Progressive Unilateral Moyamoya-like Vasculopathy After Head Trauma with Chronic Subdural Hematoma: A Case Demonstrating the Utility of Anterior Circulation Basi-Parallel Anatomical Scanning

<b>Background</b>: Moyamoya syndrome is a moyamoya-like cerebrovascular condition associated with an identifiable underlying condition. Although head trauma has historically been considered a possible contributing factor, it is currently excluded from the Japanese diagnostic criteria. We report a rare case of progressive unilateral moyamoya-like vasculopathy that developed on the ipsilateral chronic subdural hematoma (CSDH) following head trauma, with a decade-long imaging follow-up. Anterior circulation basi-parallel anatomical scanning (BPAS) provided unique insights into the progressive vessel narrowing beyond the vascular lumen, suggesting its potential utility in evaluating such rare vasculopathies. <b>Case Presentation</b>: A 40-year-old man developed a left-sided CSDH after head trauma and underwent burr hole drainage. Although his symptoms resolved, serial magnetic resonance angiography (MRA) over the subsequent 10 years revealed progressive stenosis of the left middle cerebral artery (MCA), ultimately culminating in an occlusion-like appearance. BPAS revealed moyamoya-like collateral vessels in the same hemisphere, a significant reduction in the outer diameter of the left MCA, supporting the presence of structural arterial wall changes that were not apparent on conventional MRA. Single-photon emission computed tomography revealed mildly reduced cerebral blood flow on the affected side, with a difference of less than 5% compared to non-affected side. He remained neurologically non-symptomatic, with no history of transient ischemic attacks or overt ischemic stroke. <b>Conclusions</b>: This case highlights a rare clinical course of progressive ipsilateral moyamoya-like vascular changes following head trauma and burr-hole drainage for CSDH, potentially indicating an association between head trauma, CSDH, and subsequent moyamoya-like collateral vessel development, warranting further investigation. The use of the anterior circulation BPAS contributed to the detection of structural arterial changes that were not apparent on conventional MRA, suggesting its potential utility in evaluating such vascular abnormalities.