Renal Biopsy Pattern Recognition — Intermediate

Diffuse capillary-wall thickening with granular capillary-loop IgG suggests subepithelial immune deposits, the characteristic pattern of membranous nephropathy. Electron microscopy and antigen studies help refine the diagnosis and evaluate secondary causes.

Anti-GBM antibodies bind continuously along the GBM, producing a smooth linear IgG pattern. This differs from granular immune-complex deposition and is an urgent clinicopathologic diagnosis when accompanied by rapidly progressive kidney injury or pulmonary hemorrhage.

Minimal change disease is characterized by diffuse podocyte foot-process effacement on electron microscopy with little or no immune deposition. Light microscopy may be near normal, so the diagnosis depends on clinicopathologic correlation.

Mesangial-dominant IgA staining with compatible morphology supports IgA nephropathy. The clinical picture, Oxford features, proteinuria, eGFR, and secondary causes must still be assessed before risk stratification and treatment decisions.

Crescents form after severe capillary-wall injury allows fibrin and inflammatory mediators into Bowman space, stimulating parietal epithelial proliferation and macrophage influx. Their proportion, cellularity, and chronicity carry prognostic information.

Interstitial fibrosis and tubular atrophy reflect established nephron loss and are less reversible than active inflammatory lesions. Biopsy reports should separate activity from chronicity because escalating immunosuppression cannot reverse extensive scarring.

Full-house staining means deposition of multiple immunoglobulin classes together with complement components, classically associated with lupus nephritis. It is a pattern, not a substitute for clinical, serologic, and morphologic correlation.

Renal TMA may show endothelial swelling, mesangiolysis, double contours, fibrin or platelet thrombi, and arteriolar injury. The biopsy must be integrated with platelet count, hemolysis, blood pressure, pregnancy, drugs, complement, and systemic disease.

Postinfectious GN commonly shows granular immune-complex staining and, on electron microscopy, subepithelial humps. Recent infection, low complement, hematuria, and nephritic features support the diagnosis, but mimics must be considered.

Electron microscopy identifies the location and character of deposits and podocyte injury, which can distinguish subendothelial, subepithelial, intramembranous, and organized deposits. It is especially valuable in mixed or apparently discordant patterns.