Diagnostic Ultrasound - Abdomen and Pelvis

Small Kidney
Differential Diagnoses: Kidney
DIFFERENTIAL DIAGNOSIS
Common
• Chronic Diabetic Nephropathy
• Chronic Glomerulonephritis
• Chronic Hypertensive Nephropathy
• Chronic Lupus Nephritis
• Chronic Reflux Nephropathy
• Postobstructive Atrophy
• Partial Nephrectomy/Post Ablative Therapy/Post Surgery
• Chronic Renal Allograft Rejection/Chronic Allograft
Nephropathy
Less Common
• Chronic HIV Nephropathy
• Multicystic Dysplastic Kidney
• Recurrent Infection
• Chronic Renal Artery Stenosis
• Chronic Renal Infarction
• Chronic Vascular Injury
• Post-Traumatic Renal Atrophy
• Following Acute Cortical Necrosis or Acute Tubular Necrosis
• Post Chemotherapy
Rare but Important
• Chronic Radiation Nephropathy
• Chronic Nephritis (Alport Syndrome)
• Renal Cystic Dysplasia
• Medullary cystic disease complex
• Tuberculous Autonephrectomy
• Renal Hypoplasia
• Supernumerary Kidney
• Chronic Lead Poisoning
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
• Renal atrophy is end result of many pathologic processes
• Causes of loss of renal parenchyma include
○ Acquired: Infection, inflammation, obstruction, reflux,
trauma, necrosis/ischemia, fibrosis, surgical intervention
○ Congenital: Hypoplasia, dysplasia
• Ultrasound findings are not specific for cause
• Renal size and cortical thickness are useful in differentiating
acute from chronic kidney disease
• Determine if abnormality is unilateral or bilateral, global or
focal/multifocal
• Hydronephrosis suggests ureteral obstruction or
vesicoureteral reflux
• Renal echogenicity is variable but commonly increased in
medical renal renal disease
• Usually not possible to determine cause of small echogenic
scarred kidney
• Clinical history is essential for diagnosis
• Biopsy usually not indicated if kidneys are small
Helpful Clues for Common Diagnoses
• Chronic Diabetic Nephropathy
○ Small kidneys + ↑ cortical echogenicity
○ Corticomedullary differentiation (CMD) usually
preserved, unless patient is in overt renal failure
• Chronic Glomerulonephritis
○ Small kidneys + smooth renal outline
○ Parenchyma remains echogenic
• Chronic Hypertensive Nephropathy
○ Due to progressive nephrosclerosis
○ Small kidneys + irregular cortical thinning
○ ↓ cortical vascularity due to arteriolar fibrosis and
hyaline degeneration
• Chronic Lupus Nephritis
○ Small kidneys
○ Variable renal echogenicity and CMD
• Chronic Reflux Nephropathy
○ Unilateral or bilateral vesicoureteral reflux in childhood
○ May cause focal/diffuse renal scarring and atrophy
○ Cortical scars are common in upper and lower pole
○ Dilated calyces next to scar suggest diagnosis
○ Calyces and pelvis may be dilated initially but shrink as
kidney atrophies
○ Focal areas of compensatory hypertrophy seen adjacent
to cortical scars
○ Small kidneys + irregular renal outline
• Postobstructive Atrophy
○ Caused by longstanding ureteropelvic junction (UPJ),
ureteric, or bladder outlet obstruction
○ Results in progressive decrease in renal blood flow and
glomerular filtration
○ Small kidney with cortical thinning and variable
hydronephrosis
• Partial Nephrectomy/Post Ablative Therapy/Post
Surgery
○ Small residual kidney with preserved CMD
○ Compensatory hypertrophy of contralateral kidney may
be evident
○ History is essential
• Chronic Renal Allograft Rejection/Chronic Allograft
Nephropathy
○ Irreversible cause of renal allograft dysfunction
○ Small transplant kidney with cortical thinning and
increased cortical echogenicity
○ Decreased color Doppler flow
○ Decreased arterial diastolic flow
Helpful Clues for Less Common Diagnoses
• Chronic HIV Nephropathy
○ Normal or enlarged kidneys becoming small with
progressive renal failure
○ Increased cortical echogenicity, loss of CMD and sinus fat
○ Thickened urothelium
• Multicystic Dysplastic Kidney
○ Initially unilateral enlarged kidney replaced by
noncommunicating cysts of varying sizes
○ Undergoes partial or complete involution in infancy
○ Later appears small and echogenic kidney ± cysts
○ Contralateral diseases common such as vesicoureteric
reflux, UPJ obstruction, and ureteric stenosis
• Recurrent Infection
○ Risk factors: Calculi, urinary tract obstruction, neurogenic
bladder, and urinary diversion
○ Small kidney, parenchymal scarring
○ Focal cortical thinning causing irregular outline
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