Cerebral hemispheres blood supply

The cerebral hemispheres and diencephalon receive blood from the anterior and posterior circulations (Figure 3.5). The cerebral cortex receives its blood supply from the three cerebral arteries the anterior and middle cerebral arteries, which are part of the anterior circulation, and the posterior cerebral artery, which is part of the posterior circulation. The diencephalon, basal gan-... 

The middle cerebral artery, which originates at the division of the internal carotid artery, passes through the lateral sulcus (Sylvian fissure) en route to the lateral convexity of the cerebral hemisphere, to which it supplies blood. The middle cerebral artery travels along the surface of the insular cortex, over the inner surface of the frontal, temporal, and parietal lobes, and appears on the lateral convexity. The posterior cerebral arteries originate at the bifurcation of the basilar artery, and each one passes around the lateral margin of the midbrain. 

The posterior cerebral artery supplies the occipital lobe and portions of the medial and inferior temporal lobe. The arterial supply of the spinal cord is derived from the vertebral arteries and the radicular arteries. The brain is supplied by the internal carotid arteries (the anterior circulation) and the vertebral arteries, which join at the pon tomedullary junction to form the basilar artery (collectively termed the posterior circulation). The brainstem is supplied by the posterior system. The medulla receives blood from branches of the vertebral arteries as well as from the spinal arteries and the posterior inferior cerebellar artery (PICA). The pons is supplied by paramedian and short circumferential branches of the basilar artery. Two major long circumferential branches are the anterior inferior cerebellar artery (AICA) and the superior cerebellar artery. The midbrain receives its arterial supply primarily from the posterior cerebral artery as well as from the basilar artery. The venous drainage of the spinal cord drains directly to the systemic circulation. By contrast, veins draining the cerebral hemispheres and brain stem drain into the dural sinuses. Cerebrospinal fluid also drains into the dural sinuses through unidirectional valves termed arachnoid villi. 

Cerebral blood flow (CBF) was monitored in the cerebral cortex of the ischemic hemisphere corresponding to the supply territory of the middle cerebral artery by laser-doppler flowmetry (DRT4, Moor Instruments, Devon, UK). To this aim, a rectangular bent laser-doppler probe was glued onto the parietal bone (2 mm posterior and 5 mm lateral from bregma) and local CBF was continuously measured from 20 min before the onset of ischemia until 10 min after reperfusion, keeping the animal under isoflurane anaesthesia. Flow values were collected every 5 min before MCAo and after reperfusion whereas data were collected at 10 min intervals during occlusion. 

While rMTT can depict changes in cerebral hemodynamics, which are due to vessel occlusion of cerebral arteries and the respective compensation mechanisms, the time to arrival of contrast (TTA) is sensitive to vessel diseases, which are more upstream of the arterial flow, most commonly high grade stenoses or occlusions of the carotid arteries. In such patients, blood flow in the hemisphere ipsilateral to the stenosis is mainly supplied by the contralateral carotid artery via the circle of Willis. Due to this detour, TTA is prolonged in the ipsilateral hemisphere (Reith et al. 1997). At the same time, rMTT may be prolonged in the ipsilateral hemisphere resulting from decreased blood flow (Dorfler et al. 2001). If TTP is calculated instead of MTT, the effect of the bolus delay cannot be separated from that of the perfusion decrease, because TTP is influenced by both rMTT and TTA. 

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