Bujak, Mathew MD, FRCSC; Margolin, Edward MD, FRCSC; Thompson, Andrew MD; Trobe, Jonathan D MD
Carotid-cavernous fistulas (CCFs) are typically classified into high-flow direct fistulas, which may arise after head trauma or spontaneously, and low-flow dural fistulas, which arise spontaneously, usually in elderly or postpartum women (1,2). Most high-flow direct fistulas require endovascular intervention (3). In contrast, many low-flow dural fistulas do not require intervention, as they tend to cause mild clinical manifestations and often resolve spontaneously (2-6). However, a minority of low-flow dural fistulas may cause florid signs of orbito-ocular venous hypertension, including marked vascular engorgement, proptosis, reduced eye movement, elevated intraocular pressure, retinal venous hemorrhage, optic neuropathy, and pain (7-10). In such patients, there is a temptation to intervene (2-4).
We report 2 patients whose dural CCFs caused severe clinical manifestations, One patient had a choroidal effusion with markedly narrowed anterior chamber angle and elevated intraocular pressure. Both patients had subnormal visual acuity with an afferent pupil defect indicating optic neuropathy. Before intervention, the manifestations spontaneously resolved. Time-resolved imaging of contrast kinetics (TRICKS) MRA, a noninvasive imaging technique, strongly suggested resolution of the fistulas. These patients are presented to emphasize that marked clinical manifestations are not necessarily an indication for intervention to close the fistula and may represent a harbinger of spontaneous closure.
A 72-year-old previously healthy woman developed a red right eye that worsened over the course of a few weeks together with recent onset of proptosis and binocular horizontal diplopia. Three weeks after the onset of symptoms, best-corrected visual acuity was 20/40 in the right eye and 20/20 in the left eye with a right afferent pupillary defect. Intraocular pressures were 26 mmHg in the right eye and 12 mmHg in the left eye. Prominent conjunctival corkscrew vessels were present in the right eye, which displayed 7 mm of proptosis and markedly reduced ocular ductions in all directions. The ocular ductions of the left eye were normal.
Biomicroscopy of the right eye disclosed a very shallow anterior chamber (Fig. 1A-B) and gonioscopy demonstrated a Shaffer grade 1 angle over 360. A Shaffer grade 4 angle was present in the left eye. Visante ocular coherence tomography (OCT) (Fig. 1C-D) and ultrasonic biomicroscopy (Fig. 1E-F) confirmed the anterior chamber shallowing and revealed large choroidal effusions in the right eye. The retinal veins were engorged in the right eye but not in the left eye.
CT angiography demonstrated proptosis of the right eye with enlarged extraocular muscles, edema of preseptal tissues, a dilated right superior ophthalmic vein, and early venous filling of the right cavernous sinus (Fig. 2). There were no intracranial imaging abnormalities. A presumptive diagnosis of dural CCF was made.
Endovascular intervention was planned but delayed for logistic reasons. No medications were prescribed. Meanwhile, her manifestations began to resolve, so that intervention was further postponed.
Four weeks after initial presentation, visual acuity had improved to 20/25 in the right eye, the relative afferent pupillary defect had resolved, intraocular pressure had decreased to 16 mmHg in both eyes, and ocular ductions and venous congestive retinopathy had resolved. Ultrasonic biomicroscopy disclosed that the choroidal effusions had resolved and that the anterior chamber angle had deepened to Shaffer grade 4. TRICKS MRA performed 8 weeks after the initial CT angiogram demonstrated resolution of the dural CCF (Fig. 3).
A 73-year-old woman with type 2 diabetes and coronary artery disease presented with the gradual onset of redness in both eyes and diplopia. Best-corrected visual acuity was 20/30 in both eyes, pupil reactions were normal, and intraocular pressure was 18 mmHg bilaterally. Prominent corkscrew conjunctival vessels were present in both eyes. Ocular ductions were normal except for 80% abduction of the left eye.
Three weeks later, she experienced severe headache and worsening of diplopia and redness in both eyes. Visual acuity had declined to 20/200 in the right eye and a right afferent pupillary defect was now present. Intraocular pressures were 30 mmHg in the right eye and 22 mmHg in the left eye. Abduction had decreased to 50% in both eyes. There was moderate retinal venous engorgement in both eyes.
CT angiography (CTA) demonstrated engorgement of both superior ophthalmic veins (Fig. 4) without intracranial abnormalities. TRICKS MRA confirmed bilateral cavernous sinus dural CCFs with intercavernous connections but no cortical venous reflux (Fig. 5).
Endovascular intervention was planned, but by the time it was to occur 2 weeks later, the patient had experienced spontaneous improvement of all clinical manifestations. Examination now demonstrated visual acuities of 20/30 in both eyes, no afferent pupillary defect, intraocular pressures of 16 mmHg bilaterally with no medications, normal ocular motility and alignment, and a normal retinal examination. TRICKS MRA demonstrated resolution of the CCF (Fig. 6).
These 2 patients are remarkable for the fact that dural CCFs gave rise to optic neuropathy and sufficiently severe orbito-ocular manifestations to prompt consideration of endovascular intervention. In the interval between the intent and the readiness to intervene, however, the patients' clinical manifestations dramatically improved, so that no procedures were necessary.
The florid and vision-threatening manifestations displayed by our patients are uncommon in dural CCF (2,5,11,12). Optic neuropathy, present in both of our patients, was reported in 13% of 80 patients with dural CCFs (13). Our first patient developed almost complete ophthalmoplegia, angle closure, and elevated intraocular pressure. We found only 1 case report (9) describing angle closure from choroidal detachment in dural CCF. Choroidal detachment in dural CCF has only been described in 3 cases (9,10,14).
The main clinical indication for endovascular treatment of dural fistulas is progressive visual loss, with other possible indications being intractable headache, elevated intraocular pressure refractory to medication, diplopia, or an intolerable cosmetic deformity (2-4). The indications for therapy found on neuroimaging include the presence of a pseudoaneurysm, large varix of the cavernous sinus, venous drainage to cortical veins, and thrombosis of venous outflow pathways distant from the fistula (15).
Endovascular intervention is usually successful in closing a dural CCF. In a review of 133 patients with dural CCFs, Meyers et al (3) showed that 97% had good recovery and 90% achieved complete cure. Such intervention may, however, be complicated by allergic dye reactions, impairment of renal function, cranial nerve palsy, and stroke (11).
Spontaneous closure occurs with a frequency of 3.7% to 47% (2-6). Such spontaneous closure may be explained by the fact that the arteriovenous shunt elevates venous pressure within the sinus to a critical point at which stasis occurs and thrombus formation is facilitated (16-18). Thrombus formation may cause an increase in venous pressure accounting for a paradoxical worsening in clinical presentation before resolution of the fistula (5,19). Notably, both of our patients manifested significant worsening in their symptoms before spontaneous fistula closure.
Our patients demonstrated spontaneous improvement shortly after undergoing a diagnostic CTA. Other authors have noted this phenomenon (19,20). They have postulated that the change in pressure gradients during the CTA might induce stasis and local thrombosis in the region of the fistula (20). Another proposed mechanism is that the contrast material itself induces fistula closure (21). These findings have been supported by experimental evidence showing that angiographic contrast media may exaggerate the process of leukocyte accumulation and affect vascular endothelium and erythrocytes, thereby promoting thrombus formation (21).
In the diagnosis of CCF, digital subtraction angiography (DSA) has been the gold standard. This study permits temporal resolution, which allows dynamic visualization of feeding arteries, venous drainage patterns, and assessment of flow rate, factors that are important not only for definitive diagnosis but also for management strategies. The drawbacks of DSA are its invasive nature and associated complications (22). Several time-resolved MRA techniques have been introduced to allow acquisition with temporal resolution simulating DSA (23-25). One such technique, TRICKS (24), was used in both of our patients to define the location and flow characteristics of the fistula.
The form of TRICKS we used provides a whole-head 3-dimensional image at a frame rate of approximately 1 image every 2 seconds. This magnetic resonance technique exploits several data acquisition and reconstruction concepts, including variable rate k-space sampling, temporal interpolation, and zero-filling in the slice dimension (24). This allows more rapid sampling of data and temporal resolution beyond the capabilities of conventional MRI and MRA, which provide only static images. TRICKS allows dynamic visualization of contrast bolus passage from arterial to venous phases, helping to detect vascular lesions that might remain occult on static MRI or CTA. In CCF, TRICKS provides assessment of fistulous sites of early venous filling and venous drainage rates, useful in predicting outcome and directing management. Other advantages are relatively high signal-to-noise-ratio and data acquisition in any orientation, independent of direction and rate of flow (24). TRICKS has also been useful in the imaging and management of arteriovenous malformations and tumors with high flow rates such as hemangiopericytomas (26-28).
Given our experience and previous reports of spontaneous closure of dural CCFs (2,4-6,13,16-20,29-32), we suggest that endovascular intervention be deferred even in patients who have severe orbital congestion signs at presentation. Paradoxically, expectant management may be especially appropriate when CCF clinical manifestations are worsening, as this may be a sign of sinus thrombosis and impending spontaneous resolution. TRICKS MRA is a noninvasive alternative to more invasive catheter cerebral angiography.
We thank Dr. Iqbal Ahmed, Department of Ophthalmology, University of Toronto, for providing the images of the Visante OCT and ultrasonic biomicroscopy.
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