Carotid-Cavernous Fistula Imaging 

Updated: Jun 17, 2020
Author: Robert A Koenigsberg, MSc, DO, FAOCR; Chief Editor: James G Smirniotopoulos, MD 

Practice Essentials

Carotid-cavernous fistulas (CCFs) are abnormal communications between the carotid arterial system and the venous cavernous sinus. Most often, CCFs are broadly classified as either direct (Barrow type A) or indirect (Barrow types B, C, and D), on the basis of anatomic features depicted on angiograms. Further classification is based on their etiologic and hemodynamic qualities. Direct CCFs are characterized by a direct connection between the internal carotid artery (ICA) and the cavernous sinus, whereas indirect CCFs result from an indirect connection involving cavernous arterial branches and the cavernous sinus. Direct CCFs frequently are traumatic in origin and also may be caused by rupture of an ICA aneurysm within the cavernous sinus, Ehlers–Danlos syndrome type IV, or iatrogenic intervention. Causes of indirect CCFs include hypertension, fibromuscular dysplasia, Ehlers–Danlos type IV, and dissection of the ICA.[1, 2, 3, 4, 5]  

Digital subtraction angiography (DSA) is the gold standard for diagnosis, but because of nonintrusive modalities such as CT, MRI, carotid Doppler ultrasonography, and transcranial color-coded duplex, DSA does not have to be considered the first and sole option to evaluate CCFs.[6]

When compared with angiography, CT and MRI have a much lower incidence of complications. Furthermore, CT and MRI scans depict peripheral pathologies associated with CCFs (eg, enlargement of cavernous sinus and the ophthalmic vein). Angiography is used to confirm CT or MRI findings prior to treatment.[7, 8, 9]

CT findings may be sufficient for diagnosis in most patients; however, MRI and angiography are superior in evaluating venous distention, the aneurysm lumen, and the increased flow to cavernous sinus.

Indirect signs associated with CCFs are not readily seen on angiographic images. MRIs and CT scans are limited because precise filling of the cavernous sinus and other signs of abnormal blood flow are not readily seen.

Orbital color Doppler ultrasound (OCDUS) may be used in the diagnosis of carotid-cavernous fistula (CCF) with anterior drainage and particularly whether a negative OCDUS could avoid invasive diagnostic cerebral angiography. OCDUS can also be used to exclude mimickers of CCF, including orbital tumors, dysthyroid orbitopathy, orbital inflammation, and scleritis.[10, 11, 12]

Plain radiographic findings are most useful for follow-up after embolization therapy, to evaluate balloon positioning or possible leakage.

Radionuclide cerebral angiography performed with technetium-99m pertechnetate shows increased uptake of the tracer in the area of the carotid siphons, with rapid clearance. This study is useful in the early postoperative period in a patient with a large CCF repair when angiography may be dangerous.

(See the images below.)

Carotid-cavernous fistula. Anatomic features are s Carotid-cavernous fistula. Anatomic features are shown: internal carotid artery (red) and cavernous sinus (purple).
Patient with a gunshot wound to the face in whom a Patient with a gunshot wound to the face in whom a left traumatic carotid-cavernous fistula developed. The case was further complicated with bilateral optic nerve injuries and a skull base fracture affecting the sphenoid bone and temporal bones bilaterally.
An almost complete carotid-cavernous fistula demon An almost complete carotid-cavernous fistula demonstrates only minimal runoff to the ipsilateral intracavernous carotid artery territory. Because runoff has occurred, carotid preservation remains the treatment of choice. In patients in whom absolutely no runoff is demonstrated, carotid sacrifice at the level of the carotid-cavernous fistula can be considered, if necessary, to close the fistula. Needless to say, this treatment also depends on the collateral vessels and the patient's ability to tolerate intracavernous carotid artery sacrifice.
Anteroposterior view of an almost complete carotid Anteroposterior view of an almost complete carotid-cavernous fistula demonstrates only minimal runoff to the ipsilateral intracavernous carotid artery territory. Because runoff has occurred, carotid preservation remains the treatment of choice. In patients in whom absolutely no runoff is demonstrated, consideration can be given to carotid sacrifice at the level of the carotid-cavernous fistula if necessary to close the fistula. Needless to say, this treatment also depends on the collateral vessels and the patient's ability to tolerate intracavernous carotid artery sacrifice.
CT image of the head at the level of the cavernous CT image of the head at the level of the cavernous sinuses demonstrating left cavernous sinus widening secondary to an underlying carotid-cavernous fistula.

Clinical manifestations of CCFs frequently involve ophthalmologic abnormalities; many patients initially consult an ophthalmologist.[13]  Presenting symptoms of CCFs may include a subjective bruit, diplopia, tearing, red eye, ocular foreign body sensation, blurred vision, and headache. Patients with posteriorly draining fistulas may develop neurologic symptoms, such as confusion and expressive aphasia, as well as diplopia from isolated ocular motor nerve paresis. Clinical symptoms and signs usually present acutely in cases of direct fistula and are more indolent in indirect fistulas.[1]

Symptomatic direct CCFs (type A) spontaneously resolve only in rare cases. Therefore, they almost always require urgent treatment. The goal of treatment is to eliminate flow through the fistula but also to maintain internal carotid patency.[14, 15, 16]

Radiologic techniques are used in embolization of carotid-cavernous fistulas (CCFs). Angiography is invaluable for the guidance of catheter placement and delivery of the embolization materials. Angiography, computed tomography (CT) scanning, magnetic resonance imaging (MRI), and magnetic resonance angiography (MRA) are also useful in assessing the effectiveness of treatment.[9, 17, 18, 19]

(See the image below.)

Direct carotid-cavernous fistula after embolizatio Direct carotid-cavernous fistula after embolization. The cavernous sinus is no longer filling with contrast material. Note the distinct borders of the intracavernous carotid artery.

 

Computed Tomography

CT scan findings in carotid-cavernous fistulas include the following[20] :

  • Enlargement of the ipsilateral cavernous sinus (see the image below)

  • Enlargement and tortuosity of the superior ophthalmic vein

  • Enlargement of the extraocular muscles

  • Proptosis

    CT image of the head at the level of the cavernous CT image of the head at the level of the cavernous sinuses demonstrating left cavernous sinus widening secondary to an underlying carotid-cavernous fistula.

If the superior ophthalmic vein appears to be either asymmetric or larger than 4 mm in diameter, a carotid-cavernous fistula is suggested. CT scans do not depict a CCF if it is too small or has recently formed.

Regarding false-positive findings, the superior ophthalmic vein may be enlarged in patients with other orbital pathologies, such as cavernous angioma of the orbit, or in patients with other vascular malformations with orbital venous drainage. In particular, other dural malformations of the head and neck can be associated with unusual orbital venous drainage.

Regarding false-negative findings, CCFs do not always drain into the superior ophthalmic vein. Therefore, the absence of this sign does not exclude the possibility of an underlying CCF.

 

Magnetic Resonance Imaging

MRI findings in carotid-cavernous fistulas include the following[21, 22, 18, 19] :

  • Findings similar to those at CT

  • Abnormal flow voids in the affected cavernous sinus (see the image below)

  • Decreased MRI signal in the involved cavernous sinus

  • Dilated intercavernous sinuses and intercavernous vessels

  • Lateral wall convexity of the cavernous sinus

  • Dilated superior ophthalmic vein, ipsilateral or contralateral

  • Orbital edema

    Abnormal flow void in the left cavernous sinus reg Abnormal flow void in the left cavernous sinus region is demonstrated in a patient with an underlying carotid-cavernous fistula.

The role of MRI is limited by the ability to visualize dural CCFs; however, when it is used in conjunction with contrast-enhanced CT scanning, better diagnostic capability is achieved.

Regarding false-positive findings, MRI results are similar to CT findings in that the superior ophthalmic vein may be enlarged in patients with other orbital pathologies (eg, cavernous angioma of the orbit) or in patients with other vascular malformations with orbital venous drainage. In particular, other dural malformations of the head and neck can be associated with unusual orbital venous drainage resulting in enlargement of the orbital veins.

Regarding false-negative findings, MRI results are similar to CT findings in that CCFs do not always drain into the superior ophthalmic vein. Therefore, the absence of enlargement or lack of a prominent flow void does not exclude the possibility of an underlying CCF.

 

Ultrasonography

Orbital color Doppler ultrasound (OCDUS) is a reliable, noninvasive tool in the diagnosis of CCF; a negative OCDUS could avoid invasive digital subtraction angiography in patients suspected of anterior-draining CCF. Orbital sonograms demonstrate signs similar to those on CT scans and MRIs. In addition, an orbital sonogram may demonstrate a reversal of flow direction in the superior ophthalmic vein. OCDUS can also be used to exclude mimickers of CCF, including orbital tumors, dysthyroid orbitopathy, orbital inflammation, and scleritis.[10, 11, 12]

Dilated tortuous veins may be prominent on B-scan echograms. With the A-scan method, dilated ophthalmic veins may be evident.[10] The scans may also demonstrate evidence of arterialized blood coursing through the ophthalmic veins, which are seen as several low-amplitude spikes that are in constant motion. A-scan ultrasonography also can show thickening of the optic nerve. 

 

Angiography

To accurately identify a carotid-cavernous fistula, selective catheterization of the right and left external and internal carotid arteries and the vertebral arteries is necessary. Including the entire skull in lateral projection imaging is important.

The degree of confidence is high. Angiography unequivocally demonstrates the presence or absence of a CCF.

The angiographic appearance of a CCF can be variable and depends on the flow velocity of the blood and the anatomy of the affected arteries and veins.[17]

(See the images below.)

Typical carotid-cavernous fistula. Lateral project Typical carotid-cavernous fistula. Lateral projection subtraction angiogram demonstrates characteristic filling of the internal carotid artery with the cavernous sinus secondary to a tear in the intracavernous carotid artery. Filling of both the superior (arrowhead) and inferior (arrow) ophthalmic veins is present. Courtesy of Gerard Debrun, MD.
Anteroposterior projection demonstrates a carotid- Anteroposterior projection demonstrates a carotid-cavernous fistula, with opacification of the cavernous sinuses seen bilaterally. Courtesy of Gerard Debrun, MD.
Carotid-cavernous fistula in a patient after ballo Carotid-cavernous fistula in a patient after balloon embolization with fistula closure.
Digital subtraction angiogram demonstrates a carot Digital subtraction angiogram demonstrates a carotid-cavernous fistula that arose secondary to spontaneous rupture of an underlying cavernous carotid aneurysm into the cavernous sinus. Note that the venous drainage extends to the right. The patient's complaints were related to right ocular ecchymosis.
Digital subtraction angiogram showing cortical ven Digital subtraction angiogram showing cortical venous drainage pathways over the right convexity to the superior sagittal sinus in a patient with a carotid-cavernous fistula.

On an intracavernous carotid arteriogram in a patient with direct CCF, arteriovenous shunting into the cavernous sinus is evident.

Immediate filling of the petrosal sinus and/or the ophthalmic vein is commonly evident when the intracavernous carotid artery is injected. Frame rates greater than 5 frames per second and intracavernous carotid arterial injection rates greater than 7 mL/s may aid in evaluating the morphology of high-flow fistulas.

The Mehringer-Hieshima maneuver may also be useful in improving delineation of the lesion. This maneuver involves a 2 to 3 mL/s injection into the ipsilateral intracavernous carotid artery with manual compression of the artery below the catheter tip in the neck. This compression allows flow control within the artery to aid in demonstrating the location of the tear.

The Huber maneuver involves an injection of the ipsilateral vertebral artery, with lateral-projection angiography performed by using manual compression of the affected carotid artery during the injection (see the image below). The retrograde siphon filling of the cavernous sinus is evident. The maneuver helps identify the upper extent of the fistula, and it can further help demonstrate double-hole traumatic fistulas and complete cavernous-intracavernous carotid artery transection.

Huber maneuver demonstrates filling of the carotid Huber maneuver demonstrates filling of the carotid-cavernous fistula resulting from retrograde intracavernous carotid artery flow into the fistula.

In a study by Benson et al of 18 patients suspected of having a CCF on CTA and subsequently underwent digital subtraction angiography, superior ophthalmic vein dilatation/enhancement and arterial-phase contrast within the cavernous sinus were found to be the most sensitive findings. Asymmetric cavernous sinus enlargement had poor specificity and could result in false-positive diagnoses of CCFs. False positive cases were less likely to have an optimally timed contrast bolus.[23]

In the Benson et al study, superior ophthalmic vein early enhancement and dilatation had 100.0% sensitivity and 77.8% specificity; arterial-phase contrast in the cavernous sinus had 88.9% sensitivity and 66.7% specificity; and periorbital edema had 88.9% sensitivity and 77.8% specificity. The most specific markers of CCF were superior petrosal sinus and inferior ophthalmic vein dilatation/enhancement (100%, 95% CI 88.8-100.0; and 88.9%, 95% CI 44.4–100.0, respectively); the specificity of asymmetric cavernous enlargement was 44.4% (95% CI 11.1–77.7).[23]