Foramen tympanicum

Dr Yune Kwong et al.

The foramen tympanicum (also known as foramen of Huschke) is an anatomical variation in the external acoustic canal (EAC), where a bony defect connects the EAC to the temporomandibular joint (TMJ).

Most cases are asymptomatic, but a patent foramen tympanicum has been reported as being the cause of persistent ear discharge following mastication due to the connection with the TMJ or fistula with the parotid gland ^1,4,5. During TMJ arthroscopy, the foramen tympanicum may lead to inadvertent passage of the endoscope into the TMJ, with resulting damage ^6-7. Spread of infection between the EAC and infratemporal fossa can also occur through this anatomical variation ¹.

Gross anatomy

Development

The external ear canal is incompletely formed at birth, and further post-natal development results in two prominences (anterior and posterior) growing towards each other to form the EAC inferiorly. Lack of fusion of the anterior and posterior prominences with each other results in a persistent gap, the foramen tympanicum ⁶. Of note, the foramen tympanicum can close at up to 5 years of age, and hence it should only be diagnosed after this age ¹.

Radiographic features

CT

High resolution CT of the petrous temporal bone is the imaging study of choice. The foramen tympanicum arises in the antero-inferior part of the EAC, and is postero-medial to the TMJ. The opposite side should be examined with care, as bilateral cases have been reported in 6% ².

Treatment and prognosis

The foramen tympanicum is an incidental finding in most cases and does not need treatment in these cases. However, its presence should be sought if a patient presents with persistent ear discharge. Surgical treatment to obliterate the space between the EAC and TMJ is usually successfu l⁸, and any other unusual specific pathology can be addressed at the time, e.g. parotid duct fistula, or herniation of TMJ synovium ⁹.