What are the next steps if the right (Rt) kidney is not visualized on imaging?

When the Right Kidney is Not Visualized on Imaging

Immediate Technical Troubleshooting

If the right kidney is not visualized on ultrasound, immediately optimize your scanning technique before assuming pathology—use multiple acoustic windows, patient positioning, and probe selection to overcome common technical limitations. 1

Systematic Re-scanning Protocol

• Reposition the patient to left lateral decubitus or prone position to improve the hepatic acoustic window 1
• Have the patient take a deep breath and hold to extend the liver window inferiorly and bring the kidney into view 1
• Switch to an intercostal approach between the anterior axillary line and posterior midline if bowel gas obscures the subcostal view 1
• Use a small footprint or phased array probe to scan between ribs and minimize rib shadowing 1
• Place the transducer parallel to the intercostal spaces (approximately 45 degrees counter-clockwise from the body's long axis) with the probe indicator toward the head 1
• Scan with the patient in decubitus position with a bolster under the lower side and the upper arm fully abducted to spread the intercostal spaces 1
• Obtain separate views of superior and inferior poles as the entire kidney may not be visible in a single window 1

Differential Diagnosis When Kidney Remains Non-Visualized

Congenital Absence or Ectopia

• Renal agenesis (unilateral absence) occurs but is uncommon 2
• Ectopic kidney may be located in the pelvis, contralateral side, or thorax 2
• Crossed fused ectopia where both kidneys are on the left side 2

Pathologic Causes

• Severe atrophy from chronic obstruction with complete parenchymal loss 3
• Prior nephrectomy (surgical removal—verify surgical history) 2
• Replaced by mass lesion (tumor occupying the renal fossa) 2
• Severe hydronephrosis that distorts normal architecture beyond recognition 3, 4

Technical/Anatomic Factors

• Interposed bowel gas is the most common reason for non-visualization on ultrasound 1
• Unusual kidney position—the right kidney can be abnormally high (occurs in 5% of cases) or low 2
• Hepatomegaly or hepatatrophy altering the acoustic window 2

Mandatory Next Steps

Proceed immediately to CT urography (CTU) or contrast-enhanced CT of the abdomen and pelvis to definitively locate the kidney and identify any pathology—ultrasound failure to visualize a kidney mandates cross-sectional imaging. 1, 3

Advanced Imaging Algorithm

• CT urography is the gold standard for comprehensive genitourinary tract evaluation when ultrasound is non-diagnostic 1, 3
• MR urography is an alternative if renal impairment exists (creatinine elevation) or radiation exposure is a concern 1, 3
• Non-contrast CT can identify stones and anatomic abnormalities if IV contrast is contraindicated 1
• Always image both kidneys to exclude bilateral disease or confirm a solitary kidney situation, which dramatically changes management urgency 1, 3

Laboratory Evaluation

• Check serum creatinine and estimated GFR to assess whether the contralateral kidney is compensating adequately 3
• Obtain urinalysis to evaluate for infection, which would require urgent intervention if obstruction is present 3
• Review surgical history for prior nephrectomy or renal procedures 2

Critical Clinical Scenarios

If Patient is Symptomatic (Flank Pain, Fever, Acute Kidney Injury)

Urgent CT imaging within hours is mandatory to rule out obstructive uropathy, infected hydronephrosis, or other surgical emergencies 1, 3, 4

• Obstructive uropathy with infection (pyonephrosis) requires emergency decompression via percutaneous nephrostomy or retrograde stenting 3
• Acute kidney injury with non-visualized kidney may indicate complete obstruction that ultrasound missed—CT has superior sensitivity 4
• Moderate to severe hydronephrosis on ultrasound warrants CT to identify the obstructing lesion and guide intervention 1

If Patient is Asymptomatic

Proceed with non-urgent CT urography or MR urography to document kidney location, function, and any underlying pathology 1, 3

• Congenital absence or ectopia requires documentation and long-term monitoring of the solitary kidney 3
• Atrophic kidney from chronic obstruction may not require intervention if contralateral kidney function is normal 3

Common Pitfalls to Avoid

• Never assume the kidney is absent based on ultrasound alone—technical factors frequently prevent visualization 1
• Do not delay CT imaging in symptomatic patients while attempting multiple ultrasound techniques—ultrasound has limited sensitivity for stones (32-39% for left kidney, 52-57% for right kidney) 5
• Avoid scanning with a distended bladder as this can cause artifactual hydronephrosis in the visualized kidney and may compress ureters 1, 3
• Do not rely on renal echogenicity alone to assess kidney disease—72% of patients with kidney echogenicity equal to liver have normal renal function 6
• Always verify both kidneys are imaged as bilateral disease or solitary kidney dramatically increases the urgency of any intervention 1, 3