Perforation of the External Auditory Canal or Middle Cranial Fossa
Gary Warburton and Nawaf Aslam-Pervez
Introduction
Open and arthroscopic surgeries of the temporomandibular joint (TMJ) are common and effective treatments for selected patients with TMJ disorders. However, complications inevitably occur, even in the hands of experienced TMJ surgeons. An understanding of the surrounding anatomy, as well as a knowledge of the potential complications, is essential and not only helps in avoiding these complications but also in their recognition and appropriate management, when they do occur. The TMJ is located in a complex anatomical region within the head and neck. It is bounded posteriorly by the external auditory canal and superiorly by the middle cranial fossa. Consequently these structures are at risk during open surgery and arthroscopy with the potential for serious complications.
Perforation of the External Auditory Canal (EAC)
Pathophysiology
The external auditory canal (EAC) runs from the auricle to the tympanic membrane. The EAC does not follow a straight course, but rather an S shape, first curving pos- terosuperiorly then anteroinferiorly. The EAC is angled toward the TMJ and lies in very close proximity as can be seen on computed tomography (CT) (Fig. 4.1).
The EAC is divided into two parts. The outer third has cartilaginous walls and the inner two-thirds have bony walls. The cartilaginous EAC is continuous with the auricular cartilage and has a fibrous attachment to the rim of the bony meatus.
G. Warburton, DDS, MD, FDSRCS, FACS (*)
N. Aslam-Pervez, MB ChB, BA, B. Dent. Sc, MRCSI
Oral & Maxillofacial Surgery, University of Maryland Dental School, Baltimore, MD, USA e-mail: This email address is being protected from spam bots, you need Javascript enabled to view it
© Springer International Publishing AG 2017
G.F. Bouloux (ed.), Complications of Temporomandibular Joint Surgery, DOI 10.1007/978-3-319-51241-9_4
Fig. 4.1 Axial CT showing course of the EAC and TMJ proximity
The bony canal is mostly composed of the C-shaped tympanic portion of the temporal bone, and the superior wall is the squamous and petrous parts of the temporal bone. Foramen tympanicum (foramen of Huschke) in the tympanic plate of the temporal bone normally closes by 5 years of age, but may persist in up to 18% of individuals as an area of incomplete ossification [1, 2]. If present, the foramen is located at the anteroinferior aspect of the EAC, posteromedial to the TMJ. The presence of this foramen may increase the chance of otologic complications during arthroscopy of the TMJ [3]. The cartilaginous and bony portions of the canal are lined with skin containing hairs, sebaceous glands, and ceruminous glands. The adult EAC is approximately 35 mm in length measured from the tip of the tragus to the inferior portion of the tympanic membrane (TM). The diameter of the EAC is approximately 9 mm in the cartilaginous canal and becomes narrower in the bony canal.
The deepest part of the EAC terminates at the TM, which lies obliquely and separates the EAC from the middle ear. The TM has three layers with the outer layer lined by a stratified squamous epithelium and the inner layer lined by a ciliated
Fig. 4.2 Left tympanic membrane
columnar epithelium with the intervening layer being fibrous. The fibers are attached to the malleus ossicle and also radiate out to the periphery where circumferential fibers are found forming a thickened ring. The TM is divided into the pars tensa and the much smaller pars flaccida superiorly (Fig. 4.2).
Medial to the TM is the middle ear and tympanic cavity, which is lined by ciliated columnar epithelium and connected to the nasopharynx by the Eustachian tube. The tympanic cavity contains the ossicles (malleus, incus, and stapes), the tensor tympani tendon, and the chordae tympani of the facial nerve. The joints between the ossicles are synovial with elastic capsules and supported by several ligaments. Medial to the middle ear, deep in the temporal bone, is the inner ear with its osseous labyrinth of semicircular canals, cochlea, and vestibule.
Violation of the EAC is possible during open joint surgery if regional anatomy is not kept in mind with good spatial awareness on the part of the surgeon. However, perforation/puncture into the EAC and the middle ear is also possible during TMJ arthroscopy. Gonzales reported two cases of EAC puncture in 670 arthroscopies but no TM injuries [4]. Van Sickels reported a case of EAC and middle ear injury after junction of the cartilaginous and bony canal was penetrated [5]. Herzog also reported that a persistent foramen of Huschke might be a risk factor for otologic complications in arthroscopy [3].
Puncture into the cartilaginous portion of the EAC is much more likely, but puncture into the bony portion is possible when using the sharp trocar with excessive force. Once the EAC is entered with the trocar, it is possible to puncture the
Fig. 4.3 TM puncture from an arthroscope with exposure of the ossicles. White arrow TM perforation, red arrow stapes
TM and enter the middle ear, causing disruption of the ossicles and hearing loss (Fig. 4.3).
The consequences of puncturing the EAC can vary from minor to serious depending primarily on the location and depth of the puncture. Early recognition of the EAC perforation will often enable the surgeon to redirect instruments and avoid further damage.
Potential Sequelae of Puncture into the EAC
Canal wall laceration and bleeding
Otitis externa Injury isolated to EAC
Stricture
Cholesteatoma
Perforation of the TM Otitis media
Otorrhea Injury involving TM and ossicles
Disruption of the ossicles
Conductive hearing loss Vertigo
