A 42 year old woman has had a feeling of abdominal discomfo for the past 8 months. Abdominal CT scan demonstrates a 6 cm cystic mass involving the right ovary with small areas of calcification. Post removal, the ovary grossly, the mass on sectioning is filled with abundant hair and sebum. Microscopically, the mass has glandular spaces lined by columnar epithelium, squamous epithelium with hair follicles, cailage, and dense connective tissue. What type of tumour is it?

**Core Concept**
The underlying principle being tested is the identification of a specific type of ovarian tumor based on its histological characteristics. This involves understanding the **pathological features** of various ovarian tumors, including **dermoid cysts**. The presence of **hair**, **sebum**, and **calcification** within the tumor is key to its identification.

**Why the Correct Answer is Right**
The tumor in question contains a variety of tissues such as **hair follicles**, **cartilage**, **squamous epithelium**, and **dense connective tissue**, which are characteristic of a **mature cystic teratoma**, also known as a **dermoid cyst**. This type of tumor is a form of **germ cell tumor** that arises from the ovary and can contain several different types of tissues, reflecting the potential of germ cells to differentiate into various cell types.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect because it does not match the description given.
**Option B:** Would be incorrect because it does not match the description given.
**Option C:** Would be incorrect because it does not match the description given.
**Option D:** Is not provided to assess.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **dermoid cysts** are a type of **benign ovarian tumor** but can be at risk for **torsion** or **malignant transformation**, making their identification and management important.

**Correct Answer:** D. Mature Cystic Teratoma (Dermoid Cyst)

✓ Correct Answer: D. Teratoma