Magnetic resonance appearance of slow flow vascular malformations of the brainstem

Twelve patients with slow flow brain stem vascular malformations had magnetic resonance scans performed on a 1.5 Tesla scanner using T1 (TR = 400-800 ms, TE = 25 ms) and T2 (TR = 2000 ms, TE = 20, 25, 80 ms) weighted scans. Eight patients (70%) had solitary brainstem vascular malformations while 4 (30%) had multiple lesions both supra and infratentorially. Five patients had venous angiomas demonstrated by angiography and MR. There were 26 lesions seen on MR of which only 14 were identified by CT. These lesions demonstrated a specific MR image pattern indicative of subacute or chronic parenchymal hematoma. It was characterized by an iso to hyperintense central signal surrounded by a well defined thin band of low signal intensity. The central zone could appear to be single or multilocular. In multilocular lesions the hemorrhages within different cells could be of different ages. One patient did not have findings of a chronic hematoma but exhibited only low signal secondary to calcification and a venous angioma. None of these lesions had surrounding edema. Despite the variable etiologies of slow flow vascular malformations of the brainstem, their MRI manifestations seem to indicate a final common pathway of chronic hematoma. These lesions are quite distinct from MS or tumor, the usual clinical considerations in the differential diagnosis.