What is the next step in managing an adult patient with a history of kidney stones, musculoskeletal issues, or abdominal problems, presenting with left side pain radiating to the back for 2 weeks, with negative Urinalysis (UA) and culture results?

CT Abdomen and Pelvis with IV Contrast is the Next Step

For a patient with left-sided pain radiating to the back for 2 weeks and negative urinalysis and culture, obtain a CT abdomen and pelvis with intravenous contrast as the primary diagnostic study. 1, 2

Why CT with Contrast is Essential

• Approximately one-third of patients with flank pain have extraurinary pathology, making comprehensive imaging critical even when urinalysis is negative 2
• Contrast-enhanced CT identifies clinically significant non-urological diagnoses in 15% of cases in patients with flank/back pain and negative urinalysis 1
• IV contrast is specifically recommended when urinalysis is negative because it better characterizes alternative diagnoses beyond urolithiasis 1
• Non-contrast CT alone has 98-100% sensitivity for stones but may miss vascular, inflammatory, and soft tissue pathology that requires contrast enhancement 2

Critical Differential Diagnoses to Evaluate

Gastrointestinal Causes

• Left colonic diverticulitis can present as left-sided flank pain mimicking renal pathology and is a common alternative diagnosis 3, 2
• Gastroenteritis, colitis, or inflammatory bowel disease may manifest with flank pain 2
• Appendicitis can present with atypical pain patterns and negative urinalysis 1

Urological Causes Despite Negative UA

• Up to 15% of patients with urolithiasis have negative urinalysis, particularly with small stones or early obstruction 2, 4
• Early ureteral obstruction may not produce hematuria initially 1

Vascular and Splenic Pathology

• Splenic infarction or subcapsular hematoma can cause left flank pain with referred patterns 2
• Renal subcapsular hematoma (Page kidney) can present with flank pain, hematuria, and hypertension 5

Pancreatic and Retroperitoneal

• Pancreatic tail pathology, including pancreatitis or masses, may present with left flank pain 2

Musculoskeletal

• Lumbar spine pathology (facet joint arthropathy, disc disease) causes position-dependent referred flank pain 2
• Paraspinal muscle strain typically worsens with movement and palpation 2

Gynecological (in Women)

• Benign adnexal masses, ovarian torsion, tubo-ovarian abscess, endometriosis, or pelvic congestion syndrome 1, 2
• Check β-hCG in women of reproductive age even with negative urinalysis to exclude ectopic pregnancy 1

Red Flags Requiring Urgent Evaluation

• Fever, chills, or systemic infection signs may indicate pyelonephritis even with negative urinalysis—obtain urine culture 2
• Inability to urinate or decreased output suggests complete obstruction requiring urgent intervention 2
• Hemodynamic instability may indicate vascular catastrophe including aortic pathology 2
• Age over 60 years warrants evaluation for abdominal aortic aneurysm 1
• History of cancer, unexplained weight loss, progressive neurological deficits require urgent evaluation 1

Common Pitfalls to Avoid

• Do not assume negative urinalysis excludes urological pathology—early obstruction or anatomical abnormalities may not produce hematuria initially 1
• Do not delay imaging if pain is severe—immediate hospital admission and imaging are warranted if pain fails to respond to analgesia within 1 hour 1
• Do not overlook the 33% of patients with extraurinary causes by anchoring on kidney stones 2
• Avoid ordering non-contrast CT alone when urinalysis is negative, as this misses important non-stone pathology 1

Additional Immediate Assessment

• Check vital signs to exclude shock or systemic infection 1
• Examine abdomen for peritoneal signs, masses, or pulsatile abdominal aortic aneurysm, particularly if over 60 years old 1
• Perform straight-leg raise testing and brief neurological exam if back pain radiates to legs to assess for radiculopathy 1

Follow-up Based on CT Results

• If CT shows minimal hydronephrosis, obtain follow-up ultrasound in 1-6 months to ensure resolution 1
• If musculoskeletal causes are identified, manage according to low back pain guidelines with conservative therapy unless red flags are present 1
• If diverticulitis is diagnosed, antibiotics may be avoided in uncomplicated cases without significant comorbidities or sepsis 3