Address for correspondence : Sang Heon Lee, MD, PhD, Department of Otolaryngology-Head and Neck Surgery, College of Medicine, Wonkwang University, 895 Muwang-ro, Iksan 570-711, Korea
Tel : +82-63-859-1443, Fax : +82-63-841-6556, E-mail : perricomo@gmail.com

Introduction

Even though intratympanic membrane cholesteatomas (ITMCs) are commonly encountered following otologic surgery as small epidermic pearls,¹⁾ primary ITMCs without history of surgery or trauma are very rare. In such cases, congenital or embryologic origin should be considered. Congenital ITMC is a rare condition that is characterized by accumulation of keratinous debris within the tympanic membrane, without history of trauma or surgery. ITMC is thought to be developed on the periphery of the tympanic membrane due to persistence of epithelial rest which contributes to the formation of the tympanic membrane (TM) and tympanic ring. Characteristically, keratin debris accumulates between the outer epidermic layer and middle fibrous layer of the tympanic membrane without extending into the middle ear cavity. Although many of the previous reports recommend early surgical intervention, we experienced a case which showed a natural healing course. Thus we thought that careful periodic observation could be an option for the treatment of the ITMCs.

Case

Case 1
A 25-month-old girl was referred to our hospital by a local Otolaryngology clinic with abnormal findings in her left tympanic membrane. Otomicroscopic examination revealed a small whitish mass on the umbo of her left TM (Fig. 1). The right TM and external auditory canal (EAC) were normal. There was no history of otitis media, ear trauma, or otologic surgery. The CT scan showed a 1.2×1.5 cm soft tissue mass in the center of the left TM without extension into the middle ear cavity. No change in size or location was observed at 1-month follow-up. Early surgical intervention was determined because many previous reports recommended early surgery for the prevention of possible complications. Through the endaural approach, the small, pearl-shaped cholesteatoma localized in the space between the epithelium and the middle layer of the TM was easily enucleated without damage to the middle layer. The underlying middle fibrous layer was normal. Histopathology confirmed a cholesteatoma. At 6-month follow-up after the operation, TM was completely cured and there was no evidence of recurrence.

Case 2
A 5-month-old boy with bilateral otitis media with effusion was referred to our hospital with an abnormal whitish mass in the right TM. He had no history of otorrhea, ear trauma, or otologic surgery, except recent bilateral otitis media with effusion for 1 month. Otomicroscopic examination revealed a bulging whitish mass in the posterosuperior quadrant of the right tympanic membrane that was difficult to distinguish from the tympanic annulus (Fig. 2). Air bubbles were observed within the left middle ear. The temporal bone CT scan showed a soft tissue mass occupying the posterior portion of the right TM without invading the middle ear cavity. Both mastoid processes were poorly aerated, and in the middle ear, there was a small amount of soft tissue that was considered an effusion. 7 month later, the mass increased in size and moved posteriorly to the tympanic annulus. It was not clearly separated from the annulus. We were able to use an endaural approach to remove the lesion from the underlying intact middle fibrous layer of the TM. Histopathology confirmed that the lesion was a cholesteatoma.

Case 3
A 26-month-old girl was referred to our department with a growing mass in her right ear canal. The mass had first been detected when she was 19 months old, but her parents refused treatment at that time. Otomicroscopic examination revealed a huge whitish mass blocking half of the ear canal and attached to the posterior wall of the EAC and the posterior portion of the TM (Fig. 3). She had no history of trauma, surgery, or infection. The high-resolution CT scan showed a soft tissue mass that filled the inside of the EAC across the TM and EAC, but the mass did not invade the middle ear. Twenty-six months after the first diagnosis, when she was 45 months old, the patient visited our hospital again. On otomicroscopic examination, the mass was reduced in size and had moved laterally to the EAC. It seemed to be confined within the ear canal without connection to the TM. The mass was easily removed with a Rosen needle without anesthesia. The base of the mass was attached to the posterosuperior quadrant of the tympanic membrane. The underlying middle layer was normal (Fig. 3D).

Discussion

Congenital cholesteatoma within the tympanic membrane is very rare. It has been given several names, such as congenital cholesteatoma in the tympanic membrane; intratympanic membrane cholesteatoma; and intramembranous cholesteatoma.^2,3,4,5) In many reported cases, the middle layer of the tympanic membrane was intact after removal of the cholesteatoma.^3,6,7) Thus, the precise histologic designation of this lesion is thought to be ITMC. ITMCs were incidental, postmortem findings in temporal bone specimens from patients with chronic otitis media.⁴⁾ ITMCs usually occur as a complication of tympanoplasty in the form of small keratin pearls even after use of the underlay technique.¹⁾ ITMC found at an early age without a history of ear trauma, surgery, or middle ear infection, can be thought of as congenital. There are no diagnostic criteria for congenital ITMC yet.
After ITMC was first described by Hinton in 1863, dozens of cases were reported by many authors. However, the exact pathogenesis, natural history, and prognosis are still unknown. The pathogenesis of ITMC seems to be unrelated to congenital middle ear cholesteatomas.⁸⁾ There are 3 theories of the pathogenesis of ITMC: 1) papillary proliferation theory, 2) persistence of epidermoid formation, and 3) alteration of the cell growth pattern.^9,10) In cases with evidence of recurrent inflammation, theory 1 could be considered because recurrent inflammation causes basal cell proliferation, which could result in cholesteatoma; this occurred in our second case. ITMC may develop from proliferation of the basal cell layer of the tympanic membrane epithelium in response to an inflammatory process (papillary proliferation theory).¹⁰⁾ This is supported by many cases including our second case, in which there was an evidence of recurrent otitis media. Aimi⁹⁾ proposed that persistence of embryonic epithelial rests, which contribute to the development of the tympanic membrane and tympanic ring and disappear after these structures are fully developed, results in the development of ITMC. This theory is supported by some cases, such as our third case in which involvement of the tympanic ring is observed. In our first case, there was no history of trauma, surgery, or middle ear infection. Embryological origin is suspected.
Although the natural course of ITMC is not well understood, ITMC likely increases in size over time. Suzuki, et al.,¹¹⁾ reported that if a ITMC ruptures into the EAC in the early stage and keratin debris is completely discharged, the cholesteatoma can heal spontaneously. In our third case, we also observed a decrease in size and a lateral movement of the ITMC. Such cases suggest that ITMC may disappear in its natural course.
On the other hand, if ITMC enlarges into the middle ear, it can cause several complications, such as ossicular involvement and subsequent conductive hearing loss similar to any other middle ear cholesteatoma. Yoshida, et al.⁶⁾ and Pasanisi, et al.²⁾ reported 2 cases of ITMC extending into the middle ear.

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