**Question:** A 67 year old man presented initially after a single episode of gross painless haematuria. An excretory urogram demonstrated a 1.5 mm round filing defect in the right lower renal infundibulum. The best study to obtain next is -

A. Computed Tomography (CT)
B. Ureteroscopy
C. Intravenous Pyelogram (IVP)
D. Nephrostogram

**Correct Answer:** D. Nephrostogram

**Core Concept:** Nephrostogram, also known as retrograde pyelography, is an imaging technique used to visualize the kidney, ureter, and bladder by injecting contrast medium through the urethra. This is essential for assessing the renal pelvis, calyces, and ureter, as well as evaluating for any obstructive uropathy or stone formation.

**Why the Correct Answer is Right:** In this scenario, a nephrostogram would be the most appropriate next study to obtain because it allows for an accurate assessment of the renal pelvis and calyces, which are crucial structures for diagnosing the right lower renal infundibulum defect observed in the excretory urogram. Nephrostogram provides detailed images of the renal pelvis and ureter, enabling a proper evaluation of the defect and potential underlying cause.

**Why Each Wrong Option is Incorrect:**

A. Computed Tomography (CT) - While CT is a valuable imaging modality, it is not specifically designed for assessing the renal pelvis and ureter, which is crucial in this case. CT is primarily used for assessing the kidney, collecting system, and urinary tract stones.

B. Ureteroscopy - This procedure is used to examine the ureter and bladder directly, not for imaging purposes. It is usually performed when there is suspicion of a stone or stricture in the ureter.

C. Intravenous Pyelogram (IVP) - IVP focuses on the kidney and collecting system, not the renal pelvis and ureter, which are the primary concern in this scenario. It is primarily used for assessing the kidney and ureteral calyces.

**Clinical Pearls:**

1. Nephrostogram is a valuable tool for evaluating the renal pelvis and ureter, which is crucial in diagnosing the renal defect observed in the excretory urogram.
2. In cases where a detailed assessment of the renal pelvis and ureter is essential, nephrostogram should be considered. This is particularly relevant when evaluating potential causes of gross hematuria, obstructive uropathy, or suspected ureteral pathology.
3. IVP and CT are valuable imaging techniques but focus on the kidney and collecting system, not the renal pelvis and ureter. Ureteroscopy is used for direct examination of the ureter and bladder, not for imaging purposes.

In conclusion, nephrostogram is the correct choice due to its specific focus on the renal pelvis and ureter, allowing for accurate evaluation of the renal defect and potential underlying cause of gross hematuria, obstructive uropathy, or suspected ureteral pathology.