Spontaneous carotid-cavernous sinus fistula with fibromuscular dysplasia: illustrative case.

backgroundA carotid artery cavernous sinus fistula (CCF) is an abnormal shunt of blood vessels, allowing blood to flow directly or indirectly from the carotid artery into the cavernous sinus. The most common cause of spontaneous CCF (s-CCF) is ruptured internal carotid-cavernous sinus aneurysms, while fibromuscular dysplasia (FMD) is rare. FMD is a rare, idiopathic, segmental, noninflammatory, and nonatherosclerotic disease of medium-sized arteries, characterized by abnormal cell proliferation and distortion of arterial wall architecture. The authors report the case of a patient with CCF with FMD. OBSERVATIONS: The authors report the case of a young woman with s-CCF who was effectively treated with coiling and balloon compression. Subsequently, she was shown to have FMD susceptibility genes using single nucleotide polymorphism (SNP) testing in the follow-up phase. LESSONS: The authors report the case of s-CCF caused by FMD in a young patient. SNP testing validated the existence of FMD susceptibility genes. The patient successfully recuperated following endovascular embolization therapy. For patients with s-CCF, the possibility of FMD should be considered, especially in young women with a family history. https://thejns.org/doi/10.3171/CASE24622.