Discussion Author: Michael Ian Seidman-Zager
Cholesteatomas can be divided into two catagories, aquired cholesteatomas caused by traumatic, infectious or post surgical causes and congenital ectopic tissue rests.
Clinical criteria: pearly white mass medial to an intact tympanic membrane, a normal pars tensa and flaccida, and no history of otorrhea, perforation, or previous otologic procedure
Clinical presentation: Most common presentation is a white retrotympanic mass noted on routine otoscopy. Now typically noted around the age of 4-5 years old. If they go undetected other symptoms are determined by the middle ear structure they interfere with. Facial nerve paralysis, conductive or sensorineural hearing loss, vertigo and extension into the middle fossa are all possibilities. The most common complication is a conductive hearing loss due to fixation of the ossicles by the mass. However, some large cholesteatomas can allow for sound conduction through the cholesteatoma itself.
Location: Most commonly found in the anterior superior quadrant of the tympanic membrane when found early, but as they grow they tend to migrate to the posterior hypotympanum.
Pathophysiology: There are four theories on how a congenital cholesteatoma is formed, the most widely accepted is the epithelial rest theory
- Epithelial rests: Teed-Michael theory, ectodermal implants have been found in the 10 week old fetus between the first branchial cleft and pouch which is distinct from the surrounding tissue. They have an unknown function and typically are resorbed at 33 weeks gestion. If they do not involute then they may form a chronic cholesteatoma. While there is histologic evidence of rests prior to 33 weeks there are now two documented histological cases such rests persisting after 33 weeks.
- Invagination: This theory suggested that tissue from the external canal invaginates through the tympanic membrane due to a very small inflammatory injury near the neck of the malleus which causes adherence of squamous tissue to the malleus. This may occur in utero or during childhood. Another related theory is that there is no actual macroscopic perforation of the tympanic membrane, only microperforations of the basal layer. This allows for squamous epithelium to enter the middle ear space.
- Implantation: This is actually a theory against the existence of congenital cholesteatomas and implies that they are actually formed by unrecognized perforations of the tympanic membrane.
- Metaplasia: This theory explains that epithelial tissue in the middle ear is via metaplasia to keratinizing squamous epithelium, although this theory appears to be unlikely due to the fact that most congenital cholesteatomas occur in one quadrant of the middle ear.
Histology: Stratified squamous epithelial lined cyst which is filled with keratinous debris, this histology of a congential cholesteatoma is exactly the same as an acquired cholesteatoma.
Radiology: High resolution CT of the temporal bone is the ideal modality for imaging congenital cholesteatomas, especially since most patients are young and without other ear pathology found in patients with aquired cholesteatomas. On CT a cholesteatoma appears as a hypodense lesion with well defined margins which does not enhance with constrast.
MR imaging of the temporal bone may also be used. This will show low signal on T1W with moderately high signal on T2W images. It does not enhance with gadolinium. MR imaging is useful for differentiating a cholesteatoma from other intracranial processes.
Treatment: Surgical resection with either complete removal of the cholesteatoma matrix or permanent exteriorization is curative. Depending on the size and location of the cholesteatoma a transtympanic, transmastoid, middle cranial fossa approach or a transphenoidal approach may be used.
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