A 54-year-old Asian female presented to the hospital with a gradual onset headache, binocular diplopia and chest tightness. Her medical history included hypertension, hyperlipidemia and previous hepatitis B. CT and MRI angiography of the head and neck identified a right M1 branch of the middle cerebral artery (MCA) occlusion with numerous collaterals concerning for moyamoya disease given her ethnicity (Figure 1A and B). She was referred to the neurovascular surgery service and prescribed daily aspirin. Her diplopia self-resolved within 7 days and was attributed to a partial fourth nerve palsy. Digital subtraction angiography found no occlusion of the right MCA but identified its origin arising from the anterior cerebral artery (ACA) (Figure 2). There was additionally no evidence of moyamoya disease or moyamoya syndrome.

Figure 1.

CT angiography of the reported right M1 segment of the middle cerebral artery (MCA) occlusion and an artery originating from the right anterior cerebral artery (ACA). Axial (A) and coronal (B) slices are depicted. The white arrow demonstrates the reported MCA occlusion and the yellow arrow demonstrates the additional vessel off the right ACA.

Figure 2.

Digital subtraction angiography with 3D reconstruction from contrast injection into the right internal carotid artery (ICA), anterior-posterior view. The yellow circle encompasses the “stump” off the terminal right ICA. The yellow arrow identifies the origin of the right M1 segment of the middle cerebral artery off the right anterior cerebral artery.

The MCA is one of the most complex cerebral arteries arising from the internal carotid artery (ICA), supplying the lateral cortical surfaces of the brain including eloquent areas (e.g., primary motor and somatosensory cortices) and nearly all of the basal ganglia. Around day 28 of prenatal development, the ICA divides into a caudal and cranial branch where the ACA is considered a direct continuation of the cranial branch. By day 39–41, the MCA becomes a prominent stem with plexiform arteries that supply the striatum ^{Reference Uchiyama1} Interruption during the fusion and regression of these plexiform arterial twigs may result in anomalies including an accessory MCA, duplicated MCA, duplicated origin of the MCA and fenestration ^{Reference Crompton2–Reference Gailloud, Albayram and Fasel7}

The incidence of an accessory MCA is between 0.3% and 4% ^{Reference Komiyama, Nakajima and Nishikawa8} It was first described in 1962 by Crompton ^{Reference Crompton2} as a vessel passing into the Sylvian fissure with the MCA and later refined by Teal et al. (1973) ^{Reference Teal, Rumbaugh and Bergeron3} as an MCA origin arising from the ACA often near the anterior communicating artery. Theories regarding its development have been limited. One theory postulates that this anomaly represents a hypertrophied recurrent artery of Heubner ^{Reference Handa, Shimizu and Matsuda9} (RAC) that normally originates at the A1–A2 junction of the ACA. This theory was disputed by Teal et al. ^{Reference Teal, Rumbaugh and Bergeron3} who demonstrated the presence of the RAC in conjunction with the accessory MCA and suggested that the accessory MCA courses lateral to the RAC and sends cortical branches to areas normally supplied by the MCA.

We present a case of an anomalous origin of the MCA from the ACA, without associated accessory or duplicated MCA. To our knowledge, only one other case has been reported. ^{Reference Matanov, Sirakov and Sirakov10} In our case, there is evidence of a “stump” off the terminal ICA (Figure 2). Matanov et al. (2022) ^{Reference Matanov, Sirakov and Sirakov10} similarly the identified presence of this “stump”; thus, it is possible this represents a remnant of the traditional origin of the MCA off the ICA that did not normally develop versus a terminal ICA aneurysm. Understanding the anatomical variants of the MCA is critical to perform safe and successful endovascular procedures, including endovascular thrombectomy for acute ischemic stroke. In the present case, the “stump” requires longitudinal follow-up, and if an aneurysm develops in the right MCA territory, treatment should be considered given the complexity and tortuosity of the anomalous origin of the MCA.