A dermoid cyst of the ovary is a benign tumor that grows from egg cells and can contain surprisingly varied tissues, including hair, teeth, fat, skin, and even small amounts of thyroid or brain tissue. Officially called a mature cystic teratoma, it’s the most common benign ovarian tumor in adults and adolescents. These cysts account for roughly 70% of benign ovarian tumors in women under 30 and about 50% of ovarian tumors found in children and teens.
Why They Contain Hair and Teeth
Dermoid cysts develop from germ cells, the same reproductive cells that would normally become eggs. These cells are pluripotent, meaning they have the ability to develop into almost any type of tissue in the body. When a germ cell begins growing abnormally, it can produce tissue from all three of the body’s foundational cell layers. That’s why a single cyst can contain such a bizarre mix: skin and hair (from the outer layer), bone and muscle (from the middle layer), and thyroid tissue (from the inner layer).
The result is a sac filled with thick, oily sebum, clumps of hair, and sometimes solid structures like teeth or bone fragments. Despite how strange this sounds, dermoid cysts are overwhelmingly benign. They aren’t cancerous growths but rather disorganized collections of normal tissue growing in the wrong place.
How Fast They Grow
Dermoid cysts are slow growers. In premenopausal women, the average growth rate is about 1.8 millimeters per year, and the average size at diagnosis is around 3.7 centimeters. In postmenopausal women, they tend not to grow at all and may even shrink slightly over time. Many people have a dermoid cyst for years without knowing it, and it’s often discovered incidentally during an ultrasound or imaging scan done for an unrelated reason.
Symptoms and How They’re Found
Small dermoid cysts usually cause no symptoms. As they grow larger, you might notice a dull ache or pressure on one side of your pelvis, bloating, or discomfort during sex. The most common way these cysts are discovered is through a routine pelvic ultrasound, where they have a very distinctive appearance.
On ultrasound, dermoid cysts produce recognizable patterns. The most common feature is a “dermoid plug,” an echogenic mass inside the cyst made up of clumped hair, teeth, or fat. Another hallmark is the “tip of the iceberg” sign, where matted hair and sebum inside the cyst create a bright area that casts a dense shadow, obscuring the deeper portions. A visible fat-fluid level (where oily contents float above watery fluid) is another giveaway. When two or more of these features appear together, the diagnosis can be made with high confidence on ultrasound alone, often without needing further imaging.
Bones or teeth inside the cyst are sometimes visible on pelvic X-rays or CT scans, making dermoid cysts fairly unmistakable even on basic imaging.
Complications to Watch For
The most significant complication is ovarian torsion, where the weight of the cyst causes the ovary to twist on its blood supply. This happens in roughly 20% of women who end up having surgery for a dermoid cyst. Torsion causes sudden, severe pelvic pain, often with nausea and vomiting, and requires emergency surgery to restore blood flow before the ovary is permanently damaged. In adolescents, untwisting the ovary to preserve its function is often possible.
Rupture is less common but can occur, spilling the oily contents into the abdominal cavity and causing intense inflammation. Large cysts are more likely to cause both torsion and rupture.
Malignant Transformation
Cancerous change within a dermoid cyst is rare, occurring in roughly 1 to 3% of cases. When it does happen, squamous cell carcinoma is the most common type, accounting for about 75% of these transformations. Other rare cancers, including adenocarcinoma and melanoma, have been reported. This risk is highest in older women with larger cysts, and it’s one reason postmenopausal patients are more likely to have the entire ovary removed rather than just the cyst.
When Surgery Is Recommended
Not every dermoid cyst needs to be removed. Small, asymptomatic cysts can be monitored with periodic ultrasounds, especially since they grow so slowly. Surgery is typically recommended when a cyst is large, growing, causing pain, or raising concern about torsion.
For women of reproductive age, the standard approach is ovarian cystectomy, where the cyst is removed while preserving the healthy ovarian tissue around it. This is almost always done laparoscopically (through small incisions) when the cyst is under about 12 centimeters. Larger cysts may require open surgery through a traditional incision. For postmenopausal women, or when multiple cysts have overtaken the ovary and there’s no healthy tissue left to save, the entire ovary is removed instead.
After cystectomy in younger women, the five-year recurrence rate is about 11%. Having cysts on both ovaries or a larger initial tumor size increases that risk. Interestingly, the recurrence rate after removing the entire ovary is higher (around 20%), likely because the remaining ovary can develop a new cyst independently.
Dermoid Cysts During Pregnancy
Dermoid cysts are sometimes discovered for the first time during a routine prenatal ultrasound. If the cyst is 5 centimeters or smaller and looks clearly benign, it generally doesn’t require treatment or even follow-up during pregnancy, as many resolve on their own. Cysts larger than 5 centimeters, or those with features that look less straightforward, are typically re-evaluated after 16 weeks of pregnancy.
If surgery becomes necessary during pregnancy (because of persistent growth, concerning features, or torsion), it’s ideally scheduled between 16 and 20 weeks. This timing balances giving the cyst a chance to resolve on its own against the increased difficulty of operating later in pregnancy when the uterus is much larger. Both laparoscopic and open approaches are options, depending on the cyst’s size and the surgeon’s expertise. The decision is made on a case-by-case basis, weighing risks to both the pregnancy and the patient.