Definition of cholesteatoma: Cholesteatoma is defined as a cystic bag like structure lined by stratified squamous epithelium on a fibrous matrix. This sac contains desquamated squamous epithelium. This sac is present in the attic region. Cholesteatoma is also defined as 'skin in wrong place'. Cholesteatoma is known to contain all the layers of skin epithelium. The basal layer (germinating layer) is present on the outer surface of cholesteatoma sac in contact with the walls of the middle ear cleft.
Theories of bone invasion by cholesteatoma:
1. Pressure theory - states that increase in the pressure caused by enlarging cholesteatoma cause bone erosion. Ischemia has been attributed as the cause in this theory.
2. Enzymatic theory: Inside the cholesteatoma are present multinucleated osteoclasts and histiocytes. These cells release acid phosphatase, collagenase and other proteolytic enzymes. These enzymes are known to cause bone erosion.
3. Pyogenic osteitis: Pyogneic bacteria may release enzymes which could cause bone resorption.
Types of cholesteatoma:
1. Congenital cholesteatoma
2. Primary acquired cholesteatoma
3. Secondary acquired cholesteatoma
Congenital cholesteatoma: is known to arise from embryonic cell rests present in the middle ear cavity and temporal bone. These cell rests are known to commonly occur in cerebello pontine angle and petrous apex. Infact congenital cholesteatoma is seen as a whitish mass behind an intact tympanic membrane.
Derlacki and Clemis laid down the following as criteria to diagnose congenital cholesteatoma:
1. The patient should not have previous episodes of middle ear disease
2. Ear drum must be intact and normal
3. It is purely an incidental finding
4. If discharge and ear drum perforation is present then it should be contrued that congential cholesteatoma has managed to erode the tympanic membrane.
Clinical features: The disorder is an incidental finding. The common location of congenital cholesteatoma is the antero superior quadrant of tympanic membrane, postero superior quadrant being the next common site of involvement. Anteriorly situated congenital cholesteatomas are known to affect the eustachean tube function causing conductive deafness due to middle ear effusion, where as posterior congenital cholesteatoma is known to cause conductive deafness due to impairment of ossicular chain mobility.
Staging of congenital cholesteatoma:
Staging as suggested by Derlacki and Clemis: They were the first to stage congenital cholesteatoma. They classified congenital cholesteatoma into
1. Petrous pyramid cholesteatoma
2. Cholesteatoma involving the mastoid cavity
3. Cholesteatoma involving the middle ear cavity.
Potsic suggested the following staging mechanism:
Stage I : Single quadrant involvement with no ossicular / mastoid involvement.
Stage II : Multiple quadrant involvement with no ossicular / mastoid involvement
Stage III : Ossicular involvement without mastoid involvement
Stage IV : Mastoid extension
Type I : Involvement of mesotympanum without involvement of incus / stapes
Type II : Involvement of mesotympanum / attic along with erosion of ossicles without extension into the mastoid cavity
Type III : Involvement of mesotympanum with mastoid extension
Staging this disease will help in deciding the modality of treatment and in predicting the long term prognosis.
Acquired Cholesteatoma: can be divided into two types, primary acquired and secondary acquired cholesteatomas.
Primay acquired cholesteatoma: In this condition there is no history of preexisting or previous episodes of otitis media or perforation. Lesions just arise from the attic region of the middle ear.
Secondary acquired cholesteatoma: always follows active middle ear infection which manages to destroy the ear drum along with the annulus. This type of destruction is common in acute necrotising otitis media following exanthematous fevers like measles etc.
Theories to explain pathogenesis of cholesteatoma:
Various theories have been postulated to explain the pathogenesis of cholesteatoma. They are:
1. Cawthrone theory: This theory suggested by cawthrone in 1963 suggested that cholesteatoma always originated from congential embryonic cell rests present in various areas of the temporal bone.
2. Theory of immigration: This theory was suggested by Tumarkin. He was of the view that cholesteatoma was derived by immigration of squamous epithelium from the deep portion of the external auditory canal into the middle ear cleft through a marginal perforation or a total perforation of the ear drum as seen in acute necrotising otitis media.
3. Theory of invagination: This theory was suggested by Toss. He theorised that persistent negative pressure in the attic region causes invagination of pars flaccida causing a retraction pocket. This retraction pocket becomes later filled with desquamted epithelial debris which forms a nidus for the infection to occur later. Common organisms known to infect this keratin debris are Psuedomonas, E. coli, B. Proteus etc.
Toss also classified attic retraction pockets into 4 grades:
1. Grade I: The retracted pars flaccida is not in contact with the neck of the malleus.
2. Grade II: The retracted pars flaccida is in contact with the neck of the malleus to such an extent that it seems to clothe the neck of the malleus.
3. Grade III: Here inaddition to the retracted pars flaccida being in contact with the neck of the malleus there is also a limited erosion of the outer attic wall or scutum.
4. Grade IV: In this grade in addition to all the above said changes there is severe erosion of the outer attic wall or scutum.
4. Metaplastic theory: This theory was first suggested by Wendt in 1873. He took into consideration the histological changes seen in various portions of the middle ear cavity. The attic area of the middle ear cavity is lined by pavement type of epithelium. This epithelium undergoes metaplastic changes in response to subclinical infection. This metaplastic mucosa is squamous in nature there by forming a nidus for cholesteatoma formation in the attic region.
Of all the above mentioned theories, the theory of invagination appears to be the most plausible one currently explaining the various pathologic features of cholesteatoma.
Clinical features of acquired cholesteatoma:
Ear discharge: is scanty and foul smelling. Infact the odur is best described as musty in nature. This is due to the presence of saprophytic infection and osteitis.
Hearing loss: is commonly conductive in nature. Some patients may even surprisingly have a normal hearing despite the presence of a huge cholesteatoma. This normal hearing could be attributed to the bridging effects of cholesteatomatous mass.
Sensorineural hearing loss if present could be attributed to the absorption of toxins through the round window membrane, or may be due to use of ototoxic antibiotics topically on a long term basis.
Ear ache: if present could be attributed to the presence of co existing otitis externa, or presence of extradural abscess.
Tinnitus if present may indicate imminent sensorineural hearing loss.
Vertigo may be present if there is erosion of lateral semicircular canal by the cholesteatomatous matrix. Fistula test if performed is positive in these patient.
Fistula test: This test is positive if there is a third window is present in the laryrinth due to the erosion of the labyrinthine bone. This commonly occurs in the lateral semicircular canal area. This test is performed using a snugly fitting siegles pneumatic speculum and slowly applying pressure by compressing the pneumatic bulb. If labyrinthine fistula is present the patient will feel giddy and will have nystagmus.
Facial palsy may indicate erosion of facial nerve canal with involvement of facial nerve.
There is destruction of the outer attic wall, with presence of attic perforation. Cholesteatomatous flakes may be seen through the perforation like cotton wool.
There is associated sagging of the posterior superior meatal wall.
Hearing tests indicate conductive deafness commonly if labyrinth is uninvolved. It may turn out to be sensorineural hearing loss if there is associated erosion of the labyrinth.
X ray mastoids may show slcerosis with presence of cavity.
Since this is a surgical problem modified radical mastoidectomy is advocated in almost all of these patients.
The aims of the surgical procedure is as follows:
1. To exteriorise the disease
2. To create adequate ventilation to the middle ear cavity
3. To create a permanent skin lined cavity exposed to the exterior.