Intracranial Arteriovenous Malformation (AVM & Spetzler-Martin Grading)

• Seen in young adults (peak presentation age 20–40 years, equal sex distribution). Unruptured AVMs present with new-onset generalized or focal seizures (most common non-hemorrhagic symptom, 50%), progressive chronic pulsatile headache, or progressive focal neurological deficits from vascular steal. Ruptured AVMs present catastrophically with sudden intracerebral hemorrhage (ICH), intraventricular hemorrhage (IVH), or subarachnoid hemorrhage (SAH).
• Caused by high-flow congenital vascular malformation characterized by a direct, abnormal communication between cerebral feeding arteries and draining veins without an intervening capillary bed:
• (1)
  The Vascular Nidus: A tangled, compact or diffuse nidus of dysplastic, high-flow vascular channels replacing normal brain parenchyma.
• (2)
  Spetzler-Martin Grading System (Predicts Surgical Morbidity/Mortality, Scores 1 to 5):
• 1.
  Size of Nidus: Small (<3 cm) = 1 point; Medium (3–6 cm) = 2 points; Large (>6 cm) = 3 points.
• 2.
  Eloquence of Adjacent Brain: Non-eloquent cortex = 0 points; Eloquent cortex (sensorimotor, language, visual, thalamus/hypothalamus, internal capsule, brainstem, cerebellar peduncles) = 1 point.
• 3.
  Deep Venous Drainage: Superficial cortical veins only = 0 points; Presence of any deep venous drainage (internal cerebral veins, basal vein of Rosenthal, straight sinus) = 1 point.

Imaging Findings

• Magnetic Resonance Imaging (Brain MRI - Nidus Architecture Gold Standard):
• –
  Hallmark 'Bag of Black Worms': Classic appearance on T2WI consisting of a tightly packed, tangled conglomerate of multiple, dilated, tortuous, serpentine vascular channels exhibiting profound signal flow voids (dark on T2WI and T1WI).
• –
  Adjacent Gliosis & Steal: Surrounding rim of T2/FLAIR hyperintensity reflecting chronic parenchymal ischemia ('vascular steal phenomenon') and gliosis.
• –
  Hemosiderin Rim: Prominent dark rim of blooming susceptibility artifact on SWI/GRE surrounding the nidus, indicating prior silent micro-hemorrhages.
• –
  Time-of-Flight MRA & Dynamic 4D MRA: Exquisitely demonstrates the early arterial-phase filling of the nidus with immediate early opacification of draining veins.
• –
  **SWI / T2* GRE: Extremely sensitive for detecting the tangled vascular nidus (serpentine flow/susceptibility effects), prior silent microhemorrhages (hemosiderin blooming**), and dystrophic vascular wall calcifications.
• –
  DWI / ADC: Unruptured AVM nidus shows no parenchymal diffusion restriction; DWI is used to detect perinidal ischemic steal infarcts or acute post-embolization/post-surgical ischemic complications.
• Digital Subtraction Angiography (Catheter DSA - Unchallenged Gold Standard):
• –
  Definitive Confirmation of Early Draining Veins: Pathognomonic hemodynamic hallmark. Demonstrates premature opacification of draining cerebral veins during the early arterial phase of the injection.
• –
  High-Risk Angioarchitectural Features (Herald AVM Rupture):
• 1.
  Associated Intranidal or Feeding Artery Aneurysms (present in 15–20%, responsible for >50% of hemorrhages).
• 2.
  Deep Venous Drainage (internal cerebral veins / Galen).
• 3.
  Venous Outflow Stenosis or Ectasia (focal variceal pouching).
• 4.
  Compact single-channel versus diffuse plexiform nidus architecture.

Differential Diagnosis

Important Points to Remember

• Diagnostic Pitfall: Confusing an AVM with a Developmental Venous Anomaly (DVA) and attempting intervention! A DVA is a benign, congenital variant of normal cerebral venous drainage ('medusa head' sign). Embolizing, resecting, or coagulating a DVA will cause catastrophic, fatal venous infarction of the normal brain drained by the collector. A true AVM has a high-flow arterialized nidus and early draining veins, whereas a DVA has normal arterial inflow and drains normal brain parenchyma. DVAs are strictly 'Do Not Touch'.
• Crucial Review Areas:
• 1.
  Exact maximum nidus diameter (<3 cm, 3–6 cm, >6 cm) to assign Spetzler-Martin size points.
• 2.
  Location relative to eloquent brain (sensorimotor strip, Broca/Wernicke areas, visual cortex, deep nuclei).
• 3.
  Draining veins: look for deep internal cerebral veins or straight sinus to determine deep venous drainage score.
• 4.
  Catheter DSA for intranidal or flow-related arterial aneurysms, which represent the immediate culprit for rupture.
• Radiologist Safe Practice & Management:
• 1.
  Multidisciplinary Neurovascular Review: Combined evaluation by neurovascular surgeon, interventional neuroradiologist, and stereotactic radiosurgeon to determine Spetzler-Martin grade and management strategy.
• 2.
  Complete Catheter Angiography (DSA): Comprehensive 6-vessel cerebral angiography with 3D rotational imaging to map all arterial feeders and identify high-risk flow aneurysms.
• 3.
  Microsurgical Resection: Gold standard treatment for low-grade Spetzler-Martin I and II AVMs; achieves complete immediate anatomical cure with low morbidity.
• 4.
  Stereotactic Radiosurgery (SRS - Gamma Knife / CyberKnife): Preferred for small (<3 cm), deep, or eloquent AVMs (e.g. thalamus, basal ganglia, brainstem); induces gradual endovascular thrombosis over 2–3 years.
• 5.
  Endovascular Embolization (Onyx / Squid): Typically utilized as a preoperative adjunct to reduce nidus size, occlude deep inaccessible feeding pedicles, or target high-risk flow aneurysms.