Diagnosis: Occult Cholesteatoma
The patient's history of episodic vertigo is most suggestive of a migraine etiology. He had distinct episodes, accompanied by a visual aura (flashing lights/dark spots or change in vision) and occasional headaches. The main question was whether the vertigo episodes were related to his previous ear surgery. His audiogram showed that he had high-frequency sensorineural hearing loss, indicating an abnormality in the inner ear or nerve. It was conceivable that his vertigo could also be due to an infection that had been causing the hearing loss and vertigo.
Without any information on the patient's previous surgery, it was best to first try to obtain his medical records. In this case, the patient could not recall his surgeon's name or where the surgery was performed. Our concern was that a labyrinthine fistula, an opening in the membranous labyrinth, may have occurred at the time of the surgery or over the progression of his previous disease. It is uncommon for chronic otitis media without a cholesteatoma to cause a labyrinthine fistula. When caused by chronic otitis media or a cholesteatoma, a labyrinthine fistula does not generally result in a perilymph leak, unlike fistulas of the oval or round windows. The bone of the otic capsule that surrounds the cochlea and the vestibule is the hardest bone in the body. Intense inflammation in the form of granulation tissue could unusually cause a bony destruction and labyrinthine fistula. Erosion of the semicircular canals usually occurs from a cholesteatoma. The most common part of the inner ear involved in a cholesteatoma-related labyrinthine fistula is the horizontal semicircular canal, followed by the superior and posterior canals. Destruction of the cochlea is extremely rare, but can certainly happen. Erosion of the horizontal canal—to the point where the membranous labyrinth comes in contact with the cholesteatoma or the surrounding granulation tissue—can occur in the absence of any symptoms. Once inflammatory mediators enter the inner ear, the patient will start developing dizziness and hearing loss.
Another form of labyrinthine dysfunction from chronic otitis media that can cause hearing loss and dizziness is when inflammatory mediators enter the cochlea through the round window membrane. This occurs with intense middle ear inflammation. This form of dysfunction commonly occurs in a case of acute otitis media where bacteria and/or inflammatory molecules (cytokines) enter the basal turn of the cochlea, potentially causing high-frequency hearing loss and dizziness. Hearing loss caused by labyrinthine fistula, usually the horizontal canal fistula, tends to start at high frequencies and can develop into total deafness from resultant labyrinthitis that could be serous or infected. The dizziness caused by labyrinthine fistula would generally manifest as constant imbalance and difficulty focusing. A patient with this condition can have intense vertigo with pressure changes such as pressing the tragus against the ear canal. The patient can also have an intensified caloric response to suctioning of that ear canal.
When dealing with a patient suffering from dizziness and hearing loss who had a previous ear surgery that we don't know much about, the first thing to do is to rule out a horizontal canal fistula. The best method is by getting a high-resolution CT of the temporal bones. In the case of this patient who has high-frequency sensorineural hearing loss, it was also important to determine if he had a retrocochlear abnormality. It's also important to consider the possibility of a recurrent cholesteatoma. To determine the presence of a cholesteatoma that could be in the mastoid and out of an examiner's view, imaging is required. A CT scan of the temporal bones cannot distinguish between the fluid from a fibrous scar tissue, inflamed mucosa, or cholesteatoma. MRI of the internal auditory canal on its own may not determine the presence of a cholesteatoma either. The clinician must request diffusion-weighted imaging sequence to help diagnose an occult cholesteatoma in the mastoid.
Two types of diffusion-weighted imaging can be obtained. Axial (horizontal) diffusion-weighted imaging is primarily used to determine ischemic strokes in the brain and the presence of ischemia and possible dead tissue. However, cholesteatomas tend to also appear bright in diffusion-weighted images due to the presence of dead skin (keratin) in a cholesteatoma. The primary limitation of axial diffusion weighted imaging (DWI) in finding a cholesteatoma is the significant artifact at the interface between the brain and temporal bone. This leads to a loss of resolution at the superior aspect of the mastoid and middle ear (tegmen), where most cholesteatomas tend to recur. This results in a resolution of approximately 5 mm, i.e., a cholesteatoma has to be at least 5 mm before it can be visualized well. The coronal (superior to inferior, parallel to the face) diffusion-weighted imaging sequence (called the HASTE sequence) is significantly advantageous, as it doesn't show any artifacts at the roof of the temporal bone, allowing the visualization of a cholesteatoma that's as small as 3mm in size. If a clinician wants to evaluate for the presence of cholesteatoma, a coronal HASTE sequence should be requested instead. The false negative rate of axial DWI is too high and should be avoided as the sole sequence on the MRI for ruling out cholesteatoma.
Due to its high water content, a cholesteatoma appears bright on T2-weighted imaging and appears isointense (same color as the brain) on T1-weighted images. This patient underwent a CT scan of the temporal bones that showed the horizontal semicircular canal was intact (Fig. 2). An MRI of internal auditory canals showed hyperintensity (bright) on T2-weighted images, which could indicate fluid or cholesteatoma (Fig. 3), isointensity on T1-weighted images (Fig. 4), and hyperintensity on diffusion-weighted imaging (Fig. 5), indicating a large recurrent cholesteatoma.
BONUS 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 (horizontal) CT of the right temporal bone showing the defect in the previous mastoidectomy and soft tissue/fluid and air in the mastoid.
- Video 2. Axial CT of the left temporal bones showing a normal mastoid for comparison.
- Video 3. Coronal (vertical) CT of the left temporal bone showing the horizontal canal but no frank dehiscence.
- Video 4. Axial T2-weighted MRI of the temporal bones showing hyperintensity in the right mastoid (left side of the images).
- Video 5. Axial CISS of the temporal bone showing an intact horizontal canal membranous portion on the right side (left side of images).
- Video 6. Coronal DWI-weighted MRI of the brain (HASTE sequence) showing hyperintensity in the right mastoid (left side of the images).
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