Low-flow vascular malformations without arteriovenous shunting of the central nervous system: a pictorial review

This review aims to provide a comprehensive pictorial review of low-flow vascular malformations (LFVMs) of the central nervous system (CNS) without arteriovenous shunting, focusing on their epidemiology, pathophysiology, imaging features, and associations with other vascular anomalies. LFVMs - developmental venous anomalies (DVAs), cavernous malformations (CMs), brain capillary telangiectasias (BCTs), and sinus pericranii (SP) - are typically benign and incidental but may cause symptoms or hemorrhage. Differentiating LFVMs from neoplastic, inflammatory, or high-flow vascular lesions is critical to avoid misdiagnosis and inappropriate treatment. MRI is the reference technique. DVAs show a "caput medusae" venous pattern; CMs have a mulberry-like core with a complete hemosiderin rim on T2*/SWI; BCTs are often occult on routine MRI but may display brush-like enhancement and subtle SWI hypointensity; SP consists of an extracranial venous mass communicating with a dural sinus through a transosseous vein. Familiarity with the imaging spectrum and typical associations of CNS LFVMs enables confident diagnosis and helps avoid unnecessary invasive procedures. CRITICAL RELEVANCE STATEMENT: By illustrating key imaging features of low-flow CNS vascular malformations, this article critically addresses frequent diagnostic pitfalls. It advances radiological practice by guiding differentiation from neoplastic or high-flow lesions and improving multidisciplinary patient care. KEY POINTS: LFVMs (DVAs, CMs, capillary telangiectasia, SP) are frequently incidental but may cause hemorrhage, seizures, or neurological deficits. DVAs are typically benign drainage variants; hemodynamic congestion on perfusion weighted imaging explains occasional symptoms and the frequent association with acquired CMs. CMS presents as "mulberry-shaped" lesions with a hemosiderin rim on SWI sequences, reflecting microhemorrhages and the absence of intervening brain parenchyma. Capillary telangiectasia most often occurs in the pons; recognition of the characteristic SWI hypointensity with faint enhancement prevents misdiagnosis as a neoplasm or ischemia. AP shows trans‑osseous venous channels connecting dural sinuses to epicranial varices; CT characterizes bony defects, and MRI depicts venous communication.