Which of the following is diagnostic of the ‘Rim sign’ in a nephrogram?
**Core Concept**
The 'Rim sign' in a nephrogram refers to a radiographic finding indicative of pyelonephritis or renal infarction, characterized by a thin, circumferential rim of contrast enhancement surrounding a non-enhancing area in the renal parenchyma.
**Why the Correct Answer is Right**
The 'Rim sign' is a result of the inflammatory response or necrosis in the renal parenchyma leading to a decrease in blood flow and contrast enhancement in the affected area. The thin, circumferential rim of contrast enhancement is due to the preservation of the renal cortex surrounding the affected area, which maintains its blood supply. This finding is often seen in pyelonephritis or renal infarction.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not describe the characteristic radiographic finding of the 'Rim sign'. A 'Urographic bladder outline' would be more indicative of ureteral obstruction.
* **Option B:** This option is incorrect as it describes a different radiographic finding, 'Renal cortical thinning', which is indicative of chronic kidney disease or long-standing hypertension.
* **Option C:** This option is incorrect as it describes a different radiographic finding, 'Renal artery stenosis', which would typically show a 'String sign' or 'Renal artery notching' rather than the 'Rim sign'.
**Clinical Pearl / High-Yield Fact**
The 'Rim sign' is a key radiographic finding in the diagnosis of pyelonephritis or renal infarction, and its recognition can help differentiate these conditions from other renal pathologies.
**Correct Answer: D. Rim sign in a nephrogram**