Otosclerosis.ppt

Otosclerosis Introduction Otosclerosis (OS) is a fibrous osteodystrohpy of the human otic capsule Primarily conductive hearing loss Autosomal dominant with incomplete penetrance Male : Female = 1 : 2 Schwartze sign 1873 Reddish hue behind a intact TM, due to increased vascularity of cochlear promontory in active OS lesion. This phase is known as otospongiosis 10% of OS Embryology The maturation of bony labyrinth plays a role in the pathogenesis of OS. Otic capsule arises from mesenchyme. At 8 weeks, the cartilaginous framework is begun. At 16 weeks, endochondral bony replacement of this framework. The fissula ante fenestram, anterior to oval window is the last area of endochondral bone formation. This region is affected in 80~90% of patients Predilection for Otosclerosis Border of round window Apical medial wall of cochlear Area posterior to cochlear aqueduct Stapes footplate Region adjacent to the semicircular canal Three Forms of Otosclerosis Early phase: otospongiosis Transitional phase Late phase: otosclerosis History Schwartze sign is that osteocytes resorb bone around preexisting vessels, which causes widening of the vascular channels and dilation of microcirculation. The areas grow rich in amorphous ground substance and deficient in mature collagen, resulting in formation of new spongy bone. HE stains described as blue mantles of Manasse. Pathophysiology The most common type involves the stapes Beginning at the fissula ante fenestram Progressive involvement of the footplate can create a thick focus of OS that fills the OW niche (obliterative OS) fissula ante fenestram In adult, contains cartilage, fibrous tissue, or both Is formed by resorption of precartilage May be an appendage of perilymphatic space 這裂隙是在胎生期內耳和中耳有過交通，臨床上是耳硬化症好發部位 If OS involves only the footplate and spares the annular ligament, minimal fixation may occur. Such a thickened footplate is called a biscuit footplate. Higher risk of post-OP SNHL because biscuit footplate can become mobilize