2 Diagnosis of Cholesteatoma
Cholesteatoma is an epidermal inclusion cyst localized in the middle ear, whose capsule and matrix is formed from stratified squamous epithelium. The desquamating debris includes pearly white lamellae of keratin that accumulate concentrically, forming the cholesteatoma mass. The term cholesteatoma is actually a misnomer. It is derived from the Greek words “chole” or bile, “steatos” or fat, and “oma” or tumor. There is no relation between cholesteatoma and bile or fat. The suffix “oma” (tumor), however, is more appropriate because cholesteatoma can be considered an epidermal inclusion cyst forming a tumor in the ear. Fetid otorrhea and hearing loss are the main complaints in most of cholesteatoma patients. In addition, complicated cases can manifest with vertigo and/or facial nerve paralysis. Vertigo occurs as a result of labyrinthine fistula, which is most commonly located in the lateral semicircular canal. Facial paralysis can be caused by pressure of the cholesteatoma sac or neuritis.
The most important finding for diagnosing cholesteatoma is usually obtained in micro-otoscopy in the outpatient clinic. Clue for diagnosis may be scant, such as a very small erosion in the pars flaccida, or small whitish mass behind the tympanic membrane. Therefore, it is essential to carefully check the entire tympanic membrane using either a microscope or an endoscope if patients visit with some otologic complaints. We prefer to use an endoscopy in the outpatient clinic, since it gives a picture of the entire tympanic membrane even if there is a tight curve in the meatus. If presence of cholesteatoma is diagnosed or speculated, radiological examination with high-resolution computed tomography (CT) is indicated. The thickness of each slice should be less than 1 mm to visualize middle ear structures. Even though CT is not able to discriminate cholesteatoma from other soft tissues and effusions, it gives abundant information regarding extension of the disease and bony erosions that serves for surgery. If there is any doubt of meningoencephalic herniation or extension to the petrous apex, magnetic resonance imaging (MRI) is indicated. The MRI gives excellent contrast between cholesteatoma and other soft tissues when proper modality is applied. Since diffusion-weighted modality gives high signal in cholesteatoma, it is also useful for detection of residual lesion after tympanoplasty and subtotal petrosectomy. In cases of petrous bone cholesteatoma, otoscopy may be irrelevant or only demonstrates pars flaccida perforation or an open mastoid cavity with evidence of otorrhea. When a patient presents with hearing loss (sensorineural or mixed) and/or facial nerve paralysis with or without a retrotympanic mass, the possibility of petrous bone cholesteatoma (PBC) should be considered. The MRI is fundamental to evaluate such cases. Once petrous bone cholesteatoma is identified, it is necessary to perform a high-resolution CT scan of the temporal bone to evaluate extension of the cholesteatoma.
The PBCs are locally aggressive, and may extend to the clivus, nasopharynx, sphenoid sinus, the infratemporal fossa, and intradural compartment.
Regarding the source of the squamous epithelium, cholesteatoma can be classified into two types: acquired and congenital (▶Table 2.1); the acquired ones are much more common than the congenital ones, comprising the majority of surgical cases.
In acquired cholesteatoma, the squamous epithelium originates from the skin covering either the tympanic membrane or the external auditory canal. The acquired ones can be divided into two categories: primary and secondary. The primary cholesteatoma is formed from a retraction pocket that becomes so deep that keratin debris can no longer be expelled, leading to its accumulation and subsequent cholesteatoma formation. Cause of such retraction is not known fully, but dysfunction of the eustachian tube related to some infectious condition, such as sinusitis, allergy, and otitis media, seems to play a key role. Such retraction pockets often remain asymptomatic until they become infected, resulting in otorrhea and hearing loss. In some cases, the only symptom might be a progressive hearing loss due to erosion of the ossicular chain. The primary cholesteatomas are subclassified according to its initial localization. The pars flaccida (or epitympanic) type originates from the pars flaccida that seems more susceptible to negative pressure in the middle ear. The pars tensa (or mesotympanic) type is less frequent, originating from the pars tensa of the tympanic membrane, usually the posterosuperior quadrant. Since it erodes the incudostapedial joint from the beginning, patients are likely to present with considerable hearing loss. In cholesteatoma of the external auditory canal, destruction of the temporal bone starts from the external auditory canal, and inflamed skin with debris infiltrates the middle ear. Different from the former two types, ischemic condition of the bone is speculated to play a key role. Secondary cholesteatoma is formed by the skin advanced into the middle ear through a disrupted barrier formed by the tympanic membrane and the skin in the external auditory canal. The disruption occurs in a chronic perforation of the tympanic membrane, that is, chronic otitis media. Marginal perforations and tympanosclerosis increase risk of the skin crossing the border. Medical intervention can tuck the squamous epithelium into the middle ear. Such procedures include myringotomy, insertion of the ventilation tube, and tympanoplasty. The tuck of the skin also occurs in traumatic tympanic membrane perforation and temporal bone fracture.
Source of skin
Localization or cause
Pars flaccida (epitympanic)
Pars tensa (mesotympanic)
External auditory canal
Chronic otitis media
Primary or secondary
Medial to labyrinth
Abbreviation: PBC, petrous bone cholesteatoma.
Congenital cholesteatoma is speculated to be derived from entrapped ectodermal cellular debris during embryonic development. When it involves the middle ear, it appears as a whitish retrotympanic mass that may be localized either anterior or posterior to the malleus. In rare cases, cholesteatoma may arise in some part of the temporal bone away from the tympanic membrane. In such cases, the tympanic membrane seems intact, or the only indication is presence of middle ear effusion. In such cases, the lesion may be recognized in radiological examinations performed after some neurological symptoms appear, or only by chance.
When cholesteatoma involves the petrous part of the temporal bone that is medial to the labyrinth, it is termed petrous bone cholesteatoma. The source of the skin can be either congenital or acquired, as a consequence of advanced lesion. Because of its localization, the petrous bone cholesteatoma can invade the labyrinth, cochlea, posterior and middle fossa dura, the internal auditory canal, and the petrous apex, and may cause various neurological symptoms and life-threatening conditions.
2.1 Epitympanic Retraction Pocket
It is not always easy to establish a clear distinction between epitympanic or posterosuperior retraction pockets and cholesteatoma (see ▶Fig. 2.1 and ▶Fig. 2.2). We prefer to follow up these patients with otomicroscopy and endoscopy. A 30-degree endoscope is useful to see clearly the bottom of the retraction. Radiological examination using high-resolution CT may give additional information regarding the safety of the retraction. If the retraction pocket becomes deep, or accumulation of debris starts, a tympanoplasty is indicated. Because of the early stage of the disease, surgery can be done in a single stage.
2.2 Epitympanic Cholesteatoma
The epitympanic cholesteatoma is the most frequent form of acquired cholesteatoma. The cholesteatoma arises from an epitympanic retraction pocket as described above, and usually does not cause any symptom until it gets infected, interrupts the ossicular chain, erodes the labyrinth, or injure the facial nerve (see ▶Fig. 2.3, ▶Fig. 2.4, ▶Fig. 2.5, ▶Fig. 2.6, ▶Fig. 2.7, ▶Fig. 2.8, ▶Fig. 2.9, ▶Fig. 2.10, ▶Fig. 2.11, ▶Fig. 2.12, ▶Fig. 2.13, ▶Fig. 2.14, ▶Fig. 2.15, ▶Fig. 2.16, ▶Fig. 2.17, ▶Fig. 2.18). Most of them can be diagnosed by careful otoscopic inspection. Therefore, it is definitely prohibited to say “OK” to the patient who is complaining ear problems after seeing only the easy-to-access pars tensa. In very rare cases, the orifice of cholesteatoma can be obscured with a re-epithelized granulation tissue covering the pars flaccida. Since only radiological examinations give definitive clue, high grade of suspicion with knowledge is required to diagnose such cases.
In some cases, invagination of the skin in the pars flaccida and the pars tensa coexist, or extend to each other making categorization of primary cholesteatoma into two not possible. The situation can be called epimesotympanic cholesteatoma.