* Ultrasound Division, ASL Roma B, Rome, Italy.
** Reparto di ostetricia e ginecologia, Ospedale Fatebenefratelli San Pietro Rome, Italy.
*** Ultrasound Division, Ceprano Hospital, Ceprano, Italy.
The middle cerebral artery (MCA) originates at the bifurcation of the ICA (internal carotid artery) as the larger and more direct branch. It is divided into four segments; M1 is the horizontal segment, M2 is the insular segment, M3 is the opercular segment and M4 are the cortical branches also known as the M4 segments [Image 1].
At the high point of the border between the insula and the frontal cortex, the MCA usually bifurcates in the superior and inferior trunks.
Normally, the middle cerebral artery courses for an approximately 1.5 cm from its origin before it bifurcates. The bifurcation which occurs closer than 1.5 cm from the MCA origin leads to early bifurcation. This is considered a normal variant and should be differentiated from a duplicated middle cerebral artery, in which an extra branch of the middle cerebral artery arises from the internal carotid artery prior to its terminal bifurcation and runs parallel to the main M1 segment.
Other congenital anomalies of the MCA are hypoplasia and aplasia, accessory MCA, partial duplication or fenestrated MCA, anomalous origin of MCA branches and a single non-bifurcating MCA trunk.
Due to an increased hemodynamic stress, congenital anomalies of the intracranial arteries predispose to the formation of saccular aneurysms. The presence of anatomical variations of the MCA can be detected later in life by transcranial Doppler scan and mistaken for abnormal findings and may affect decision making process regarding the therapy of the patients with acute stroke. MCA variations are found incidentally on cranial magnetic resonance angiography (MRA).
Image 1: Image shows M1, M2 and M3 segments of the middle cerebral artery.
The following case presents some images of bilateral early bifurcation of MCA in a fetus in the third trimester. The patient was monitored at term for a decreased amount of the amniotic fluid (AFI 7 cm). Right MCA was better visualized at 36 weeks. At 37 weeks the fetus had changed position and the left MCA could be scanned optimally. A cesarean section was performed for dystocia and a healthy baby was born at 39 weeks.
Images 2,3: 36 weeks, right middle cerebral artery with bifurcation.
Images 4,5: 37 weeks, left middle cerebral artery with bifurcation.
Image 6: Power Doppler of the middle cerebral artery.
Video: 36 weeks, bifurcated right middle cerebral artery.
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