What does an arterial‑venous malformation (AVM) look like on lumbar magnetic resonance imaging (MRI)?

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Lumbar MRI Appearance of Arteriovenous Malformations

On lumbar MRI, an arteriovenous malformation (AVM) appears as serpentine flow voids (areas of signal loss) representing abnormal vessels on both T1- and T2-weighted sequences, often accompanied by spinal cord edema showing as T2 hyperintensity, with the intramedullary nidus appearing as a focal area of low signal intensity within the cord. 1, 2

Key MRI Features

Primary Vascular Findings

  • Serpentine flow voids: The hallmark finding consists of multiple tubular areas of signal loss (flow voids) representing enlarged, tortuous vessels surrounding or within the spinal cord, visible on T2-weighted sequences 1, 2
  • Intramedullary nidus: When the AVM is intramedullary (within the cord), the nidus appears as a focal area of low signal intensity within the spinal cord parenchyma on both T1- and T2-weighted images 1, 2
  • Prominent perimedullary vessels: Enlarged vessels are typically visible around the cord surface, appearing as flow voids on standard sequences 3, 2

Secondary Cord Changes

  • Spinal cord edema: T2 hyperintensity within the cord substance indicates edema or myelomalacia, often seen in symptomatic cases with venous congestion 3, 2, 4
  • Cord expansion: The spinal cord may appear swollen or enlarged at the level of the AVM 2, 4
  • Peripheral T2 hypointensity: A rim of low signal around areas of T2 hyperintensity may be present, reflecting venous congestion 4

Additional Findings

  • Hemosiderin deposition: Areas of signal loss on T2-weighted images may indicate prior hemorrhage, appearing as dark staining around the lesion 5, 2
  • Cord scalloping: Indentation of the cord surface may occur from enlarged epidural veins compressing the cord 3, 2

Important Distinctions by AVM Type

Intramedullary AVMs

  • The nidus is contained within the spinal cord parenchyma 1, 6
  • More commonly located in cervical or thoracic regions (84% of cases), though can occur in lumbar cord 6
  • Typically present with hemorrhage as the initial symptom 6
  • Show rapid contrast transit, indicating high-flow lesions 6

Dural Arteriovenous Fistulas

  • No intramedullary nidus component visible 1, 6
  • The fistula itself is located in the intervertebral foramen, not within the cord 6
  • 96% occur in low thoracic or lumbar regions 6
  • Present with progressive myelopathy rather than hemorrhage 6, 4
  • Show findings of venous congestive myelopathy: peripheral T2 hypointensity outlining central T2 hyperintensity in a swollen cord 4

Paravertebral AVMs with Epidural Drainage

  • Large epidural veins may be visible compressing the spinal cord 3
  • The malformation itself is outside the dura but drains into epidural venous plexus 3
  • May show cord compression without intramedullary signal abnormality 3

Critical Imaging Pitfalls

A well-defined soft tissue mass is NOT typically identified in AVMs 5—this is an important distinction from vascular tumors. The absence of a discrete mass with the presence of flow voids should raise suspicion for AVM rather than a neoplasm.

Standard MRI sequences may not show slow flow: In some cases, particularly with thrombosed or low-flow components, vessels may not appear as obvious flow voids 2

Contrast enhancement is essential: IV contrast demonstrates intense enhancement of involved vascular structures and helps differentiate the AVM from other pathology 5, 4

Recommended Imaging Protocol

  • MRI with and without IV contrast is the primary modality for initial detection and characterization of spinal AVMs 5, 1
  • Contrast-enhanced MRA has become instrumental in localizing the fistula site, particularly for dural AVFs 4
  • Flow-sensitive sequences are valuable for depicting intramedullary AVMs and differentiating nidus from old hematoma 2
  • Angiography remains the gold standard for definitive characterization of the angioarchitecture and is essential for treatment planning 5, 4

References

4
Research

Venous manifestations of spinal arteriovenous fistulas.

Neuroimaging clinics of North America, 2003

5
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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