Carotid-Cavernous Fistula Imaging
- Author: Robert A Koenigsberg, MSc, DO, FAOCR; Chief Editor: James G Smirniotopoulos, MD more...
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 or indirect, on the basis of anatomic features depicted on angiograms. (See the images below.)
Further classification is based on their etiologic and hemodynamic qualities. Clinical manifestations of CCFs frequently involve ophthalmologic abnormalities; many patients initially consult an ophthalmologist.
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.[2, 3, 4]
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.[5, 6, 7, 8] (See the image below.)
CT and MRI are the preferred radiologic modalities. 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.[9, 5, 10]
CT findings may be sufficient for diagnosis in most patients; however, MRI and angiography are superior in evaluating venous distension, 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.
Plain radiographic findings are most useful for follow-up after embolization therapy, to evaluate balloon positioning or possible leakage.
CT scan findings in carotid-cavernous fistulas include the following :
Enlargement of the ipsilateral cavernous sinus (see the image below)
Enlargement and tortuosity of the superior ophthalmic vein
Enlargement of the extraocular muscles
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, 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.
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[12, 13, 7, 8] :
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
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.
Orbital sonograms demonstrate signs similar to those on CT scans and MRIs. In addition, orbital sonogram may demonstrate a reversal of flow direction in the superior ophthalmic vein.
Dilated tortuous veins may be prominent on B-scan echograms. With the A-scan method, dilated ophthalmic veins may be evident. 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.
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.
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 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. (See the images below.)
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 of greater than 5 frames per second and intracavernous carotid arterial injection rates of 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 in identifying the upper extent of the fistula, and it can further help in demonstrating double-hole traumatic fistulas and complete cavernous-intracavernous carotid artery transection.
The degree of confidence is high. Angiography unequivocally demonstrates the presence or absence of a CCF.
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