Diagnosis: Iatrogenic Cholesteatoma with Horizontal Canal Fistula
Many surgeons perform cholesteatoma surgery to remove the skin growth, make sure that no cholesteatoma remains, and reconstruct the ossicles. When dealing with patients with previous ear surgery (particularly two surgeries in quick succession), clinicians tend to presume that the surgery was for cholesteatoma. However, clinicians should thoroughly examine the ear of these patients. First, pay close attention to the post-auricular wound to determine if a previous mastoidectomy was performed. This helps rule out a mastoid fistula. Palpation of the wound may reveal a depression, which would likely correspond to a previous mastoidectomy. In children, the mastoid cortex tends to grow and close over time. Therefore, a depression may not always be palpated in a child who underwent a mastoidectomy.
Next, examine the tympanic membrane and pars tensa thoroughly. All debris should be removed from the tympanic membrane, preferably using a microscope and a small hook to separate the debris from the membrane. This is done to make sure that no perforations or new cholesteatomas are present. Keratin debris coming out of a cholesteatoma often appear as cerumen on the tympanic membrane. Using the term “wax on the TM” in patient charts, which is a common practice, should be avoided because cerumen-like debris on the tympanic membrane is highly suggestive of cholesteatoma. This debris needs to be removed for a full examination of the tympanic membrane. If it cannot be easily removed, ear drops can be applied to soften the debris and allow for suction.
Granulation tissue on the tympanic membrane or at the medial aspect of the canal should always be met with suspicion. Granulation, especially in the posterior superior quadrant or the pars flaccida area, should be considered as a possible sign of cholesteatoma. This condition causes an intense inflammatory reaction that may result in the development of granulation tissue. Since the pars flaccida area (superiorly) and the posterior superior quadrant are the most common areas of cholesteatoma development, any granulation tissue in those areas needs treatment and further workup to uncover the underlying cholesteatoma. Deep retractions are likely cholesteatomas that need further imaging workup, particularly if the patient experiences recurrent drainage. The depth of a retraction can be measured using an angled endoscope or a blunt angled 3 mm hook to palpate the depth of the retraction under microscopy. Check on the patient soon to make sure he or she does not get lost to follow-up.
Finally, the posterior canal wall needs to be evaluated from the tympanic membrane level to the meatus. This necessitates pulling the speculum out a bit to evaluate the lateral aspect of the canal. Since the debris in the ear canal can obscure a mastoid fistula, the posterior canal should be gently palpated with an angled curette to find any occult fistulas.
Horizontal nystagmus that occurs when pumping the tragus is a worrisome sign in a patient who has undergone previous surgery. The differential diagnosis of this phenomenon includes perilymph fistula or semicircular canal dehiscence. Traditionally called Hennebert's sign, this condition was considered sign of perilymph fistula and has been associated with syphilitic ear disease during the pre-antibiotic era. Syphilis can cause destruction of the inner ear (otic capsule) bone and lead to canal dehiscence. Today, Hennebert's sign is associated with superior canal dehiscence. However, the case of this patient was most suspicious for horizontal canal fistula caused by occult cholesteatoma. Examination of her CT scan showed an erosion of the horizontal canal anteriorly (Fig. 1). The large defect in the lateral canal wall and mastoid suggested a mastoid-canal fistula development, which is usually iatrogenic and caused by not straightening the lateral canal (Koerner) flap at the end of the surgery. In chronic ear surgery, an incision is generally made in the posterior ear canal skin so the tympanic membrane can be seen through the post-auricular wound. At the end of the surgery, these two flaps need to be straightened. If the tip of the lateral or medial canal flap is folded under, the folded skin can continue to grow and form an iatrogenic cholesteatoma, which can grow for many years before it is diagnosed.
The patient's imaging showed a large defect in the mastoid (Figs. 2 and 3). It is unclear if the defect was from previous surgeries or from a canal-mastoid fistula or cholesteatoma. However, MRI imaging can help differentiate cholesteatoma from fluid, scar tissue, or other soft tissue. T2-weighted imaging can show if the tissue has high water content and appear brighter than the brain (Fig. 4). Cholesteatomas as small as 5 mm can be detected using axial (echoplanar) diffusion-weighted imaging (DWI). A non-echoplanar diffusion-weighted imaging sequence (a.k.a. HASTE sequence) can differentiate cholesteatomas as small as 3 mm. In this patient, the DWI sequence showed that the soft tissue in the mastoid was most likely a cholesteatoma (Fig. 5).
To treat a cholesteatoma that causes horizontal canal fistula, the fascia has to be removed and covered immediately. Ideally, the membranous canal is covered with the fascia, bone putty, and a thin Silastic® sheet, which is placed to prevent the adherence of other tissues (e.g., cartilage tissue). This way, the canal is less likely to get injured in any future ear surgery.
In some cases, the cholesteatoma may be strongly adherent to the membranous portion of the horizontal canal and cannot be separated without potentially injuring the membranous canal. Violating the membranous canal can cause deafness if inflammatory mediators or bacteria enter the perilymphatic space. Therefore, in these cases, the cholesteatoma is left on the membranous canal and exteriorized. This allows any keratin (dead skin) produced by the cholesteatoma to exit into the ear canal and not accumulate and cause more destruction. However, this leaves the patient with the same dizziness problem when pressure is place on the ear.
BONUS ONLINE VIDEOS: VISUAL DIAGNOSIS
Read this month's Clinical Consultation case, then watch the accompanying videos from Hamid R. Djalilian, MD, to review the patient's imaging for yourself.
- Video 1. Axial CT of the right temporal bone showing the dehiscence of the horizontal canal.
- Video 2. Coronal CT of the right temporal bone showing a likely cholesteatoma filling the mastoid.
- Video 3. Sagittal CT of the right temporal bone showing an intact tegmen (bone separating the brain from the mastoid).
- Video 4. Axial T2-weighted MRI of the brain showing hyperintensity in the right mastoid cavity, which indicates high water (proton) content.
- Video 5. Axial T1 post-contrast MRI images showing no enhancement in the right mastoid, which indicates dead (non-vascular) tissue.
- Video 6. Axial diffusion-weighted MRI showing hyperintensity in the mastoid, which likely indicates cholesteatoma.
Watch the patient videos online at thehearingjournal.com https://journals.lww.com/thehearingjournal/Pages/collectiondetails.aspx?TopicalCollectionId=23.Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.