Congenital and Acquired Incudomallear Joint Fusion

Incudomallear (IM) fusion is a rare anomaly of the ossicular chain that may lead to conductive hearing loss. Primary IM fusion may occur either in conjunction with external auditory canal (EAC) malformations such as congenital aural atresia or as part of a hereditary syn- drome such as Goldenhar (1). Incomplete or altered development of the first and second branchial arches result in stenotic ear canals and a wide range of ossicular malformations involving the malleus and incus (1). The mechanism underlying IM fusion in these cases is thought to be due to the abnormal transformation of cartilage to bone during fetal development (2). The etiology of secondary IM fusion is less clear but has been reported to occur in cases of extensive exostosis, tympanosclerosis and even otosclerosis (3). Conductive hearing loss may occur if a bony bar adheres from one or both of the ossicles to the lateral or superior wall of the epitympanum (2,3). Herein, we present two cases of IM joint fusion to histologically assess the cellular nature of the fused IM joint. The first is a case of complete, congenital IM fusion in a young patient with congenital aural atresia. The second is a case of near complete IM joint obliteration with resultant ossicular fusion in a patient with fenestral otosclerosis. We seek to understand the major histologic differences in congenital versus acquired IM joint fusion to better inform the otologic surgeon on management of hearing loss in affected individuals.