‘Stipple sign’ in transitional cell carcinoma of the renal collecting system is best demonstrated by
**Core Concept**
The "stipple sign" in transitional cell carcinoma (TCC) of the renal collecting system refers to a characteristic radiographic appearance where small, stippled calcifications are visible on imaging studies. This phenomenon is often associated with the malignant transformation of urothelial cells in the renal pelvis or calyces.
**Why the Correct Answer is Right**
The stipple sign is best demonstrated by intravenous urography (IVU) or retrograde pyelography (RP), which involve the intravenous administration of contrast material to visualize the urinary tract. The stippled calcifications are thought to result from the deposition of calcium salts within the tumor, which is a common feature of TCC. As the contrast material flows through the collecting system, it highlights the stippled calcifications, making them more visible on the radiograph.
**Why Each Wrong Option is Incorrect**
**Option A:** Computed Tomography (CT) scans may show some calcifications but are not the best modality for demonstrating the stipple sign due to their lower spatial resolution and potential for artifacts.
**Option B:** Magnetic Resonance Imaging (MRI) is highly sensitive for detecting soft tissue abnormalities but is not ideal for visualizing calcifications or the stipple sign.
**Option C:** Ultrasound is a valuable tool for assessing renal anatomy and detecting hydronephrosis but is not typically used to demonstrate the stipple sign.
**Clinical Pearl / High-Yield Fact**
The stipple sign is a valuable diagnostic clue for TCC, especially in patients with a history of smoking or chronic kidney stones. However, it is essential to consider other imaging modalities and clinical findings to confirm the diagnosis.
**Correct Answer:** C.