What is the purpose and procedure of a nephrostogram (nephro- meaning kidney, -stogram meaning record of the kidney)?

Nephrostogram: Purpose and Procedure

A nephrostogram is a diagnostic radiological procedure that evaluates the renal collecting system by injecting contrast material through a nephrostomy tube to assess urinary tract patency, identify obstruction, and guide therapeutic interventions. 1

Purpose of Nephrostogram

• Nephrostograms are primarily performed to evaluate the patency of the urinary collecting system in patients with nephrostomy tubes, particularly to assess for obstruction 1
• They help determine if urinary tract obstruction is present and identify the specific location and cause of obstruction 1
• Nephrostograms can confirm proper nephrostomy tube placement and function before tube removal 2
• They are used to evaluate for complications such as urine leaks, fistulas, or strictures in the collecting system 3
• Nephrostograms can help determine if a nephrostomy tube can be safely removed by confirming unobstructed drainage into the bladder 2

Procedure of Nephrostogram

Pre-procedure Preparation

• The patient is positioned on a fluoroscopy table, typically in a supine or slightly oblique position 1
• The nephrostomy tube site is assessed and prepared using sterile technique 1
• Vital signs are monitored throughout the procedure 1

Procedure Steps

1. The nephrostomy tube is accessed and any existing urine is drained 1
2. Contrast material is injected through the nephrostomy tube under fluoroscopic guidance 1
3. Real-time fluoroscopic images are obtained to visualize the renal collecting system, ureter, and bladder 1, 3
4. The radiologist evaluates for:
   • Proper nephrostomy tube position 3
   • Filling of the pelvicalyceal system 3
   • Patency of the ureter 3
   • Drainage into the bladder 3
   • Presence of obstruction, strictures, or leaks 1, 3
5. Pressure measurements may be taken during contrast injection to assess for functional obstruction (ureteral opening pressure) 4

Alternative Techniques

• Contrast-enhanced ultrasound (CEUS) nephrostogram is emerging as an alternative to fluoroscopic nephrostogram, using microbubble contrast agents instead of iodinated contrast 3, 5
• CEUS nephrostogram has shown comparable accuracy to fluoroscopic nephrostogram in assessing nephrostomy tube position and urinary drainage 3

Clinical Applications

• Evaluation of suspected urinary tract obstruction, particularly in patients with hydronephrosis 1
• Assessment of renal function and drainage after percutaneous nephrolithotomy (PCNL) 2
• Evaluation of urinary tract patency before nephrostomy tube removal 2
• Guidance for conversion of nephrostomy to internal ureteral stent 1
• Diagnosis of complications such as urine leaks, fistulas, or strictures 3

Interpretation and Clinical Significance

• Visualization of contrast material in the bladder indicates unobstructed antegrade ureteral flow 5
• Failure of contrast to pass beyond a certain point suggests obstruction at that level 1, 5
• Distal ureteral obstruction on nephrostogram may predict prolonged urinary leakage after nephrostomy tube removal 2
• Elevated ureteral opening pressure (>14 cm water) during nephrostogram is highly predictive of significant obstruction 4

Common Pitfalls and Considerations

• False-negative results may occur if the contrast injection pressure is insufficient to overcome partial obstruction 4
• Distal ureteral obstruction seen on nephrostogram may be temporary due to edema or blood clots and often resolves spontaneously 2
• The distal ureter is the most challenging segment to visualize on both fluoroscopic and contrast-enhanced ultrasound nephrostograms 3
• Nephrostogram findings must be correlated with clinical presentation and other imaging studies for optimal management decisions 1