Dermoid Ovarian Cyst
A dermoid cyst, known medically as a mature cystic teratoma, is a benign ovarian growth that develops from a germ cell—the same type of cell that would become an egg. Because germ cells are capable of forming any tissue in the body, these cysts contain fully formed mature tissues in the wrong place: most commonly skin, hair, and fatty material, and often teeth, bone, or cartilage. This sounds alarming and is frequently distressing to read about, but the essential facts are reassuring. Dermoid cysts are benign, they are the most common ovarian tumour in young women, malignant change is rare, and many require no treatment beyond periodic monitoring. Their main clinical significance is that their weight makes the ovary more likely to twist.
What is it?
The ovaries contain germ cells, the cells that mature into eggs. Germ cells are pluripotent, meaning they retain the capacity to develop into any tissue type in the body—this is the property that allows a fertilised egg to build an entire person.
A dermoid cyst arises when a germ cell begins developing without fertilisation and produces mature tissues in a disorganised way. The medical name, mature cystic teratoma, describes this precisely: mature because the tissues are fully formed rather than primitive, cystic because it forms a fluid-filled sac, and teratoma from the Greek for monster, an unfortunate historical term that reflects how these lesions struck early anatomists rather than anything about their behaviour.
The contents reflect this origin. Dermoid cysts characteristically contain tissues derived from all three embryonic layers, with skin-type tissue predominating—hence the name dermoid. Typical contents include thick greasy sebaceous material produced by skin glands, hair, and skin itself. Teeth are present in a substantial proportion. Bone, cartilage, fat, and occasionally fragments of thyroid, nerve, or respiratory tissue also occur. The tissues are entirely normal in structure; they are simply in the wrong location.
Two things are worth stating clearly because people commonly wonder about them. A dermoid cyst is not a failed or absorbed twin, despite a persistent popular belief to that effect. And it is not the result of anything a woman did, ate, or was exposed to.
Most dermoid cysts are slow-growing, typically enlarging by only a millimetre or two each year. This slow growth is one of the reasons observation is a reasonable approach for small cysts.
Several variants and associations are worth knowing.
Bilateral cysts occur in roughly 10 to 15 percent of cases, which is why the other ovary is examined carefully whenever one is found, and why it is reassessed during surgery.
Struma ovarii is an uncommon variant in which thyroid tissue predominates within the teratoma. It can produce thyroid hormone and, rarely, cause symptoms of an overactive thyroid.
Immature teratoma is a distinct and genuinely malignant tumour containing primitive rather than mature tissue. It occurs predominantly in adolescents and young women, is uncommon, and is treated as a cancer—but it is a different diagnosis rather than a progression from a dermoid cyst.
Malignant transformation of a dermoid cyst does occur but is rare, reported in approximately 1 to 2 percent. It is concentrated in women over 45 and in larger cysts, typically those above about 10 centimetres, and most commonly takes the form of squamous cell carcinoma arising from the skin-type tissue within the cyst. This risk is the main reason age and size influence management decisions.
An unusual but important association is anti-NMDA receptor encephalitis, a condition in which the immune system reacts against nerve tissue within an ovarian teratoma and attacks the brain. It presents with psychiatric symptoms, confusion, seizures, and movement disorders, often in young women, and is frequently mistaken for a primary psychiatric illness. Removing the teratoma is a central part of treatment and often leads to substantial recovery. It is rare, but it is the reason a young woman presenting with unexplained encephalitis or acute psychiatric symptoms may be scanned to look for an ovarian mass.
Most dermoid cysts cause no symptoms and are found incidentally—on a scan for unrelated abdominal pain, during pregnancy ultrasound, at a routine examination, or during surgery for another reason.
When symptoms occur they generally relate to size. A dull ache, dragging sensation, or feeling of pressure in the lower abdomen is common. Larger cysts cause bloating, a palpable mass, and pressure on the bladder or bowel producing urinary frequency or constipation. Pain during intercourse can occur.
Three acute complications matter, and they account for most of the urgency surrounding this otherwise benign condition.
Ovarian torsion is the most common and most important. Dermoid cysts are disproportionately associated with torsion because their solid, fatty, sometimes calcified contents make them heavy, giving the ovary the mass and leverage to twist on its supporting ligaments. This cuts off the blood supply and constitutes a surgical emergency. It presents with sudden severe one-sided pelvic pain, frequently with nausea and vomiting, and sometimes with pain that comes and goes as the ovary twists and untwists. The risk of torsion is the single most common reason removal is recommended for cysts above a certain size.
Rupture is uncommon but consequential. Spilling the thick sebaceous contents into the abdominal cavity provokes intense chemical irritation of the peritoneum, producing severe pain, abdominal rigidity, and fever, and can lead to widespread inflammation and adhesions. Rupture may occur spontaneously, following trauma, or during surgery—which is why surgeons take considerable care to remove these cysts intact.
Infection is rare but can occur.
Diagnosis is usually straightforward, because dermoid cysts have an unusually distinctive appearance.
Ultrasound is the primary test and is frequently diagnostic on its own. The characteristic features reflect the contents: a bright echogenic nodule projecting into the cyst cavity, known as a Rokitansky nodule or dermoid plug, which typically contains hair, teeth, or bone; bright linear echoes and dots representing strands of hair within fluid; a fat-fluid level, where the lighter fatty material floats above denser fluid; and dense acoustic shadowing behind calcified components, which can be so pronounced that it obscures the back of the cyst entirely. This last feature produces an appearance sometimes called the tip of the iceberg sign, where only the front of the lesion is visible.
MRI confirms the diagnosis when ultrasound is inconclusive. Its particular value is demonstrating fat directly using fat-suppression sequences—the signal from fatty components drops away, which is essentially diagnostic and distinguishes a dermoid from blood within an endometrioma, which can look similar on other sequences.
CT shows fat density and calcification clearly, and dermoid cysts are commonly identified incidentally on CT performed for unrelated reasons, occasionally with a visible tooth.
CA-125 has no useful role here and may be mildly raised without significance, which is worth knowing because an unnecessary test can generate unnecessary worry. In younger women with atypical imaging, germ cell tumour markers may be measured to assess for the malignant germ cell tumours that affect that age group.
The differential includes endometrioma, haemorrhagic functional cyst, and bowel, all of which can mimic a dermoid on ultrasound, and where imaging is uncertain MRI usually resolves the question.
Important to Know
The central message is that a dermoid cyst is benign, common, and often requires nothing more than periodic monitoring. Care is typically coordinated by gynaecologists, with specialist input where fertility is a consideration or where imaging is atypical.
The contents of these cysts cause understandable distress when women read about them, and it is worth addressing that directly. Finding hair and teeth inside an ovarian cyst sounds shocking, but it reflects nothing more than the versatility of the cell the cyst came from. It carries no implications for a woman’s health beyond the practical issues of size and torsion risk, and no implications for future pregnancies.
Observation is a legitimate approach for small, asymptomatic cysts with typical features on imaging. Given growth rates of only a millimetre or two per year and the benign nature of the lesion, monitoring with periodic ultrasound—initially at intervals of several months and then annually if stable—is reasonable. Many women choose this and never require surgery.
Surgery is generally recommended in several situations: cysts causing symptoms, cysts above a size threshold commonly set around five to six centimetres because torsion risk rises with size, cysts that are growing on follow-up, cysts with features that are not clearly typical of a dermoid, and cysts in women over 45 where the small malignant transformation risk is concentrated. Thresholds vary between centres and the decision is individualised.
Laparoscopic cystectomy is the preferred operation. It removes the cyst while preserving the ovary, which matters considerably for a condition affecting young women. Careful technique aims to remove the cyst intact, because spilling the contents causes chemical peritonitis and adhesions—and where spillage does occur, thorough washing of the abdominal cavity substantially reduces this risk. Modern evidence indicates that with appropriate technique, laparoscopic removal is safe and the historical concern about spillage should not push women toward open surgery.
Ovarian preservation deserves emphasis. Removing the whole ovary in a young woman reduces her remaining egg reserve unnecessarily when cystectomy is feasible. Cystectomy does remove a small amount of surrounding normal ovarian tissue, so there is a modest cost to ovarian reserve, but this is far less than losing the ovary entirely. For women concerned about fertility, this is a reasonable point to discuss explicitly with a surgeon.
Torsion is the complication to be alert to, and women with a known dermoid cyst should understand what it feels like: sudden severe pain on one side, often with nausea and vomiting, requiring immediate assessment. Pain that eases does not mean the problem has resolved, since the ovary may untwist temporarily and twist again.
In pregnancy, dermoid cysts are commonly found on routine scans. Most are managed expectantly, since torsion risk must be weighed against the risks of surgery during pregnancy. Where surgery is needed, the second trimester is generally preferred. Torsion during pregnancy requires prompt surgery regardless of gestation.
Recurrence after removal is possible, either in the same ovary or the other, and is reported in a small percentage of women. This is one reason follow-up is sometimes continued and why new symptoms should be assessed rather than assumed to be unrelated.
After menopause, a newly identified complex ovarian mass is approached more cautiously than in a young woman, since the possibility of malignancy is higher in that age group and typical dermoid features carry less reassurance than they do at 25. Assessment in this situation usually involves specialist review.
Care is typically coordinated by gynaecology, with radiology input for characterisation and fertility specialist involvement where relevant. Imaging and clinical findings are interpreted alongside age, symptoms, cyst size and growth, and reproductive plans rather than in isolation.
Patient education plays an important role, largely because the nature of these cysts is so often misunderstood. Understanding that a dermoid cyst is benign, that its contents reflect the cell it grew from rather than anything abnormal about the woman, that small cysts can safely be watched, that surgery preserves the ovary in most cases, and that the main risk to be alert to is torsion all contribute to appropriate care and to considerably less anxiety.
Red flag symptoms include sudden severe pain on one side of the lower abdomen or pelvis, particularly with nausea or vomiting, which suggests ovarian torsion and requires immediate emergency assessment; severe pelvic pain that comes and goes in waves; sudden severe abdominal pain with a rigid, exquisitely tender abdomen and fever, which may indicate rupture; rapid increase in abdominal size; fever with pelvic pain suggesting infection; dizziness, fainting, or a racing heart alongside pelvic pain; and in a woman with a known cyst, any new severe pain rather than the familiar dull ache. These require urgent medical assessment.