Study Design and Setting

This study was conducted in the Department of Pathology at Government Medical College, Nagpur, in collaboration with the Forensic and Toxicology Department. The research period extended from December 1995 to November 1997. The study focused on the renal assessment, both gross and microscopic, in medico-legal autopsies performed at the institution.

Study Population

The study included 150 postmortem cases, comprising 93 males and 57 females, ranging in age from 1 to 85 years. The cases selected represented individuals who had suffered sudden or acute deaths. Accidental deaths were excluded due to the lack of clinical data. No selectivity criteria or consecutive case series were applied.

Ethical Considerations

Consent for the removal and examination of kidneys was obtained from the next of kin or surviving relatives in the presence of forensic experts, in accordance with ethical and legal guidelines.

Autopsy Procedure

Autopsies followed a standardized protocol based on established techniques by Otto Saphir (1958) and Ludwig (1979).

1. Inspection of the Body: External body examination was performed to identify signs of renal pathology, such as facial edema indicating potential renal failure.

2. Incision: A Y-shaped incision was made, extending bilaterally from the anterior margins of the axillae to the xiphoid process of the sternum. A longitudinal incision from the sternal notch to the symphysis pubis was also performed.

3. Abdominal Cavity Examination: After inspecting the peritoneal cavity, kidneys were exposed for detailed examination.

Kidney Removal and Gross Examination

The Virchow technique, involving organ removal one by one, was employed. After excising the upper abdominal aorta, the surrounding adipose and connective tissue of the kidneys were carefully removed. Congenital anomalies (e.g., horse-shoe kidney) and abnormalities in the renal vasculature were noted. Kidneys were dissected to reveal the cortex, medulla, pelvis, and ureters, which were opened longitudinally for inspection.

Gross renal features were recorded within six hours of removal. Parameters assessed included kidney size, weight, capsule consistency, cortical thickness, vascular integrity, and surface appearance (granularity, scars, cysts, and petechiae). The cortico-medullary ratio was evaluated, and renal vessels were examined for stenosis, thrombosis, or arteriosclerotic lesions.

Gross Morphological Examination Grading

Gross pathological findings were assessed following the criteria outlined by Rezek and Millard (1963). ¹³ Kidney atrophy was defined as one kidney weighing less than 100 g and the other weighing approximately 120 g. ¹⁴ Consistency changes, such as softening in acute inflammation or nephrosis and firmness in fibrosis or chronic venous congestion, were also examined as per Rezek and Millard (1963). ¹³

Capsular adherence was categorized as either easily stripped off in cases of edema (e.g., nephrosis or glomerulonephritis) or difficult to strip in cases of fibrosis or chronic inflammation. Cortical scars were classified by size and shape, with small scars (<0.5 cm) and large scars (0.5–5 cm) assessed for associated conditions such as pyelonephritis or arteriosclerosis. Granularity was categorized as fine (<1 mm) or coarse (1–3 mm), reflecting conditions like arteriosclerosis and chronic pyelonephritis. Hemorrhagic findings, including petechiae and larger hemorrhages, were evaluated for their association with conditions such as glomerulonephritis, hypertension, trauma, or coagulation disorders.

Histopathological Examination: ^{1, 14, 15, 16}

Kidney specimens were fixed in 10% formalin immediately after removal. Representative sections from the renal cortex, medulla, and pelvis were embedded in paraffin, sectioned at 3–4 μm thickness, and stained with hematoxylin and eosin (H&E) for routine histopathological evaluation. Special stains, including Periodic Acid-Schiff (PAS) and Masson’s trichrome, were used to highlight basement membrane changes, interstitial fibrosis, and other specific pathological features when necessary.

Histopathological examination was performed to evaluate multiple renal compartments. In the glomeruli, cellular changes such as hypercellularit and glomerulosclerosis were assessed, along with basement membrane alterations including thickening or wrinkling, and the presence of necrosis, adhesions, or capillary tuft abnormalities was noted. For the tubules, the examination focused on identifying atrophy, necrosis, or regenerative changes, as well as the presence of intratubular casts and epithelial desquamation. The interstitium was evaluated for evidence of edema, fibrosis, or infiltration by inflammatory cells, such as lymphocytes and plasma cells. Vascular lesions were also examined, with attention to arteriolar hyalinization and intimal thickening in hypertensive nephropathy, as well as fibrinoid necrosis and concentric "onion-skin" arteriolitis in cases of malignant hypertension.

Histological Examination Grading

Histological evaluation was conducted using the grading system introduced by Pirani et al. (1975), which examines four principal compartments of the kidney—glomeruli, tubules, interstitium, and vessels—with each feature scored on a scale from 0 (normal) to 4+ (severe). Chronic glomerulonephritis was analyzed following the methodologies of Cotran et al. (1996) and Rezek and Millard (1963), emphasizing glomerular sclerosis, cortical thinning, and interstitial fibrosis. Diabetic glomerulosclerosis was identified by the presence of nodular (Kimmelstiel-Wilson lesion) and diffuse glomerular alterations as described by Cohen et al. (1996) and Porter (1978). Hypertensive nephropathy was classified into benign and malignant forms per Cotran et al. (1996) and Striker et al. (1992), with evaluation of vascular hyalinization and fibrinoid necrosis. These assessments are in line with current recommendations provided by the KDIGO 2012 Clinical Practice Guidelines for the Evaluation and Management of Chronic Kidney Disease. ^{15, 16}

Evaluation of Acute and Chronic Renal Injuries

Acute tubular necrosis (ATN) was assessed using criteria established by Rezek and Millard (1963) and Porter (1978), focusing on tubular epithelial necrosis, the presence of hyaline casts, and evidence of regeneration. Tubulo-interstitial nephritis (TIN) was evaluated based on the descriptions provided by Rezek and Millard (1963), Cohen et al. (1996), and Heptinstall (1983), with considerations including interstitial edema, inflammatory infiltrates, and tubular atrophy or damage. Contemporary guidelines from KDIGO also endorse these histopathological criteria for a comprehensive evaluation of both acute and chronic renal pathologies. ^{15, 16}

Diagnostic Focus

Histological features were correlated with gross findings to diagnose conditions such as glomerulonephritis, diabetic nephropathy, acute tubular necrosis, and tubulointerstitial nephritis.

Statistical Analysis

Descriptive statistics were used to summarize the morphological findings, including gross and histopathological parameters. Categorical data were expressed as percentages. The association between renal lesions and causes of death was qualitatively analyzed.

Demographic and Cause-of-Death Distribution

The study included 150 cases of medico-legal autopsies. The majority of cases (33; 22%) were in the 20–30 years age group, followed by 30–40 years (30; 20%) (Table 1). 93 cases (62%) were males.

The leading cause of death was accidents, recorded in 68 cases (45.33%), with a notable predominance in males (59 cases) compared to females (9 cases). Burns were the second most common cause, accounting for 37 cases (24.66%), primarily involving females (32 cases) compared to males (5 cases). Deaths due to unknown causes accounted for 19 cases (12.66%), with a nearly equal gender distribution. Accidents and burns accounted for the majority of deaths, particularly in younger adults, with males being more frequently involved in accidents and females in burns-related cases.

Gross Morphological Findings of Kidneys

Gross examination identified abnormalities in 66 cases (44%) and normal findings in 84 cases (56%). Table 2 presents the general findings, while Table 3 focuses on detailed surface findings.

Table 2 highlights those 66 cases (44%) showed gross abnormalities, with cysts being the most common finding (33 cases; 22%), predominantly retention cysts in older individuals. Bilateral contracted kidneys were noted in 16 cases (10.66%), and congenital anomalies such as horseshoe kidney and ectopic kidney were observed in 9 cases (6%). Rare findings included obstructive uropathy (2 cases; 1.33%), hemorrhagic kidneys (2 cases; 1.33%), and a single case of renal adenoma (0.66%).

Surface and Size Variations of Kidneys

Capsular adherence was normal in 33.33%, increased in 22.66% (indicative of fibrosis), and decreased in 44% (suggesting edema). Scars were observed in 45 cases (30%), with small scars being the most common. Cortical granularity was seen in 38 cases (25.33%), predominantly fine granularity in older individuals. Size abnormalities included bilateral contracted kidneys (16 cases; 10.66%), unilateral atrophy (1 case), and large kidneys (2 cases).

Histological Examination in 150 Cases

Histological findings were assessed in all 150 cases. Of these, 94 cases (63%) showed abnormalities, while 26 cases (17.33%) were normal indicating no underlying renal pathology. Other 22 cases (14.66%) exhibited post-mortem changes, characterized by congestion of glomeruli and vessels, denudation of tubular lining, and bacterial colonies and 8 cases (5.33%) were autolyzed, precluding detailed histological assessment (Table 3).

Table 3 outlines the histological abnormalities identified in 94 cases with abnormal findings. The most frequent lesion was acute tubular necrosis (ATN), observed in 35 cases (37.23%), including ATN without interstitial nephritis (IN), ATN with hemorrhagic IN, and ATN with chronic IN. Notably, 17 cases of ATN appeared grossly normal, highlighting the importance of histological examination. Tubulo-interstitial nephritis (TIN) was the second most commonlesion, found in 28 cases (29.78%), predominantly in chronic forms. This lesion correlated with gross abnormalities in 22 cases, while 6 cases showed no gross changes. Nephrosclerosis was identified in 18 cases (19.14%), primarily in the form of benign nephrosclerosis, with two cases showing malignant features. It was grossly abnormal in 14 cases and appeared normal in 4 cases.

Other findings included cystic changes (9 cases; 9.57%) (Figure 1), vacuolar tubular nephropathy (2 cases; 2.12%), and rare lesions such as diabetic glomerulosclerosis (1 case) and renal adenoma (1 case), both associated with gross abnormalities. The correlation between histological lesions and gross findings revealed that 28 cases appeared grossly normal but exhibited significant histological abnormalities, underscoring the diagnostic value of histopathology in detecting subclinical renal pathologies.

Table 4 highlights the correlation between histological lesions, age groups, and causes of death in the 94 abnormal cases. Acute tubular necrosis (ATN) was the most common lesion, observed in 22 cases, predominantly in younger individuals (20–40 years). Burns were the leading cause (18 cases), reflecting hypovolemic and inflammatory damage, while other cases were attributed to accidents and unknown causes. ATN with interstitial nephritis (IN) was seen in 13 cases, mostly in adults over 40 years, primarily due to burns.

Tubulo-interstitial nephritis (TIN) was identified in 28 cases, commonly in adults aged 20–60 years, and was often an incidental finding in individuals who died from accidents (17 cases). Nephrosclerosis, observed in 18 cases, was associated with older age (40–80 years) and was linked to accidents and unknown causes, reflecting chronic vascular damage.

Cystic changes were noted in 9 cases, mainly in individuals over 40 years, with causes including burns, accidents, and miscellaneous factors. Rare findings included diabetic glomerulosclerosis in a 49-year-old male who died in an accident and renal adenoma in a 55-year-old male, both identified as incidental findings.