Congenital cholesteatoma is defined as an epidermoid cyst that develops behind an intact tympanic membrane in a patient with no history of otorrhea, trauma, or previous ear surgery. Michaels studied fetal temporal bones and demonstrated the presence of an epidermoid structure between 10 and 33 weeks of gestation. This structure tends to involute spontaneously until it completely disappears. Michaels hypothesized that the persistence of this structure could act as anlage and lead to congenital cholesteatoma. The fact that the most classic location of congenital cholesteatoma, namely in the anterosuperior part of the tympanum, corresponds to the site of the fetal Michaels structure supports this theory. In our cases, however, and contrary to the few studies reported in literature (Derlacki and Clemis 1965, Friedberg 1994, Levenson et al 1986, Cohen 1987), the most common site of congenital cholesteatoma was the posterior mesotympanum. To clearly describe the location of congenital cholesteatomas, we introduced a classification designating mesotympanic localization type A. The type A is subclassified into two: anteri- or localization type A1 (▶Fig. 8.1), and posterior localization type A2 (▶Fig. 8.2). Congenital cholesteatomas localized in the attic are classified as type B (▶Fig. 8.3). If the cholesteatoma occupies both the mesotympanum and the attic, it is classified as type A/B (▶Fig. 8.4). According to our experience out of 44 cases, half of congenital cholesteatomas arise from the retromalleolar area, and premalleolar localization is uncommon (▶Table 8.1). As no existing theory can truly explain the origin of congenital cholesteatoma in the posterior location, a strong conjecture can be made that these lesions might represent a different entity from those of the anterior location that may arise from residue of transiently formed epidermis in fetal period.
Diagnosis is either occasional in the asymptomatic patient, or the patient may complain of hearing loss, or checked in the hearing examination in childhood due to erosion of the ossicular chain. On the other hand, hearing disturbance may be minimal in some cases due to sound transmission through cholesteatoma. In childhood, patients usually do not complain or even aware of hearing disturbance. Recurrent attacks of either acute or secretory otitis media caused by its presence may take the patient to the outpatient clinic, giving chance to be diagnosed. A high degree of suspicion and thorough examination are essential in detecting the presence of these lesions. Anterosuperior cholesteatoma tends to be found in earlier infancy under otoscopic examination, but diagnosis of posterosuperior cholesteatomas tends to be delayed, until screening of hearing. A high-resolution computed tomography (CT) usually reveals either a round-shaped soft tissue density, or a soft tissue filling the middle ear with disrupted ossicular chain. However, in limited cases of open-type cholesteatoma, a disrupted ossicular chain together with scanty thickening of soft tissue around the oval window may be the only finding in radiology, and differential diagnosis from congenital ossicular chain anomaly is difficult (Kim). Cholesteatoma matrix covered with small amount of debris is verified during surgery.
Basic strategy of surgery for congenital cholesteatoma is the same as acquired ones. In case of child, preservation of the posterior wall should be tried as much as possible. Anterosuperior cholesteatoma can be removed with retroauricular transcanal approach with preservation of the ossicular chain. The incus, then the head of the malleus should be removed if there is a risk of leaving matrix behind. In limited cases of small posterosuperior cholesteatoma, removal can be carried out through transcanal approach. However, the majority of posterosuperi- or cholesteatomas and advanced cholesteatomas require canal wall up mastoidectomy to explore the mastoid, the facial recess, and the medial wall of the attic. Even when the mastoid seems normal in radiologic examinations, open-type cholesteatoma may reach the antrum. Sufficient, but not excessive thinning of the posterior meatal wall and large posterior tympanotomy play key role in large cases. Reconstruction of the ossicular chain is carried out either in the same stage or in the second stage depending on the status of mucosa and possibility of residual. If there is any risk of residual disease, staging strategy is applied. In very limited cases of advanced cholesteatoma, application of canal wall down technique is mandatory. Since the disease can be bilateral, or might be complicated with contralateral middle ear anomaly, or deafness, it is also important to check contralateral hearing before surgery using objective hearing test such as the auditory brainstem response (ABR), when pure-tone audiometry is not possible. In cases with possible contralateral hearing loss, there is one-stage surgery with ossicular chain reconstruction.
Table 8.1 Localization of congenital cholesteatoma of the middle ear (our experience)