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PA27.17 | Kidney Disease & Tumour Morphology — Practical — SDL Guide (Part 4)

Integrative Pattern Recognition: Putting It All Together

A renal pathology pattern-recognition diagram compares gross kidney appearances, key microscopic patterns, and final diagnoses for benign nephrosclerosis, diabetic nephropathy, chronic pyelonephritis, ADPKD, and hydronephrosis. — **Panel A:** Decision matrix linking gross appearance, key microscopic pattern, and diagnosis for common renal pathology patterns. **Panel B:** Benign nephrosclerosis: finely granular small bilateral kidneys, narrowed arteriole, hyaline arteriolosclerosis. **Panel C:** Diabetic nephropathy: finely granular kidney, Kimmelstiel-Wilson nodules, efferent arteriolar hyalinosis. **Panel D:** Chronic pyelonephritis: irregular cortical scarring, calyceal blunting, thyroidisation of tubules. **Panel E:** ADPKD: massively enlarged bilateral kidneys, grape-cluster cysts, compressed residual parenchyma. **Panel F:** Hydronephrosis: dilated renal pelvis and calyces, thin compressed cortex, thin compressed medulla.

Use this decision matrix at the bench:

Gross appearance	Key micro pattern	Diagnosis
Finely granular, small, bilateral	Hyaline arteriolosclerosis	Benign nephrosclerosis
Finely granular, small, bilateral	KW nodules + efferent hyalinosis	Diabetic nephropathy
Finely granular, small, bilateral	Thyroidisation + calyceal blunting	Chronic pyelonephritis
Massively enlarged, bilateral cysts	Grape-cluster cysts, compressed parenchyma	ADPKD
Dilated calyces, thin rim	Thinned cortex + medulla	Hydronephrosis
Cortical abscess, yellow streaks	WBC casts + microabscesses	Acute pyelonephritis
Pale, swollen, cortex widened	Focal tubular necrosis, muddy-brown casts	ATN
Petechial 'flea-bitten' surface	Onion-skin + fibrinoid necrosis	Malignant nephrosclerosis
Golden-yellow cortical mass	Clear cells + chicken-wire vessels	Clear-cell RCC
Large child's mass, pseudocapsule	Triphasic: blastema + stroma + epithelium	Wilms tumour
Papillary pelvic mass	Transitional epithelium, papillary cores	Urothelial carcinoma

Special stain summary for examiners:
• PAS: best for GBM thickening, KW nodules, mesangial matrix
• Silver (Jones): spike-and-dome of membranous nephropathy
• H&E: all routine tissue patterns
• Congo red: amyloid (apple-green birefringence)

CLINICAL PEARL

The three 'finely granular, small kidney' mimics always trip students in viva:

Benign nephrosclerosis: hyaline arteriolosclerosis (afferent ± efferent), ischaemic glomerular obsolescence
Diabetic nephropathy: KW nodules, efferent arteriolar hyalinosis (not seen in any other condition)
Chronic GN (end-stage): glomeruli show global or segmental sclerosis corresponding to the original GN type; no hyaline arteriolosclerosis unless hypertension co-exists

When the gross alone cannot distinguish them, look for:
• Hyaline in arterioles → nephrosclerosis or diabetes
• KW nodules → diabetes only
• Glomerular residua (mesangial hypercellularity, membranous deposits) → chronic GN

If you can confidently say 'efferent hyalinosis present' → the examiner nods and moves on.