Bilateral Small Kidneys
Sara M. O’Hara, MD, FAAP
DIFFERENTIAL DIAGNOSIS
Common
End-Stage Renal Disease (ESRD)
Cystic/Hereditary/Congenital Causes
Glomerulonephritis
Vasculitis
Scarring
Recurrent Infections
Vesicoureteral Reflux
Less Common
Congenital Hypoplasia/Dysplasia
Medically Induced/Iatrogenic
Radiation Nephritis
Chemotherapy Induced
Organ Transplant Induced
Shock/Trauma/Cortical Necrosis
Arterial Insufficiency
Fibromuscular Dysplasia
Renal Artery Stenosis
Polyarteritis Nodosa
Mid Aortic Syndrome
Rare but Important
Tuberculosis
Medullary Cystic Disease and Nephronophthisis
Alport Syndrome
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Imaging appearance of ESRD is same regardless of cause
Bilaterally small kidneys
Poor corticomedullary differentiation
Poor contrast excretion
Contours may be smooth or lobulated
Imaging without contrast preferred when renal function is compromised
Ultrasound often 1st modality
Doppler useful to assess renal vascular state
CT, MR, VCUG, and nuclear scans all complimentary modalities
Medical history helpful in narrowing differential causes
Biopsy for histologic diagnosis often needed as imaging cannot differentiate causes
Refer to pediatric renal size charts to determine if kidneys are small
Rule of thumb for renal length
Newborn: 3.5-5 cm
7-year-old child: 7-10 cm
Teenager: 10-12 cm
Helpful Clues for Common Diagnoses
End-Stage Renal Disease (ESRD)
Causes
Cystic/hereditary/congenital (33%)
Glomerulonephritis (25%)
Vasculitis (11%)
Patients on peritoneal or hemodialysis or with renal transplant
> 6,000 new cases diagnosed yearly
5-year survival rates
With renal transplant (93%)
On hemodialysis (77%)
On peritoneal dialysis (82%)
Deaths most often related to
Cardiovascular complications, likely due to prolonged hypertension and fluid overload, &/or lipid abnormalities
Infections
Other systemic signs
Growth retardation
Anemia
Oliguria/polyuria
Hypertension
Renal osteodystrophy
Lipid/triglyceride abnormalities
Scarring
Most often caused by recurrent infections or vesicoureteral reflux
Ultrasound and DMSA renal scans most often used to follow progression
Scars also seen on CT, MR, and angiography
Differentiate scars from fetal lobation and junctional defects
Scar = cortical loss over pyramid
Fetal lobation or junctional defect = divot between pyramids
Helpful Clues for Less Common Diagnoses
Congenital Hypoplasia/Dysplasia
Typically diagnosed in infancy
May present with renal insufficiency, edema, failure to thrive
Search family history for inherited disorders
Medically Induced/Iatrogenic
Past medical history makes this diagnosis
Children with history of prior malignancy
Radiation and chemotherapy can cause renal enlargement acutely
Long-term effect is global scarring and atrophy
Radiation-induced findings can be unilateral, based on XRT port
Organ transplant recipients
Develop gradual nephropathy likely related to medications/immune modulation
High incidence of cystic changes in this population
Renal cysts seen in 30% of liver transplant patients at 10-year follow-up
Shock/Trauma/Cortical Necrosis
Acute insult causes renal enlargement but leads to scarring
Cortical necrosis may develop dystrophic calcification
Arterial Insufficiency
Not necessarily symmetric or even bilateral
Appearance dependent on artery involved
Hypertension often symptom
Pediatric etiologies in decreasing order
Fibromuscular dysplasia
Renal artery stenosis
Polyarteritis nodosa
Mid-aortic syndrome
Other vasculitides
Iatrogenic causes
Following grafting or stenting
Following trauma
Helpful Clues for Rare Diagnoses
Tuberculosis
Rarely seen in developed countries
Consider travel history and TB exposure in setting of suppurative pyelonephritis
Medullary Cystic Disease and Nephronophthisis
Rare, inherited diseases
MCKD1 and MCKD2 autosomal dominant gene mutations
NPH1, NPH2, and NPH3 are recessive gene traits
Similar pathophysiology
Bilateral small corticomedullary cysts
Tubulointerstitial sclerosis
Kidneys of normal or reduced size
Symptoms: Salt wasting, polyuria, anemia, growth retardation
End-stage renal disease by age 20-60
Earlier in familial nephronophthisis
Alport Syndrome
Hereditary disorder
Family history often prompts initial evaluation
Mutations in COL4A3, COL4A4, and COL4A5 (collagen biosynthesis genes)
Faulty type 4 collagen network
Leads to abnormal basement membranes in kidney, inner ear, and eye
Progressive nephritis and deafness
Hematuria and proteinuria
Renal insufficiency & ESRD by age 30-50
SELECTED REFERENCES
1. 2008 Annual Report of USRDS, Section 8: Pediatric ESRD, published on US Renal Data System website, www.usrds.org/adr.htm
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