Brainstem congestion due to carotid-cavernous fistula via a shunt from the external carotid artery

Abstract

Venous congestion of the brainstem is an extremely rare complication of carotid-cavernous fistula (CCF). Here, we report a case in which MR imaging revealed characteristic changes associated with a simultaneous increase in pressure in the ophthalmic vein and anterior pontomesencephalic vein. Our patient was a 76-year-old woman who had been diagnosed with spinocerebellar ataxia type 31, had exophthalmos, conjunctival congestion in her left eye, worsening dysarthria, and gait instability. Ten days later, she was admitted to our hospital. A neurologic examination conducted upon admission revealed mydriasis, loss of light reflex, impaired superolateral movement of the left eye, and worsening ataxia with gait difficulty and slurred speech. Laboratory examinations revealed only high levels of serum anti-cardiolipin IgG antibody and the presence of cerebrospinal fluid myelin basic protein, but no other suggestive data of an inflammatory event. T2-weighted MRI revealed a dilated left superior ophthalmic vein and hyperintensity of the pons, mainly on the left side (Fig. 1a), which was depicted as low signal area with a linear high signal lesion in diffusion-weighted images (Fig. 1c), and T1-weighted imaging revealed an isointense mass with ring-shaped contrast enhancement after injection of gadolinium (Fig. 1b). Cerebral angiography confirmed the presence of a very weak, direct, highflow CCF in the left external carotid artery (Fig. 1d, e). The MR venography and venous phase of the angiography did not show any occlusion of veins. Methionine positron emission tomography revealed no tracer uptake in the lesion, which excluded the possibility of a brain tumor. Her symptoms were rapidly getting well before we tried an endovascular treatment. At 4 months, the MRI images showed a high signal spot at the left cerebellar peduncle and slight high signal on the left side of the pons (Fig. 1a). Most cases of idiopathic and traumatic CCF have been reported to be caused by dural arteriovenous fistulas (DAVF) [1]. The providing angiography images showed a shunt from the external carotid artery to the cavernous sinus. According to the Barrow classification, we diagnosed this case as an indirect fistula [2]. The pathomechanisms of venous congestion of the brainstem in CCF remain unknown, but variations in the drainage pattern of the superior petrosal sinus (SPS) and engorged veins in the surrounding brainstem were speculated to be important factors in most of the cases. A large flow volume shunted via the CCF [3, 4], occlusion of the superior or inferior petrosal sinus [5, 6], thrombosis of the dural sinuses or veins of the posterior fossa [4], and variations in venous drainage [7] have been speculated to be primary triggers for venous congestion. The most likely pathomechanism in this patient is that the CCF initially drained via the ophthalmic vein and recruited the prepontine venous plexus for drainage following partial thrombosis of the cavernous sinus. For the cause of the partial thrombosis, we speculate the possible mediation of antiphospholipid-related antibodies because antiphospholipid antibodies are known to be associated with cerebral venous thrombi, and recent studies have suggested that venous congestion and retrograde flow may cause a dysfunctional venous circulation [8]. Y. Ito N. Sanjo (&) K. Ishikawa O. Tao T. Yokota H. Mizusawa Department of Neurology and Neurological Science, Graduate School of Medical and Dental Science, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan e-mail: n-sanjo.nuro@tmd.ac.jp