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Module 3 · Visual Grammar

Compartment-Based Pattern Recognition

See the compartment first. Every biopsy finding is localized before it is named.

For any image or case, answer these five questions in order: Which compartment is primarily abnormal? · What stain or modality am I seeing? · What is the pattern? · Is the finding active or chronic? · What is the likely clinical significance?

Glomerular

Compartment

Tuft cellularity, capillary wall changes, mesangial expansion, sclerosis, crescents, deposits.

Image placeholder — Glomerular compartment
Reveal the five-question walkthrough
  1. Compartment: Glomerular
  2. Stain/modality: PAS or silver highlights tuft architecture; IF for immune identity; EM for deposit location.
  3. Pattern: e.g. mesangial hypercellularity, capillary wall thickening, crescentic, MPGN, TMA.
  4. Active vs chronic: cellular crescent (active) vs global sclerosis (chronic); mesangial hypercellularity (active) vs segmental scar (chronic).
  5. Clinical significance: nephritic vs nephrotic syndrome; RPGN when crescents are prominent.

Tubular

Compartment

Epithelial injury, simplification, dilation, cast formation, brush border loss, regenerative changes.

Image placeholder — Tubular compartment
Reveal the five-question walkthrough
  1. Compartment: Tubular
  2. Stain/modality: H&E and PAS for brush border and epithelial detail.
  3. Pattern: acute tubular injury with epithelial simplification and granular casts, or chronic tubular atrophy.
  4. Active vs chronic: active injury with regenerative epithelium vs atrophic tubules with thickened basement membranes.
  5. Clinical significance: AKI, cast nephropathy, ischemic or toxic tubular injury.

Interstitial

Compartment

Inflammation, edema, tubulitis, granulomas, fibrosis.

Image placeholder — Interstitial compartment
Reveal the five-question walkthrough
  1. Compartment: Interstitial
  2. Stain/modality: H&E for cell type; trichrome for fibrosis; PAS to see tubulitis crossing basement membranes.
  3. Pattern: interstitial inflammation with tubulitis (AIN); interstitial fibrosis (chronic TIN).
  4. Active vs chronic: active AIN (edema + inflammation) vs IFTA (chronic).
  5. Clinical significance: drug-induced AIN, autoimmune TIN, infection-related, granulomatous causes; CKD progression.

Vascular

Compartment

Arteriolar hyalinosis, arteriosclerosis, thrombi, vasculitis, endothelial injury.

Image placeholder — Vascular compartment
Reveal the five-question walkthrough
  1. Compartment: Vascular
  2. Stain/modality: H&E and trichrome for arteriosclerosis; PAS and silver for arteriolar hyalinosis.
  3. Pattern: arteriolar hyalinosis, intimal fibrosis, TMA-type endothelial injury, vasculitis.
  4. Active vs chronic: acute TMA / fibrinoid necrosis (active) vs arteriosclerosis and hyalinosis (chronic).
  5. Clinical significance: hypertension, diabetes, TMA syndromes, ANCA vasculitis, calcineurin-inhibitor toxicity.
Next: Glomerular patterns →Back to Visual Grammar