Introduction
The external auditory canal is intimately related to the temporomandibular joint, separated only by its bony anterior wall, which is of variable thickness.Reference Lacout, Marsot-Dupuch, Smoker and Lasjaunias1 Neoplasia, trauma or inflammation in this area can result in herniation of the temporomandibular joint into the ear canal, giving rise to a range of otological symptoms including tinnitus, otalgia, deafness and otorrhoea.
Spontaneous herniation of the temporomandibular joint into the ear canal is rare. The first such case was reported by Hawke et al. in 1987.Reference Hawke, Kwok, Mehta and Wang2 Only 13 more cases have subsequently been reported.
Here, we report a case of spontaneous herniation of the temporomandibular joint, emphasising the diagnostic and radiographic features. We also discuss the embryonic origins of this phenomenon and the options for its management.
Case report
An 87-year-old woman was referred with a left ear canal mass and a four-month history of left-sided, yellow otorrhoea and otalgia, after her left ear had been syringed by her general practitioner's practice nurse. She had a past medical history of emphysema and congestive cardiac failure.
Examination revealed a normal right external auditory canal and tympanic membrane, but a mass in the left external auditory canal surrounded by necrotic debris. Microsuction was carried out, more clearly demonstrating the mass, which appeared soft and polypoid, although there was a firmer area within it which resembled a small area of cartilage (Figure 1). This mass had a firmer consistency than granulation tissue or a middle-ear polyp, and could not be removed by suction. It was non-tender and appeared to be arising from the anterior ear canal. When the patient opened her mouth to speak, the lesion disappeared (Figure 2).
Fig. 1 Otoscopic view of the left external auditory canal at presentation, showing herniation of the temporomandibular joint through the anterior wall.
Fig. 2 Otoscopic view of the left external auditory canal on mouth-opening, showing that the pseudotumour has resolved and a clear view of the tympanic membrane is now possible.
Subsequent investigation utilised high-resolution computed tomography (CT) of the patient's temporal bones, which confirmed an 8.6 mm defect in the antero-inferior portion of the left external ear canal, with herniation of retrodiscal soft tissues (Figure 3).
Fig. 3 Axial high resolution computed tomography scan of the left temporal bone, showing a defect in the anterior wall of the external auditory canal, with herniation of the soft tissues of the temporomandibular joint.
Discussion
Spontaneous herniation of the temporomandibular joint has been attributed to persistence of the foramen of Huschke. This is a transient structure present during embryological development of the temporal bone, and was first described in the nineteenth century by Emil Huschke, professor of anatomy at the University of Jena. The term foramen is somewhat misleading, as the foramen of Huschke does not normally convey any structures, and so in strictest parlance it should be referred to as a dehiscence. It is not normally present in the adult temporal bone, having usually undergone complete involution by the age of five years.
Development of the external auditory canal begins at eight weeks' gestation, when the first branchial cleft begins to deepen. A funnel-shaped tube is formed, which is subsequently enclosed by cartilage to form the outer third of the ear canal. A week later, a solid epidermal plate develops at the medial end of this tube and spreads towards the midline until it contacts the epithelium of the first pharyngeal pouch. This core of cells persists until the beginning of the second trimester, when it is resorbed to leave a ring of ectodermal tissue which forms the medial two-thirds of the primitive ear canal. Ossification of this structure begins from four points in the surrounding mesenchyme, which fuse to give rise to the primordial tympanic ring. At birth, bony prominences form on the anterior and posterior portions of this ring, growing towards each other until they eventually fuse, separating the tympanic ring into the ear canal superiorly and the foramen of Huschke inferiorly. The foramen of Huschke normally undergoes complete involution due to ongoing bony growth, and is not normally present in adult temporal bones.
Failure of involution results in persistent dehiscence of the bony wall of the external auditory canal. Because of ongoing downward and forward displacement of the mastoid bone, the ear canal rotates with growth, meaning that a persistent foramen of Huschke results in a defect of the anterior canal wall. In adults, it is positioned just postero-medial to the temporomandibular joint.
Previous studies have reported the incidence of a patent foramen of Huschke in the normal adult population as being between 4.6 and 7.2 per cent, judging from temporal bone high resolution CT and autopsy, respectively.Reference Lacout, Marsot-Dupuch, Smoker and Lasjaunias1, Reference Wang, Bingham and Hawke3 In the vast majority of individuals, a patent foramen of Huschke is asymptomatic. However, previously reported cases show that it can weaken the antero-inferior portion of the ear canal and predispose to symptomatic temporomandibular joint herniation.
In cases of temporomandibular herniation through a patent foramen of Huschke, the mean age at presentation is 55 years, with 80 per cent of patients aged over 50 years. There is a female preponderance (12 of 15 reported cases). It has been postulated that herniation of the temporomandibular joint through a patent foramen of Huschke is only possible after years of mechanical stress from mastication. This results in weakening and widening of the foramen with age, and would explain the age distribution of reported cases. Patients have presented with histories of otalgia,Reference Heffez, Anderson and Mafee4 hearing loss,Reference Hawke, Kwok, Mehta and Wang2 tinnitusReference Moriyama, Kodama and Suzuki5 and otorrhoea.Reference Lacout, Marsot-Dupuch, Smoker and Lasjaunias1
In the present case, our patient was referred because of otalgia after ear syringing, associated with a mass in the ear canal. The underlying cause of this mass could have easily been missed, if on evaluation a correlation had not been made with the relative position of the temporomandibular joint. It is important to be aware of this potential diagnostic trap when assessing lesions within the external ear canal. Patients should be asked to open their mouth when a lesion of the ear canal is evident, especially when this lesion is anterior.
The management of temporomandibular joint herniation depends on the symptoms experienced by the patient, and the patient's enthusiasm and suitability for surgical correction. The latter two points are especially important given the often late age at presentation. In our case, as in many others, symptoms were trivial and the patient decided on conservative management.
• Spontaneous herniation of the temporomandibular joint into the external auditory canal is rare
• It is thought to be caused by persistence of the foramen of Huschke
• Patients presenting with an external auditory canal mass should be examined (using otoscopy or microscopy) with their mouth both closed and open
• Surgical closure is possible in confirmed cases, but management should be guided by patient symptoms
However, patients with significant symptoms can be offered surgery. Saeed et al. and Merrit et al. have described techniques by which an overlay graft of tragal cartilage can be used to prevent prolapse of peri-articular tissues into the ear canal, following iatrogenic damage to the anterior canal wall.Reference Saeed, Saeed and Brooke6, Reference Merritt, Bent and Porubsky7 Moriyama et al. have reported using the same technique to close a spontaneous herniation, with the repair still sound after five years.Reference Moriyama, Kodama and Suzuki5 Annand et al. have described an alternative technique involving fixation using a polypropylene implant, with excellent results in two cases of spontaneous herniation, although follow up was only for 18 months.Reference Annand, Latif and Smith8
