Prior to this pandemic, the study neuropathologists (D.W.N. and I.H.S.) had not seen megakaryocytes in brain vessels, and we find no reference to this in the literature. A recent report showed these cells in an infarcted brain in COVID-19,
4 suggesting they could have been present in the brain circulation and entered the parenchyma during hemorrhage.
Multiple lines of evidence indicate endothelial dysfunction may contribute to severe COVID-19 illness. Lung examination demonstrates megakaryocytes,
5 and the cells have now been reported in other organs.
6 One possibility is that altered endothelial or other signaling is recruiting megakaryocytes into the circulation and somehow permitting them to pass through the lungs. Although this initial study does not investigate mechanism, it is notable that we found megakaryocytes in cortical capillaries in 33% of cases examined. Because the standard brain autopsy sections taken sampled at random only a minute portion of the cortical volume, finding these cells suggests the total burden could be considerable. By occluding flow through individual capillaries, these large cells could cause ischemic alteration in a distinct pattern, potentially resulting in an atypical form of neurologic impairment.
