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Segmental arterial mediolysis with mesangial cell hyperplasia; A review with supplementary comments concerning its pathogenesis

Richard E Slavin and Pall S Leifsson

Background: Segmental arterial mediolysis (SAM) a rare arteriopathy causing massive bleeding or ischemic symptoms, is suspected of representing a vascular disease of the peripheral sympathetic nervous system. It is initiated by the supra physiological release of norepinephrine from the efferent branches of the peripheral sympathetic nerves that innervate the large and medial sized muscular arteries targeted in SAM. Recognized stimuli for this response are iatrogenic sympathomimetic agonists and some B-2 agonists. However, these stimuli were not always apparent in published cases of SAM casting doubt on this hypothesis. Methods and findings: SAM, reported in kidneys of slaughtered pigs, was believed to represent a dysfunctional development in a fight and flight response. Additionally some stenotic renal arteries described in cases of pheochromocytomas reportedly were caused by arterial spasm and fibromuscular dysplasia changes found in the evolution of SAM. Varying degrees of mesangial cell hyperplasia accompanied SAM in swine, dog and scattered human cases of SAM. Segmental sclerosis of glomerular loops accompanied the mesangial cell hyperplasia in a few cases of SAM. The hyperplasia was not extensive so that its role in regulating blood flow and urine volume through glomerular capillaries was probably inconsequential. It represented a collateral lesion created by SAM’s norepinephrine driven pathogenesis. Conclusion: These findings provide indirect evidence that SAM additionally may be initiated by conditions causing the adrenal medulla to release supra physiologic levels of circulating norepinephrine. Supra physiologic release of norepinephrine from the peripheral sympathetic nerves also can cause mesangial hyperplasia that can be accompanied with segmental glomerular loop sclerosis-making it another precursor lesion of focal segmental glomerulosclerosis.