A case of aplastic or twig-like middle cerebral artery associated with a ruptured A1 aneurysm at the origin of the anomalous collateral artery

Abstract

A 60-year-old woman with a severe headache and decrease in consciousness, who had been diagnosed with an asymptomatic right middle cerebral artery (MCA) stenosis on magnetic resonance angiography (MRA) at another hospital 7 years ago, was transferred to our hospital. Head computed tomography (CT) showed a diffuse subarachnoid hemorrhage and an intracerebral hematoma in the right mediobasal frontal lobe. Subsequent CT and digital subtraction angiograms revealed a ruptured small aneurysm at the origin of an anomalous collateral artery with twig-like networks that extended from the right A1 segment to the distal end of the M1 segment, bypassing the missing main trunk of the proximal M1 segment of the right MCA. The aneurysm was successfully treated with coil embolization. Recently, Shin et al. described this kind of MCA anomaly as a subtype of aplastic or twig-like MCA, which was named as “twig-like networks of an anomalous collateral artery”. To our knowledge, only six cases of this type of anomaly associated with A1 aneurysm at the origin of the collateral artery have been reported including our case so far. Even though the size of all the aneurysms was small (≤5 mm), five of them (83%) ruptured. These data may indicate the vulnerability of this type of flow-related aneurysms to rupture, probably due to hemodynamic stress and the fragile nature of their immature arterial walls. To prevent such devastating complications, early surgical or endovascular intervention might be justified for these aneurysms, even for those of a small size without symptom.