A 44-year-old woman presented with a swelling in the midline floor of the mouth that elevated the floor of mouth and tongue. The mucosa over the cyst was yellowish in colour.

Dermoid cysts are cystic lesions that develop from abnormal inclusion of skin tissue during embryonic development. These cysts can occur along the midline of the body, including in the oral region. In the oral cavity, they can be found either above or below the mylohyoid muscle.

When a dermoid cyst is located above the mylohyoid muscle, it causes a bulge into the floor of the mouth. On the other hand, if it is located below the mylohyoid muscle, it expands into the submental soft tissue. The mylohyoid muscle is a muscle located in the floor of the mouth that separates the oral cavity from the submental region below the chin.

Histological examination refers to the microscopic analysis of the cyst’s tissue. When a dermoid cyst is examined under a microscope, the lining of the cyst resembles epidermis, which is the outermost layer of the skin. This means that the tissue inside the cyst looks similar to the surface of the skin.

Additionally, adnexal structures are often found within dermoid cysts. These structures include hair follicles, sebaceous glands (oil glands), and smooth muscle. Hair follicles are responsible for hair growth, while sebaceous glands produce oil to moisturize the skin and hair. Smooth muscle is a type of muscle tissue that is not under voluntary control and is typically found in the walls of organs.

The presence of these adnexal structures within the lining of the cyst helps to confirm the diagnosis of a dermoid cyst. The combination of the epidermis-like lining and the presence of hair follicles, sebaceous glands, and smooth muscle is characteristic of dermoid cysts.

It’s important for dental students to be aware of dermoid cysts because they can present in the oral region and may require surgical intervention for removal. Proper diagnosis and treatment planning are crucial to ensure optimal patient care.