Remnant cartilage in the middle ear.

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Congenital malformations of the middle ear occur during development, and most frequently result in missing- or fixed-forms of ossicles (Jahrsdoerfer 1980). Excessive development of cartilage in the external ear, like an accessory tragus, is common; however, to our knowledge, excessive cartilage development in the middle ear has not been previously reported. Here we present a case of remnant cartilage in the middle ear that was mistaken for a congenital cholesteatoma. A 9-year-old boy visited our clinic for an incidentally identified middle ear mass. He had not experienced any traumatic event or otologic medical history. A small whitish mass was identified in the left eardrum, but it did not cause any symptoms. The mass was located on the anterior inferior quadrant of the tympanic membrane (Fig. 1A). A pure tone audiogram (PTA) and computed tomography (CT) scan were performed for evaluation of the mass. PTA showed normal hearing on both sides. A dense mass was shown on CT scan (Fig. 1B), located close behind the tympanic membrane and was not compressing or eroding surrounding structures. The mass appeared as a bone-density rather than a soft tissue-density mass on the CT scans. Though the findings showed slight differences from the typical characteristics of clinically congenital cholesteatoma, this was the suspected diagnosis. Early detection of congenital cholesteatomas is necessary because they tend to grow and extend over time, destroying surrounding structures (Lim et al. 2012). Considering the natural course of this disease, the patient was scheduled to undergo removal of the mass even though he had no associated symptoms. Under general anesthesia, the tympanic cavity was exposed through a transcanal approach. The tympanomeatal flap was elevated, and the whitish mass was found to be abutting the I-S joint (incudostapedial joint). The mass was easily separated and removed from the middle ear space (Fig. 1C). Exposed ossicles were in normal shape, and mobility of the ossicular chain was intact. The tympanomeatal flap was repositioned, and the external auditory canal was packed with gelfoam. The surgical specimen was sent to the pathology department, and the final tissue pathology was reported as “degenerative cartilage tissue” (Figs. 1D). At 2 months following the operation, the patient showed no postoperative complications or recurrence. The auditory ossicle develops from two different primordiums, and it is well known that the upper part of the ossicular chain is derived from the first branchial arch, and the lower part develops from the second branchial arch (Anson et al. 1973). Blastemal tissue from each cartilage protrude toward each other, and they connect in the seventh fetal week. Around this same time, blastemal tissue differentiates into true cartilage. These ossicular growths occur as cartilaginous models until approximately the 15th week of gestation, at which point maximal chondral size is attained, the adult morphology is fully manifest, and ossification of the cartilage occurs (Takanashi et al. 2013). Ossification is usually completed by the 26th week of gestation and begins the lifelong remodeling process. Although the pathogenesis of most malformations of the middle ear is poorly defined, many can be explained based on embryology. The present case showed an intact tympanic membrane and middle ear structure, including normal shape and function of ossicles and joints, with extra cartilaginous tissue in the supra-stapes area. It can be assumed that excessive blastemal tissue differentiated into cartilaginous tissue, the normal part of which was ossified to leave extra cartilage. And the extra cartilaginous tissue was thought to be derived from the first branchial arch based on its location. Congenital malformation of the middle ear is extremely rare. Though missing- or fixed-forms of ossicle malformations have been defined and classified in otology society, other anomalies are so rare that they are only described in individual case reports. This is the first literature report of remnant cartilage in the middle ear, and it is a good example of the importance of consideration of congenital malformations in the presence of unusual findings. The authors have no funding, financial relationships, or conflicts of interest to disclose.