**Question:** An 18-year old girl who has not attained menarche comes to casualty with acute retention of urine. The most likely diagnosis is:

A. Hypothyroidism
B. Congenital adrenal insufficiency
C. Myoma
D. Urinary calculi

**Core Concept:** Acute retention of urine is a situation where the bladder becomes completely or almost completely emptied, leading to sudden inability to pass urine despite a full bladder. This can be caused by various physiological and pathological conditions affecting the urinary system or other systems that result in bladder dysfunction.

**Why the Correct Answer is Right:** The correct answer is option A (Hypothyroidism) because hypothyroidism can lead to autonomic neuropathy, affecting the autonomic nervous system's function in various organs, including the bladder. In this case, hypothyroidism may cause bladder dysfunction, leading to acute retention of urine.

**Why Each Wrong Option is Incorrect:**

A. Congenital adrenal insufficiency (CAI) is a genetic disorder affecting the adrenal glands, not the bladder. Therefore, it is not the most likely diagnosis for acute retention of urine in this case.

B. Myoma is a benign tumor of the uterus, not related to the bladder or urinary system. Acute retention of urine due to myoma would typically present with lower abdominal pain, not urethral obstruction.

C. Urinary calculi are kidney stones, which cause ureteric obstruction and not acute retention of urine.

**Clinical Pearl:** In medical exam scenarios, remember to consider hypothyroidism as a differential diagnosis for acute retention of urine, especially in patients with no known risk factors or history of bladder or urethral pathologies. Recognizing and treating the underlying thyroid disorder promptly can prevent further complications and improve the patient's condition.