Diagnosis: Skull Base Osteomyelitis
This patient's condition was somewhat complex. It is always important to understand how a patient's symptoms began. The most critical aspect of this patient's history is the supposed “ear infection” that started this whole process. Acute otitis media primarily affects children; it's very uncommon among adults with no history of ear disease. Therefore, any history of acute middle ear infection in this context must be questioned. This means that either the initial diagnosis was incorrect or the patient was suffering from an underlying immune deficiency or autoimmune condition that resulted in acute otitis media.
The patient's CT scan showed a well-developed mastoid, which is very uncommon in people with previous chronic ear infection. Therefore, the CT scan is evidence that the patient has had good Eustachian tube function for most of her life. An adult with normal Eustachian tube function generally would not develop acute otitis media. The presence of serous fluid when the initial otolaryngologist placed a tube in the patient's ear also suggests that she didn't have acute otitis media. Upon resolution, an acute middle ear infection would result in a mucoid (thick, mucus-like) effusion behind the tympanic membrane, not in a serous (faint, yellowish, clear fluid) effusion.
Examination of the patient's CT scan of the neck showed evidence of significant soft-tissue inflammation around the carotid artery (Fig. 2). An angiogram showed an aneurysm in the left carotid artery (Fig. 3). It appeared that the attempted drainage may have led to the development of an aneurysm in the carotid artery. This may have occurred because the infection around the carotid may have compromised the normally thick arterial wall.
When the patient arrived at our hospital, we first addressed her carotid artery. A balloon occlusion test was performed, which showed a good blood flow in the left side of the brain. In this test, the brain is monitored with an EEG, and the carotid artery is occluded with a balloon angiography for five minutes. No EEG change indicates that there is good collateral circulation to the brain and the carotid artery can be occluded. Any change in the EEG means the carotid artery would have to be bypassed before occlusion to prevent a stroke.
Once the carotid artery was occluded, we went back to the initial question on what had caused the problem. Based on the review of the CT scan and the edema of the ear canal, it was suspicious that the patient may have had skull base osteomyelitis, which was partially treated with oral ciprofloxacin, but the infection may have migrated to the soft tissues of the skull base and the neck. This migration of the infection may have resulted in what looked like a peritonsillar (immediately behind the tonsil) or parapharyngeal (deeper behind the tonsil) infection, which misled the initial physician into attempting to drain the infection. Laboratory studies were performed with erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), which were found to be significantly elevated. A technetium bone scan found positive evidence of infection in the left mastoid/skull base region (Fig. 4). The infection was most significant around the stylomastoid foramenand, and it had affected the facial nerve causing paralysis (Fig. 5).
Skull base osteomyelitis, otherwise known as malignant otitis externa, is a severe, life-threatening infection of the temporal bone that generally starts in the ear canal. At first, it commonly goes unnoticed as its presentation is like otitis externa. One characteristic of this condition when the infection involves the temporal bone is that it causes the development of fluid within the mastoid. This fluid is usually serous and concentrates around the ear canal. Therefore, a patient presenting with serous fluid and ear pain in the absence of an upper respiratory infection needs further investigation, as there may be another underlying process causing the combination of symptoms.
Skull base osteomyelitis usually occurs with immune suppression or diabetes. This patient is a rarity in that she did not have diabetes or a known condition causing immunosuppression—factors that may have misled her previous physicians. The patient's facial paralysis—a red flag in the setting of serous effusion—also warranted further investigation. At the very least, an MRI with contrast could have identified the significant infection around the skull base. The progression and spread of the infection along the skull base and involvement of the soft tissues led to the appearance of a possible neck infection.
This condition is best diagnosed with a technetium bone scan. Treatment involves long-term antibiotic use—typically six to 12 weeks of intravenous antibiotic therapy. Resolution of the infection is monitored using a gallium bone scan.
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 bone window (showing bony detail) CT (horizontal) of the neck showing the mastoid inflammation on the patient's left side (right side of the images). Note that since this is a CT of the neck, it starts in the upper chest and runs through the mid-skull.
- Video 2. Axial soft-tissue window (showing soft tissue detail) CT (horizontal) of the neck demonstrating the inflammation around the carotid and in the parapharyngeal space on the patient's left side (right side of the images).
- Video 3. Angiogram of the left internal carotid artery (right side of images) showing the large aneurysm in the internal carotid artery.
- Video 4. Fused technetium-99 SPECT with the axial CT (horizontal) showing the inflammation (intense yellow) at the skull base on the patient's left (right side of images).
- Video 5. Composite technetium-99 scan showing the location of the inflammation (bright white) at the skull base on the left. The video runs as if the patient's skull is being rotated on a chair as we are viewing the images.
- Video 6. Axial CT (horizontal) of the temporal bones showing the mastoid inflammation and damages in the facial nerve around the stylomastoid foramen.
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