A 20-year-old woman has an ovarian tumor removed. The surgical specimen is 10 cm in diameter and cystic. The cystic cavity is found to contain black hair and sebaceous material. Histologic examination of the cyst wall reveals a variety of benign differentiated tissues, including skin, cailage, brain, and mucinous glandular epithelium. What is the diagnosis?

**Core Concept**
The question is testing the student's knowledge of a rare type of ovarian tumor known as a dermoid cyst (also called a mature teratoma). A dermoid cyst is a type of germ cell tumor that contains a mixture of mature tissues from all three embryonic layers: ectoderm, endoderm, and mesoderm. This diversity of tissues is a hallmark of dermoid cysts.

**Why the Correct Answer is Right**
The presence of black hair, sebaceous material, and a variety of differentiated tissues (such as skin, cartilage, brain, and mucinous glandular epithelium) within the cystic cavity is characteristic of a dermoid cyst. Dermoid cysts arise from the ovary's germ cells and contain a mix of mature tissues that can include skin, hair, teeth, cartilage, and other structures. The presence of these tissues in the surgical specimen is a strong indication of a dermoid cyst.

**Why Each Wrong Option is Incorrect**
**Option A:** A serous cystadenoma would not contain such a diverse mix of tissues, nor would it typically have a cystic cavity containing hair and sebaceous material.
**Option B:** A mucinous cystadenoma may contain mucinous glandular epithelium, but it would not have the same diversity of tissues as a dermoid cyst.
**Option C:** An ovarian fibroma would not contain a mix of differentiated tissues, and it would not have a cystic cavity with hair and sebaceous material.

**Clinical Pearl / High-Yield Fact**
Dermoid cysts are also known as mature teratomas because they contain a mix of mature tissues from all three embryonic layers. They are a type of germ cell tumor and are often found in young women.

**Correct Answer:** D. Dermoid cyst (mature teratoma).

✓ Correct Answer: D. Teratoma