The most common cause of urinary obstruction in a male infant is:
**Core Concept**
The most common cause of urinary obstruction in a male infant is related to abnormalities in the development of the urogenital system, particularly the urethra and bladder. This condition is often associated with anatomic anomalies that affect the normal flow of urine.
**Why the Correct Answer is Right**
The most common cause of urinary obstruction in a male infant is **Posterior Urethral Valve (PUV)**. PUVs are abnormal folds of tissue in the urethra that can cause a blockage, leading to urinary retention and potential renal damage. The condition occurs due to the abnormal development of the urethral folds during embryonic development, resulting in the formation of these obstructive valves. PUVs are often associated with a narrowing of the urethral lumen and an increase in the urethral pressure.
**Why Each Wrong Option is Incorrect**
**Option A:** Other causes of urinary obstruction in infants, such as neurogenic bladder or bladder outlet obstruction due to benign prostatic hyperplasia, are less common in this age group.
**Option B:** Meatal stenosis, a narrowing of the external urethral meatus, is a potential cause of urinary obstruction but is not the most common cause in male infants.
**Option C:** Ureterocele, a cystic dilation of the distal ureter, can cause urinary obstruction but is more commonly seen in older children and adults.
**Clinical Pearl / High-Yield Fact**
A key clinical feature of PUV is the presence of palpable abdominal masses or a distended bladder in an infant with urinary retention.
**Correct Answer: C. Ureterocele.**