Diagnosis: Carotid Cavernous Fistula
Pulsatile tinnitus is a somewhat common complaint of patients in a neurotology or an otolaryngology practice. There is no universally accepted workup for these patients. Some clinicians recommend performing a temporal bone CT and CT angiography of the head. Some perform an MRI of the temporal bone/internal auditory canal. The workup may also include magnetic resonance angiography (MRA) or magnetic resonance venography (MRV).
Pulsatile tinnitus has a long differential diagnosis that includes tumors of the temporal bone or skull base. The sudden unilateral development of pulsatile tinnitus warrants a complete head and neck exam, audiogram, and imaging studies. Conductive hearing loss can lead to hearing internal sounds and thus pulsatile tinnitus. This can be seen in patients with otosclerosis, middle ear effusion, and superior canal dehiscence. Additionally, abnormalities of the venous sinuses (e.g., transverse sinus narrowing, sigmoid sinus diverticulum, and intracranial hypertension or increased intracranial pressure) can lead to pulsatile tinnitus.
Auscultation of the neck and mastoid is a useful adjunct to a thorough ear exam. While very rare, significant carotid stenosis or arteriovenous malformations can be heard when a clinician uses a stethoscope to listen to the neck or mastoid. This patient had normal head and neck exam results and auscultation of the mastoid, although orbital auscultation was not performed.
The gold standard in ruling out intracranial hypertension is a lumbar puncture (spinal tap). Due to its invasive nature, this procedure is reserved for patients who are at high risk of developing intracranial hypertension (obese, middle-aged women with other conditions) or have imaging findings that are suggestive of this condition (sigmoid sinus abnormalities, spontaneous CSF leak, dilated optic nerve sheaths, Meckel's cave diverticulum, empty sella, among others). Our general approach is to obtain an MRV if the MRI of the temporal bone shows negative results. In this case, the patient's MRV showed a carotid cavernous fistula (CCF).
The carotid artery enters the skull base under the temporal bone and traverses anteromedially. It is also in direct contact with the cavernous sinus, a large area of venous blood channels creating a sinus cavity bordered by the sphenoid bone and temporal bones. The cavernous sinus is a critical skull base structure due to its location and contents. Multiple cranial nerves traverse the cavernous sinus, including the third (oculomotor), fourth (trochlear), and sixth (abducens) cranial nerves, as well as the first (ophthalmic nerve) and second branches (maxillary nerve) of the fifth cranial (trigeminal) nerve. The third, fourth, and sixth cranial nerves are responsible for eye movements, and an abnormality in one of these nerves causes double vision. An abnormal connection between the carotid and cavernous sinus increases the venous pressure in the sinus. This can put pressure on the cranial nerves and weaken their function. The pressure on the veins that drain into the cavernous sinus also increases, causing an enlargement of the veins around the eye and increasing the intraocular pressure, which typically leads to glaucoma.
CCF is caused by an abnormal connection between the carotid artery and cavernous sinus. The most common (70%-90%) etiology of CCF is trauma from a skull base fracture that results in a microscopic tear in the internal carotid artery (ICA) at the level of the cavernous sinus. The most common causes of injury include motor vehicle collisions, fights, and falls. Patients with CCF usually present with eye symptoms such as conjunctival redness (chemosis or injection), proptosis (abnormal protrusion of an eye), double vision (diplopia), eye pain, and pulsatile tinnitus.
An uncommon case is indirect fistula, wherein a branch of the carotid artery connects with the cavernous sinus. This can happen from a spontaneous rupture of an existing aneurysm or atherosclerotic artery, which tends to occur in postmenopausal, hypertensive women. Indirect fistulas usually have less severe symptoms and a slow onset. Affected patients usually experience mild eye congestion and mild proptosis.
The differential diagnoses for CCF include vascular lesions such as arteriovenous malformation and cavernous sinus thrombosis, cavernous sinus tumors, orbital tumors, skull base tumors, and mucocele. CCF usually leads to the three classic signs and symptoms of proptosis (Fig. 2), conjunctival chemosis (redness), and cranial bruit (pulsatile sound on auscultation of the head or eye).
Beyond clinical suspicion, imaging studies are needed for diagnosis. On MRI of the orbits or temporal bone with contrast, CCF may present with an enlarged superior ophthalmic vein (SOV; Fig. 3), thick extraocular muscles, and evidence of an enlarged cavernous sinus with a convexity of the lateral wall. These changes can only make a clinician suspect a fistula. MRA (Fig. 4) and MRV (Fig. 5) may show some of the higher-flow fistulas but do not provide the details necessary to complete the evaluation. Doppler ultrasound images of the orbit may show the arterialized blood flow in a dilated SOV (fast flow of blood in the vein). Angiography (by placing a catheter through the groin to reach the carotid artery and injecting contrast) of both internal and external carotid arteries is necessary to completely characterize the arterial supply and drainage of the carotid cavernous fistula. The procedure has some risks, so it is reserved for when a therapeutic intervention is planned.
Most CCFs are not life-threatening but can put the affected eye at risk. Treatment may be undertaken if the patient has glaucoma, double vision, intolerable pulsatile tinnitus or headache, and severe proptosis. Spontaneous closure is rare but can occur from thrombosis of the cavernous sinus. Dural fistulas may close spontaneously, especially after diagnostic angiography. Surgical closure of the external and internal carotid arteries is rarely needed. The most common intervention is balloon embolization using particles, glue, detachable balloons, and thrombogenic microcoils. This procedure has a 90 percent success rate, although a transient paresis of the third cranial nerve can happen in up to 30 percent of patients. Treatment of cavernous dural arteriovenous fistulas is usually performed by an endovascular neurosurgeon or an interventional neuroradiologist using a transarterial or transvenous approach. This patient was referred back to a neuro-ophthalmologist for further examination.
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. Subtraction MR arteriography (three-dimensional view of all arteries) of the patient with spinning in the lateral direction showing the blushing of vessels around the cavernous carotid.
- Video 2. Axial (horizontal), thin-sliced MRI with time-of-flight sequence showing the arterial flow (bright) with clouding around the cavernous carotid artery.
- Video 3. Subtraction MR venography mixed with arteriography (three-dimensional view of all arteries and veins) demonstrating the normal venous anatomy in the posterior fossa with abnormality around the cavernous carotid artery.
- Video 4. Axial (horizontal) T1 post-contrast MRI of the orbits showing the enhancement (bright area) around the left petrous carotid (right side of images) and the enlarged left superior ophthalmic vein.
- Video 5. Axial (horizontal) T2 MRI of the brain showing the proptosis of the left eye (right side of images).
- Video 6. CT angiography subtracted images of the intracranial arterial flow that fails to demonstrate the carotid cavernous fistula.
Watch the patient videos online at thehearingjournal.com.Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.