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Cholesteatoma

Introduction

The term ‘cholesteatoma’ was first introduced by Johannes Muller in 1838. Cholesteatoma is a benign cystic structure characterized by a keratinizing epithelial lining, commonly located in the middle ear and mastoid. Despite its benign nature, cholesteatoma can cause significant destruction of local anatomical structures, including the ossicular chain and the otic capsule. Such destruction can result in various complications, including hearing loss, vestibular dysfunction, facial paralysis, and intracranial disease or infection.

In its normal state, the middle ear cleft is lined by various types of epithelium, which vary by region: ciliated columnar epithelium in the anterior and inferior parts, cuboidal epithelium in the middle part, and pavement-like epithelium in the attic. Notably, the middle ear lacks keratinizing squamous epithelium, the presence of which in the middle ear or mastoid characterizes a cholesteatoma. Essentially, cholesteatoma is described as “a wrong skin in the wrong place.” The term “cholesteatoma” is a misnomer, as it neither contains cholesterol crystals nor qualifies as a tumour to warrant the suffix “oma.” Nevertheless, the term persists due to its widespread use.

Structure and Composition of cholesteatoma

Cholesteatoma consists of two primary components:

  • the matrix, comprising keratinizing squamous epithelium resting on a thin stroma of fibrous tissues, and
  • a central white mass composed of keratin debris produced by the matrix. Consequently, it is also referred to as epidermosis or keratoma.

Origin of Cholesteatoma

Cholesteatomas most commonly originates from a retraction pocket in the pars flaccida or the posterosuperior part of the pars tensa. The initiating factor is likely the dysfunction of the Eustachian tube, resulting in negative middle ear pressure. Due to their greater blood supply compared with the rest of the tympanic membrane, the pars flaccida and the posterosuperior quadrant of the pars tensa are more susceptible to inflammatory cell infiltration in acute otitis media (AOM) and otitis media with effusion (OME). This susceptibility may result in a thinner fibrous layer in these areas compared to the rest of the tympanic membrane.

The genesis of cholesteatoma is a subject of debate. Any theory must account for the appearance of squamous epithelium in the middle ear cleft.

Various theories include:

  1. Presence of congenital epidermal cell rests: This forms congenital cholesteatoma.
  2. Invagination of tympanic membrane from the attic or posterosuperior part of pars tensa in the form of retraction pockets (Wittmaack’s retraction pocket theory): The outer surface of the tympanic membrane, lined by stratified squamous epithelium, invaginates to form the cholesteatoma matrix, depositing keratin in the pocket.
  3. Basal cell hyperplasia (Ruedi’s theory): Pseudopods are formed in the basal layer of the squamous epithelium of the pars flaccida epithelium which invade the sub-epithelial tissue, fuse together, resulting in the formation of cholesteatoma.
  4. Epithelial invasion (Habermann’s migration theory): The epithelium from the bottom of the meatus or the outer epithelial surface of the tympanic membrane grows and migrates into the middle ear through a pre-existing perforation, especially of the marginal type where part of annulus tympanicus has already been destroyed.
  5. Squamous metaplasia (Sade’s theory): Middle ear mucosa undergoes metaplasia due to repeated infections, transforming from cuboidal to squamous epithelium.
  6. Implantation theory: Cholesteatomas may result from the implantation of squamous epithelium into the middle ear, potentially due to trauma or by surgery. This mechanism, however, likely accounts for only a small proportion of cholesteatomas.

 Types of Cholesteatoma

  1. Congenital cholesteatoma
  2. Acquired primary
  3. Acquired secondary

1.Congenital Cholesteatoma: A relatively rare disease arising from embryonic epidermal cell rests in the middle ear cleft or temporal bone. It occurs at three primary sites: the middle ear, petrous apex, and the cerebellopontine angle, presenting symptoms based on its location. A middle ear congenital cholesteatoma appears as a pearly white mass with keratinized stratified squamous epithelium behind an intact tympanic membrane, causing conductive hearing loss. It may be discovered during routine examination of children or at myringotomy, or it may spontaneously rupture through the tympanic membrane, presenting as chronic suppurative otitis media.

– Diagnosis criteria of congenital cholesteatoma (Levenson, 1989):

  • Pearly white mass with keratinized stratified squamous epithelium behind an intact tympanic membrane.
  • No history of otorrhea.
  • No history of tympanic membrane perforation.
  • No history of otologic procedures.

2. Primary Acquired Cholesteatoma: Occurs without previous otitis media or a pre-existing perforation.
– Theories include:

  1. Invagination of pars flaccida: Persistent negative pressure in the attic causes a retraction pocket, accumulating keratin debris. When infected, the keratin mass expands toward the middle ear.
  2. Basal cell hyperplasia: Proliferation of the basal layer of pars flaccida due to subclinical childhood infections, leading to cholesteatoma breaking through pars flaccida, forming an attic perforation.
  3. Squamous metaplasia: The normal pavement epithelium of the attic undergoes metaplasia to keratinizing squamous epithelium due to subclinical infections.

3. Secondary Acquired Cholesteatoma: Occurs with a pre-existing perforation in pars tensa, often associated with posterosuperior marginal perforation or large central perforation.
– Theories include:

  1. Migration of squamous epithelium: Keratinizing squamous epithelium from the external auditory canal or outer surface of the tympanic membrane migrates through the perforation into the middle ear, facilitated by altered migration behavior due to recurrent infections.
  2. Metaplasia: Middle ear mucosa undergoes metaplasia due to repeated infections through the pre-existing perforation.

Expansion and Bone Destruction

Once cholesteatoma enters the middle ear cleft, it invades surrounding structures, initially following the path of least resistance and subsequently through enzymatic bone destruction. An attic cholesteatoma may extend backward into the aditus, antrum, and mastoid, downward into the mesotympanum, and medially surrounding the incus and/or head of the malleus.

Cholesteatoma exhibits the capacity to destroy bone, potentially causing the destruction of ear ossicles, erosion of the bony labyrinth, canal of the facial nerve, sinus plate, or tegmen tympani, leading to several complications. Bone destruction by cholesteatoma is attributed to various enzymes, such as collagenase, acid phosphatase, and proteolytic enzymes, released by osteoclasts and mononuclear inflammatory cells associated with cholesteatoma. The earlier theory that cholesteatoma causes bone destruction by pressure necrosis is no longer widely accepted.

———- End of the chapter ———–

Learning resources.

  • Scott-Brown, Textbook of Otorhinolaryngology Head and Neck Surgery.
  • Glasscock-Shambaugh, Textbook of  Surgery of the Ear.
  • P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
  • Salah Mansour. Textbook of Middle Ear Diseases Advances in Diagnosis and Management.
  • Gordon B. Hughes, Textbook of Clinical Otology.
  • Mario Sanna, Textbook of Color Atlas of Endo-Otoscopy.
  • Marcos V Goycoolea, Atlas of Otologic Surgery and Magic Otology.
     
    Author:

Dr. Rahul Bagla ENT Textbook

Dr. Rahul Bagla
MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Designation: Faculty, Associate Professor
Government Institute of Medical Sciences,
Greater Noida, India
Mail: msrahulbagla@gmail.com

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