AOVM（Angiographically Occult Vascular Malformation）の症候学的特色とMRI所見

Clinical Presentations and MRI Findings of Angiographically Occult Vascular Malformations

I．はじめに

　Angiographically Occult Vascular Malformation（以下AOVM）とは，脳血管撮影によっては描出されない，脳血管奇形の総称であり，病理学的には，血栓化した脳動瀞脈奇形，静脈奇形，海綿状血管腫，capillary telangioectasiaあるいはこれらが混合したものを含むと考えられている^{2,4,9,10,13）}．これらは，CT，MRI所見のみならず，それぞれの発症年齢，発症部位，発症様式などの臨床的特徴も比較的類似していることが知られている^5）．

　AOVMは，しばしば偶発的に発見されることがあり，無症状のまま経過することも多く，出血，痙攣発作などで症候性となる頻度についてはまだ十分に解明されていない^1,8）．今回当院で経験したAOVMについて，臨床的特色とMRI所見とを検討し，それぞれの関連性について報告する．

　Various clinical features as well as MRI findings of AOVM (angiographically occult vascular malformation) were studied. Amongst our patients, since January 1988, there have been 30 cases of symptomatic AOVM (20 males, 10 females) including 3 cases with multiple lesions. The age ranged from 3 to 60 years of age, with a mean of 33.4 years. The locations of symptomatic lesions were in the cerebral hemisphere (15) , the thalamus (4) , the brain stem (8) and in the cerebellum (3). The initial presentations of these 30 cases were either by hemorrhage (18), convulsive seizure (9) or by progressive neurological deficits (3). The initial presentation was not related to the patient's age and the size of the lesion, but apparently related to the location of AOVM. Most of the lesions in the cerebral hemisphere presented seizures, but all of the lesions in the thalamus, the brain stem and the cerebellum disclosed hemorrhage as an initial presentation. In fact it was noticed that brain stem lesions tend to cause repetitive hemorrhage in a relatively short period. AOVM lesions were clearly visualized with T2-weighted MRI images, consisting of high intensity cores with surrounding low intensity rims. Most of the symptomatic lesions were partially enhanced by Gd-DTPA with varied intensity. Dynamic changes in size and enhancement pattern on MRI were occasionally seen, usually accompanied with episodes such as hemorrhage or neurological deterioration. Although AOVMs were angiographically negative some strands indicating draining veins were observed on MRI in several cases. In contrast, none of the nonsymptomatic lesions (22 lesions) demonstrated enhancement effects with Gd-DTPA.