8.15\ Mastoidectomy

Complications

8.15.1\ Discussion

Imaging after mastoidectomy may be performed to evaluate for a variety of complications, including abscess formation surrounding the mastoidectomy bowl, including intracranially (Fig. 8.64), chronic infection of a canal wall-­down mastoidectomy cavity, which may be associated with an unstable cavity and high facial ridge (Fig. 8.65), excess granulation tissue (Fig. 8.66), recurrent cholesteatoma, (Figs. 8.67 and 8.68), and facial nerve injury (Fig. 8.69), which can lead to formation of reparative neuromas (Fig. 8.70), cerebrospinal fluid leakage (Fig. 8.71), and encephaloceles (Fig. 8.72). Profound sensorineural hearing loss and vestibular weakness can also occur if the surgeon violates the labyrinth with the drill.

It is common for exteriorized mastoid cavities to become infected on a chronic or recurrent basis, and this may lead to the need for frequent office visits to clean debris, to treat granulation tissue, and to apply antimicrobial medications. The stability of a canal wall-down mastoidectomy­ cavity is highly dependent on surgical technique, and there are several factors notable on CT imaging that may be implicated in cavity instability including a large open mastoid tip filled with debris, a small or absent meatoplasty, a high residual ridge of the bone overlying the mastoid segment of the facial nerve (defined as 2 mm or greater proximal to the chorda tympani facial nerve junction), numerous residual diseased air cells, the absent or perforated tympanic membrane, or residual cholesteatoma.

Historically, recurrent cholesteatoma was encountered in one-third to one-half of patients treated with canal wall-up mastoidectomy and roughly 10% of those treated with canal wall-­down mastoidectomy. Due to the high failure rate of canal wall-up surgery, a planned second-look procedure or planned radiologic imaging is usually part of the treatment scheme. Imaging usually consists of CT or MRI with non-EPI diffusion-weighted imaging usually obtained 9–12 months after surgery. Recurrent cholesteatomas tend to show restricted diffusion, while granulation tissue does not. CT has a high negative predictive value when it shows a clear middle ear and mastoid cavity. However, CT

is nonspecific, while MRI is well suited for elucidating the differential when there is soft tissue in the postoperative cavity. Although both recurrent cholesteatomas and granulation tissue are typically hyperintense on T2-weighted and hypo-/isointense on T1-weighted MRI sequences, recurrent cholesteatomas tend to show rim enhancement, while postoperative granulation tissue fills in with contrast. It is also important to distinguish recurrent cholesteatomas from encephaloceles and cholesterol granulomas. Residual cholesteatoma after surgical removal is most often found in the sinus tympani, the oval window niche, the anterior epitympanum, and the supratubal recess/protympanum, but can even be extratemporal. Residual cholesteatoma found within the mastoid itself, although possible, is surprisingly uncommon except in extensive cases or in cases that involve complex canal wall-down mastoidectomy cavities. The main differential diagnosis of recurrent cholesteatoma is postsurgical granulation tissue and encephalocele.

Facial nerve injury is an uncommon complication of tympanomastoidectomy. The tympanic and proximal mastoid segments of the facial nerve are most likely to be involved. This may result in a reparative granuloma. Nerve cable grafts are sometimes used to repair the transected nerves. On CT, reparative neuromas appear as bulbous enlargement of the nerve, and on MRI, enhancement of the lesion can be appreciated. Thus, the location and presence of enhancement help differentiate post-mastoidectomy reparative neuroma from recurrent cholesteatoma.

If postoperative cerebrospinal fluid leak is suspected, as discussed earlier, thin-section CT with multiplanar reformatted imaging is the first-­line imagingmodalityforevaluation.CT­cisternography is helpful when there are multiple defects. However, thin-section coronal double inversion recovery MRI is particularly useful for evaluating suspected encephalocele after mastoidectomy, which usually results from tegmen dehiscence. This information is important for guiding subsequent surgical repair. Tegmen defects can be repaired using a variety of techniques, including fibrin glue, fascia grafts, muscle graft, fat graft, bone graft, hydroxyapatite (Fig. 8.73), or a combination of these. Some of these materials can resorb over time, predisposing to recurrent cerebrospinal fluid leak and/or encephalocele.

Fig. 8.64  Coronal post-contrast T1-weighted MR image shows a peripherally enhancing lesion in the right temporal lobe (arrow) overlying the right canal mastoidectomy bowl in a patient with a history of mastoiditis

Fig. 8.65  Unstable mastoid cavity. Coronal CT image shows opacification of the residual mastoid air cells and debris along the margins of the mastoidectomy bowl

Fig. 8.68  Extratemporal cholesteatoma recurrence. The patient has a history of right mastoidectomy for cholesteatoma. Axial T2-weighted MRI (a), post-contrast fat-­

suppressed T1-weighted MRI (b), and ADC map (c) show a cystic lesion in the right preauricular subcutaneous tissues with restricted diffusion (arrows)

Fig. 8.70  Facial nerve injury with reparative neuroma. Axial CT image shows enlargement of the tympanic segment of the facial nerve (arrow), which is dehiscent following mastoidectomy and tympanoplasty. Axial post-contrast T1-weighted MRI (b) shows enhancement of the lesion (arrow)

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Fig. 8.71  Cerebrospinal fluid leak after mastoidectomy. The patient presented with otorrhea after transmastoid biopsy. Axial image from a CT cisternogram with intrathecal injection of contrast demonstrates a small dehiscence in the tegmen tympani and contrast in the mastoid defect (arrow)

Fig. 8.73  Repair of tegmen defect with hydroxyapatite. Coronal CT image shows a large defect in the tegmen following canal wall-up mastoidectomy, which has been repaired using hydroxyapatite (arrow) as well as temporal fascia

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Fig. 8.72  Encephalocele after mastoidectomy. Coronal T2-weighted (a) and double inversion recovery (DIR) T1-weighted (b) MR images show a defect in the tegmen with extension of the brain and cerebrospinal fluid in the mastoid bowl (arrows)