Arteriovenous malformations (AVMs) are congenital vascular abnormalities that typically present between the ages of 20 and 40 years with spontaneous hemorrhage or, less commonly, seizure (1,2). A slight male predominance may be present among AVM patients, but not more than 3:2 (1,2). AVMs have been reported throughout the central nervous system (CNS), but they are most common in the cerebral hemispheres. Rare cases of AVM occur in familial clusters, sometimes as part of the Wyburn-Mason syndrome (3,4). Imaging of AVMs includes angiography by traditional methods as well as magnetic resonance (MR) and computed tomography (CT). In the classical setting, AVMs appear as superficial intraparenchymal tangles of large and small blood vessels with a nidus, or focal dense collection of vessels, present centrally (5). In a longitudinal study, the risk of hemorrhage in an AVM patient following diagnosis was approximately 4% per year, with a 1% annual risk of mortality (2).

Treatment for AVM comprises three approaches that may be used in combination with the goal of reducing risk of future hemorrhage. The therapeutic approach in any individual case is determined by the risk of surgical resection, as defined by the Spetzler-Martin grading scale, which awards risk for lesion size, location in an eloquent site, and the presence of deep venous drainage (6). Stereotactic radiosurgery is the least invasive modality and is effective for low-risk lesions, whereas endovascular catheter embolization is the initial treatment for high-risk cases. Surgery may be used as an initial approach in low-risk lesions but often follows reduction by one of the other modalities in high-risk cases.

The microscopic appearance of AVMs reflects their gross configuration, with disorganized arrays of individual vessels penetrating through the
brain parenchyma, each separated from each other by gliotic brain tissue (Figure 14-1). The component vessels vary in caliber and wall thickness, some with muscular arterial sides and internal elastic lamina (Figure 14-2) and others with thinner venous walls lacking smooth muscle or elastic lamina. Intermediate forms may also be seen. Variable amounts of inflammation, gliosis, and hemosiderin-laden macrophages are common in the
intervening brain tissue. Previously embolized resections contain intravascular foreign material.

Because the histologic appearance of AVM can overlap significantly with cavernous malformations (Figure 14-3), and clinical diagnoses incorporate in vivo observations (A-V shunting) that are not evident histologically, a more generic diagnosis of “vascular malformation” may be appropriate when the histology is unclear.

The age and anatomic distributions of cavernous malformations are similar to those of AVM, being most commonly diagnosed in the third through fifth decades (mean, ∼35 years) in the cerebral hemispheres (6,7). No significant sex predilections exist. Most cavernous malformation patients present with seizures, focal deficits, or headaches, but only 10% or fewer present with hemorrhage, compared with 30% to 70% for AVMs (7,8). As with AVMs, some families show a predisposition toward cavernous malformations (9). The classic appearance of cavernous malformation on magnetic resonance imaging (MRI) is of a discreet, well-circumscribed nodular mass with no significant edema and little mass effect. T2-weighted images show a mixed intensity “core” and a characteristic hypointense penumbra of hemosiderin deposition (10).

Most cavernous malformations occur sporadically and are widely considered congenital. A much smaller subset develops de novo years after cranial irradiation for a neoplastic process (10). Ironically, radiosurgery is also a common method for reducing or involuting symptomatic cavernous malformations (11).

In contrast to AVMs, cavernous malformations contain no arteriovenous shunt; thus, they are less likely to have thin-walled vessels exposed to arterial pressures and less likely to hemorrhage. The annual risk of hemorrhage in a cavernous malformation is less than 1%, a fact underscoring the importance of distinguishing them from AVMs. Only when cavernous malformations produce significant symptoms, are they resected or undergo radiosurgery. Occasional resections are performed to rule out a radiologic suspicion for a hemorrhagic neoplasm.