Case History

A 39-year-old man was found down on the street. His friends said that he complained of a headache and vomited before losing consciousness. He had a seizure 1 month ago but did not seek medical evaluation.

Diagnosis: Arteriovenous Malformation

Image 3.6A: Axial CT image demonstrates a left occipital lobe hemorrhage and intraventricular blood. Images 3.6B and 3.6C: Axial T2-weighted image demonstrates flow voids in the left occipital lobe typical for an AVM, and MR angiogram demonstrates the AVM (red arrow). Image 3.6D: Gross pathology of AVM (image credit The Armed Forces Institute of Pathology).

Introduction

  Arteriovenous malformations (AVMs) are collections of vessels composed of one or more enlarged feeding arteries that then drain into enlarged veins without an intervening capillary network. The veins then drain into the main venous system of the brain. They are considered congenital abnormalities, though they may enlarge over time.

  There are two types of AVMs. Compact AVMs are sharply demarcated from the adjacent brain parenchyma with tightly woven vessels. In contrast, diffuse AVMs have neural tissue intermixed and lack clear borders.

  AVMs are the most common symptomatic vascular malformations in the CNS. The vast majority are solitary, and multiple AVMs are associated with hereditary syndromes such as hereditary hemorrhagic telangiectasia.

Clinical Presentation

  They can present with seizures, frank hemorrhage and severe headaches from rupture, neurological symptoms due to local mass effect, and symptoms of elevated intracranial pressure. Less commonly, patients develop slowly progressive neurological deficits.

  They are often clinically silent and found incidentally on scans done for other reasons.

  Spinal AVMs are uncommon, but are a potentially treatable cause of progressive myelopathy. They can be located anywhere in the spinal canal (intramedullary, intradural, dural, or extradural). They typically occur in middle-aged patients with progressive weakness, sensory deficits, and bladder incontinence. There may be periods of abrupt worsening if there is hemorrhage in the spinal cord. Abrupt worsening may also occur during exercise or changes in posture.

Radiographic Appearance

  On CT scans, engorged, hyperdense draining veins can be seen in large AVMs.

Images 3.6E and 3.6F: Axial CT images demonstrate enlarged, hyperdense vessels in the right frontal lobe due to an AVM.

  AVMs are better visualized on MRI. On T2-weighted images, the abnormal vessels appear as multiple dark flow voids within the brain parenchyma. The surrounding brain is often atrophic and gliotic, as blood supply is preferentially drained from the brain to the AVM. Increased flow may lead to aneurysms of both the arteries and the veins. There is avid enhancement with the administration of contrast.

  Catheter angiography provides the most detailed anatomical view. The feeding arteries, nidus of the AVM, and draining veins are best visualized on angiography. The AVM appears as a dense mass, and dilated draining veins can be seen in the arterial phase. The appearance has been likened to a “bag of worms.”

  Less than 15% of AVMs are located infratentorially. With spinal AVMs, an MRI may reveal the diagnosis. As within the brain, the abnormal vessels appear as multiple dark flow voids. There is often intrinsic hyperintensity of the spinal cord. Spinal angiograms best reveal the anatomy of the lesion.

Treatment

  Symptomatic AVMs are treated with a combination of open surgical ligation or resection, endovascular embolization, and radiation. Compact AVMs are more amenable to surgical resection compared to diffuse AVMs.

Images 3.6G and 3.6H: Postcontrast axial T1-weighted images demonstrate contrast within the vessels of an AVM.

Images 3.6I–3.6K: Catheter angiogram demonstrates an AVM originating from a branch of the MCA. The “bag of worms” appearance is shown.

Images 3.6L and 3.6M: Sagittal and axial T2-weighted images demonstrate multiple flow voids in the lumbar spine due to an AVM. Image 3.6N: The AVM is visualized on spinal angiogram.

Images 3.6O and 3.6P: Hematoxylin and eosin (H&E) stain and brain section demonstrate the findings of an AVM.

Image 3.6Q: Intraoperative picture of an AVM resection.

  Ruptured AVMs have an annual rebleeding risk of approximately 5%. Unruptured AVMs have a much lower bleeding risk of approximately 2% to 3% annually. Older patients have an increased risk of rupture. The ARUBA trial found that conservative management of unruptured AVMs was superior to interventional approaches over a 33-month period, though there were multiple criticisms of the study design and interpretation.

References

1.  Mohr JP, Parides MK, Stapf C, et al. Medical management with or without interventional therapy for unruptured brain arteriovenous malformations (ARUBA): a multicentre, non-blinded, randomised trial. Lancet. February 2014;383(9917):614–621.

2.  Kim H, Al-Shahi Salman R, McCulloch CE, Stapf C, Young WL, MARS Coinvestigators. Untreated brain arteriovenous malformation: patient-level meta-analysis of hemorrhage predictors. Neurology. August 2014;83(7):590–597.

3.  Cohen-Gadol A, Conger A, Kulwin C, Lawton M. Diagnosis and evaluation of intracranial arteriovenous malformations. Surg Neurol Int. 2015;6:76.

4.  Lawton MT, Kim H, McCulloch CE, Mikhak B, Young WL. A Supplementary grading scale for selecting patients with brain arteriovenous malformations for surgery. Neurosurgery. April 2010;66(4):702–713.