed by the first author (M.T.). To achieve the best possible intraoperative view on the intratympanic area between the cochleariform process and the stapes, the endaural From the Department of Otorhinolaryngology–Head and Neck Surgery (M.T., S.R., G.R.), The Paracelsus Private Medical University of Salzburg, Salzburg, Austria; Department of Anatomy, Histology and Embryology (A.G.), Semmelweis University, Budapest, Hungary; Faculty of Dentistry (M.P.), University of Szeged, Szeged, Hungary; and the Institute of Neuroradiology (J.-M.H.), University Medical Center of the Johannes Gutenberg University, Mainz, Germany. Editor’s Note: This Manuscript was accepted for publication January 21, 2016. This work was performed at the Department of Otorhinolaryngology–Head and Neck Surgery, General Hospital Salzburg, University Hospital of Paracelsus Medical University, Salzburg, Austria. The authors have no funding, financial relationships, or conflicts of interest to disclose. Send correspondence to Mikl os T oth, MD, Department of Otorhinolaryngology–Head and Neck Surgery, General Hospital–Paracelsus Medical University Salzburg, M€ ullner Hauptstrasse 48, 5020 Salzburg, Austria. E-mail: [email protected] DOI: 10.1002/lary.25922 Laryngoscope 126: December 2016 T oth et al.: Perilymph Leakage and Unilateral SNHL