CAROTID-CAVERNOUS FISTULATION

= Abnormal communications between the carotid arterial system and the venous cavernous sinus
Broadly classified as either direct or indirect, on the basis of anatomic features depicted on angiograms

Symptomatic direct CCFs (type A):
 - Spontaneously resolve only in rare cases
 - Almost always require urgent treatment, goal: to eliminate flow through the fistula but also to maintain internal carotid patency

Angiography, computed tomography (CT) scanning, magnetic resonance imaging (MRI), and magnetic resonance angiography (MRA) are also useful in assessing the effectiveness of treatment

CT and MRI are the preferred radiologic modalities compared with angiography:
 - Lower incidence of complications
 - Ability to 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

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

CT finding:

Enlargement of the ipsilateral cavernous sinus
Enlargement and tortuosity of the superior ophthalmic vein
Enlargement of the extraocular muscles
Proptosis

MRI finding:

= CT
Abnormal flow voids in the affected cavernous sinus 
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

USG:

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. A-scan ultrasonography also can show thickening of the optic nerve.

Nuclear Medicine:

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.

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.

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. 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.