Focal recurrent hemorrhage on magnetic resonance at 0.5 tesla. An aid to the diagnosis of cryptic cerebral vascular malformations.

The MR appearance of focal recurrent hemorrhage is characteristic and highly suggestive of an underlying cryptic vascular malformation. We reviewed the MR findings in 14 cases (3 biopsy proven), 9 in the brainstem and 5 supratentorial. CT in all cases demonstrated the lesion to be hyperdense before contrast with minimal to moderate enhancement post contrast. The angiograms were negative in all 14 cases demonstrating mass effect in some but no blush or neovascularity. MR showed focal hyperintensities on both short (T1) and long (T2) TR sequences surrounded by a well-circumscribed hypointense rim particularly on the long TR sequence. Focal central hyperintensity is felt to be secondary to the presence of methemoglobin and indicates relatively recent hemorrhage. In our experience hyperintensity in a solitary hemorrhage usually resolves in 4-6 weeks. In 8 cases serial MR studies over 2-3 years demonstrated evidence of repeated hemorrhage as manifested by increases in size and persistent or new hyperintensity. The intense rim due to a short T2 did not correlate with vessels angiographically nor with calcification on the pre-contrast CT and, therefore, does not represent the vascular malformation itself but rather some portion of the hematoma, possibly the hemosiderin laden capsule. Using CT and angiography alone it is difficult to differentiate cryptic arteriovenous malformations from a neoplasm particularly in the brainstem. MR's specific configuration of focal recurrent hemorrhage can make a more definitive diagnosis at 0.5 T as well as at 1.5 T.