A dermoid cyst is a sac-like growth that contains tissues you would normally find on the surface of the body, including skin, hair follicles, oil glands, and sometimes even sweat glands or teeth. These cysts form before birth when skin cells and other tissue types get trapped in the wrong place during early embryonic development. They can appear almost anywhere, from a child’s eyebrow to an adult’s ovary to, rarely, the brain. Most are benign and slow-growing, but their contents and location determine how much trouble they cause and how urgently they need to come out.
What Is Actually Inside a Dermoid Cyst
Opening a dermoid cyst is one of those moments in medicine that tends to surprise people. The lining looks like skin turned inside-out, because that is essentially what it is: keratinizing, layered skin tissue that sheds dead cells into the cyst’s interior the same way your outer skin sheds into the environment. One study of craniofacial dermoid cysts found every single cyst contained this skin-like lining, a buildup of keratin (the protein in your hair and nails), and actual hair. Sebaceous glands, the tiny oil-producing structures in your skin, were present in most of them.1PubMed Central. Craniofacial Dermoid Cysts: Histological Analysis and Inter-site Comparison The result is a cyst filled with a thick, waxy, yellowish paste made of oil, keratin, and hair, sometimes described by surgeons as resembling cheesy or buttery material.
Dermoid cysts are sometimes confused with epidermoid cysts, which look similar on the outside but are simpler structures. The distinction matters for pathologists: an epidermoid cyst has only a layer of squamous epithelium, while a dermoid cyst additionally contains hair, sebaceous glands, and sometimes sweat glands.2PubMed. Teratomas, dermoids, and epidermoids of the head and neck In the ovary, the terminology shifts further. Ovarian dermoid cysts are often called mature cystic teratomas because they can contain tissues derived from all three embryonic cell layers, meaning they might include not just skin and hair but also bone fragments, cartilage, thyroid tissue, or even rudimentary tooth structures.3PubMed Central. Mature Cystic Teratoma: An Integrated Review A multicenter study of oral dermoid cysts found sebaceous glands in nearly all cases, usually clustered around a central hair follicle in what pathologists call a pilosebaceous unit.4Brazilian Oral Research. Clinicopathologic analysis of oral dermoid and epidermoid cysts: a multicenter study
Dermoid Cysts Near the Eye in Children
The most common setting where parents first encounter dermoid cysts is on a child’s face, usually near the eye. Orbital dermoid cysts tend to sit along the bony rim of the eye socket, and superficial ones are often noticed during the first year of life as painless, smooth, firm bumps that move freely under the skin.5PubMed Central. Orbital dermoid cyst in children: A case report They form at suture lines, the seams between the skull bones that have not yet fused in a young child. In one surgical series of 30 children, the outer corner of the eyebrow area was the most frequent location, accounting for roughly nine out of every ten cases. About two-thirds of the cysts were superficial enough to feel their edges completely, while a third extended deeper beyond the orbital rim and required imaging to map out.6PubMed. Orbital dermoid cyst of childhood: clinical pathologic findings, classification and management
Deeper orbital dermoid cysts may not announce themselves until later in childhood. Instead of a visible bump, they can slowly push the eyeball forward, a symptom called proptosis. Because children may not complain about gradual changes in their vision or the way their eye looks, deeper cysts can grow for years before someone notices. The standard treatment for both superficial and deep orbital dermoid cysts is surgical removal, partly for cosmetic reasons and partly because an intact cyst is easier to remove than one that has ruptured. When a dermoid cyst ruptures, its oily contents leak into surrounding tissue and trigger a strong inflammatory reaction.7PubMed Central. Craniofacial Dermoid Cysts: Histological Analysis and Inter-site Comparison
When Location Raises the Stakes
Not all craniofacial dermoid cysts carry the same risk. Midline nasal dermoid cysts, the ones that appear on the bridge of the nose, have long been flagged as potentially dangerous because they can extend inward through the skull bones and reach the brain’s coverings. But research has shown the concern should not be limited to the nose. Frontal, temporal, and occipital cysts can be just as risky, if not more so, for intracranial extension.8PubMed. Risk of Intracranial Extension of Craniofacial Dermoid Cysts A systematic review pooling data from over 700 pediatric patients found that intracranial extension occurred in roughly 9 percent of cases. Almost all of those were midline lesions; only two patients with purely orbital cysts had extension into the skull.9PubMed. Lesion location and surgical outcomes in pediatric frontonasal and orbital dermoid cysts: A systematic review
When a midline frontonasal dermoid does extend inward, surgery becomes considerably more involved. In one series of frontonasal dermoid cases, about one in five required a transcranial surgical approach to address intracranial extension, and one of those lesions had actually breached the dura, the tough membrane surrounding the brain.10Plastic and Reconstructive Surgery. The Management of Midline Frontonasal Dermoids This is why doctors almost always order imaging, usually an MRI, for any dermoid cyst along the midline of the face. The cyst itself might look small and innocent on the surface while a thin stalk trails inward toward the brain.
Dermoid Cysts in the Mouth
The floor of the mouth is another classic dermoid cyst location. These sublingual dermoid cysts typically present as a painless, soft, movable mass in the midline beneath the tongue. They grow slowly, but if they get large enough, they can push the tongue upward and interfere with speech and swallowing.11PubMed Central. Sublingual Dermoid Cyst: Review of 14 Cases Even in very young children, these cysts can reach a noticeable size. A case report described a cyst in a two-year-old that measured about 15 millimeters across, discovered as a painless lump on the floor of the mouth.12PubMed Central. Sublingual Dermoid Cyst in Young Child Treatment is surgical excision, typically through the mouth, and recurrence after complete removal is rare.
Ovarian Dermoid Cysts
By far the most commonly encountered dermoid cysts in adults are ovarian dermoid cysts, also called mature cystic teratomas. These account for roughly 70 percent of ovarian germ cell tumors in young women, making them the single most common type.13PubMed Central. Mature Cystic Teratoma: An Integrated Review Many are discovered incidentally during a pelvic ultrasound done for another reason. Around 20 percent produce no symptoms at all. When symptoms do occur, they usually amount to pelvic pain or a sense of pressure. Ovarian dermoid cysts can grow to impressive sizes, sometimes exceeding 10 centimeters, though many hover in the range of several centimeters.
On ultrasound, ovarian dermoids produce some of the most distinctive images in radiology. Because the cyst contains a mix of fat, fluid, and solid tissue, it creates characteristic patterns: a visible fat-fluid level where the oily component floats on top, a dense bright area called a dermoid plug, or a pattern of tangled echoes called “dermoid mesh” caused by hair floating inside the cyst. When two or more of these typical features are present, a confident diagnosis can be made on ultrasound alone.14PubMed Central. Ultrasound of ovarian dermoids 15Ultrasound. Ultrasound in the diagnosis of ovarian dermoid cysts: a pictorial review of the characteristic sonographic signs CT and MRI can confirm the diagnosis when the ultrasound picture is ambiguous, and fat within the cyst lights up on CT in a way that is almost unmistakable.
Torsion and Rupture
The main acute risk with ovarian dermoid cysts is torsion, where the ovary twists on its blood supply. This is a surgical emergency that causes sudden, severe pelvic pain. Research on dermoid cysts and torsion has found that younger women were significantly more likely to experience torsion than older women. Interestingly, the size of the cyst was not a reliable predictor of who would develop torsion; it occurred with cysts as small as 55 millimeters and as large as 100-plus millimeters. The clinical tip-off for torsion on top of pain was nausea and vomiting, which was present in nearly half of torsion cases compared to fewer than one in ten women with non-twisted dermoids.16PubMed. Dermoid cysts causing adnexal torsion: What are the risk factors?
Rupture is the other serious complication. When the oily, waxy contents of a dermoid cyst spill into the abdominal cavity, they can trigger chemical peritonitis, a sterile but intense inflammatory reaction of the lining of the abdomen. A subgroup analysis found a substantially elevated risk of chemical peritonitis when cyst rupture occurred.17PubMed Central. Dermoid Cyst Spillage Resulting in Chemical Peritonitis: A Case Report and Literature Review Spontaneous rupture is rare, but spillage during surgical removal is a well-known concern, especially during laparoscopic procedures where the cyst is being extracted through small incisions. When spillage does happen during surgery, thorough washing of the abdominal cavity with fluid and placement of a drain can minimize the risk of a significant inflammatory response.18PubMed Central. Laparoscopic treatment of ovarian dermoid cysts is a safe procedure When a dermoid ruptures spontaneously, prompt surgical removal and thorough peritoneal lavage are the standard approach.19PubMed Central. Chemical peritonitis resulting from spontaneous rupture of a mature ovarian cystic teratoma: a case report
How Often Do Dermoid Cysts Become Cancerous
The vast majority of ovarian dermoid cysts are benign. Malignant transformation does occur, but it is rare. A systematic review analyzing published cases of squamous cell carcinoma arising within ovarian mature cystic teratomas estimated the incidence at about 0.3 percent.20PubMed Central. Squamous cell carcinoma transformation in mature cystic teratoma of the ovary: a systematic review The average age at diagnosis for this transformation was in the mid-fifties, well above the typical age range for a benign dermoid cyst. When malignant change does happen, the cancer most often arises from the squamous epithelial lining of the cyst, producing squamous cell carcinoma.21PubMed Central. Squamous cell carcinoma arising in mature cystic teratoma of ovary This is one reason doctors sometimes recommend removing larger or growing dermoid cysts in postmenopausal women rather than watching them, since the already-low risk of malignancy inches up with age.
A Rare Neurological Link
One of the more striking associations with ovarian dermoid cysts is anti-NMDA receptor encephalitis, a serious autoimmune condition that affects the brain. In this scenario, neural tissue within the dermoid cyst triggers the immune system to produce antibodies that mistakenly attack NMDA receptors in the brain.22PubMed Central. Anti-N-Methyl-D-Aspartate (NMDA) Receptor Encephalitis Secondary to an Ovarian Dermoid Cyst Patients, usually young women, develop psychiatric symptoms, seizures, involuntary movements, and sometimes a progressive decline in consciousness. Before this condition was recognized in the late 2000s, many affected patients were misdiagnosed with psychiatric illness. The treatment involves removing the tumor and suppressing the immune response. Once the dermoid cyst is gone, many patients recover substantially, though the timeline can stretch over months.
Dermoid Cysts Inside the Skull and Spine
Dermoid cysts can also form within the central nervous system itself, not just extend into it from outside the skull. Intracranial dermoid cysts are uncommon and usually sit along the midline of the brain. They grow slowly, and many are found incidentally on imaging done for unrelated reasons. The concern is rupture: when an intracranial dermoid cyst bursts, it releases fat droplets into the cerebrospinal fluid. These droplets spread across the brain surface and sometimes drift down into the spinal canal. About 8 percent of reported intracranial dermoid cyst ruptures lead to chemical meningitis, an inflammatory reaction in the membranes surrounding the brain that can closely mimic bacterial meningitis. The presence of multiple fat droplets in the fluid spaces on MRI helps distinguish the two conditions.23PubMed Central. Chemical Meningitis after a Golf Swing-induced Dermoid Cyst Rupture In rare cases, ruptured intracranial contents can progressively disseminate into the spinal canal over time, creating an ongoing management challenge.24PubMed Central. Ruptured intracranial dermoid cyst with progressive spinal dissemination: illustrative case
Associations with Goldenhar Syndrome
While most dermoid cysts are isolated findings with no broader genetic implications, they occasionally appear as part of recognizable congenital syndromes. Goldenhar syndrome, a condition that affects the development of the face, ear, and spine, has been associated with intracranial dermoid cysts. Reports have described patients with Goldenhar syndrome who were found to have dermoid cysts in the posterior fossa of the skull.25Pediatric Neurosurgery. Posterior Fossa Dermoid Cyst in a Patient with Goldenhar Syndrome Skull defects and other intracranial abnormalities have also been documented alongside the syndrome.26PubMed. Cranial defects in the Goldenhar syndrome The embryonic disruption causing both the facial anomalies and the dermoid cyst is thought to occur during the same narrow window, between the third and fifth week of development. Genetic testing of patients with Goldenhar syndrome has not consistently identified a single causative mutation, suggesting it involves complex developmental pathways rather than a single-gene defect.27American Journal of Ophthalmology Case Reports. Goldenhar syndrome associated with lacrimal system agenesis: A case report
Dermoid Sinus in Dogs
Dermoid cysts are not unique to humans. One of the best-studied animal parallels is the dermoid sinus in Rhodesian Ridgeback dogs. The distinctive dorsal hair ridge in these dogs is caused by a duplication of a DNA segment containing several fibroblast growth factor genes, and this same mutation predisposes them to dermoid sinus, a tube-like tract of skin that burrows inward from the surface, sometimes reaching the spinal canal.28Nature Genetics. Duplication of FGF3, FGF4, FGF19 and ORAOV1 causes hair ridge and predisposition to dermoid sinus in Ridgeback dogs A large study covering over 12,700 puppies found the overall prevalence of dermoid sinus was about 2.5 percent, with evidence of a decreasing trend over time as breeders have worked to reduce it. The genetics turned out to be more complex than a simple single-gene inheritance pattern, with a heritability estimate suggesting strong but not straightforward genetic influence.29PubMed. Prevalence and segregation analysis of dermoid sinus in Rhodesian Ridgebacks This animal model has been useful for researchers studying how misplaced skin cells during development can create dermoid-type growths, reinforcing the idea that the fundamental problem, skin trapped in the wrong layer during embryogenesis, is a conserved biological phenomenon across species.