Diagnosis: Skull Base Osteomyelitis
When dealing with an ear canal mass, clinicians should ideally try to determine the origin of the mass and consider obtaining a tissue biopsy and imaging for workup. It's important not to miss a malignant process in that ear, but at the same time, clinicians need to be judicious about performing a biopsy of the mass on a patient's first visit. Rarely, the mass represents a glomus jugulare tumor that came through the tympanic membrane or penetrated the ear canal and presents as an ear canal mass. Biopsy of a glomus tumor can lead to extensive bleeding, as it is a very vascular tumor. In the case of this patient with an end-stage renal disease where platelet function is often not normal, a biopsy of a glomus tumor can cause significant hemorrhage.
An ear canal mass is more likely to be granulation tissue than a malignancy or glomus tumor. However, the clinician must be vigilant to determine the origin of the mass. In some cases, the clinician may use some instruments to move the mass and determine its origin and have a better idea of its nature. When in their early stages, malignancies could be localized to a small area of the ear canal; however, they tend to become more broad-based over time. Granulation tissue can generally be flattened with pressure using a silver nitrate stick. Granulation tissue in the absence of recent otologic surgery tends to be more peduncular and develops from a single spot in the ear canal, with a large part of the mass in the lumen of the canal. The clinician can twirl a silver nitrate stick to separate the granulation tissue and cauterize its base. The removed mass could then be sent for pathology. Even if the mass represents granulation tissue, it is important to question why granulation tissue developed in the patient to begin with. Imaging could also be obtained to help determine the cause of the mass.
In this patient, CT scan of the temporal bones showed that the mastoid was opacified and likely filled with fluid. In addition, the anterior canal wall appeared to have some destruction and the bony structures of the TMJ had a moth-eaten appearance. Specifically, the condyle of the mandible, which normally looks ovoid and smooth on CT scans, appeared to have been eroded in several areas (Fig. 1).
This patient's biopsy of the ear canal mass, performed at a different hospital, showed an inflammatory tissue and a middle ear effusion. The mass was found to emanate from the bony cartilaginous junction and extend to the tympanic membrane. The mass did not involve other parts of the canal skin or the tympanic membrane. Results of the pathology specimen were consistent with inflammatory changes and granulation tissue.
Another interesting finding on this patient's scan is the presence of an apparent mass in the skull base involving the nasopharynx figure. A CT scan of the neck showed extension of the nasopharyngeal edema into the pharynx behind the right tonsil as well as destruction of the bone surrounding the carotid artery in the temporal bone (Figs. 2-4). The patient was transferred to our care given the possible skull base mass.
Review of the records and imaging on arrival of the patient showed that we have a patient with immunosuppression (end-stage renal disease and diabetes), granulation tissue in the ear canal, severe pain of the ear, erosion of the bone around the ear, and a possible mass in the skull base. When presented with the combination of immune suppression, ear pain, and granulation in the ear canal, the most likely ideology is skull base osteomyelitis (also called malignant otitis externa or necrotizing otitis externa). The degree of destruction around the TMJ is consistent with the progression of the infection into the TMJ area. The apparent nasopharyngeal edema without a distinct mass seen on imaging is consistent with extension of the infection along the skull base tissue planes into the nasopharynx. Rarely, skull base osteomyelitis presents with pain and nasopharyngeal mass because the otitis portion is treated so the ear canal examination has normalized, but the infection in the bone of the skull base spreads and involves other structures.
Skull base osteomyelitis is a condition that nearly always affects patients with immunosuppression (Laryngoscope. 2008 Nov;118(11):1917). The most common immunosuppression etiology is diabetes but can include HIV infection, chemotherapy, organ or bone marrow transplant, and end-stage renal disease. The diagnosis is clinical and confirmed with a technetium 99 bone scan (a nuclear medicine study). We prefer obtaining a technetium SPECT scan that creates sliced images for a more precise localization of the infection.
Granulation tissue emanating from the bony cartilaginous junction is another common sign of malignant otitis externa. The middle ear and mastoid will commonly have serous fluid as the infected bone leads to serous fluid accumulation in the mucosal surfaces. Treatment of skull base osteomyelitis involves intravenous antibiotics directed at the bacterial culture (Otol Neurotol. 2006 Feb;27(2):250). Culture can be obtained from the ear or sometimes by performing a tissue biopsy of granulation from the ear canal or nasopharynx. In rare cases, antibiotics are stopped temporarily until a culture can be obtained to allow a more precise antibiotic selection. Patients are followed by serial blood tests while in the hospital (ESR and CRP) and later with gallium 67 SPECT scans. Some patients with advanced infections require several months of intravenous antibiotics.
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 changes in the anterior ear canal.
- Video 2. Axial (horizontal) bone-window CT of bilateral temporal bones showing the difference between the two skull base appearances.
- Video 3. Axial (horizontal) soft tissue window CT of skull base demonstrating the edema in the skull base and nasopharynx.
- Video 4. Coronal (vertical, parallel to face) CT of the right temporal bone showing the temporal bone changes in the coronal plane.
- Video 5. Sagittal (vertical, parallel to auricle) CT of the right temporal bone showing the extent of changes to anterior ear canal and TMJ.
- Video 6. Coronal (vertical, parallel to face) soft tissue window CT of the neck showing the extension of edema to the pharynx from the skull base.
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