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| Year : 1999 | Volume
: 47
| Issue : 2 | Page : 112-7 |
Posterior circulation abnormalities in moyamoya disease : a radiological study.
Jayakumar PN, Vasudev MK, Srikanth SG
Department of Neuroradiology, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India.
Correspondence Address:
Department of Neuroradiology, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India.
Moyamoya disease (MMD) is an uncommon entity outside Japan. Though the clinical and radiological features are well described, involvement of the posterior circulation has not been highlighted. Out of 10 patients of MMD studied, the posterior circulation was involved in 9 (3 bilateral, 6 unilateral). The P1 segment was most commonly affected. Interestingly, no infarcts were seen in the territory of the posterior circulation in any patient. Five patients showed recent haemorrhages on scan. It was thalamic haemorrhage in four and subarachnoid in one patient. The posterior circulation is frequently involved in MMD as evident on angiography. However, ischaemic events of the posterior circulation are not frequent, as the posterior circulation acts as collateral pathway for the diseased anterior circulation till later stages of the disease.
How to cite this article:
Jayakumar P N, Vasudev M K, Srikanth S G. Posterior circulation abnormalities in moyamoya disease : a radiological study. Neurol India 1999;47:112 |
Moyamoya disease (MMD) is a well known entity.[1] Though the angiographic features have been elucidated in detail, the reports generally pertain to the anterior circulation.[2],[3],[4] Studies of the posterior circulation in MMD are very few.[5] The present study discusses the neuroradiological findings in the posterior circulation territory in MMD.
The neuroradiological records of 10 patients were studied. All the patients underwent transfemoral and serial selective internal carotid and vertebral angiography. Based on the angiograms, the changes in the anterior circulation have been classified into 5 stages.[2] The abnormalities in posterior circulation angiograms have been classified into 3 groups.[5] i) normal or slightly involved group with mild narrowing of the branches of the posterior cerebral artery (PCA), ii) moderately involved group with the enlarged abnormal vascular network irrigating the thalamus and basal ganglia and iii) severely involved group with the involvement of basilar and vertebral arteries and reduction of the abnormal vascular network. The changes in the posterior circulation and the anterior circulation were compared. The angiographic findings were compared with the findings seen in scans of infarcted brains.
There were 5 female and 5 male patients. Their ages ranged from 2 years to 40 years. There were five patients below the age of seventeen at the time of clinical presentation. In two patients, the illness had started in the paediatric age. The common clinical presentation was of motor weakness in seven patients, followed by loss of consciousness in three, aphasia in two and headache and generalised seizures in one patient each [Table I].
Out of the 20 angiograms in 10 cases of the anterior circulation studied; 5 could be grouped in stage V, 9 in stage IV, 4 in stage III and one each in stages I and II. In the posterior circulation, abnormality was seen in 9 patients. It was bilateral in 3 and unilateral in 6 cases. P2 and P3 segments were involved on 6 sides each and Pl on 8 sides [Table II]. The vertebral artery was irregular and mildly dilated in one patient. While the disease was of mild nature in 2 patients, it was of moderate degree in 4 and severe in three. Comparison of the angiographic stages of the anterior circulation to the grade of disease of the posterior circulation showed that most of the patients with moderate to severe disease of the posterior circulation were in angiographic stages IV and V of the anterior circulation. Basal moyamoya was seen in all the cases, as none of them were in stage VI [Figure 1]. The volume of the basal moyamoya correlated with the angiographic stages of the disease. However, with increasing severity (Stages IV and V), the volume of the basal moyamoya dropped [Figure 2].
The CT findings include an intense basal ganglionic blush, which was seen in 3 patients. Enhancing infarcts were seen in the frontal region in 3 patients [Figure 1]. Multiple enhancing hyperdense specks were seen in the opercular and basal ganglionic region in 3 patients. Haemorrhages were seen in 5 patients; four in the thalamus and one subarachnoid. Eight patients had evidence of atrophy on scan. Subcortical atrophy was seen in four hemispheres and cortical atrophy in two hemispheres while both cortical and subcortical atrophy was seen in seven hemispheres. Four hemispheres were normal. Atrophy could not be assessed in two hemispheres due to an acute infarct.
Infarcts on scan were predominantly in the frontal, temporal and parietal lobes. Basal ganglionic infarcts were seen in 6 hemispheres. Occipital lobe infarcts were not seen in any patient.
Moyamoya disease is a well established clinical and pathological entity.[1],[6],[7] Classically, it is characterised by progressive stenosis and occlusion of the internal carotid arteries and their major branches with the development of net-like vessels at the base of the brain.[4] While almost all the studies concentrate on the anterior circulation, there are very few studies on the posterior circulation in MMD.[5] The angiographic findings of the anterior circulation in Indian patients have been discussed earlier.[8]
Contrary to the observations on the anterior circulation, where the arterial disease is proximal, the site of disease in the posterior circulation in our study is predominantly distal (64.7%). This corroborates the observations of Miyamoto et al.[5] However, the site of exact arterial disease is not clear from that study. Interestingly, with progression of the disease in the anterior circulation, the disease of the PCA progresses distally to involve the P2 and P3 segments. In addition, with progression of the diseases of both the anterior and posterior circulations, the basal moyamoya decreases and finally completely disappears (stage VI). Infarction in the region of the territory of the PCA including the thalami has been variably reported in the literature.[3],[9],[10],[11],[12] They are nevertheless infrequent. Takeuchi et al[11] in their study of 18 cases, did not find infarct in the posterior circulation territory on CT. In the largest study of posterior circulation in MMD to date, 11 of the 82 cases studied showed infarction in the territory of the PCA.[5] There was however, no patient with thalamic infarction in any of the studies. This discrepancy could be probably due to the differences in the stages of the patients between the studies and the extensive posterior basal Moyamoya providing collateral circulation to the distal parenchyma of not only the occipital lobe but also the parietal lobes. This has also been corroborated by regional cerebral blood flow studies.[13] However, infarctions of the watershed zone in the parieto-occipital region are more frequent with progressive stenosis of the basal arteries.[5]
Intracerebral haemorrhage is an unusual presentation of MMD, seen more often in adults. Children usually present with ischaemic infarcts.[1] Intracranial haemorrhage was seen in 14 of 215 cases of MMD in an earlier review.[14] While four of our cases had thalamic haemorrhage, one patient had subarachnoid haemorrhage. This has been attributed to disruption of the internal elastic lamina and connective tissue replacing the media in the anterior choroidal artery.[15] Aneurysms of the posterior choroidal artery have also been demonstrated in an earlier study.[16] The location of the haemorrhage in the thalamus is not surprising considering the extensive hypervascularity of the basal Moyamoya and the fragility of the vessel walls.[14]
The aetiology of MMD is obscure. Involvement of cervical region of the internal carotid artery in as many as five of our patients and the vertebral artery in one of our recent cases is significant. The presence of small vessel disease in MMD in an Indian patient was recently reported for the first time.[17] While it may be interesting to consider the possibility of `arteritis' to account for the involvement of the cervical region of the internal carotid artery and small vessel disease, the exact cause remains undetermined.
Posterior circulation is an important collateral arterial route in the earlier stages of the disease. With progression of the disease, these vessels become gradually affected. With total occlusion of the posterior circulation and posterial basal Moyamoya net work, the external carotid artery, the vault Moyamoya and the orbital Moyamoya remain the only route of arterial supply to the brain.
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