<p>Pathophysiological mechanisms underlying hematoma expansion in spontaneous intracerebral hemorrhage (ICH) remain poorly understood, and most data are derived from postmortem studies or serial neuroimaging studies performed over hours to days from onset. Our unique case report of a hypertensive ICH serendipitously captured by serial CT provides valuable in vivo data from the very onset of hematoma formation in an aging individual. A 76-year-old hypertensive man underwent elective carotid CT angiography to evaluate a previously known asymptomatic right carotid stenosis. During scanning, he developed severe right hemispheric neurological deficit signs. Immediate rescanning and subsequent follow-up imaging revealed the hyperacute evolution of a right putaminal ICH. We co-registered four scans (from 00 h:00 min, 00 h:06 min, 00 h:21 min, and 24 h:58 min) to a common template in 3D and made volumetric measurements of the growing hematoma also assessing the spatial relationship of expansion with the sources of bleed seen as contrast extravasation (“spot signs”). We found that spot signs appeared on the periphery of the initial hematoma, and further expansion was seen in the directions determined by these spot signs. Most of the final ICH volume developed in the first 20 min post-onset, highlighting the hyperacute nature of hematoma growth. Our findings support the hypothesis that hematoma expansion in hypertensive ICH, particularly in aging individuals, results from multiple sources of bleeding due to a cascade of secondary vessel ruptures with eccentric expansion rather than a single source and continuous bleeding with concentric expansion reflecting the global fragility of the cerebral vasculature. The therapeutic time window for hematoma expansion prevention is very narrow.</p>