Middle cerebral artery (M1-segment)

At a glance

English

Middle cerebral artery (M1-segment)

Latin (TA2)

Arteria cerebri media (Pars M1)

System

Artery

Region

Head

Side

Paired, left and right

About the middle cerebral artery (m1-segment)

The middle cerebral artery is the larger of the two terminal branches of the internal carotid artery and the main supply of the lateral surface of each cerebral hemisphere. Its opening stretch, the M1 or sphenoidal segment, starts where the internal carotid divides below the anterior perforated substance and runs laterally, roughly parallel to the lesser wing of the sphenoid bone, towards the limen of the insula. It is sometimes called the horizontal segment, though in many people it slopes up, down or backwards.

The M1 segment is short but crowded with branches. From its upper surface rise the lateral lenticulostriate arteries, a row of thin vessels that plunge straight through the anterior perforated substance into the depths of the hemisphere. Small cortical branches such as the temporopolar and anterior temporal arteries may also come from it and run to the front of the temporal lobe. At its lateral end the segment usually divides into an upper and a lower trunk, or sometimes three, which continue over the insula as the M2 segment, then through the opercula (M3) to the cortical surface (M4).

Through its perforating branches the M1 segment supplies deep grey and white matter: much of the putamen and caudate nucleus, the outer globus pallidus and the upper part of the internal capsule, where motor and sensory fibres for the opposite side of the body run close together. Its downstream trunks carry blood to the lateral frontal, parietal and temporal cortex, including the motor and sensory areas for the face and arm and, in the dominant hemisphere, the main language areas.

A clot lodged in the M1 segment is one of the commonest causes of a large stroke. It can produce weakness and loss of feeling in the face and arm of the opposite side, loss of half the visual field, a gaze turned towards the damaged side, and either aphasia or neglect of one side of space depending on which hemisphere is affected. Such clots are now often removed by passing a catheter up to the artery. The lenticulostriate branches, being small end-arteries under high pressure, are a frequent site of deep bleeding and of small lacunar infarcts in people with long-standing high blood pressure.

Course and supply

Arises from

Arises from the terminal division of the internal carotid artery, below the anterior perforated substance at the medial end of the lateral sulcus.

Ends in

Ends at or near the limen of the insula by dividing into superior and inferior trunks, which continue as the insular (M2) segment.

Supplies

Through lateral lenticulostriate branches supplies the putamen, parts of the caudate and globus pallidus and the internal capsule; carries all blood onward to the middle cerebral territory of the lateral hemisphere.