Classifications of tunnel-like structure of human petrotympanic fissure by cone beam CT.

The discomallear ligament (DML) runs through a narrow space of bony petrotympanic fissure, which joins the articular disc of the temporomandibular joint (TMJ) and the malleus in the tympanic cavity. Previous report suggest that an anatomical feature gives rise to TMJ pain and dysfunction. Recently, the movement of the malleus caused by hypertension on the discomallear ligament is important to the function of the TMJ. The purpose of this study is to define its morphological features using the cone beam CT (CBCT) and anatomical dissection of Japanese cadavers. Petrotympanic fissure and DML were observed in 14 cadavers (eight males and six females). It is revealed that a wide tunnel-like structure was found on CBCT images in the middle region of the petrotympanic fissure to the malleus in the tympanic cavity consisting of mainly three types: a wide tunnel-shaped structure (29.2%, 7/24, type 1), a tunnel-shaped structure widely open in the entrance of the petrotympanic fissure to the mandibular fossa and gradually thinning out in the tympanic cavity (20.8%, 5/24, type 2), and a tunnel-shaped structure widely open in the entrance of the mandibular fossa, middle region with flat-shaped tunnel structure and narrow exit in the tympanic cavity (41.7%, 10/24, type 3). These structures between the entrance of the petrotympanic fissure and the exit at the tympanic cavity are important to define the limited movement of the malleus. Therefore, morphological feature of the ligaments in malleus may relate to TMJ pain, dysfunction and hearing function.