Preoperative Imaging

There is little question about which imaging techniques should be used for the preoperative evaluations of individuals known or suspected to have cholesteatoma. Computed tomography (CT) scanning is the modality of choice.1 Contrast is rarely necessary. While plain film radiographs can provide a limited amount of useful information, they have generally been abandoned for use with cholesteatoma. Magnetic resonance imaging (MRI) scanning should be used only when very specific problems involving surrounding soft tissues are expected, including dural involvement or invasion, sub- or epidural abscess, the presence of herniated brain into the mastoid cavity, inflammation of the membranous labyrinth or facial nerve, or sigmoid sinus thrombosis.1

Because CT scanning provides excellent bony resolution, it can detect subtle defects such as: scutal erosion, labyrinthine fistula, defects in the tegmen, details of ossicular involvement, erosion or discontinuity, and anomalies or invasion of the fallopian canal.

However, CT scanning cannot always distinguish between granulation tissue and cholesteatoma and/or effusion. Therefore, CT scans cannot reliably determine the full extent of dis ease and, consequently, the surgeon cannot predict precisely what will need to be done in the operating room. Both the operating surgeon and the patient or parent must understand the limitations of this imaging technique and be prepared for intraoperative surprises.

Although there is wide agreement among physicians about the use of CT scanning as the technique of choice, there is little agreement as to which patients should receive preoperative imaging. Some surgeons believe that all individuals scheduled for tympanomastoid surgery should have CT imaging preoper-atively. These physicians believe that useful information is obtained in every circumstance; consequently, the expense and radiation exposure are always justified. Other surgeons reserve preoperative imaging for special cases and are quite comfortable performing surgery without preoperative imaging in most patients with cholesteatoma. The following special cases would qualify for CT scans:

1. When the diagnosis is in doubt: The diagnosis may be in doubt in individuals with small attic retractions. CT scanning may show only a retraction without soft tissue extension into the epitympanic space and without bony erosion. In some of these circumstances, it may be permissible simply to observe the patient carefully. If bony erosion or an extensive soft mass is seen, operation is probably advisable. The diagnosis is frequently in doubt in individuals who have already had tympanomastoid surgery. In this group of patients, a white mass behind the tympanic membrane could represent tympanosclerosis, cartilage, or recurrent cholesteatoma, and CT scanning can frequently resolve such questions.

2. When a patient wishes to avoid operation: If an individual is a poor surgical candidate or for other reasons wishes to avoid operation, CT scanning can help assess the risk of conservative management. The presence of extensive disease, labyrinthine fistula, encroachment around the fallopian canal, and involvement of the oval window niche, increase the risk of expectant management, and the patient should be so advised. Most otologic surgeons prefer to avoid operating on an only hearing ear. Preoperative scanning can not only help determine the risk of observation, but if no evidence of disease is seen in the middle ear space, a modified radical mastoidectomy (without tympanoplasty) can be justified. Some surgeons believe that avoiding surgery in the middle ear space reduces the risk of postoperative hearing loss.2

3. For preoperative risk assessment: In some circumstances, it may be especially important to patients or parents to have some assessment of the risk of ossicular involvement and postoperative conductive hearing loss. This is especially true in children with cholesteatoma who have normal hearing. Preoperative scanning can often help determine the likelihood of ossicular involvement. If ossicular involvement is apparent on preoperative CT scans, parents can be counseled that ossicular removal may be necessary and that significant postoperative conductive hearing loss should be expected.

4. In revision cases: When the underlying anatomy is indeterminate and the extent of the disease is unclear.

5. In cases in which congenital anomalies might be reasonably expected: These include cases of atresia or individuals with craniofacial anomalies.

6. When there is concern about the presence ofcomplicating factors: If labyrinthine fistula or erosion of the fallopian canal is suspected, CT scanning remains the procedure of choice. If intracranial invasion, dural inflammation, meningitis, abscess, or sigmoid sinus thrombosis is suspected, MRI should be used.

7. To help identify associated conditions: These conditions include nasal septal deviation and chronic sinusitis.

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