What is the best imaging approach for a patient with right lower quadrant (RLQ) pain, proteinuria, and right mid-back pain, considering potential underlying kidney issues?

Imaging for Right Lower Quadrant Pain, Proteinuria, and Right Mid-Back Pain

Obtain a contrast-enhanced CT scan of the abdomen and pelvis immediately, as this presentation suggests potential renal pathology (given proteinuria and flank pain) with concurrent intra-abdominal pathology (given RLQ pain), and CT provides comprehensive evaluation of both systems with high diagnostic accuracy. 1, 2

Primary Imaging Recommendation

CT abdomen and pelvis with IV contrast is the imaging modality of choice for this clinical presentation because:

• The combination of RLQ pain with right mid-back (flank) pain and proteinuria creates diagnostic ambiguity requiring evaluation of multiple organ systems simultaneously 2
• CT has >95% sensitivity for detecting acute appendicitis, diverticulitis, urolithiasis, and renal pathology that could explain proteinuria 1
• The American College of Radiology rates CT as "usually appropriate" (7-9/9) for evaluating RLQ pain when the diagnosis is unclear 1
• CT can identify alternative diagnoses including right colonic diverticulitis (8% of RLQ pain cases), bowel obstruction (3%), infectious enterocolitis, inflammatory ileitis, and ureteral stones 1

Critical Consideration: Proteinuria and Contrast Safety

Exercise caution with gadolinium-based contrast if renal function is severely impaired (eGFR <30 mL/min/1.73m²), but IV iodinated contrast for CT is generally safe in most CKD patients and should not be withheld when diagnostic benefit outweighs risk. 1

• Proteinuria indicates underlying kidney dysfunction and warrants checking serum creatinine/eGFR before contrast administration 3, 4
• If the patient is dialysis-dependent or has eGFR <30, consider non-contrast CT first, though this reduces diagnostic accuracy 1
• The guideline specifically warns against gadolinium in severe renal dysfunction (nephrogenic systemic fibrosis risk), but this applies to MRI, not CT contrast 1

Alternative Imaging Approaches

When to Consider Ultrasound First:

• Pregnancy: If the patient has reproductive organs and pregnancy cannot be excluded, start with ultrasound of the abdomen and pelvis 5
• Radiation concern in young patients: Ultrasound has 96% sensitivity when combining pyeloureteral dilation, direct stone visualization, and absence of ureteral ejaculation 6
• Limitation: Ultrasound is operator-dependent and has reduced sensitivity for appendicitis and other bowel pathology compared to CT 1, 7

When to Use MRI:

• Pregnant patients with inconclusive ultrasound: MRI is preferred over CT to avoid radiation exposure 1, 5
• Contraindication to CT contrast: MRI without and with contrast (if eGFR permits) can evaluate both renal parenchyma and intra-abdominal pathology 1
• MRI sensitivity: 84-86% for detecting urgent diagnoses including diverticulitis, bowel obstruction, and urinary tract disorders 1

Diagnostic Algorithm Based on Pain Location

The combination of RLQ pain + right flank pain + proteinuria suggests:

1. Renal/ureteral pathology (right-sided urolithiasis, pyelonephritis, renal infarction) - explains flank pain and proteinuria 6, 4
2. Appendicitis with atypical presentation - can present with referred flank pain 1, 2
3. Right colonic diverticulitis - can mimic both appendicitis and renal colic 1
4. Inflammatory bowel disease (Crohn's terminal ileitis) - can cause RLQ pain and secondary renal involvement 1, 7

Critical Pitfalls to Avoid

• Do not delay CT beyond 12 hours if serious pathology is suspected, as conditions like mesenteric ischemia, perforated appendicitis, or renal infarction require urgent intervention 2
• Do not rely on non-contrast CT alone - critical findings like bowel wall enhancement, abscess formation, and vascular complications cannot be detected without IV contrast 8
• Do not assume proteinuria alone indicates the pain is purely renal - proteinuria may be chronic and unrelated to the acute presentation, while the acute pain could be from appendicitis or other intra-abdominal pathology 3, 9
• Do not skip imaging based on clinical assessment alone - studies show CT alters the leading diagnosis in 49% of patients with non-traumatic abdominal pain and changes management in 42% 1

What to Look for on CT

The radiologist should specifically evaluate:

• Appendix: diameter >6mm, wall thickening, periappendiceal fat stranding, abscess 1, 2
• Right colon: wall thickening, diverticula, pericolic fat stranding 1
• Kidneys: hydronephrosis, stones, parenchymal abnormalities, perinephric stranding, cortical enhancement patterns 6, 4
• Ureters: stones, obstruction, periureteral stranding 6
• Mesentery/vessels: mesenteric lymphadenitis, ischemia, inflammatory changes 1, 7