Persistent foramen tympanicum

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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