## **Core Concept**
Hematocolpos refers to the accumulation of blood in the vagina, often due to an obstruction that prevents menstrual blood from exiting. This condition can arise from various causes, including **imperforate hymen**, which is a congenital anomaly where the hymen completely covers the vaginal opening.

## **Why the Correct Answer is Right**
The presence of an intact hymen and the finding of hematocolpos upon incision strongly suggests that the patient has an **imperforate hymen**. This condition leads to the accumulation of menstrual blood in the vagina (hematocolpos), causing pelvic pain due to the distension of the vagina. The imperforate hymen acts as a physical barrier, preventing menstrual blood from flowing out of the vagina.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While certain **uterine anomalies** can be associated with menstrual abnormalities, they are not directly linked to hematocolpos due to an intact hymen.
- **Option B:** **Vaginal agenesis** (Mayer-Rokitansky-Küster-Hauser syndrome) involves the congenital absence of the vagina and uterus, which does not match the clinical presentation of an intact hymen and hematocolpos.
- **Option D:** **Ovarian cysts** can cause pelvic pain but are not directly associated with hematocolpos or an intact hymen causing menstrual blood accumulation.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation to remember is that **imperforate hymen** often presents with **cyclic pelvic pain** in adolescents with primary amenorrhea. A physical examination finding of a bulging, intact hymen with a bluish discoloration (due to the accumulated blood) is highly suggestive of this diagnosis. Timely surgical intervention, such as hymenotomy or hymenoplasty, can relieve symptoms and prevent complications.

## **Correct Answer:** . Imperforate hymen.