**Question:** A 67-year-old chronic heavy smoker presents with 2 weeks history of frank hematuria. USG pelvis shows a filling defect. Most probable diagnosis:

A. Ureteric calculus
B. Prostatic calculus
C. Renal cell carcinoma
D. Urethral calculus

**Core Concept:** Hematuria, also known as blood in urine, can be caused by various medical conditions, particularly in patients with a history of smoking. A filling defect on ultrasound suggests the presence of a calculus.

**Why the Correct Answer is Right:**

A. Ureteric calculus: Calculi can obstruct urinary flow causing hematuria. The filling defect on ultrasound is consistent with this diagnosis.

B. Prostatic calculus: While prostatic calculi can cause hematuria, they are less common than ureteric calculi in this patient population.

C. Renal cell carcinoma: Hematuria due to cancer is usually non-transient and non-obstructive. The filling defect is not specific to renal cell carcinoma.

D. Urethral calculus: Urethral calculi are less common and not the expected site for a filling defect on ultrasound.

**Why Each Wrong Option is Incorrect:**

A. Ureteric calculus (Option A) is not a correct answer because prostatic calculi are less common in this age group, and the filling defect is more consistent with ureteric calculi.

B. Prostatic calculus (Option B) is not a correct answer due to its rarity in this patient population and the filling defect being more consistent with ureteric calculi.

C. Renal cell carcinoma (Option C) is not a correct answer because the hematuria is not expected to be transient and obstructive, and the filling defect is not specific to renal cell carcinoma.

D. Urethral calculus (Option D) is not a correct answer as urethral calculi are less common, and the filling defect is not consistent with this diagnosis.

**Clinical Pearls:**

1. Chronic heavy smokers are at higher risk for ureteric calculi due to pH changes in urine and increased calcification risk.
2. Transient and obstructive hematuria in this patient population should raise suspicion for renal cell carcinoma.
3. Ultrasound findings should be correlated with clinical history and physical examination to narrow down the differential diagnosis.
4. Hematuria secondary to urethral calculi is usually due to direct irritation or obstruction, but the filling defect on ultrasound is not consistent with this diagnosis.

**Correct Answer:** Option A (Ureteric calculus) is the most likely diagnosis in a chronic heavy smoker presenting with transient and obstructive hematuria, and a filling defect on ultrasound.

**Core Concepts:**

Smoking causes changes in urine pH and calcification risk, increasing the likelihood of calculi formation in the urinary tract. Transient and obstructive hematuria in this patient population should raise suspicion for renal cell carcinoma. The filling defect on ultrasound is most consistent with a calculus causing direct obstruction or irritation.