Radiology Resident Case of the Week: October 24, 1996

Temporal Lobe AVM

Bao Nguyen, M.D.
Peer Review Status: Internally Peer Reviewed by Daniel Crosby, M.D.

History:
This 35-year-old, previously healthy woman presented with new onset partial complex seizures. A head CT, MRI and cerebral angiogram were obtained during the course of her medical work-up.

Etiology/Pathophysiology:
As the name implies, arteriovenous malformations (AVMs) are a comglomeration of abnormal vascular channels that shunt blood from arteries to veins without an intervening capillary network. AVMs have been likened to a vascular "bag of worms," which can cause a steal phenomena leading to ischemia and atrophy of adjacent brain.

The majority of AVMs are assymptomatic until adulthood, presenting as a progressive neurologic deficit, seizure or acute intracranial hemorrhage between the ages of 20 and 40 years. One fourth of all AVMs hemorrhage within the first 15 years of life. The anual risk of intracranial hemorrhage is believed to be 2-4%, with each episode of hemorrhage carrying a 30% risk of death and 25% likelihood of long-term morbidity.

The majority of AVMs are solitary, but a small number, roughly 2%, are multiple and usually associated with neurocutaneous disorders such as Osler-Weber-Rendu or Wyburn-Mason Syndromes. Their typical location is within the cerebral hemispheres. A minority (15%) occur in the posterior fossa.

Miscellaneous:
Thrombosed AVMs may not opacify during angiography and may only be recognized as areas of avascular mass effect or very subtle arteriovenous shunting.

Imaging:

The enhanced head CT is degraded by beam hardening artifact along the floor of the middle cranial fossa, but appears grossly unremarkable with the exception of a small focus of hyperdensity in the anterior aspect of the left temporal lobe.

The spin-echo MRI confirms the presence of a 1-2 cm intra-axial lesion in the left temporal lobe which exhibits minimal mass effect and contains multiple signal voids. There is a hint of hemosiderin staining along the periphery of the lesion (see arrow).

Both the AP and oblique left internal carotid arteriograms show a tightly packed tangle of dilated vessels associated with early shunting during the capillary phase through an enlarged draining vein.

The gross intraoperative image, displayed here with inserts from a conventional and 3D CT angiogram, was obtained after a small bleeder was cauterized.

DDX:
Small Left Temporal Lobe AVM (Arteriovenous Malformation).

The findings in this case are classic for an AVM, but occasionally a vascular tumor may be mistaken for a similar lesion.

Key References:
1. Osborn, Ann. Diagnostic Neuroradiology. 1994. Mosby. St. Louis.

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See related Provider Topics Brain and Nervous System, Brain Cancer or Cancers.

See related Patient Topics Brain and Nervous System, Brain Cancer or Cancers.

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