71
CHAPTER 21 Acquired Cholesteatoma
Ellen G. Hoeffner
Epidemiology
Most acquired cholesteatomas result from complications of chronic middle ear infections. Loss of col- lagen fi bers and structural support of the tympanic membrane along with negative middle ear pressure results in a retraction pocket lined with squamous epithelium. Continued negative middle ear pressure and accumulation of epithelial cells, keratin, and cellular decay expand the pocket. Bone destruction of the tympanum and ossicles ensues secondary to direct pressure from the expanding cholesteatoma, biochemical factors related to chronic infl ammation and the cholesteatoma itself, and osteoclastic activity. Most cholesteatomas involve the weaker pars fl accida with less common involvement of the pars tensa.
Other potential etiologies of cholesteatoma formation include epithelial invasion through a tympanic membrane perforation, squamous metaplasia of middle ear epithelium, and basal cell hyperplasia.
Clinical Features
Otorrhea and a conductive hearing loss are the most common complaints associated with a choles- teatoma. Patients often have a history of multiple earaches in childhood followed by chronic ear prob- lems. Physical exam demonstrates retraction of the eardrum, often with a perforation, and surrounding bony erosion. Patients with ossicular erosion typically present with a 30- to 60-dB conductive hearing loss. On otoscopic examination, the characteristic clinical fi nding is the presence of a “pearly white mass” behind the tympanic membrane. However, the tympanic membrane often becomes scarred and retracted in chronic infl ammation and the otologist may not be able to accurately assess the middle ear cavity.
Pathology
Cholesteatomas are lined by stratifi ed squamous epithelium and contain desquamated keratin and purulent material.
Treatment
Surgical excision or exteriorization is the treatment of choice. In patients who cannot tolerate surgery, disease can be controlled with repeated cleansing under a surgical microscope.
Imaging Findings
CT
Computed tomography (CT) is the preferred modality when imaging cholesteatomas, as the defi ning feature is bone destruction. Cholesteatomas typically present as a nondependent middle ear soft tissue mass in a characteristic location associated with bone and ossicular erosion.
10
Th 97
20 Th Bo
10 02
The Prussak space is the site of origin of the more common pars fl accida cholesteatomas, displac- ing the malleus head and incus body medially and eroding the scutum. The mass can expand into the epitympanum and eventually the antrum and mastoid air cells via the aditus ad antrum, which is often widened by the cholesteatoma.
Less common pars tensa cholesteatomas typically involve the facial recess and sinus tympani of the posterior tympanum. The malleus head and incus body are displaced laterally as these masses extend into the attic. These cholesteatomas also grow medially and can destroy the otic capsule, resulting in a labyrinthine fi stula, most commonly involving the lateral semicircular canal.
Other important features to evaluate on CT include involvement of the facial nerve, dehiscence of the tegmen tympani, sigmoid sinus plate destruction, degree of cellularity or sclerosis of the mastoid, level of the dura laterally, and any prior postoperative changes ( Fig. 21–1 ).
MRI
Due to its inability to visualize fi ne bony detail, magnetic resonance imaging (MRI) is more limited in the evaluation of cholesteatomas compared with CT. One area where MRI excels, however, is distin- guishing granulation tissue from cholesteatoma. Both of these entities appear similar on CT; however, granulation tissue enhances on MRI whereas a cholesteatoma does not. Diffusion-weighted imaging
A B
10.1055/978-2-58890-647-2c021_f001
Figure 21–1 Computed tomography (CT) fi ndings of choles- teatoma. (A) Axial image shows a focal soft tissue mass located within the middle ear cavity ( large arrow ). The manubrium of the malleus ( arrowhead ) and stapes ( small arrow ) are intact. However, the long process of the incus is absent, indicating that it is eroded.
These fi ndings are characteristic of a cholesteatoma. (B) Axial CT obtained at the level of the epitympanum shows the head of the malleus ( arrow ) is intact but the short process of the incus is ab- sent. (C) Coronal CT shows a focal soft tissue mass in the middle ear cavity that extends superiorly into the epitympanum ( large arrow ). The mass extends medially to the capitulum of the stapes ( arrowhead ).
C
72 III MIDDLE EAR AND MASTOID
21 ACQUIRED CHOLESTEATOMA 73
may help differentiate recurrent cholesteatoma from granulation tissue, with the former having high signal on diffusion-weighted images.
Magnetic resonance imaging is also useful in the evaluation of intracranial complications of chole- steatomas such as meningitis, cerebritis, abscess formation, and dural venous sinus thrombosis. In the presence of erosion of the tegmen tympani, MRI can search for a meningocele or meningoencepha- locele. With bony involvement of the facial nerve canal or otic capsule, MRI may be helpful in search- ing for thickening and enhancement of the facial nerve or labyrinth, suggesting infl ammation of these structures ( Fig. 21–2 and Fig. 21–3 ).
PE ARL S
•
A nondependent middle ear mass with bone destruction or ossicular erosion on CT is a choles- teatoma 90% of the time. However, only 50% of cholesteatomas have these fi ndings.•
MRI is most helpful in searching for intracranial complications.•
Recurrent cholesteatomas may have high signal on diffusion-weighted images distinguishing them from granulation tissue.10.1055/978-2-58890-647-2c021_f002
Figure 21–2 Magnetic resonance imaging (MRI) fi ndings of cholesteatoma. Coronal contrast-enhanced MRI demon- strates a nonenhancing focal soft tissue mass located in the left middle ear cavity ( arrow ). Note the enhancement of the tympanic portion of the facial nerve ( arrowhead ). The patient had left facial nerve palsy. This was due to the cholesteatoma directly abutting the facial nerve resulting in acute infl amma- tion of the nerve. These fi ndings were confi rmed at surgery.
A B
10.1055/978-2-58890-647-2c021_f003
Figure 21–3 MRI fi ndings of cholesteatoma. (A) Axial con- trast-enhanced T1-weighted MRI shows a nonenhancing mass ( arrow ) located in the middle ear cavity in a patient who had undergone two prior ear surgeries and presented with
chronic otorrhea, indicative of recurrent choles teatoma. (B) Diffusion-weighted imaging shows the high signal within the mass ( arrow ), also suggestive of recurrent cholesteatoma.
•
Other etiologies to be considered in the differential diagnosis of destructive middle ear masses on CT include histiocytosis, giant cell tumor, xanthoma, squamous cell carcinoma, rhabdomyosar- coma, and metastases.Suggested Readings
Canalis RF, Lambert PR. Chronic otitis media and cholesteatoma. In: Canalis RF, Lambert PR, eds. The Ear: Comprehensive Otology. Philadelphia: Lippincott Williams & Wilkins, 2000:409–431
Chee NWC , Tan TY . The value of pre-operative high resolution CT scans in cholesteatoma surgery. Sin- gapore Med J 2001 ; 42 : 155 – 159
Harnsberger HR. Hand Book of Head and Neck Imaging, 2nd ed. St. Louis: Mosby, 1995
Maheshwari S , Mukherji SK . Diffusion-weighted imaging for differentiating recurrent cholesteatoma from granulation tissue after mastoidectomy: case report. AJNR Am J Neuroradiol 2002 ; 23 : 847 – 849
Maroldi R , Farina D , Palvarini A , et al . Computed tomography and magnetic resonance imaging of pathologic conditions of the middle ear. Eur J Radiol 2001 ; 40 : 78 – 93
Nemzek WR, Swartz JD. Temporal bone: infl ammatory disease. In: Som PM, Curtin HD, eds. Head and Neck Imaging, 4th ed. St. Louis: Mosby, 2003:1173–1229
Yates PD , Flood LM , Banerjee A , et al . CT scanning of middle ear cholesteatomas: what does the surgeon want to know? Br J Radiol 2002 ; 75 : 847 – 852
74 III MIDDLE EAR AND MASTOID
75
CHAPTER 22 Cholesterol Granuloma
Hemant Parmar