**Core Concept**
Papillary necrosis is a condition characterized by necrosis of the renal papillae, typically due to analgesic nephropathy, diabetes mellitus, or sickle cell disease. On an excretory urogram, papillary necrosis appears as a filling defect or a non-visualized calyx.

**Why the Correct Answer is Right**
The correct answer is a radiological finding that is NOT characteristic of papillary necrosis on an excretory urogram. Papillary necrosis typically presents as a non-visualized calyx, a filling defect, or a "ring sign" due to sloughing of the papilla. The correct answer may appear as a normal or dilated calyx, which is not a feature of papillary necrosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is a characteristic finding of papillary necrosis, as the sloughed papilla may appear as a filling defect or a non-visualized calyx on an excretory urogram.

**Option B:** This option is a feature of papillary necrosis, as the condition often leads to a non-visualized calyx due to the sloughing of the papilla.

**Option C:** This option is a feature of papillary necrosis, as the condition may present with a filling defect or a "ring sign" due to the sloughing of the papilla.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that papillary necrosis can be bilateral and may be associated with other radiological findings, such as caliectasis or pelvic dilatation.

**Correct Answer:** D