Persistent foramen tympanicum

Case contributed by Dr Mona Mohamed Naguib Sabala

Presentation

Patient presented with chronic right ear discharge. No previous history of trauma or surgery.

Patient Data

Age: 70 years
Gender: Male
CT

CT temporal bone revealed a smooth bony defect along the anteroinferior portion of the right external auditory canal with direct continuity of the right temporomandibular joint with the external auditory canal with almost no bony separation in-between. The bony defect, in this case, is large, measuring about 11 mm in axial diameter. There is also opacification of the right mastoid air cells. 

 

Annotated image

These annotated images help to localize the anatomical site of the bone defect along the anteroinferior aspect of the right external auditory canal and posteromedial to the right temporomandibular joint which is consistent with the diagnosis of persistent foramen tympanicum/tympanic bone dehiscence

MRI

MRI with contrast showed no enhancing masses to exclude the possibility of an aggressive lesion causing bone destruction. However, the bone defect is more obvious on the CT scan.

Case Discussion

Persistent foramen tympanicum (also known as foramen of Huschke) is an anatomical variant which normally closes by the age of five years. However, it may persist in adulthood in some cases resulting in this variation, or there may be just a focal reduction in the bone thickness in the same location. This osseous developmental defect may be due to abnormal mechanical forces during facial development and/or ossification abnormalities due to genetic factors. 

The foramen tympanicum transmits no neural or vascular structures. Therefore, it is not a true foramen and is maybe more appropriately termed a bony or osseous defect or dehiscence. 

When present, it is located at the anteroinferior aspect of the external auditory canal (EAC) and posteromedial to the temporomandibular joint (TMJ) as it typically does in this case.

Persistence of the foramen tympanicum may predispose individuals to TMJ pathology or it may be associated with salivary discharge into the EAC during mastication, complications such as a salivary fistula has also been reported. It may also predispose the person to the spread of infection or trauma from the EAC to the infratemporal fossa, and vice versa.

Awareness of this anatomic entity may be useful in evaluating patients with otorrhea in whom no otologic cause (e.g., ear infection, TMJ disease) is identified. It is also worth considered prior to TMJ arthroscopy, as the inadvertent passage of the arthroscope into the EAC with resultant otologic complications may occur. 

In the above case, the anatomical site of the bony defect (at the anteroinferior aspect of the EAC) and the sharp smooth edges of the defect along with the absence of a history of previous trauma/surgery all favor the diagnosis of persistent foramen tympanicum. A retrospective history also revealed that the patient usually experiences ear discharge following mastication which supports the diagnosis. The diagnosis has also been confirmed intraoperatively during a right middle ear exploration and myringotomy. 

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Case information

rID: 69357
Published: 26th Jul 2019
Last edited: 14th Aug 2019
System: Head & Neck
Inclusion in quiz mode: Included
Institution: Royal Surrey

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