**Question:** Spider-leg sign on IVP is suggestive of: March 2010

**Core Concept:** The spider-leg sign on intravenous pyelography (IVP) is a radiographic pattern characterized by the appearance of dilated collecting systems with a segmental dilatation resembling the legs of a spider. This sign is indicative of a renal pelvic obstruction.

**Why the Correct Answer is Right:** The spider-leg sign on IVP is generally associated with a ureteric obstruction, specifically an obstruction at the level of the renal pelvis. This obstruction causes the dilated collecting system to extend into the renal pelvis, resulting in the characteristic appearance of dilated "legs" radiating outwards from the renal pelvis, resembling a spider's legs.

**Why Each Wrong Option is Incorrect:**

A. **Option A (renal papilla dilatation):** Renal papilla dilatation is not associated with the spider-leg sign. Instead, it is seen in dilated renal calyces, which is a different radiographic pattern.

B. **Option B (renal parenchymal changes):** Renal parenchymal changes, such as parenchymal atrophy, are not typically associated with the spider-leg sign. The sign is mainly indicative of ureteric obstruction.

C. **Option C (hydronephrosis):** Hydronephrosis refers to dilation of the renal pelvis and calyces due to obstruction, but the spider-leg sign is specific to renal pelvic obstruction and does not occur in hydronephrosis.

D. **Option D (renal artery stenosis):** Renal artery stenosis is a separate radiographic sign seen in renal artery stenosis and does not represent the spider-leg sign.

**Clinical Pearl:** The spider-leg sign on IVP is an important diagnostic clue in the evaluation of patients with suspected ureteric obstruction. It helps in directing the clinician towards the level of obstruction (renal pelvis) and guides further management and investigations.

**Correct Answer:** C. Hydronephrosis

In summary, the spider-leg sign on IVP is primarily indicative of a renal pelvic obstruction (hydronephrosis) due to the dilatation of the renal pelvis radiating outwards, resembling the legs of a spider. This sign helps in pinpointing the level of obstruction and aids in formulating a proper diagnostic and management plan for the patient.