ツチ骨柄および前突起の複合奇形

Abstract

We present 4 cases of ossicular anomaly combined with anomalous tympanic membrane and/or stenosis of the external auditory canal. In 3 cases, a thick bony bridge connected the head of the malleus with the inferior posterior wall of the tympanic bone, and, in the other, a V-shaped ossicle surrounded by thick fibrous tissue was present inferior to the neck of the malleus. In 2 of the former 3 cases, a cartilageous bone was observed branching from the bony bridge anteriorly, the tip of which was clearly identified as the umbo of the malleus. Thus, the bony bridge was recognized as an anomaly which had developed on the anterior process of the malleus process of Folius in 3 cases, while in the other the malleus handle was completely absent. The area of the epithelial layer of the tympanic membrane was restricted due to partial protrusion of the tympanic bone in all cases. We speculate that the bridge anomaly developed at about the 19th week of gestation, when an intramembranous spicule (os goniale) directed towards the anteromedial surface of the immature cartilagenous malleus handle failed to fuse with it, and instead developed further to extend to the infero-posterior part of the tympanic bone. The V-shaped ossicle is thought to be an anomalous anterior process but not handle of the malleus because it is hard and does not contain any cartilaginous part characteristic to some part of the malleus handle.