Preliminary evidence for cerebral capillary shunting in adults with sickle cell anemia

Elevated flow velocities in adults with sickle cell anemia (SCA) may cause rapid erythrocyte transit through capillaries. This phenomenon could present as dural venous sinus hyperintensity on arterial spin labeling (ASL)-MRI and could be indicative of capillary shunting. Here, the prevalence of ASL venous hyperintensities and association with relevant physiology in adults with SCA was investigated. SCA (n = 46) and age-matched control (n = 16) volunteers were recruited for 3.0 T MRI. Pseudo-continuous ASL-MRI was acquired for cerebral blood flow (CBF) calculation and venous hyperintensity determination; venous signal intensity and a categorical venous score (three raters; 0 = no hyperintensity, 1 = focal hyperintensity, and 2 = diffuse hyperintensity) were recorded. Flow velocity in cervical internal carotid artery segments was determined from phase contrast data (v _enc = 40 cm/s) and whole-brain oxygen extraction fraction (OEF) was determined from T ₂-relaxation-under-spin-tagging MRI. Cerebral metabolic rate of oxygen was calculated as the product of OEF, CBF, and blood oxygen content. ASL venous hyperintensities were significantly (p < 0.001) more prevalent in SCA (65%) relative to control (6%) participants and were associated with elevated flow velocities (p = 0.03). CBF (p < 0.001), but not OEF, increased with increasing hyperintensity score. Prospective trials that evaluate this construct as a possible marker of impaired oxygen delivery and stroke risk may be warranted.