Discussion

The failure of the medial dehiscence to close between the anterior and posterior prominences of the external auditory canal results in a defect known as the foramen tympanicum or foramen of Huschke. The foramen of Huschke leads to a sinus between the external auditory canal and the TMJ. This defect is present in around 4 per cent of the population.^{Reference Hasani, Haghnegahdar, Khojastepour and Golbahar Haghighi4} The anomaly is typically located at the anterior inferior aspect of the external auditory canal, posteromedial to the TMJ.

A review of the literature showed limited case reports regarding TMJ tissue herniation through a foramen of Huschke. The causes of TMJ herniation into the external auditory canal described in the literature include infection, trauma, mass effect and rheumatoid arthritis of the TMJ. Clinical presentation is also variable, with patients presenting with hearing loss, otalgia or no symptoms. Persistence of the foramen also appears to correlate with patients who have a TMJ disorder (3.4 per cent) compared to those without (0.8 per cent).^{Reference Hasani, Haghnegahdar, Khojastepour and Golbahar Haghighi4} Asymptomatic patients are identified upon direct visualisation of the herniated tissue during otoscopy. Typically, this tissue protrudes on closure of the jaw.^{Reference Mittal, Singal, Mittal, Singal and Jindal5} There is also a suggestion of female preponderance in the literature, possibly due to reduced tympanic bone thickness, and altered development and growth of the mandible when compared to male counterparts.^{Reference Lacout, Marsot-Dupuch, Smoker and Lasjaunias6}

We note that our case does not meet the classical diagnosis of a persistent foramen of Huschke. In our patient, the bone defect is located in the antero-superior aspect of the canal, and the lesion does not protrude on a change in jaw position. This case highlights the importance for patients with a mass in the ear canal to be investigated by secondary care. As evident in Appendix 1, the size of the mass was related to a Valsalva manoeuvre. To our knowledge, there have been no reports relating expansion of external auditory canal lesions with a Valsalva manoeuvre. We therefore encourage clinicians to assess patients using a Valsalva manoeuvre as well as changing jaw position. This may aid in the diagnosis of a persistent foramen of Huschke.

The diagnosis is confirmed radiologically, and a high-resolution CT scan of the petrous temporal bone is usually sufficient to delineate the defect and soft tissue protrusion. An MRI scan may aid in defining the content of the soft tissue, particularly joint synovium or salivary tissue content.

Management of this condition is often conservative, unless the mass is causing significant issues (hearing loss or infection). Surgical intervention must be balanced with the benefit to patients and their suitability for surgery.

A review of the literature highlighted 16 cases treated surgically. A variety of techniques have been employed, most commonly mesh and/or cartilage. The most common mesh used is titanium, either in isolation or with tragal cartilage. Lim et al. reported no complications at one year following titanium mesh use and cartilage repair.^{Reference Lim, Jung, Rhee and Choi7} However, Ryu et al. used titanium mesh only, and their patient had mild residual bulging at the two-month follow up.^{Reference Ryu, Baek and Hur8} Titanium plating and collagen mesh have also been utilised. Singh et al. reported no recurrence at one year post-operatively when using a collagen mesh only.^{Reference Singh, Jain, Prasad and Rajpurohit9} Other surgeons have also used tragal or conchal cartilage alone. One centre used curettage of the lesion and split thickness skin-grafting, with no recurrence reported.^{Reference Park, Kim and Park10} As all studies are case reports, with either limited or no follow up, we cannot accurately define which surgical method is most appropriate.

Furthermore, it is important to be aware of the potential issues that a persistent foramen of Huschke may cause. There have been reports of inadvertent injury following TMJ arthroscopy, with the arthroscope passing through the defect, causing damage to the ossicular chain and facial nerve.^{Reference Applebaum, Kumar, Berg and Mafee11} Additionally, its presence can be a conduit for the spread of infection or malignancy. Salivary gland fistula, although rare, may also occur through the foramen of Huschke, resulting in discharge into the external auditory canal.^{Reference Sharma and Dawkins12}