Enlargement of kidney
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kidney enlargement nephromegaly causes
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I now have an excellent authoritative diagram plus detailed textbook content. Here is the full, well-organized answer:
Enlargement of the Kidney (Nephromegaly)
A kidney is considered enlarged when it measures >12 cm on imaging. The approach to the differential diagnosis is guided by two key features: unilateral vs. bilateral involvement, and smooth vs. irregular contour.
Classification by Laterality and Contour
The diagram below (from Comprehensive Clinical Nephrology, 7th ed.) summarizes this beautifully:
Large Kidneys (>12 cm)
Unilateral
| Contour | Causes |
|---|---|
| Smooth | Compensatory hypertrophy, Renal vein thrombosis, Hydronephrosis |
| Irregular | Tumor (Renal cell carcinoma, Wilms' tumor), Cyst |
Bilateral
| Contour | Causes |
|---|---|
| Smooth | Infiltration (edema, lymphoma), Diabetic nephropathy (early), HIV-associated nephropathy, Renal vein thrombosis |
| Irregular | Polycystic kidney disease (ADPKD/ARPKD), Other multicystic disease, Angiomyolipoma |
Key Individual Causes - Details
1. Hydronephrosis (Unilateral, smooth)
- Dilatation of the collecting system due to outflow obstruction (ureteric stone, stricture, pelviureteric junction obstruction, extrinsic compression)
- Diagnosed on ultrasound; CT urogram identifies the level/cause of obstruction
2. Compensatory Hypertrophy (Unilateral, smooth)
- Occurs in the contralateral kidney when one kidney is absent, non-functioning, or has been removed
- Physiological - not pathological
3. Renal Vein Thrombosis (Unilateral or Bilateral, smooth)
- Causes acute swelling and tenderness; may present with haematuria and nephrotic syndrome
- Risk factors: nephrotic syndrome (especially membranous nephropathy), dehydration, hypercoagulable states
4. Polycystic Kidney Disease (Bilateral, irregular)
- ADPKD (PKD1/PKD2 mutations): most common hereditary cause; bilateral, massively enlarged kidneys with multiple large cysts; associated with hypertension, haematuria, flank pain, and progressive renal failure. Kidney size increases at ~5.3% per year. "Kidney enlargement eventually occurs in 100% of patients with ADPKD." - Comprehensive Clinical Nephrology, 7th ed.
- ARPKD (PKHD1 mutation): presents in neonates/infants; bilateral echogenic enlarged kidneys; associated with hepatic fibrosis
5. Diabetic Nephropathy (Bilateral, smooth - early)
- Early diabetic nephropathy causes glomerular hyperfiltration and kidney enlargement
- Note: In advanced disease, kidneys become small and scarred
6. HIV-Associated Nephropathy (HIVAN) (Bilateral, smooth)
- HIVAN causes enlarged, echogenic kidneys on ultrasound (characteristically large despite impaired function)
- Predominantly affects patients of African ancestry
7. Renal Lymphoma / Infiltration (Bilateral, smooth)
- Kidneys enlarged without obstruction; rapid improvement with treatment supports the diagnosis
- Criteria supporting lymphomatous infiltration: (1) kidney enlargement without obstruction; (2) no other cause; (3) rapid improvement with therapy - National Kidney Foundation Primer on Kidney Diseases, 8th ed.
8. Renal Cell Carcinoma / Wilms' Tumour (Unilateral, irregular)
- A renal mass presenting as unilateral enlargement with an irregular contour
- Haematuria and flank pain are classical features
9. Acute Pyelonephritis / Renal Abscess
- Causes transient unilateral enlargement due to oedema and inflammation
- Associated with fever, loin pain, dysuria
10. Angiomyolipoma (Bilateral, irregular)
- Associated with tuberous sclerosis; bilateral in that setting; fat-containing lesions on CT
Normal Kidney Size (Reference)
- Normal adult kidney length: 9-12 cm (right slightly smaller than left)
- Measurement is typically done on ultrasound or CT in the longest axis
Approach to Investigation
- Ultrasound - first-line: detects hydronephrosis, cysts, solid masses, size asymmetry
- CT scan (contrast + non-contrast) - characterizes masses, identifies obstruction level, staging
- MRI - used in ADPKD to monitor total kidney volume; preferred in pregnancy
- Urinalysis and dipstick - haematuria, proteinuria
- Bloods - renal function (eGFR, creatinine), glucose, HIV serology, FBC (infiltration)
- Biopsy - when diagnosis uncertain (lymphoma, rare infiltrative diseases)
Sources: Comprehensive Clinical Nephrology, 7th Edition (Fig. 6.1); National Kidney Foundation Primer on Kidney Diseases, 8th ed.; S Das Manual on Clinical Surgery, 13th ed.
Cause of unilateral enlargement of kidney
The diagram from the previous answer already covers this directly. Here is a focused, complete answer:
Causes of Unilateral Kidney Enlargement
From the authoritative flowchart (Comprehensive Clinical Nephrology, 7th ed.), unilateral large kidney (>12 cm) is classified by contour:
Smooth Contour (Unilateral)
| Cause | Key Features |
|---|---|
| Compensatory hypertrophy | Contralateral kidney absent/non-functional; physiological, benign |
| Renal vein thrombosis | Acute painful swelling; haematuria, proteinuria; risk factors - nephrotic syndrome, hypercoagulable states |
| Hydronephrosis | Obstruction of outflow (stone, PUJ obstruction, stricture, external compression); diagnosed on USS |
Irregular Contour (Unilateral)
| Cause | Key Features |
|---|---|
| Tumour (Renal cell carcinoma / Wilms' tumour) | Haematuria, flank pain, palpable mass (classic triad); Wilms' in children |
| Cyst (simple or complex) | Simple cysts are common and benign; complex cysts (Bosniak III/IV) are potentially malignant |
Additional Causes (Not Shown in Chart but Recognized)
| Cause | Key Features |
|---|---|
| Acute pyelonephritis / Renal abscess | Transient enlargement due to inflammation/oedema; fever, loin pain, pyuria |
| Xanthogranulomatous pyelonephritis (XGP) | Chronic infection, usually associated with staghorn calculus; diffuse or segmental enlargement |
| Renal trauma / Subcapsular haematoma | History of trauma; smooth enlargement from blood collection under the capsule |
| Duplex kidney | Congenital duplication of the collecting system; kidney appears elongated/enlarged |
| Horseshoe kidney | Both kidneys fused at lower poles; each "half" may appear abnormally positioned/enlarged |
| Acute renal artery occlusion / infarction | Sudden flank pain, haematuria; kidney initially swells then shrinks |
| Angiomyolipoma (solitary) | Fat-containing benign tumour; can be large; associated with tuberous sclerosis |
Memory Aid - "CHART" for Smooth Unilateral Enlargement
C - Compensatory hypertrophy H - Hydronephrosis A - Acute pyelonephritis R - Renal vein thrombosis T - Trauma (haematoma)
Investigations
- Ultrasound - first line; differentiates hydronephrosis, cyst, solid mass
- CT (contrast) - characterises mass, staging, obstruction level
- Urinalysis - haematuria, pyuria, proteinuria
- Urine culture - if infection suspected
- Doppler USS / CT venogram - if renal vein thrombosis suspected
- IVP / CT urogram - for functional assessment and obstruction mapping
Source: Comprehensive Clinical Nephrology, 7th Edition, Fig. 6.1
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