A 53-year old woman presented with a history of dizziness in low atmospheric pressure and bilateral superior canal dehiscence. She reported having balance and cognitive issues during thunderstorms or cloudy weather or when traveling to the mountains. She also reported getting headaches and right ear fullness. She underwent repair surgery of a previous bilateral superior and posterior canal dehiscence surgery and bilateral perilymphatic fistula repair. Results of her microscopic ear exam, ocular and cervical vestibular evoked myogenic potential (VEMP) test, and video head impulse test (vHIT) were normal. A previous audiogram showed normal to mild bilateral hearing loss (Fig. 1). Previous magnetic resonance imaging (MRI) showed no abnormalities. CT from post-surgery showed good repair of superior canal dehiscence.
Diagnosis: Vestibular Migraine
Pulsatile tinnitus poses a diagnostic challenge to clinicians. The differential diagnosis is very broad, and includes tumors and other life-threatening abnormalities. It is especially challenging because it does not have a universally recognized workup. As such, clinicians must first rule out possible causes in the differential diagnosis by ordering imaging and/or referring the patient to other specialists. Ultimately, a pulsatile tinnitus diagnosis may be made as a diagnosis of exclusion, which is the diagnosis of a condition that cannot be tested but may be treated. Considered first are the most pressing conditions in the differential diagnosis, which includes tumors of the brain or temporal bone.
To identify possible tumors, an MRI with contrast of the internal auditory canal may be obtained. This will help in the diagnosis of potential neoplasms (e.g., glomus jugulare tumors) and evaluation of imaging findings of idiopathic intracranial hypertension (e.g., an empty sella, tortuous optic nerves, Meckel's cave diverticula, slit-like ventricles, among others). In our workup protocol, we then obtained magnetic resonance venography (MRV) to rule out venous sinus stenosis or thrombosis.
Intracranial hypertension, which is common among middle-aged overweight women, is a potentially life-disrupting condition that can cause pulsatile tinnitus. Evaluation of this condition requires a neuro-ophthalmologic exam. Rarely, a lumbar puncture with opening pressure checks may be needed when neuro-ophthalmologic exams or imaging is concerning for intracranial hypertension.
If the sound is not extinguished when applying gentle pressure over the jugular vein on the side of the anterior neck, an MRA is obtained to evaluate for arteriovenous fistulas, carotid or other aneurysms, or dural arteriovenous fistula (AVF). Once these urgent conditions are ruled out, the clinician may order a CT scan of the temporal bones to identify any structural abnormality that may require surgical intervention. The most common abnormalities are semicircular canal dehiscence and sigmoid sinus diverticulum. Other conditions include dehiscence of the tegmen tympani with contact between the dura and the ossicles or posterior fossa plate defect. It should be kept in mind that the workup is undertaken in patients with no identifiable cause for the condition, such as conductive hearing loss from perforation, middle ear fluid, etc.
Based on the CT scan results, this patient was found to have two abnormalities that were missed by the radiologist (Figs. 1–3). First, a posterior fossa defect was found in the plate separating the dura from the mastoid (dashes arrow in Figs. 1 and 2). In surgery, we have found these abnormalities to usually harbor a small dural vein. The etiology of this abnormality is unclear. As with many forms of pulsatile tinnitus involving the intracranial venous system, intracranial hypertension may play a role in the development of this problem. Presumably, chronic increased venous pressure causes erosion of the posterior fossa plate. Sometimes, these posterior fossa plate defects are associated with cerebrospinal fluid (CSF) leakage. In this patient, however, no fluid was found in the mastoid to suggest a CSF leak. Evaluation of the coronal CT angiography (see Fig. 4 online https://bit.ly/2ROhfFK) showed that there was a layer of air cells and solid bone overlying the superior semicircular canal, indicating no superior canal dehiscence was present.
Coronal MRI of the internal auditory canals (see Fig. 5 online https://bit.ly/3iSuxgz) showed some turbulence in the blood flow within the sigmoid sinus. Normally, venous flow within the sigmoid sinus is slow and, on MRI with contrast, the presence of blood within the sigmoid sinus is apparent from the white appearance of the contrast within the sigmoid. Sometimes, if there is fast blood flow within the sigmoid sinus, the central part of the sigmoid sinus will appear dark on MRI, indicating that blood was moving too fast for the MRI to properly capture an image. However, at the periphery of the walls of the sigmoid sinus, there is friction between the blood flow and the sigmoid sinus wall. This causes the blood to flow slower. Most commonly, the sigmoid sinus appears like a slow blood flow with a white (contrast enhancement) area that fills the entire sigmoid, or its central portion appears darker to indicate the fast blood flow. In this patient, however, we found a wider white area in the medial portion of the sigmoid sinus within an irregularly shaped dark region that separated a small area of slow flow laterally (see Fig. 5 online https://bit.ly/3iSuxgz). Additionally, an area of dehiscence was seen in another section of the sigmoid sinus (see Fig. 4 online https://bit.ly/2ROhfFK). The combination of these findings (sigmoid sinus diverticulum and a posterior fossa defect) was found to be the cause of this patient's pulsatile tinnitus.
Surgical intervention is used to treat pulsatile tinnitus caused by a sigmoid sinus diverticulum and posterior fossa defect. While treatment is not necessary since pulsatile tinnitus only causes issues with the patient's quality of life, many patients choose to undergo surgical treatment. In surgery, which is best performed by an experienced neurotologist, it is critical to avoid compressing the sigmoid sinus, which would cause or exacerbate intracranial hypertension. Before undertaking any surgical intervention, the patient should be evaluated for intracranial hypertension by a neuro-ophthalmologist. If suspicion is high based on imaging findings or neuro-ophthalmology examination, a lumbar puncture should be performed to measure intracranial CSF pressure. We generally repeat the neuro-ophthalmologic exam three months after surgery to check for any changes in intracranial pressure post-surgery and other early signs of intracranial hypertension. Treatment of intracranial hypertension, if present, can significantly reduce the patient's symptomatology. Before surgical therapy, we always treat the patient with a short course of migraine prophylaxis since many patients with pulsatile tinnitus suffer from migraines, which can heighten the brain's sensitivity to internal sounds such as pulsatile tinnitus. We usually use agents that also decrease intracranial pressure, such as topiramate, acetazolamide, or verapamil in patients with high blood pressure.
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. Poschl view (parallel to the superior canal) CT of right temporal bone showing the anatomy of the superior canal and membranous narrowing post-surgery.
- Video 2. Coronal (parallel to face) CT of the right temporal bone showing the anatomy of the posterior and horizontal canals postoperatively.
- Video 3. Poschl view (parallel to the superior canal) CT of the left temporal bone showing the anatomy of the superior canal post-surgery.
- Video 4. Coronal (parallel to face) CT of the left temporal bone showing the anatomy of the posterior and horizontal canals postoperatively.
- Video 5. Coronal (parallel to face) CT of the temporal bones showing the bilaterally dehiscent superior canals before all surgeries.
- Video 6. Axial (horizontal) CT of the temporal bones showing the bilaterally intact posterior canals before all surgeries.
Watch the patient videos online at thehearingjournal.com.