Renal cortical necrosis
Renal cortical necrosis, sometimes called diffuse cortical necrosis, can be explained by the name.Renal refers to the kidneys, cortical refers to the outer layer, and necrosis refers to tissue death, so renal cortical necrosis describes the outer layer of the kidney dying—usually because of ischemia or a lack of blood flow.Normally, around 20% of the blood leaving the heart goes into the renal arteries and through cortical radial arteries to reach the renal cortex, which is where the glomeruli of the nephrons are located.And that’s a lot of blood, especially given that the kidneys are relatively smallish organs when you put them next to the brain and liver.Literally millions of glomeruli in the kidneys work to filter that large volume of blood,and they do so at a rate called the glomerular filtration rate.It’s also worth noticing that those cortical radial arteries are end arteries, meaning that they rarely anastomose with adjacent branches, and are, therefore, more susceptible to infarction—since a single blocked artery is all it takes to cause ischemia because the tissue cannot be saved by neighboring arteries.
肾皮质坏死，有时称为弥漫性皮质坏死，可由名称来解释。肾脏是指肾脏，皮质指的是外层，坏死是指组织死亡，所以肾皮质坏死是指肾脏的外层，通常是由于缺血或血液减少。正常情况下，离开心脏的大约20%的血液会进入肾动脉，通过皮质径向动脉到达肾皮质，而肾皮质是肾单位的肾小球所在的位置。那是大量的血液，特别是当你把肾脏放在大脑和肝脏的旁边时，肾脏是相对较小的器官。实际上，肾脏中有数百万的肾小球滤过大量的血液，它们以一种称为肾小球滤过率的速率进行过滤。同样值得注意的是，这些皮质的动脉是末端动脉，这意味着它们很少与相邻的分支吻合，因此，更容易发生梗死——因为单个阻塞的动脉是导致缺血的原因，因为组织不能被邻近的动脉所保护。
Some causes of reduced blood flow or a complete blockage are thrombi, which are blood clots that fill the blood vessels, and vasospasm, which is the narrowing of the blood vessel.Interestingly, renal cortical necrosis has been associated with pregnancy complications,like placental abruption—which is when the placental lining is separated from the uterus—as well as prolonged intrauterine fetal death—which is when the fetus dies and then remains dead inside the uterus—and infected abortion—which is when there's an infection of the remnants of the placenta or fetus.All of these are obviously terrible complications, and they relate back to renal cortical necrosis because they can progress to septic shock or disseminated intravascular coagulation,both conditions that can lead to the widespread formation of blood clots.So once there’s an obstruction to blood flow, tissue ischemia sets in, and it triggers inflammation in the renal cortex.
血流量减少或完全堵塞的一些原因是血栓，血栓堵塞血管，血管痉挛是血管收缩的原因。有趣的是,肾皮质坏死与怀孕相关的并发症有关,如胎盘分离，是指胎盘内衬与子宫分开，长期宫内胎儿死亡,指胎儿死亡但仍在子宫内，和感染流产,这是当有胎盘或胎儿残留物的感染。所有这些都是非常严重的并发症，它们与肾皮质坏死有关，因为它们可以进展到感染性休克或弥散性血管内凝血，这两种情况都可能导致血凝块的广泛形成。一旦血液流动受阻，组织缺血就会发生，并引发肾皮质内的炎症。
That inflammation causes fluid to leak into the interstitium of the kidney—which is the space between the cells—and triggers vasoconstriction of the afferent arterioles which bring blood to the glomeruli of the nephrons.That vasoconstriction reduces the glomerular filtration rate—which is the amount of blood that gets filtered over time.Also, some parts of the nephron that happen to be in the cortex, like the proximal tubule and the thick ascending loop of Henle, need more energy and therefore a bigger supply of blood, to carry out their job of reabsorption.Since these cells are very energy demanding, having a reduced blood supply, means that they are the first to start dying and detaching when there’s renal ischemia.The dead epithelial cells can clog up the lumen of the nephron, and cause an increase in the pressure within that nephron.Since blood likes to move from a high pressure to low pressure space whenever possible, a higher pressure inside the nephron reduces glomerular filtration rate even more.Up to this point, if the obstruction goes away and normal blood flow is recovered, the damage to the kidney cells is generally reversible, and this is also known as acute tubular necrosis.If blood flow isn't recovered, though, and the ischemia persists, then the ischemic damage eventually leads to an irreversible necrotic injury to the renal cortex.Broadly speaking, renal cortical necrosis is a type of prerenal acute kidney injury,which is a category that includes any cause of kidney injury that anatomically comes before the kidneys, like in this case a decreased blood flow in this case.
这种炎症会导致液体渗入肾间质，也就是细胞间的空隙，也会引发入球小动脉收缩，是指携带血液流向肾单位的肾小球。血管收缩会降低肾小球滤过率——这是随着时间的推移而被过滤的血液量。同样，肾单位的某些部分，如近端小管和髓袢升支，需要更多的能量，因此需要更大的血液供应，以完成重新吸收的工作。由于这些细胞的能量非常旺盛，血液供应减少，这意味着它们是第一个在肾缺血时开始死亡和分离的细胞。死亡的上皮细胞会阻塞肾管腔，导致肾内的压力增加。由于血液喜欢在可能的情况下从高压向低压力空间移动，肾单位内的高压力会使肾小球滤过率更低。到目前为止，如果梗阻消失，正常的血流恢复，肾细胞的损伤通常是可逆的，这也被称为急性肾小管坏死。如果血流量没有恢复，而缺血持续，则缺血损伤最终导致肾皮质发生不可逆转的坏死损伤。广泛地说，肾皮质坏死是一种肾前性急性肾损伤，它包括解剖上发生于肾脏之前的肾脏损伤的任何原因，如在这种情况下血液流动减少。
The decrease in blood flow leads to one of the main symptoms which is a sharp decrease
in urine output.Renal cortical necrosis makes the kidney swell up and stretches out the renal capsule, and that can cause flank pain at the costovertebral angle.The diagnosis of renal cortical necrosis is often done by getting laboratory studies in the blood and urine.The blood typically has an excess of nitrogen waste products, like BUN and creatinine, as well as other serious electrolyte and metabolic imbalances, like hyperkalemia—increased potassium levels in blood—and metabolic acidosis.The urine typically shows hematuria—blood in the urine, proteinuria—protein in the urine, and tubular cell casts which are dead tubule cells in the mold of the tubule.Since there is no blood flow to the renal cortex, imaging studies—like a contrast-enhanced CT scan—usually shows a nonenhancing renal cortex.Sometimes a very thin rim of contrast enhancement can happen, and this is known as the cortical rim sign.In a biopsy, the kidney cortex might show patchy necrosis and atrophy, whereas the renal medulla looks pretty normal.Unfortunately, by the time renal cortical necrosis is treated, the damage is usually irreversible, so the main goal is to increase blood perfusion to the renal cortex.Once kidney function is severely affected, hemodialysis may be needed.
All right, as a quick recap, renal cortical necrosis is an irreversible type of prerenal acute kidney injury caused by a sudden drop in blood perfusion to the renal cortex, and it has been associated with pregnancy complications.The reduced blood supply, due in part to the lack of anastomosis among radial end arteries,combined with the relatively high demand for blood in certain parts of the nephron like the proximal tubule and the thick ascending loop of Henle - causes ischemia to set in.
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血流量的减少导致的主要症状之一是尿量的急剧减少。肾皮质坏死使肾脏肿胀，肾小囊扩张，从而导致肋脊角腰部疼痛。肾皮质坏死的诊断通常是通过血液和尿液的实验室研究。血液中通常含有过量的氮废物，如BUN和肌酐，以及其他严重的电解质和代谢失衡，如高钾血症和代谢性酸中毒。尿通常表现为尿中血尿，蛋白尿，管型尿，是在小管模中死的管状细胞。由于没有血液流向肾皮质，成像研究——就像一种对比增强的ct扫描——通常表现为非增强的肾皮质。有时，一个非常薄的边缘增强可以发生，这就是众所周知的皮质环征。在活检中，肾皮质可能表现出片状坏死和萎缩，而肾髓质看起来很正常。不幸的是，当治疗肾皮质坏死时，损害通常是不可逆转的，所以主要的目标是增加血液灌注到肾皮质。一旦肾功能严重受损，可能需要血液透析。
好的，作为一个快速的回顾，肾皮质坏死是一种不可逆转的前急性肾损伤，是由血液灌注到肾皮质的突然下降引起的，并与怀孕并发症有关。减少的血液供应部分是由于动脉端动脉缺乏吻合口，再加上肾部某些部位对血液的需求相对较高，如近端小管和髓袢升支，导致缺血。
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