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Identification of foramen of Huschke with reversible herniation of temporomandibular joint soft tissue into the external auditory canal on multidetector computed tomography.

This article bring attention to a specific anatomical defect in the external auditory canal (EAC) that may affect the diagnosis and treatment protocol for oral and maxillofacial surgeons who deal with temporomandibular joint (TMJ) soft tissue issues, as well as otolaryngologists in their assessment of otological symptomatology. In addition, the article should make radiologists more aware of this particular defect in assessing imaging involving TMJ or otological factors. Radiology can be very helpful in determining the size and extent of the defect and tissue herniation to aid in decisions regarding whether biopsy or surgical intervention is advantageous or harmful.

CASE PRESENTATION

A 70-year-old man was referred to us for high-resolution computed tomography (HRCT) of both temporal bones. He presented with left-sided otalgia. There was associated fullness in the left ear but no discharge and no previous history of trauma, ear surgery, or instrumentation. Clinical examination revealed a pulsatile polypoidal mass bulging into the EAC on the left side. A biopsy was planned, and prebiopsy HRCT was performed on a 128-slice Philips Ingenuity Multidetector CT (Philips Medical Systems, The Netherlands) on 120 kV, 200 mAs, an ultra-high-resolution filter, 1-mm section thickness, 0.3-mm section increment, 512 X 512 matrix, and 160-mm field of view. HRCT of the temporal bone demonstrated a bony defect in the anteroinferior part of the EAC posteromedial to the TMJ (Figure 1a). Through this defect, soft tissue protrusion was seen into the EAC, along with a few air specks. An open mouth view was used, which demonstrated that the herniated soft tissue retracted back into the TMJ with a few air pockets (Figure 1b). This mass was diagnosed as a soft tissue protrusion from foramen tympanicum. The planned biopsy was abandoned, and no further treatment was given.

DISCUSSION

The temporal bone is complex and comprises squamous, petrous, mastoid, and tympanic parts and the styloid process. The EAC and tympanic cavity develop from the tympanic portion of the temporal bone. Foramen tympanicum occurs due to a congenital defect during the ossification process that leaves a bony defect that is anteriorly related to the TMJ (1). The EAC is incompletely formed at birth. Further development occurs postnatally through two bony processes, anterior and posterior, growing towards each other and forming the superior EAC and the inferior foramen tympanicum (1, 2). The term foramen is a misnomer, as no nerves or vessels pass through it.

In adults, the persistence of foramen of Huschke defines an anatomical variation that may produce clinical and otological symptoms. The incidence of persistent foramen of Huschke has ranged from 3% to 25% in various studies and is now considered a normal developmental variant. Herniation of TMJ soft tissue into the EAC is also seen in one-fourth of cases and is directly related to the size of the defect. The opening can be enlarged with softening of the bony structures around the foramen of Huschke due to mastication, with greater soft tissue herniation over the years (2-5).

Patients with persistent foramen tympanicum can be asymptomatic or can present with complaints of otalgia, otorrhea (during mastication), and soft tissue mass protruding through the EAC. The mass may be visible only with a closed mouth and may completely disappear when the mouth is open because the soft tissues retract. During mastication, ear discharge occurs because of connection of the foramen with the TMJ or connection of the fistula with the parotid gland. Minor trauma or surgical insult can result in destruction of the tympanic bone at this level.

HRCT is an excellent technique to detect foramen tympanicum because of its high spatial resolution, sharp bony algorithm, and thin sections. Although the typical location of the bony defect is considered diagnostic, if there is clinical suspicion, a variable degree of retraction of the soft tissue into the TMJ can be demonstrated on open mouth CT.

In symptomatic patients, surgical closure of the foramen may be required (2). Foramen tympanicum can cause complications during otoscopy as the endoscope can go into the opening of the foramen and cause injury to the TMJ. If inadvertent biopsy is attempted at otoscopy, it can cause TMJ damage and fistula formation. In our case, due to the patient's advanced age and minor symptoms, no surgical intervention was pursued.

(1.) Lacout A, Marsot-Dupuch K, Smoker WR, Lasjaunias P. Foramen tympanicum, or foramen of Huschke: pathologic cases and anatomic CT study. A JNR Am J Neuroradiol 2005;26(6):1317-1323.

(2.) Kim TH, Lee SK, Kim SJ, Byun JY. A case of spontaneous temporomandibular joint herniation into the external auditory canal with clicking sound. Korean J Audiol 2013;17(2):90-93.

(3.) Wang RG, Bingham B, Hawke M, Kwok P, Li JR. Persistence of the foramen of Huschke in the adult: an osteological study. J Otolaryngol 1991;20(4):251-253.

(4.) Moriyama M, Kodama S, Suzuki M. Spontaneous temporomandibular joint herniation into the external auditory canal: a case report and review of the literature. Laryngoscope 2005;115 (12):2174-2177.

(5.) Park YH, Kim HJ, Park MH. Temporomandibular joint herniation into the external auditory canal. Laryngoscope 2010; 120(11):2284-2288.

Shallini Mittal, DMRD, Samita Singal, MD, Amit Mittal, MD, Rikki Singal, MS, and Gunjan Jindal, MD

From the Department of Radiodiagnosis and Imaging, M. M. Institute of Medical Sciences and Research, Mullana (Distt-Ambala), Haryana, India.

Corresponding author: Shallini Mittal, DMRD, Department of Radiodiagnosis and Imaging, M. M. Institute of Medical Sciences and Research, Mullana, Ambala Pin Code-133203, Haryana, India (e-mail: shallini_mittal@yahoo.com).
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Author:Mittal, Shallini; Singal, Samita; Mittal, Amit; Singal, Rikki; Jindal, Gunjan
Publication:Baylor University Medical Center Proceedings
Article Type:Clinical report
Date:Jan 1, 2017
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