Rapid Progression of a Cavernous Sinus Dural Arteriovenous Fistula From Borden Type I to Type II: A Case Report.

Cavernous sinus dural arteriovenous fistulas (CSdAVFs) are typically considered benign when classified as Borden type I, which is characterized by the absence of cortical venous reflux (CVR). These lesions are often managed conservatively with long-term follow-up imaging. Although progression to higher-risk types involving CVR can occur, it is generally gradual. A 74-year-old woman presented with recurrent diplopia due to a right abducens nerve palsy. Digital subtraction angiography revealed Borden type I CSdAVFs with venous drainage exclusively via the bilateral inferior petrosal sinuses, without evidence of CVR. Conservative management with follow-up MRI was initially planned. However, three months later, the patient developed new-onset pulsatile tinnitus and conjunctival injection. Follow-up imaging demonstrated newly developed CVR and altered venous drainage patterns, consistent with progression to Borden type II. Transvenous embolization resulted in the complete resolution of symptoms and a favorable clinical outcome (modified Rankin Scale score of 0). This case highlights the potential for rapid progression of CSdAVFs, even in lesions initially classified as Borden type I. Vigilant clinical monitoring and prompt re-imaging are essential when new symptoms emerge, even within a short interval following diagnosis.