**Core Concept**
Hirsutism in teenage girls is primarily due to excess androgen exposure, most commonly from ovarian sources such as polycystic ovary syndrome (PCOS), which is the most frequent cause of ovarian disease-related hirsutism.

**Why the Correct Answer is Right**
Polycystic ovary syndrome (PCOS), the most common ovarian disease in adolescents, leads to hyperandrogenism due to increased ovarian production of androgens. This results in clinical hirsutism, acne, and irregular menses. PCOS affects up to 5–10% of adolescent girls and is characterized by insulin resistance, chronic anovulation, and enlarged ovaries. The androgen excess is not due to adrenal pathology but originates in the ovary, making ovarian disease the most common cause.

**Why Each Wrong Option is Incorrect**
Option B: Pheochromocytoma is a rare adrenal tumor causing hypertension and episodic symptoms, not hirsutism. It does not produce androgens and is not associated with hyperandrogenism.
Option C: Obesity is a risk factor for hirsutism but is a secondary contributor, not the most common cause. It may worsen PCOS but does not directly cause it.
Option D: Adrenogenital syndrome (congenital adrenal hyperplasia) presents in infancy or early childhood and causes early puberty and virilization. It is rare in teenagers and not the most common cause of hirsutism in this age group.

**Clinical Pearl / High-Yield Fact**
In teenage girls, hirsutism should always prompt evaluation for PCOS—especially with oligomenorrhea or acne—before considering other endocrine disorders. PCOS is the leading cause of hyperandrogenism in adolescents.

✓ Correct Answer: A. Ovarian disease