Specific Imaging Findings

Cerebral arteriovenous malformations (AVMs) typically present with intracranial, primarily parenchymal, hemorrhage. In most cases a small iso- or slightly hyperdense nodular or tubular defect along the periphery of hemorrhage may be seen on non-enhanced CT, with enhancement on post-contrast images. AVMs without hemorrhage may show irregular hyperdense to calcified areas with contrast enhancement on CT. MRI is the modality of choice for AVM detection, showing the pathognomonic tangle of serpiginous flow-voids, also named “bag of worms”, which is best seen on T2-weighted images. The abnormal flow-voids are typically present adjacent to the hematoma in ruptured AVMs. AVM nidus commonly also enhances with contrast. CTA shows enlarged feeding arteries, the nidus, and draining veins. Routine 3D TOF MRA may demonstrate large feeders, while MR venograms better depict the nidus and draining veins. Findings associated with the risk of future hemorrhage include evidence of previous bleed, intranidal aneurysms, venous stenosis, deep venous drainage, and deep nidus location. Secondary effects of brain AVMs that lead to nonhemorrhagic neurologic deficits include edema from venous congestion (due to stenosis and thrombosis), gliosis, arterial steal (with large shunts), and hydrocephalus (from compression).

Pertinent Clinical Information

AVMs usually become evident through intracranial hemorrhage in young adults. Other typical presentations include seizures, progressive neurological deficits, and headaches. The risk of hemorrhage depends on localization and previous bleeding, estimated at 1–4% per year. Therapeutic options comprise microsurgery (primarily for superficially located lesions), radiosurgery, and endovascular embolisation, allowing effective multidisciplinary treatment.