Dermoid Cyst

How dermoid cysts form

During the first weeks of pregnancy, the skin and other tissues fold and fuse along lines of the face and body. If a pocket of skin-forming tissue becomes trapped beneath the surface, it grows into a sac lined with skin. That lining keeps producing keratin, oil and sometimes hair, so the cyst slowly enlarges.

Ovarian dermoid cysts are slightly different: they arise from germ cells (egg-forming cells) that can develop into any tissue, which is why they can contain hair, teeth, fat, bone or even thyroid tissue. They are called mature cystic teratomas.

Types and locations

Symptoms

Skin dermoid cysts

• a smooth, painless, rubbery or firm lump under the skin
• slow growth over years
• usually does not move much because it may be attached to underlying bone
• may become red and painful if it ruptures or gets infected

Ovarian dermoid cysts

• usually no symptoms
• pelvic pressure, fullness, bloating or a dull ache if large
• sudden severe pain if the ovary twists (ovarian torsion) or the cyst ruptures

Large dermoids are the most common type of ovarian mass to cause torsion, because they are heavy.

Dermoid vs other cysts

Diagnosis

• Skin dermoids: diagnosed by examination. Ultrasound shows the cyst and whether it involves bone. Midline nasal or scalp dermoids need CT or MRI before surgery to check for extension into the skull or brain.
• Ovarian dermoids: pelvic ultrasound shows a characteristic appearance with fat, hair and calcification. MRI or CT can confirm.
• Spinal dermoids: MRI, often prompted by a dimple, hair tuft or recurrent infection over the spine.

Treatment

Dermoid cysts do not go away on their own.

• Skin dermoids: removed surgically, usually in childhood under general anesthesia, through a small incision hidden in the eyebrow or hairline. The whole cyst wall must be removed to prevent recurrence. Removal before the cyst ruptures or enlarges is simpler and leaves a smaller scar.
• Nasal and deep dermoids: may need combined surgery with neurosurgeons if they extend toward the brain.
• Ovarian dermoids: usually removed by laparoscopic (keyhole) surgery, removing only the cyst and preserving the ovary (cystectomy) whenever possible. Small, symptom-free cysts are sometimes monitored with ultrasound, particularly near menopause or in pregnancy, but removal is commonly advised to avoid torsion.
• Infected cysts: antibiotics, then removal once the infection settles.

Outlook

Removal is curative when the whole cyst is taken out. Recurrence is uncommon. Cancer arising in a dermoid cyst is very rare, occurring in a small fraction of ovarian dermoids, mostly in women after menopause. Removing an ovarian dermoid while preserving the ovary usually does not affect fertility.

Frequently asked questions

What is a dermoid cyst?

A dermoid cyst is a benign sac that forms before birth when skin cells are trapped under the surface. It is lined with skin and can contain hair, oil and sweat glands, and in the ovary sometimes teeth or bone. Most are harmless but are removed to prevent growth or complications.

Why does a dermoid cyst have hair and teeth?

Dermoid cysts, especially ovarian ones, develop from cells that can form different body tissues. They can therefore produce hair, skin, fat, bone and even teeth inside the cyst. This is harmless in itself but makes the cyst grow and become heavy.

Do dermoid cysts need to be removed?

Usually, yes. They do not shrink on their own and tend to grow slowly. Skin dermoids are removed to prevent rupture, infection and larger scars. Ovarian dermoids are removed to avoid twisting of the ovary, rupture and, rarely, cancer.

Can a dermoid cyst cause pain?

Skin dermoids are usually painless unless they become infected or rupture. Ovarian dermoids often cause no symptoms but can cause pelvic pressure, and sudden severe pain if the ovary twists. Sudden severe pelvic pain needs emergency care.

Is a dermoid cyst cancerous?

Almost never. Dermoid cysts are benign. Cancerous change occurs in a very small percentage of ovarian dermoids, mostly in older women. Removing the cyst and having it examined under a microscope confirms that it is benign.