What are the next steps for a patient with mild fullness in the left renal pelvis and no documented focal lesion or echogenic calculi?

Management of Mild Left Renal Pelvis Fullness

The next step is to obtain a detailed clinical history focusing on symptoms of renal colic, flank pain, or urinary tract obstruction, followed by CT urography (CTU) without and with IV contrast as the definitive imaging study to identify the cause of the pelvic fullness. 1

Initial Clinical Assessment

The immediate priority is determining whether this finding represents true obstruction or a benign variant. Key clinical information must be obtained:

• Assess for symptoms of renal colic or flank pain, as the presence of acute symptoms would indicate potential obstruction requiring urgent evaluation 2, 1
• Evaluate for risk factors for obstruction including history of urolithiasis, malignancy, prior pelvic surgery, or recurrent urinary tract infections 1
• Check renal function with serum creatinine, as elevated levels may indicate significant obstruction requiring urgent intervention 1
• Determine pregnancy status in women of childbearing age, since physiologic hydronephrosis occurs in 70-90% of pregnant patients (typically right-sided, though left-sided can occur) 1
• Review for hematuria, urinary frequency, or other urinary symptoms that may suggest underlying pathology 2, 1

Recommended Imaging Strategy

For Asymptomatic or Mildly Symptomatic Patients

CT urography without and with IV contrast is the preferred comprehensive evaluation for unilateral hydronephrosis of unknown cause, providing near-complete assessment of the entire genitourinary tract and identifying both intrinsic and extrinsic causes of obstruction 1. The study includes:

• Unenhanced phase to detect calculi (which ultrasound frequently misses, with CT having 97% sensitivity for stone detection) 2, 1
• Nephrographic phase to assess renal parenchyma for masses or infiltrative disease 1
• Excretory phase to evaluate collecting system anatomy and identify the level and cause of any obstruction 1

Alternative Imaging Options

• Non-contrast CT abdomen and pelvis may be considered if urolithiasis is the primary concern and contrast is contraindicated, though it provides less comprehensive evaluation 1
• MR urography (MRU) is useful if IV contrast is contraindicated or to avoid radiation exposure, providing excellent soft tissue characterization for masses or extrinsic compression 1

Special Diagnostic Considerations

If CTU Shows Persistent Hydronephrosis Without Clear Cause

Diuretic renography (DTPA or MAG3 scan) is the gold standard for determining if true functional obstruction exists versus non-obstructive hydronephrosis and should be considered when anatomic imaging shows hydronephrosis but no clear cause 1. This distinguishes between:

• True obstruction requiring intervention
• Non-obstructive dilation (extrarenal pelvis, post-obstructive dilation, or physiologic variants)

Common Pitfalls to Avoid

• Do not assume mild fullness is always benign—ultrasound has >90% sensitivity for hydronephrosis but is less useful for identifying etiology 2
• False-negative ultrasound can occur with dehydration, early obstruction, or compression of the renal pelvis by tumors or fibrosis 2
• Hydronephrosis does not always indicate obstruction—reflux, pregnancy, postobstructive dilation, or diuresis may cause collecting system dilatation 2

Red Flags Requiring Urgent Evaluation

Certain clinical scenarios demand immediate comprehensive imaging with contrast-enhanced CT:

• Fever or signs of infection (suggesting infected obstructed system) 1
• Acute severe flank pain (suggesting acute obstruction or renal colic) 2, 1
• Rising serum creatinine (indicating significant functional impairment) 1
• Bilateral hydronephrosis (suggesting lower urinary tract obstruction) 1

Follow-Up Strategy

If Specific Cause Identified on CTU

Management should be directed at the specific etiology (stone, mass, stricture, extrinsic compression) 1

If No Cause Identified and Mild Hydronephrosis with Normal Renal Function

• Repeat ultrasound in 3-6 months to assess for progression 1
• Any progression of hydronephrosis warrants urologic consultation 1
• Maintain higher fluid intake and provide patient education about warning symptoms 2

For Pregnant Patients

If pregnancy is confirmed, ultrasound is the primary imaging modality due to radiation concerns, with MRI reserved for cases where ultrasound is unrevealing and symptoms persist 2. Physiologic hydronephrosis in pregnancy typically does not require intervention unless symptomatic or associated with infection 2.