The Forgotten Second Window: A Pictorial Review of Round Window Pathologies

Abstract

The round window serves to decompress acoustic energy that enters the cochlea via stapes movement against the oval window. Any inward motion of the oval window via stapes vibration leads to outward motion of the round window. Occlusion of the round window is a cause of conductive hearing loss because it increases the resistance to sound energy and consequently dampens energy propagation. Because the round window niche is not adequately evaluated by otoscopy and may be incompletely exposed during an operation, otologic surgeons may not always correctly identify associated pathology. Thus, radiologists play an essential role in the identification and classification of diseases affecting the round window. The purpose of this review is to highlight the developmental, acquired, neoplastic, and iatrogenic range of pathologies that can be encountered in round window dysfunction. ABBREVIATIONS: LO 4 labyrinthitis ossificans; RW 4 round windowIndicates open access to non-subscribers at www.ajnr.org http://dx.

Endoscope-Assisted Cochlear Implantation in Atretic Round Window

“…On the other hand, non-syndromic RW atresia has been shown to have an association with autosomal dominant inheritance predilection. The clinical feature is mainly conductive hearing loss with an air-bone gap of 30 dB to 40 dB [ 7 ]. Interestingly, this patient had bilateral sensorineural hearing loss.…”

The Link Between Brain and Auditory System and Possible Role of Vestibular System in Hearing System as a Second Middle Ear and the Role of Melanocytes and/or Neuromelanin in this Process

“…both cochlear conductive hearing loss and Sensorineural hearing loss have been reported in RW Pathologies. Type of the hearing loss depends on the site and degree of the lesion in RW membrane and its surrounding [109,110]. Cochlear conductive hearing loss also has been reported in Meniere's disease, although another hypothesis is proposed but the Vestibular organs dysfunction because of stiffness caused by hydrops might be the reason for the conductive component hearing loss in this disease [111].…”

Role of Radiologic Imaging in Otosclerosis

“…Pre-operative knowledge of obliterative otosclerosis can be helpful for appropriate planning and patient counseling [43, 44•, 45, 46]. Additionally, CT can help identify whether otosclerosis involvement extends to the round window and whether there is obliteration, overgrowth, or occlusion of the round window which can result in failed stapes surgery [30,47]. Third window defects can also result in failed stapes surgery but are readily detected by CT.…”

“…In situations where the overhanging facial nerve crosses the oval window, the stapes footplate can directly attach to the facial nerve, placing the patient at risk for facial nerve injury if a surgical repair for otosclerosis is planned [30,50]. Pre-operative CT can define if there is a high riding jugular bulb, dehiscent jugular bulb, or jugular diverticulum, and if there is vascular encroachment upon the round window niche [47]. Non-contrast CT is sufficient to exclude aberrant internal carotid artery, to avoid surgical complication [51,52].…”