Absent Kidney

Paula J. Woodward, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Is the kidney truly absent?
- Always search for ectopic location
Is the fluid normal?
- Bilateral renal agenesis will have anhydramnios
- Remainder have normal fluid
Fetal adrenal is large and easily mistaken for a kidney, especially in 1st and 2nd trimester
- Normal adrenal has an “ice cream sandwich” appearance
  - Hypoechoic cortex surrounding a hyperechoic medulla
- In renal agenesis adrenal has a flattened, discoid, “lying down” appearance
  - Adrenal gland does not fold into “Y” or “tricorn hat” configuration if no kidney

Helpful Clues for Common Diagnoses

Bilateral Renal Agenesis
- No demonstrable renal tissue
- No urine in fetal bladder
- Anhydramnios
- “Lying down” adrenals in renal fossa, although this may be difficult to see in setting of no fluid
- Look for renal arteries, but be aware of pitfalls
  - Lumbar arteries can easily be mistaken for renal arteries
- MR very helpful for confirmation of diagnosis
Unilateral Renal Agenesis
- One kidney seen, which may show compensatory hypertrophy
- May see “lying down” adrenal ipsilateral to absent kidney
- Bladder seen to fill and empty
- Normal amniotic fluid volume

Helpful Clues for Less Common Diagnoses

Pelvic Kidney
- Empty renal fossa
- Kidney in fetal pelvis, superior to bladder
  - May be difficult to see as echogenicity similar to bowel
- Contralateral kidney is normal-sized
Crossed Fused Ectopia
- Ectopic kidney located in opposite flank creating a large bilobed kidney
  - 95% fused, 5% unfused
- Left crosses to right most often