Immunohistochemical characterisation of probable intravascular haematopoiesis in the vasa rectae of the renal medulla in acute tubular necrosis

Acute tubular necrosis is a syndrome of physiologic and pathologic dissociation

Acute tubular necrosis (ATN) is a syndrome of intrinsic renal failure secondary to ischemic or toxic insults. The histopathologic findings of ATN are inconstant. When present, they are limited to the tubulo-interstitium and often subtle despite profound dysfunction. Experimental models of ATN in healthy animals commonly use single insults that result in extensive injury, circumstances that do not parallel the human situation. Recently, there has been a shift to more clinically relevant models using an acute insult superimposed on predisposing factors. This review discusses the complex hemodynamic interrelationships of hypoxia, tubular injury, and altered glomerular filtration, suggesting new ways to understand the pathophysiology of ATN.

Difficulties in understanding human "acute tubular necrosis": limited data and flawed animal models

This review summarizes the current understanding of the renal biopsy in "acute tubular necrosis" and the attempts to mimic this phenomenon in animal models. Paradoxically, only very limited necrosis is present in the biopsy of patients with this condition and differences in biopsies of patients with sustained and recovering renal failure cannot be clearly defined. The small amount of material examined, the variation in timing of the biopsy, the ability of the nephron to recover from sublethal injury, and the complexity of the clinical situation compound the difficulties in understanding this condition. Morphological findings in the animal studies are not equivalent to those in the human biopsy of "acute tubular necrosis," because they either have too much proximal tubular necrosis (ischemia-reflow model) or show severe injury to distal nephron segments (distal nephron model), the degree of which has not been clearly documented, as yet, in human material. The direct relevance of animal models in part may be tested by new noninvasive methods that define and quantify excreted proteins that reflect nephron injury or measure the status of renal oxygenation by radiological imaging techniques. Finally, it may be time to re-examine the morphology of "acute tubular necrosis," utilizing new techniques that illustrate induction of heat shock proteins, sublethal and apoptotic cellular injury, and alteration of gene expression.

Myocardial extramedullary hematopoiesis: a clinicopathologic study

Extramedullary hematopoiesis (EMH) after fetal development is uncommon and is most often seen in patients who have hematologic disorders. EMH unassociated with hematologic disease is rare. After the recent observation of EMH in a myocardial infarct, we sought to determine the frequency and clinicopathologic setting of EMH in myocardial tissues submitted for pathologic examination. Hematoxylin and eosin (H&E)-stained sections from 805 consecutive myocardial samples (207 surgical specimens, 598 autopsy specimens) were examined retrospectively. The presence of immature erythroid or myeloid cell clusters in intramyocardial capillaries or stroma was considered sufficient for the diagnosis of EMH. Immunoperoxidase studies confirming the nature of the hematopoietic cell infiltrate were performed in selected cases. Foci of EMH (often multiple) were identified in 15 of 207 surgical hearts (7.2%) and in 22 of 598 autopsy hearts (3.7%). Patient ages (exclusive of premature infants) ranged from 2 weeks to 73 years (median, 13 years). Twenty-four of 37 (65%) EMH-positive cases were associated with infarcts in various stages of repair (accounting for 11 of 68 [16.2%] of all infarcts in surgical specimens and 13 of 86 [15.1%] of infarcts in autopsy specimens). Acute infarcts less than 72 hours old, excluding those with acute extension, were not associated with EMH. Viral myocarditis and myocardial hypertrophy with fibrosis accounted for primary diagnoses in the nonischemic, EMH-positive surgical cases, whereas seven of nine nonischemic, EMH-positive autopsy cases involved premature or term infants with no obvious myocardial disease. Another autopsy patient had sarcoidosis with myelophthisic involvement of her bone marrow and represented one of only two cases overall in which a hematopoietic disorder was coexistent or suspected. Myocardial EMH is relatively common after myocardial infarct but is rarely encountered in normal or nonischemic myocardium. Its presence in healing but not early acute stages of infarct suggests that EMH results from inflammation- or repair-associated trophic factors, not from ischemia itself.