PA27.8-17 | Renal Pathology II: Tubulointerstitial, Vascular & Neoplastic — Glossary

Multiple bilateral renal cysts developing in patients on long-term dialysis (>5–10 years); carries a significantly elevated risk (approximately 50-fold) of renal cell carcinoma.

Bacterial infection of the renal pelvis and parenchyma producing suppurative tubulointerstitial inflammation, microabscesses, and WBC casts.

Reversible acute kidney injury from ischaemic or nephrotoxic injury to renal tubular epithelial cells, characterised by cell death, granular cast obstruction, and backleak of filtrate.

A plasma metalloprotease that cleaves ultra-large von Willebrand factor multimers into smaller non-thrombotic fragments; its severe deficiency (autoantibody or hereditary) causes TTP.

Autosomal dominant polycystic kidney disease; caused by PKD1 or PKD2 mutations; characterised by progressive bilateral renal cyst enlargement leading to ESRD, with extrarenal manifestations including berry aneurysms and hepatic cysts.

Chronic tubulointerstitial disease caused by long-term NSAID or phenacetin use, producing bilateral papillary necrosis and cortical scarring.

A benign renal hamartoma composed of blood vessels, smooth muscle, and fat; sporadic or associated with tuberous sclerosis complex; fat component visible on CT.

A class of chemical carcinogens (e.g., 2-naphthylamine, benzidine) found in aniline dyes; occupational exposure in textile, rubber, and leather industries; cause urothelial carcinoma via N-hydroxylation to reactive metabolites.

Autosomal recessive polycystic kidney disease; caused by PKHD1 mutations; presents perinatally with bilateral sponge-like collecting duct cysts and obligatory congenital hepatic fibrosis.

TMA caused by dysregulation of the alternative complement pathway (CFH, factor I, MCP mutations or anti-CFH antibodies); more severe and relapsing than typical HUS; eculizumab responsive.

Passive movement of glomerular filtrate back into the peritubular interstitium through denuded tubular basement membrane in ATN, reducing effective GFR.

A saccular outpouching at arterial branch points within the Circle of Willis; present in 10–15% of ADPKD patients; rupture causes subarachnoid haemorrhage.

Ischaemic necrosis of both renal cortices (sparing the medulla), caused by prolonged vasospasm and DIC; classically complicates abruptio placentae; may lead to permanent renal failure and cortical calcification.

A radiological system (I–IV) classifying renal cysts on CT by complexity features (septa, calcifications, enhancement); guides management from reassurance (I/II) to surgical excision (III/IV).

Multiple well-defined, rounded pulmonary metastases visible on chest X-ray; characteristic of haematogenous spread of RCC via renal vein and IVC; also seen in choriocarcinoma.

A flat, high-grade, non-invasive urothelial carcinoma confined to the mucosa; appears as a red velvety patch on cystoscopy; high risk of progression to muscle-invasive disease despite lacking stromal invasion.

Proliferation of parietal epithelial cells and infiltrating monocytes in Bowman's space that compresses the glomerular tuft; the hallmark of crescentic (rapidly progressive) glomerulonephritis.

Distinctive histological feature of clear-cell RCC: delicate thin-walled vascular sinusoids forming a network between nests of clear tumour cells, resembling the pattern of chicken wire.

A rare RCC subtype (~5%) arising from intercalated cells; large pale reticulated cells with prominent cell membranes; excellent prognosis; Hale's colloidal iron stain positive.

Morphological entity characterised by coarse corticomedullary scars overlying deformed, blunted calyces, tubular atrophy, and interstitial fibrosis resulting from repeated or persistent renal infection.

The combination of haematuria, flank pain, and palpable flank mass; present together in only ~10% of RCC cases; usually indicates locally advanced disease.

The commonest RCC subtype (~75%); defined by cells with optically clear lipid-rich cytoplasm on H&E; driven by VHL loss; bright yellow-golden gross appearance.

The most common type of renal cell carcinoma, arising from proximal tubular epithelium; tumour cells have abundant cleared cytoplasm (dissolved lipid/glycogen) arranged around thin-walled vascular sinusoids.

A bile duct plate malformation associated with ARPKD, characterised by portal tract fibrosis and bile duct proliferation leading to portal hypertension without primary hepatocellular damage.

An autosomal recessive disorder of the SLC3A1/SLC7A9 dibasic amino acid transporter causing excess urinary cystine, ornithine, lysine, and arginine; cystine's low solubility results in recurrent stone formation from childhood.

Type-IV hypersensitivity reaction in the renal interstitium triggered by drugs (classically β-lactams, NSAIDs, PPIs); characterised by eosinophilic and lymphocytic interstitial infiltrate, reversible on drug withdrawal.

A monoclonal antibody targeting complement C5, blocking terminal complement activation; standard treatment for atypical HUS (complement factor H mutation), transforming its prognosis.

Presence of eosinophils in urine (detected by Hansel stain); a diagnostic clue to drug-induced allergic interstitial nephritis.

Necrosis of the arteriolar wall with infiltration of fibrin and plasma proteins, producing an intensely eosinophilic granular appearance; hallmark of malignant hypertension and necrotising vasculitis.

Concentric thickening of the intima of interlobular arteries by collagen and smooth muscle proliferation in response to chronic hypertension; contributes to progressive ischaemic nephropathy.

Non-inflammatory, non-atherosclerotic disease of medium arteries producing alternating stenoses and aneurysms (string-of-beads pattern); the commonest cause of renal artery stenosis in young women.

The concept that an entire epithelial surface (here the whole urothelium) exposed to a carcinogen undergoes malignant transformation; explains the multifocal, recurrent nature of bladder UC.

Gross appearance of the kidney in benign nephrosclerosis — bilateral shrinkage with a finely granular cortical surface reflecting alternating ischaemic scars and surviving hypertrophied nephrons.

Gross appearance of the kidney in malignant hypertension — multiple petechial cortical haemorrhages from necrotic arterioles on a relatively normal-sized kidney.

Fusion and flattening of podocyte foot processes seen only on electron microscopy; the diagnostic hallmark of minimal change disease, responsible for loss of the slit-diaphragm filtration barrier.

Histological grading system for RCC (Grades 1-4) based on nuclear size, irregularity, and nucleolar prominence; Grade 4 carries worst prognosis.

Globotriaosylceramide; the glycolipid receptor for Shiga toxin, highly expressed on glomerular endothelial and mesangial cells especially in children, explaining the renal tropism of typical HUS.

Urine casts formed by aggregation of necrotic tubular epithelial cell debris with Tamm-Horsfall protein; the morphological hallmark of ATN.

TMA clinically defined by the triad of MAHA, thrombocytopenia, and AKI; typical form is Shiga-toxin associated (children, diarrhoea prodrome); atypical form is complement dysregulation mediated.

Transcription factor that upregulates VEGF, EPO, and PDGF under hypoxia; accumulates in clear cell RCC due to VHL loss, driving angiogenesis and paraneoplastic polycythaemia.

Deposition of amorphous PAS-positive eosinophilic material (plasma proteins + basement membrane thickening) in arteriolar walls, causing luminal narrowing; the defining lesion of benign nephrosclerosis.

Dilation of the renal pelvis and calyces secondary to obstruction of urine outflow; ranges from mild pelvicaliectasis to end-stage thin-walled fluid-filled sac with minimal residual parenchyma.

Excessive urinary calcium excretion (>250 mg/day in women, >300 mg/day in men); the commonest metabolic risk factor for calcium oxalate and calcium phosphate nephrolithiasis.

The first hours-to-days of ATN in which the ischaemic or toxic insult is active; GFR begins to fall but clinical signs may be absent.

Retrograde entry of refluxed urine into the collecting ducts via compound papillae (at poles), the mechanism responsible for the polar scarring distribution in reflux nephropathy.

Complete collapse and sclerosis of a glomerular tuft due to chronic ischaemia (from arteriolar narrowing); the endpoint of nephron loss in benign nephrosclerosis.

Round, acellular, strongly PAS-positive mesangial nodules seen at the glomerular periphery in diabetic nodular glomerulosclerosis; pathognomonic of advanced diabetic nephropathy.

The established injury phase of ATN (typically 10–14 days) with oliguria, hyperkalaemia, uraemia, and maximal cast production.

The embryonic mesenchymal precursor cells of the developing kidney that, when incompletely differentiated, persist as the blastemal component of Wilms tumour.

A small, sharply demarcated focus of suppurative necrosis within renal parenchyma, formed by neutrophils destroying tubular walls; characteristic of acute pyelonephritis.

Intravascular haemolysis caused by mechanical RBC fragmentation by fibrin strands in diseased microvasculature; characterised by schistocytes on blood film and a negative Coombs test.

Urinary casts containing pigmented granular debris (myoglobin or haemoglobin) found in the urine sediment and on biopsy in acute tubular necrosis due to myoglobinuria or haemoglobinuria.

Bladder urothelial carcinoma that has invaded the muscularis propria (detrusor; T2 or higher); requires radical cystectomy ± chemotherapy; poor prognosis compared to NMIBC.

Muscle oxygen-transport protein released during rhabdomyolysis; freely filtered at the glomerulus and directly toxic to tubular epithelium; precipitates as brown casts in acidic urine.

Formation of calculi (stones) within the renal collecting system; arising when urine supersaturation with insoluble salts exceeds the capacity of natural inhibitors.

A group of autosomal recessive tubulointerstitial nephropathies caused by NPHP gene mutations; presenting with polyuria, anaemia, and medullary cysts; the commonest genetic cause of ESRD in children.

Hardening and scarring of the kidney due to vascular disease, most commonly hypertension; encompasses both benign and malignant hypertensive renal injury.

Structural or functional impairment of urine flow at any level of the urinary tract, leading to back-pressure, tubular ischaemia, and progressive renal parenchymal damage.

A benign renal epithelial tumour arising from intercalated cells of the collecting duct; mahogany-brown gross colour; central stellate scar; eosinophilic granular cells packed with mitochondria.

Concentric laminated hyperplastic intimal thickening of interlobular arteries, resembling an onion in cross-section; the classic histological feature of malignant hypertension also seen in scleroderma renal crisis.

Concentric layers of proliferating smooth muscle cells and collagen within arteriolar walls, creating a laminated onion-skin appearance; the hallmark of hyperplastic arteriolosclerosis in malignant hypertension.

Virulence factor of uropathogenic E. coli that mediates adhesion to uroepithelial receptors, facilitating ascending infection.

Ischaemic coagulative necrosis of the renal medullary papillae, commonly complicating diabetes mellitus, pyelonephritis, analgesic overuse, and sickle cell disease; sloughed papillae cause colic and a radiological filling defect.

The second most common RCC subtype (~15%); characterised by papillary architecture with foamy macrophages in stalks; associated with trisomy 7/17 and MET activation.

Concentric collagen deposition around the entire circumference of the Bowman capsule; a feature of chronic pyelonephritis that distinguishes it from glomerulonephritis-related scarring.

Extension of suppurative pyelonephritis through the renal capsule into the perirenal fat; presents with prolonged fever and flank tenderness requiring drainage.

Therapeutic plasmapheresis that removes the ADAMTS13 inhibitor antibody and replaces functional ADAMTS13; the cornerstone emergency treatment for acquired TTP.

A large transmembrane receptor encoded by PKD1; localised to primary cilia of renal tubular cells; loss disrupts mechanosensory calcium signalling and activates cyst-forming proliferative pathways.

A calcium channel protein encoded by PKD2; forms a complex with polycystin-1 at the primary cilium; mutations cause a milder form of ADPKD than PKD1 mutations.

A large-volume diuresis that follows relief of bilateral ureteric obstruction, resulting from accumulated solutes, osmotic diuresis, and tubular dysfunction; requires careful IV fluid and electrolyte monitoring.

A constellation of features — oligohydramnios, pulmonary hypoplasia, flattened facies, and limb deformities — resulting from any cause of severe reduction in fetal urine output, including ARPKD and bilateral renal agenesis.

A polypeptide secreted ectopically by RCC and other tumours that mimics PTH action at the PTH receptor, raising serum calcium (humoral hypercalcaemia of malignancy).

Pelvi-ureteric junction obstruction; an aperistaltic segment at the junction of the renal pelvis and ureter causing progressive hydronephrosis; the commonest cause of hydronephrosis diagnosed in infants and children.

Accumulation of pus in a completely obstructed infected kidney, requiring urgent percutaneous drainage.

The regeneration phase of ATN in which tubular epithelial cells proliferate along intact basement membranes; characterised by polyuria before concentration capacity recovers.

The commonest form of CPN caused by high-grade vesicoureteric reflux; polar scars result from intrarenal reflux via compound papillae at the upper and lower poles.

The commonest malignant tumour of the adult kidney, arising from renal tubular epithelium; accounts for ~85% of primary renal malignancies; clear cell subtype is most frequent.

Wedge-shaped coagulative necrosis following embolic or thrombotic occlusion of a renal artery branch; presents with flank pain, haematuria, and elevated LDH; commonest cause is AF or infective endocarditis.

Secondary hypertension caused by renal artery stenosis reducing renal perfusion, activating renin release and the RAAS; potentially curable with revascularisation.

Rapid breakdown of skeletal muscle releasing myoglobin, CK, and potassium into the circulation; a significant cause of nephrotoxic ATN.

Fragmented red blood cells (helmet cells, triangle cells) produced by mechanical shearing across fibrin strands in microvascular thrombosis; the morphological hallmark of MAHA on peripheral blood film.

A blood fluke endemic to Africa and the Middle East; eggs deposited in the bladder wall cause chronic granulomatous inflammation → squamous metaplasia → squamous cell carcinoma of the bladder (not UC).

Sudden severe hypertension and AKI in systemic sclerosis due to intimal concentric hyperplasia of renal arteries; treated with ACE inhibitors; morphologically overlaps with malignant nephrosclerosis.

AB5 toxin produced by E. coli O157:H7 and Shigella dysenteriae; binds Gb3 receptor on glomerular endothelial cells causing endothelial injury and TMA; the aetiological agent of typical HUS.

On silver (Jones methenamine) stain, GBM spikes projecting between subepithelial electron-dense deposits in membranous nephropathy; creates a spike (GBM) + dome (deposit) silhouette.

A large renal calculus that occupies the renal pelvis and extends into multiple calyces, taking the shape of a stag's horn; most commonly composed of struvite in the setting of chronic infection with urease-producing bacteria.

A paraneoplastic non-metastatic hepatic dysfunction seen in RCC; manifests as elevated liver enzymes without hepatic metastasis; resolves after nephrectomy.

A magnesium ammonium phosphate (triple phosphate) renal calculus that forms in alkaline urine produced by urease-positive bacteria (classically Proteus mirabilis); often grows into a staghorn configuration.

A pathological syndrome of endothelial injury causing microvascular platelet-fibrin thrombi, manifesting clinically as MAHA, thrombocytopenia, and AKI; the shared substrate of HUS, TTP, DIC, and scleroderma renal crisis.

TMA caused by severe ADAMTS13 deficiency (usually acquired autoantibody), presenting with MAHA, severe thrombocytopenia, and neurological features; treated with plasma exchange which reduces mortality from ~90% to <20%.

Histological appearance of dilated atrophic renal tubules filled with homogeneous colloid-like eosinophilic casts, resembling thyroid follicles; a hallmark of chronic pyelonephritis.

Dilation of renal tubules and filling with homogeneous, eosinophilic colloid-like casts resembling thyroid follicles; a distinctive microscopic feature of chronic pyelonephritis.

The characteristic microscopic pattern of Wilms tumour comprising three cell types: blastemal (primitive round cells), epithelial (abortive tubules/glomeruli), and stromal (loose mesenchyme) components.

The histological hallmark of Wilms tumour (nephroblastoma): simultaneous presence of blastemal (small round blue cells), stromal (mesenchymal), and epithelial (primitive tubular/glomeruloid) components.

Autosomal dominant neurocutaneous syndrome caused by TSC1/TSC2 mutations; associated with bilateral renal angiomyolipomas, cortical brain tubers, subependymal nodules, and pulmonary lymphangioleiomyomatosis.

A group of disorders causing primary injury to renal tubules and interstitium rather than glomeruli or blood vessels, classified by cause as ischaemic, toxic, infective, immune, metabolic, or obstructive.

Rupture and discontinuity of the tubular basement membrane in severe nephrotoxic ATN, in contrast to ischaemic ATN where the basement membrane remains intact and guides epithelial regeneration.

Rupture of the tubular basement membrane seen in severe ischaemic ATN; distinguishes ischaemic from nephrotoxic ATN morphologically.

Mechanism explaining focal cyst formation in ADPKD: a germline PKD mutation is present in all cells, but cysts form only in cells that acquire a somatic mutation in the second allele.

A renal calculus composed of uric acid, forming in persistently acidic urine (pH <5.5); radiolucent on plain X-ray; associated with gout and hyperuricosuria; uniquely amenable to dissolution by urinary alkalinisation.

A malignant tumour arising from the transitional (urothelial) epithelium lining the renal pelvis, ureter, or bladder; characterised by papillary architecture on low-grade and solid infiltrative growth on high-grade tumours.

Carcinoma arising from urothelium (transitional epithelium) lining the bladder, renal pelvis, ureters, and urethra; bladder is the most common site; papillary or flat (CIS) patterns.

Retrograde flow of urine from the bladder into the ureter and renal pelvis during micturition, predisposing to ascending pyelonephritis and reflux nephropathy.

Von Hippel–Lindau tumour suppressor gene located at chromosome 3p25; its protein normally targets HIF-1α for degradation; biallelic loss drives clear cell RCC.

A contiguous gene deletion syndrome at chromosome 11p13 causing Wilms tumour, Aniridia, Genitourinary anomalies, and intellectual Retardation; caused by deletion of WT1 and PAX6 genes.

Urine casts composed of neutrophils aggregated within renal tubules; pathognomonic of pyelonephritis (or other renal parenchymal neutrophilic inflammation) as they can only form within the kidney.

Renal tubular casts composed predominantly of neutrophils, indicating active bacterial infection within the kidney (acute pyelonephritis); their presence in urine distinguishes upper from lower urinary tract infection.

The commonest renal malignancy of childhood (ages 2–5 years); driven by WT1 loss; triphasic histology (blastemal, epithelial, stromal); presents as a painless abdominal mass; excellent prognosis.

Wilms tumour gene 1, located at chromosome 11p13; encodes a transcription factor essential for renal development; germline loss causes nephroblastoma and WAGR/Denys–Drash syndromes.