Symptom: Ear Canal Mass

Diagnosis: Meningocele

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A 36-year-old man came in for a hearing loss evaluation. He had a history of multiple ear surgeries, with his last surgery being 16 years ago. He thought that the surgeries were due to a cholesteatoma in his ear but was unsure. On examination, he was found to have a compressible soft mass in the ear canal that appeared to rise from the superior aspect of the external auditory canal. Attempts to remove the mass were unsuccessful. An audiogram showed a 40-dB conductive hearing loss. Figure 1 shows the otoscopic examination of the right ear.

Figure 1
Figure1

Figure2
Figure2

Figure3
Figure3

 

Diagnosis: Meningocele

When dealing with a mass in the ear canal, several factors must be considered. First, the physician must ensure that the mass does not represent a malignancy. A quick view of this patient's ear and palpation of the mass suggested that it most likely did not represent a malignancy. The surface of the mass was very smooth and covered by skin, so it likely did not represent a squamous cell carcinoma, a malignancy that starts in the skin of the ear canal and appears as a fleshy mass without normal skin coverage. However, the presence of skin coverage does not necessarily guarantee a benign process. Malignancy that starts in the subcutaneous tissues could expand under an intact skin and present in a very similar fashion. In the ear canal, the most common malignancy that would present subcutaneously is an adenoid cystic carcinoma. This tumor, which is commonly seen in the salivary glands, likely represents a malignancy of the ceruminous glands of the ear canal.

The compressible nature of the patient's mass is reassuring that the mass is most likely not a cancerous growth. Malignancies are generally solid, hard, and rubbery because they are densely packed with cells. Obtaining tissue diagnosis of a mass in the ear canal requires a biopsy. Extreme caution is advised when biopsying a skin-covered mass in the ear canal, especially in patients who have had previous surgery. In our clinic, our general approach is to only biopsy a mass without imaging on the patient's first visit if the mass is fleshy and exophytic, which allows a small portion to be removed. We prefer to first obtain an imaging of the temporal bone to evaluate the canal mass. We also obtain CT of the temporal bones and MRI of the internal auditory canals with and without gadolinium enhancement to better understand the nature and origin of the tumor or mass prior to a biopsy.

In patients who had previous surgeries, the mass could represent herniation of the dura, an anomalous sigmoid sinus, or, very rarely, pseudoaneurysms of the carotid artery. A biopsy done in one of the above situations could be potentially disastrous. Also, a biopsy of a glomus tumor in the ear canal will lead to a substantial amount of bleeding. While a compressible mass in the ear canal of a patient with a previous cholesteatoma could suggest recurrence of the cholesteatoma, the gravity of the potential complication from an erroneous diagnosis without imaging should caution the clinician from biopsying an ear canal mass in a patient who had undergone surgery.

This patient's CT scan showed a large defect on the tegmen mastoideum (the bone separating the brain from the mastoid). CT of the temporal bones is intended to show details of the bony anatomy. Because of the bone window setting of the CT scan, it does not show details of the soft tissue anatomy. Therefore, it gives us all the information we need about the mass and its origin. An MRI provides significant detailed information about the soft tissues around the ear. Contrast enhancement occurs when a tissue has dense vascularization such as a tumor. Generally, due to the low density of water molecules and hydrogen in bones and air-contained spaces in the temporal bone, an MRI provides almost no information about the bony structures of the temporal bone. The patient's MRI showed that the mass did not enhance with contrast, making it unlikely to be a tumor (Fig. 2). The T2 MRI, in which water-containing fluids appear bright, showed that the mass was a fluid-filled sac that was connected to the cerebrospinal fluid (CSF) space (Fig. 3). Called meningocele, this protrusion of the dura containing CSF extends into the temporal bone. When a meningocele contains brain tissue, it is called encephalocele or meningoencephalocele.

Around the brain, meningoceles can occur in any area where the dura is in contact with the thin bone overlaying the air spaces of the temporal bone or in the paranasal sinuses. The dura can slowly herniate through the dehiscences (openings) of the thin bone separating the air spaces of the temporal bone or the sinuses, then enter the air spaces. Patients with a history of cholesteatoma are prone to this problem because the cholesteatoma can erode the tegmen (the bone separating the dura from the middle ear and mastoid). In addition, mastoidectomy and the surgical procedure to remove a cholesteatoma can rarely cause or enlarge a small opening in the tegmen. Over time, the overlying dura, aided by pulsations of the brain, can push through these small openings and lead to an encephalocele.

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The treatment of large meningoceles, such as this patient's case, requires a middle cranial fossa craniotomy with reduction or removal of the meningocele sac and repair of the middle fossa floor (tegmen). When a meningoencephalocele is present and the sac contains brain tissue, the entire sac is usually reduced or removed as the sac has non-functional brain tissue. Small meningoceles can be managed with a mastoidectomy that involves reduction of the sac and bipolar cautery and multilayer closure of the defect. To close off the defect, abdominal fat can be used. In rare cases, free flaps are used for infected defects (Skull Base. 2002;12[4]:209; J Am Acad Audiol. 2012;23[8]:635).

Hamid R
Hamid R

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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 cut) CT of the right temporal bone showing the previous mastoidectomy defect and the mass in the ear canal.
  • Video 2. Coronal (vertical and parallel to the face) CT of the right temporal bone showing the extent of the defect in the tegmen mastoideum (bone layer separating the brain from the mastoid).
  • Video 3. Sagittal (vertical parallel to the ear) CT of the right temporal bone demonstrating the outside-in view of the temporal bone.
  • Video 4. Axial T1-weighted post-gadolinium MRI of the right temporal bone showing the mass in the ear canal is not enhancing (bright).
  • Video 5. Coronal T1-weighted post-gadolinium MRI of the right temporal bone showing the mass in the ear canal is connected to the brain.
  • Video 6. Coronal T2-weighted MRI of the right temporal bone showing the fluid-filled nature and extent of the mass.

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