Angioarchitecture and classification of adult intracranial pial arteriovenous fistulas: a multicenter study

Pial arteriovenous fistulas (AVFs) are rare cerebrovascular shunts characterized by direct connections between pial arteries and veins. Despite increasing recognition in adults, their anatomical features and clinical implications remain poorly understood. The authors aimed to characterize the clinical and radiological features of adult intracranial pial AVFs, propose an angioarchitectural classification, and assess treatment outcomes.

The authors conducted a nationwide, multicenter, retrospective cohort study of adult intracranial pial AVFs in Japan between 2013 and 2024. Imaging data were centrally reviewed to confirm diagnoses and classify lesions based on angioarchitecture. Lesions were defined as microfistulas when the diameter of the shunt feeder was < 2 mm and as macrofistulas when it was ≥ 2 mm. Clinical features, treatment strategies, and outcomes were compared descriptively between the groups.

A total of 66 patients with 72 pial AVFs were analyzed. Compared with macrofistulas, microfistulas were more common (74.2%) and occurred more often in older patients (median age 66 vs 32 years, p < 0.001). Furthermore, dural AVFs (42.9% vs 5.9%, p = 0.006) and a history of cerebrovascular events (24.5% vs 0%, p = 0.027) were more frequently observed in microfistulas. Varix formation and multiple draining veins were commonly seen in macrofistulas (94.7% vs 7.5%, p < 0.001 and 21.1% vs 0%, p = 0.004, respectively). Among 72 lesions, 70.8% underwent intervention, with transarterial embolization being the most common modality (51.0%). Complete obliteration was achieved in 78.4% of treated cases. Each lesion was further subclassified into distinct subtypes based on angioarchitectural configuration. One macrofistula subtype (5.6%), characterized by multiple feeders connecting to different multiple draining veins, showed lower obliteration rates and higher complication rates in the few treated cases.

Adult pial AVFs exhibit considerable angioarchitectural heterogeneity, which may relate to variations in clinical presentation and management. Our proposed classification scheme may provide a descriptive framework for characterizing these lesions, although further validation is needed.