**Core Concept:** The "spider leg" deformity in excretory urogram is a sign observed during radiographic imaging studies of the urinary system, particularly in conditions involving the ureter. This deformity represents dilated ureteric branches.

**Why the Correct Answer is Right:** The correct answer, option D (Multiple Ureteric Rings - MUR), refers to a condition where multiple rings of dilated ureters are seen in an excretory urogram. This is due to obstructive uropathy, where there is a blockage in the urinary tract, preventing urine from flowing freely. As a result, the ureters become dilated, forming multiple, radiopaque rings, which is known as the "spider leg" deformity.

**Why Each Wrong Option is Incorrect:**

A. (Multiple Ureteric Junction - MUJ) is incorrect because the MUJ refers to multiple ureteric junctions or bifurcations, which are not related to the deformity seen in an excretory urogram.

B. (Renal Artery Stenosis - RAS) is not accurate because the "spider leg" deformity is a radiographic sign, while RAS is a clinical condition characterized by narrowing or obstruction of the renal artery supplying the kidneys. These two conditions are unrelated.

C. (Ureteric Stenosis - US) is incorrect as the "spider leg" deformity is seen in conditions causing ureteric obstruction, not ureteric stenosis which refers to a narrowing of the ureter.

D. (Multiple Ureteric Rings - MUR) is not the correct answer because MUR refers to multiple rings of dilated ureters, which is different from the "spider leg" deformity observed in MUR. The "spider leg" deformity indicates obstructive uropathy, while MUR refers to a structural abnormality in the ureters.

**Clinical Pearl:** The "spider leg" deformity is a valuable sign to identify obstructive uropathy and can help differentiate it from other urinary system conditions, such as MUR, RAS, and US. In suspected cases, further imaging tests, like CT urography or retrograde pyelography, should be considered to confirm the diagnosis and plan appropriate management.