What could cause left mild hydronephrosis and left upper abdominal pain in an adult with a possible history of urinary tract issues or abdominal problems?

Differential Diagnosis of Left Mild Hydronephrosis with Left Upper Abdominal Pain

The most likely causes of left mild hydronephrosis with left upper abdominal pain are urolithiasis (kidney stone), ureteropelvic junction obstruction, or extrinsic compression from adjacent pathology—and this presentation demands urgent imaging evaluation to identify the etiology and prevent permanent nephron loss. 1, 2, 3

Most Common Etiologies

Urolithiasis (Kidney Stones)

• Obstructing ureteral calculi are the most frequent cause of symptomatic unilateral hydronephrosis with flank/upper abdominal pain. 1, 2
• Stones cause acute obstruction leading to collecting system dilation and characteristic colicky pain radiating from flank to groin 4, 5
• Even mild hydronephrosis in the setting of renal colic indicates higher risk of stone passage failure and may require intervention 1

Ureteropelvic Junction (UPJ) Obstruction

• Can be congenital or acquired from scarring, inflammation, or vessel-related compression 1, 2
• May present with intermittent pain exacerbated by increased fluid intake 5
• Often causes mild to moderate hydronephrosis before becoming symptomatic 2

Extrinsic Compression

• Retroperitoneal pathology including masses, fibrosis, or inflammatory processes can compress the ureter externally. 1, 2
• Inflammatory bowel disease (particularly Crohn's disease) can cause hydronephrosis even without intestinal symptoms 6
• Renal artery aneurysm, though rare, can compress the ureter at the UPJ causing hydronephrosis 7

Malignant Obstruction

• Tumors of the urinary tract or adjacent structures (colon, pancreas, retroperitoneal lymphoma) can cause ureteral obstruction 1, 2
• Upper tract urothelial carcinoma should be considered, especially with risk factors 2

Stricture Formation

• Post-inflammatory, post-traumatic, or iatrogenic ureteral strictures can cause progressive obstruction 1, 2
• May develop after prior instrumentation, radiation, or infection 2

Upper Urinary Tract Infection

• Pyelonephritis can cause temporary obstruction from inflammatory edema 1, 2
• Difficult to distinguish pyonephrosis from simple hydronephrosis even on CT, though collecting system density may help 1

Critical Clinical Pitfall

Do not assume "mild" hydronephrosis is clinically insignificant—progressive obstruction causes irreversible nephron loss even when initially appearing minimal, and prompt treatment prevents permanent renal damage. 1, 8, 3

• Upper urinary tract deterioration in adults is often clinically silent and detected with nonspecific symptoms 1, 8
• Serum creatinine can remain normal in unilateral obstruction due to contralateral kidney compensation 8
• Prolonged obstruction leads to permanent nephron loss that cannot be recovered even after decompression 8, 2

Recommended Diagnostic Algorithm

Initial Imaging for Symptomatic Hydronephrosis

CT urography (CTU) without and with IV contrast is the preferred comprehensive evaluation, providing both morphological detail to identify the cause and functional information about the degree of obstruction. 1, 8

• CTU includes unenhanced images (optimal for stone detection) followed by nephrographic and excretory phases acquired at least 5 minutes after contrast injection 1, 8
• Thin-slice acquisition with multiplanar reconstructions provides detailed anatomic visualization 1

Alternative: Non-contrast CT abdomen/pelvis is highly effective if urolithiasis is the primary suspected etiology and can avoid contrast-related risks. 1

• Particularly useful when moderate to severe hydronephrosis is present on ultrasound, as these patients have higher risk of stone passage failure 1

Functional Assessment

MAG3 renal scan with diuretic administration is the gold standard for differentiating true functional obstruction from non-obstructive dilation. 8, 2

• Provides perfusion, extraction, and excretion phase information to determine if obstruction is functionally significant 1, 8
• Essential when imaging shows hydronephrosis but the clinical significance is uncertain 8

Role of Ultrasound

• Color Doppler ultrasound can identify hydronephrosis and evaluate ureteral jets, but is less useful for identifying the specific etiology 1
• Ultrasound is highly specific (94.4%) for detecting symptomatic renal stones when moderate or greater hydronephrosis is present 2
• Elevation of resistive indices is nonspecific but can be seen with obstruction 1

Key Pertinent History and Physical Examination Findings

History Elements to Elicit

• Character and radiation of pain: Colicky pain radiating to groin suggests stone; constant dull ache suggests chronic obstruction 4, 5
• Prior history of nephrolithiasis, urologic procedures, or pelvic/abdominal malignancy 1, 2
• Urinary symptoms: hematuria, dysuria, frequency, urgency 3, 5
• Constitutional symptoms: fever (suggests infection), weight loss (suggests malignancy) 3
• Medication history: cyclophosphamide, ketamine can cause drug-induced hydronephrosis 1, 2
• Inflammatory bowel disease symptoms (even if absent, Crohn's can present with hydronephrosis first) 6

Physical Examination Findings

• Costovertebral angle tenderness on the affected side 3, 5
• Palpable flank mass (suggests severe/giant hydronephrosis or renal mass) 4
• Abdominal distension or peritoneal signs if acute complication 4
• Fever and tachycardia if infected obstructed system (urologic emergency) 3

Management Principles

The underlying cause must be identified and treated urgently to prevent permanent renal damage, as progressive dilation of the upper urinary tract can lead to acute kidney injury and irreversible nephron loss. 1, 8, 3

• Obstructing stones may require urologic intervention (ureteroscopy, lithotripsy) if unlikely to pass spontaneously 2
• Malignant obstruction requires treatment of underlying malignancy or palliative drainage 2
• Strictures may need endoscopic dilation or surgical reconstruction 2
• Infected obstructed systems require emergent decompression (nephrostomy or ureteral stent) plus antibiotics 3