SUMMARY Tomogrephic images of cerebral blood flow (CBF) and oxygen extraction fraction (OEF) using the U O continuous inhalation technique, and positron emission tomography, were obtained from a patient with cerebral ischemia distal to an occluded left internal carotid artery. There was a focal mismatch between CBF and oxygen metabolism in the brain supplied by tbe middle cerebral artery where CBF was decreased and OEF increased ("misery-perfusion syndrome" as opposed to "luxury-perfusioa syndrome"). These abnormalities were most marked in tbe parieto-ocdpital watershed area. After left superficial temporal to middle cerebral artery anastomosis, the clinical attacks ceased and a repeat study did not demonstrate tbe prerious CBF and OEF abnormalities. This suggests that this pattern of abnormalities indicates potential liable tissue. The concept of "mlsery-perfuslon" may be of some importance In tbe patbophysiological mechanisms of hemodynamic cerebral ischemia and serve as a rational basis for rerascularization procedures.

Endovascular coil embolization seems to be a reliable technique, with good anatomic and clinical results, that provides protection against rebleeding of ruptured aneurysms.

A xenon-133 method was used to measure cerebral blood flow (CBF) before and after cerebrospinal fluid (CSF) removal in patients with normal pressure hydrocephalus (NPH). Preliminary results suggested that shunting should be performed on patients whose CBF increased after CSF removal. There was a significant increase in CBF in patients with NPH, which was confirmed by the favorable outcome of 88% of patients shunted. The majority of patients with senile and presenile dementia showed a decrease or no change in CBF after CSF removal. It is suggested that although changes in CBF and clinical symptoms of NPH may have the same cause, i.e., changes in the cerebral intraparenchymal pressure, there is no simple direct relation between these two events. The mechanism underlying the loss of autoregulation observed in NPH is also discussed. (Stroke 1987;18:1074-1080)

To evaluate the long-term results of endovascular treatment with particles in the management of thoracic intramedullary arteriovenous malformations (AVMs), the authors retrospectively reviewed the angiographic and clinical findings in 35 patients. Follow-up was 1-15 years (mean, 6 years) in 28 patients and 6-10 months (mean, 7 months) in seven. A total of 158 embolization procedures were performed in 35 patients. Revascularization occurred frequently, necessitating multiple endovascular sessions. Long-term clinical evaluation showed clinical improvement, compared with the initial status before treatment, in 63% of the patients. Clinical aggravation due to embolization was observed in seven patients (20%) after 12 of the 158 endovascular sessions (8%). These results are better than those reported after surgery and indicate that embolization with particles is an efficient and safe tool in the treatment of thoracic intramedullary AVMs.

SUMMARY Twelve patients, eleven with a carotid obstruction and one with an occlusion of the middle cerebral artery, were studied before and after a successful unilateral extra-intracranial arterial by-pass, (EIAB) using PET and the 15-0 steady-state technique to measure regional cerebral blood flow (CBF), oxygen extraction fraction and oxygen metabolic rate (CMRO 2 ). In the whole group of patients, both CBF and CMRO, increased significantly on both cerebral hemispheres after EIAB, returning toward control levels defined in age-matched subjects. Mean oxygen extraction fraction, on the other hand, was not affected. Individually, three different effects of EIAB emerged: 1) Alleviation of a state of long standing unilateral "misery-perfusion", as reported earlier; 2) parallel increase of CBF and CMRO2 bilaterally, which appeared due to improvement of a hemodynamic depression of metabolism, the precise mechanism of which remains obscure; 3) Complex, unexpected changes in the CBF-CMRO 2 couple again resulting in increases in CMRO 2 . This metabolic improvement afforded by EIAB in our patients has not been reported before; it suggests that long-standing hemodynamic failure may induce a metabolic depression that is still potentially reversible by surgical revascularization. Stroke Vol 16, No 4, 1985 THE CONTINUOUS OXYGEN 15 INHALATION METHOD provides a regional measurement of the cerebral blood flow (CBF) and oxygen metabolic rate (CMRO,). Earlier semi-quantitative studies carried out by this method 1 -2 showed the disappearance, after an extra-intracranial by-pass operation (EIAB), of two different patterns of focal functional anomaly. The first one, termed misery-perfusion, consists of a lowered CBF and an increased oxygen extraction fraction (OEF) downstream from a carotid occlusion. This pattern reflects the relative maintenance of the CMRO, and was interpreted as evidence of a drop in the cerebral perfusion pressure to a point beyond the lower threshold of CBF auto-regulation. For the second type, involving a reduced CBF with no rise in the OEF, no satisfactory pathophysiological interpretation was put forward. 2However in these semi-quantitative studies it was possible neither to measure the CMRO, nor to detect bilateral effects of the EIAB, both of which objectives form the centre of present work. Patients and MethodsThe study involved 12 consecutive patients in whom the permeability of the EIAB was verified. One preoperative study was an isolated CBF measurement (case No. 3). Eleven of these patients suffered from internal carotid artery (ICA) obstruction and the last a middle cerebral artery (MCA) occlusion. Mean age was 56 ± 9.3 years.Individual clinical, angiographic and CT Scan data Received July 16, 1984; revision #1 accepted December 7, 1984. are summed up in table 1. The advisability of EIAB was judged on the basis of clinical and angiographic criteria, independently of pre-operative PET results. Clinical signs of "hemodynamic" ischemia was the deciding factor in 5 cases (patients No. 5,6,9,11,12) ...