PMC7728105_01
Lung section with consolidated aspect
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F1
On the section surface, the right lower lobe appeared dry, red-brown, and consolidated (Figure 1).
Intracardiac recent thrombus
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F2
Other autopsy findings were cardiomegaly with dilation of the right ventricle and blood clots in the heart (Figure 2), moderate hepatomegaly, and small hemorrhagic foci in the kidneys.
Histopathology of the lungs showed (A) massive interstitial stasis, edema and hemorrhage, (B) PAS-positive depositions, and (C-F) a productive-proliferative accumulation of mononuclear, epithelial (arrows) and fibroblastic cells (arrow heads). HE staining: (A and F) x200; (C-E) x400. PAS staining: (B) x400. HE: Hematoxylin-Eosin; PAS: Periodic Acid-Schiff.
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F3
There was a massive interstitial stasis, and the alveolar spaces were replaced by edema and hemorrhage (Figure 3A), with a glycoproteinaceous exudate forming isolated PAS-positive globular condensations (Figure 3B), and a productive-proliferative accumulation of admixed mononuclear, epithelial and fibroblastic cells in most of the alveolar spaces (Figure 3C,3D,3E,3F). Overall, areas with plasma cells, macrophages and fibroblasts predominated (Figure 3C), and seemed to alternate with less dense areas filled mostly with denudated and hypertrophic epithelial-looking cells (Figure 3D) and foamy macrophages (Figure 3E). Even more dense regions were also present with a more homogenous population of whorled fibroblasts-fibrocytes forming round/ovoid structures (Masson-like bodies) (Figure 3F).
Histopathology of the lungs (continued) revealed (A) only rare thromboses, (B) loss of elastic and collagen fibers (C). However, silver staining for reticulin fibers revealed a massive proliferation of these stromal elements in the parenchyma (D and E), and spectral separation and quantification revealed (F-I) a massive increase in reticulin fibers compared to control tissue and collagen fibers. PAS staining: (A) x200. Orcein staining: (B) x200. Masson's trichrome staining: (C) x200. Silver staining: (D, E, G and H) x400. In (I), error bars represent standard deviation. ***p<0.001 on ANOVA testing. PAS: Periodic Acid-Schiff; ANOVA: Analysis of variance; RGB: Red, green, blue; COVID-19: Coronavirus disease 2019; ctrl: Control
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F4
Although there was abundant stasis and hemorrhage, there were only rare thromboses, and only in larger caliber vessels (Figure 4A). While it was not surprising that elastic fibers were almost completely missing from the remnant interstitial stroma (Figure 4B), a trichrome staining identified almost no collagen fibers in the remaining septae or in the proliferative areas (Figure 4C). Slides were subjected to multispectral unmixing in order to separate and quantify reticulin-collagen ratios, and if we compared the pattern of this lung with a control tissue, this revealed that while in control lungs collagen and reticulin participate almost in the same ratios (non-significant statistical difference), there was a significant disproportionate massive increase in reticulin (p<0.0001) with a small decrease in collagen for the COVID-19 case (Figure 4D,4E,4F,4G,4H,4I).
Histopathology of the heart revealed (A) recent intracardiac thrombosis, (B) thrombi in the small sub-epicardium vessels (C), and (D) a massive interstitial edema that obliterated the intercalated disks between the myocardial cells. The liver showed (E) moderate lymph cell infiltrate in portal spaces, and (F) enlargement (arrows) of the sub-endothelial Disse spaces. HE staining: (A, B, D and E) x200; (C and F) x400. HE: Hematoxylin-Eosin
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F5
In the heart, there was recent intracardiac thrombosis (Figure 5A), vascular leukostasis with thrombi formation mainly in the small sub-epicardium vessels (Figure 5B), and a massive interstitial edema that obliterated the intercalated disks in between the myocardial cells (Figure 5C). On occasion, scant mononuclear inflammatory cells were present, as well as petechial hemorrhages (Figure 5D). In the liver, there was a moderate lymph cell infiltrate in portal spaces (Figure 5E), passive hyperemia with an unusual enlargement of the sub-endothelial Disse spaces (Figure 5F).
Histopathology of the kidney showed (A) dystrophic epithelial lesions and tubular necrosis in proximal convolute tubules with remnant distal tubules (arrows), (B) widespread focal microthrombosis, (C and D) stasis and petechial hemorrhages. HE staining: (A and C) x200; (B and D) x400. HE: Hematoxylin-Eosin
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F6
Kidneys present dystrophic lesions and focal tubular necrosis at the level of proximal convolute tubules, with an apparent preservation of the distal tubules (Figure 6A), few hematic intratubular cylinders, vascular stasis and widespread focal microthrombosis (Figure 6B). In the renal medulla, stasis and petechial hemorrhages were frequent (Figure 6C and 6D).
Immunohistochemistry in the lungs showed (A) alpha-SMA-positive myofibroblasts were present mainly in the thickened alveolar spaces, with most of the cells proliferating in the alveolar spaces being (B) CD68-positive macrophages, and (C) CD3-positive T-cells, with a only a few (D) CD20-positive B-cells. (A-D) images: x400. alpha-SMA: Alpha-smooth muscle actin; CD: Cluster of differentiation
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F7
Despite the dense cellular proliferations, alpha-smooth muscle actin (alpha-SMA)-positive myofibroblasts were present mainly in the thickened alveolar spaces (Figure 7A), and most of the cells proliferating in the alveolar spaces were cluster of differentiation 68 (CD68)-positive macrophages (Figure 7B) and T-lymphocytes (Figure 7C), with only very rare B-lymphocytes (Figure 7D).
Immunohistochemistry in the lungs (continuation) also showed (A and B) extensive proliferated and thickened pneumocytes immunopositive for pan-CK AE1/AE3 and CK7, and apparent intact (C) CD31-positive endothelial cells, and (D) collagen IV-positive basement membranes. (A, B and D) images: x400; (C) image: x200. CK: Cytokeratin; CD: Cluster of differentiation
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F8
As already suggested by HE-stained slides, a staining for pan-cytokeratin (CK) AE1/AE3 or the CK7 revealed extensive proliferated, thickened and/or detached epithelial cells through the alveolar septae, even there where alveolar spaces were completely filled with the proliferative cellular areas (Figure 8A and 8B). While the overall architecture of blood vessels seems also intact even in these proliferative regions, staining for endothelial cells (CD31, Figure 8C), and basement membranes (collagen IV, Figure 8D) revealed discontinuous and fragmented vascular profiles.