Neuroimaging in the Evaluation of Epilepsy
Neuroimaging in the Evaluation of Epilepsy
Cavernous angiomas (CAs) are congenital or acquired clusters of dilated sinusoidal vascular channels lined by a single layer of endothelium, without intermixed normal brain. CAs contain blood products of different ages, calcification, and occasionally gliosis. CAs appear as nonspecific high-density regions on CT, sometimes with faint postcontrast enhancement. Angiographically, no feeding arteries are seen, although occasionally an early filling vein or subtle blush may be visualized.
MRI has provided increased sensitivity to visualizing these malformations (Fig. 6). The heterogenous appearance of the core or internal part of a CA results from the presence of blood products at different ages of degradation. On T2WI, both acute and chronic blood products (i.e., oxyhemoglobin, deoxyhemoglobin, and hemosiderin) appear hypointense and subacute blood products (i.e., methemoglobin) appear hyperintense. The heterogenous appearance of the core has been likened to the appearance of a kernel of popped popcorn.
(Enlarge Image)
Figure 6.
Cavernous angioma. A 58-year-old right-handed man with partial complex seizures with occasional secondary generalization. (A,B) Coronal and axial T2-weighted magnetic resonance imaging (MRI) shows a well circumscribed lesion in the right inferior temporal lobe. The internal contents of the lesion appear heterogenous (areas of T2 hyper- and hypointensity), due to blood products of varying age. The lesion is surrounded by a confluent rim of T2 hypointensity due to hemosiderin. (C) Axial gradient echo MRI shows susceptibility artifact consistent with blood products.
The outer rim of the cavernous malformation is T2 hypointense due to chronic blood products at the interface between the CA and surrounding brain parenchyma. GRE or SWI sequences are highly sensitive for detecting CAs, though the intrinsic "blooming artifact" associated with these sequences can actually obscure the smaller structural features of the malformation. Edema and mass effect are not seen with CAs, except in the setting of acute hemorrhage.
These lesions usually do not produce life-threatening hemorrhages, though hemorrhage into and beyond a CA can occur. The effects of a CA primarily result from the location of the lesion. Overall, 35–70% of patients with CA present with seizures. Approximately 40% of these individuals progress to medically refractory epilepsy. A recent systematic literature review revealed that in the setting of a single cavernoma and consistent electroclinical seizures, up to 75% of patients become seizure free after lesion removal. In the same review, the most important predictors of good postoperative seizure control were found to be achievement of a gross total resection and early intervention. In addition, some groups have reported improved seizure outcomes with a more extensive resection including removal of the hemosiderin ring.
Cavernous Angiomas
Cavernous angiomas (CAs) are congenital or acquired clusters of dilated sinusoidal vascular channels lined by a single layer of endothelium, without intermixed normal brain. CAs contain blood products of different ages, calcification, and occasionally gliosis. CAs appear as nonspecific high-density regions on CT, sometimes with faint postcontrast enhancement. Angiographically, no feeding arteries are seen, although occasionally an early filling vein or subtle blush may be visualized.
MRI has provided increased sensitivity to visualizing these malformations (Fig. 6). The heterogenous appearance of the core or internal part of a CA results from the presence of blood products at different ages of degradation. On T2WI, both acute and chronic blood products (i.e., oxyhemoglobin, deoxyhemoglobin, and hemosiderin) appear hypointense and subacute blood products (i.e., methemoglobin) appear hyperintense. The heterogenous appearance of the core has been likened to the appearance of a kernel of popped popcorn.
(Enlarge Image)
Figure 6.
Cavernous angioma. A 58-year-old right-handed man with partial complex seizures with occasional secondary generalization. (A,B) Coronal and axial T2-weighted magnetic resonance imaging (MRI) shows a well circumscribed lesion in the right inferior temporal lobe. The internal contents of the lesion appear heterogenous (areas of T2 hyper- and hypointensity), due to blood products of varying age. The lesion is surrounded by a confluent rim of T2 hypointensity due to hemosiderin. (C) Axial gradient echo MRI shows susceptibility artifact consistent with blood products.
The outer rim of the cavernous malformation is T2 hypointense due to chronic blood products at the interface between the CA and surrounding brain parenchyma. GRE or SWI sequences are highly sensitive for detecting CAs, though the intrinsic "blooming artifact" associated with these sequences can actually obscure the smaller structural features of the malformation. Edema and mass effect are not seen with CAs, except in the setting of acute hemorrhage.
These lesions usually do not produce life-threatening hemorrhages, though hemorrhage into and beyond a CA can occur. The effects of a CA primarily result from the location of the lesion. Overall, 35–70% of patients with CA present with seizures. Approximately 40% of these individuals progress to medically refractory epilepsy. A recent systematic literature review revealed that in the setting of a single cavernoma and consistent electroclinical seizures, up to 75% of patients become seizure free after lesion removal. In the same review, the most important predictors of good postoperative seizure control were found to be achievement of a gross total resection and early intervention. In addition, some groups have reported improved seizure outcomes with a more extensive resection including removal of the hemosiderin ring.