Unilateral isolated trochlear nerve palsy due to bilateral dural carotid-cavernous sinus fistulas

Pulsating exophthalmos, bruit, episcleral venous distention, conjunctival and (eye)lid edema, ophthalmoplegia, and ocular pain have long been regarded as the classic symptoms and signs of idiopathic dural carotid cavernous sinus fistula(CCF). We experienced a 39-year-old woman who presented with headache and cyclovertical diplopia. On neurologic examination, we found isolated left trochlear nerve palsy only. The past medical history was not remarkable. Intracranial magnetic resonance angiography revealed abnormal signals around the carotid siphon on both sides. Conventional angiography confirmed bilateral dural CCFs, leaking predominantly from the left side. Diplopia and headache had improved spontaneously over 3 weeks after the onset. Occasionally, isolated oculomotor or abducens nerve palsy has been reported as the sole clinical finding of symptomatic dural CCF. But isolated trochlear nerve palsy with dural CCF is extremely rare. Although the exact mechanisms of isolated trochlear nerve palsy by dural CCF is unclear, various mechanisms have been proposed, including compression of trochlear nerve by venous congestion or direct shunted flow in cavernous sinus, vascular steel phenomenon, and venous thrombosis.