Highest Resolution MicroCT Scan of the Human Brainstem Reveals Putative Anatomical Basis for Infrequency of Medial Medullary Syndrome

Abstract

Posterior circulation or brainstem strokes account for approximately 25% of acute strokes, affecting arterial territories in the medial or lateral divisions of the midbrain, pons, or medulla. Out of all brainstem regions, medial medullary strokes are the rarest, making up fewer than 1% of reported posterior circulation cases. Medial Medullary Syndrome (MMS) is a clinical triad of contralateral hemiplegia, loss of fine touch / position sense, and hypoglossal palsy that may result from ischemia or hemorrhage of small perforating branches of the anterior spinal, vertebral, or basilar arteries. The relative infrequency of MMS is surprising given the prevalence of stroke in other perforator artery territories as these vessels are more susceptible to small vessel disease. Indeed, small perforator‐type vessels from other parent arteries contribute to more than 50% of all strokes in a population (e.g. lacunar branches of the middle cerebral artery and paramedian pontine branches of the basilar artery). This disparity in prevalence remains unexplained in part because clinical anatomy has been historically limited by an unfavorable ratio of fine blood vessel size to coarse MRI and CT scan resolution. Here, we capture and digitally dissect the highest‐ever‐resolution diffusible iodine‐based contrast‐enhanced CT (diceCT) scanned images of a cadaveric brainstem to map MMS arteries in never‐before‐captured detail. A cadaveric brain was fixed in formalin and stained using a 3% concentration of Lugol’s iodine (I2KI) for 12.5 weeks (refreshed every 2 weeks), before microCT scanning at 57 microns (a scale twice as fine as any previous scans). The resulting image stack was segmented in Avizo 2020.1. Results show that within the MMS anterior spinal artery territory, there are numerous, small sulcal artery branches perforating the medulla within the anterior median fissure. These branches proceed in parallel through the anteroposterior depth of the medulla as expected; however, we also identify a network of intraparenchymal, rostrocaudal anastomoses between these sulcal perforating branches. This network of intraparenchymal sulcal artery anastomoses has never been described, and may provide a significant collateral supply of oxygenated blood flow throughout the medial medulla. By ramifying deeper tissues, this anastomosis can help explain the infrequency of MMS.