What is an Ovarian Dermoid and Why Does It Grow Teeth!?

Photo Credit CMDRC.com

My first experience with an ovarian dermoid tumor was in medical school. I saw a picture in our text book and was immediately repulsed – how can something that creepy be a real-life finding?!

Though the tumors continue to be one of the stranger pathologies I deal with, the repulsion-factor has subsided. So, what in the heck is an ovarian dermoid and why would an ovary have teeth inside it?

What I’m calling a “dermoid” is just another name for the most common type of ovarian germ cell tumor, in textbooks it will usually be called a mature teratoma. Dermoid came about in modern medicine after the discovery that dermal elements frequently predominate the tumors.

The origination of the word teratoma is from the Greek word teras, which means monster. Since they can contain fully formed teeth, bone, hair, and other weirdness, it is not hard to figure out why this would have been the name people gave it way back before we knew about how the out-of-place tissue got there.


If you haven’t read the book “Brain on Fire” by Susannah Cahalan you need to get your hands on it. We read it for book club in residency and all the spouses enjoyed it as well, it’s definitely not targeted at medical audiences. Dermoid tumors are occasionally (rarely) associated with an unusual condition called NMDA-Receptor Encephalitis and this is a fascinating and well-written memoir by a New York Post reporter documenting her long and life-threatening journey to this diagnosis.

Pathophysiology, Diagnosis, Treatment…

Dermoids are neoplasms which arise from primordial germ cells and there are several types of teratomas. For board exam purposes, here’s some broad, quick, key-word references:

  • Mature Teratoma = Common = Benign
         – AKA: Dermoid/Cystic Teratoma
  • Immature Teratoma = Rare = Malignant
        – AKA: Teratoblastoma or Embryonal Teratoma

Teratomas in general are defined by the fact that they arise from a single germ cell, meaning they have the capability to differentiate into any of the germ cell layers and frequently contain all three (endoderm, ectoderm, mesoderm). This is why they’re so weird – they are comprised of tissue that would not normally be found in the ovary!

There’s also a less common type of teratoma called “monodermal teratoma.” This tumor differentiates to one special tissue, most commonly thyroid tissue, which is called struma ovarii and can present as thyroid storm!

What’s the most common tissue in an ovarian teratoma?
  • Ectodermal Elements
    – Skin
    – Sebaceous & Sweat Glands
    – Hair
    – Teeth
How in the world does this happen?
  • A single cell in an oocyte gets a wild hair and goes rogue, this is the most common theory
    – So, genetically the DNA is 46, XX
    – Embryonic tissue can develop, but they do not undergo complete embryogenesis
How do they present?
Cystic Teratomas have a classic appearance on ultrasound imaging. Photo Credit to WISC Radiology
  • Ovarian Torsion
    – Patient presenting to the Emergency Dept with sudden onset abdominal pain and an adnexal mass is the most common way we find these. About 15% of Dermoid Cysts will eventually cause ovarian torsion. This happens because the fatty elements, which are low density, tend to make up a large portion of the cyst and this allows the mass to “float” in the abdominal cavity. Thus, they can easily roll/twist along the Infundibulopelvic (or Suspensory) Ligament of the ovary.
So, what if they are malignant?
  • I know, I just said they aren’t – and about 99% of the time they’re not, but they can be. If a mature cystic teratoma IS malignant, it will usually be a squamous cell carcinoma.
    Why? Refer back to the most common tissue type – skin!
  • Skin cancer in the ovary…yup.
How are they treated?
  • If symptomatic, treatment is via surgical removal with ovarian cystectomy or oophorectomy. Asymptomatic ovarian dermoids can be removed to prevent torsion or left in hopes of avoiding surgery.
What do they look like? 
Photo Credit to Queensway Gynecology
  • Here’s a great picture from Queensway Gynecology. Click on their link to see really cool videos of laparoscopic surgical removal of a dermoid cyst or click here or here or here to see some of the more interesting teras-esque internal pathology shots.


Twin-Twin Transfusion Syndrome

I want to start sharing a bit more educationally-focused information here. However, in line with my long history of utilizing social media to connect with patients and understand the human side of the story, I hope to employ my non-medical, digital-friends to inspire these topics.

Case courtesy of Dr Alexandra Stanislavsky, Radiopaedia.org. From the case rID: 51114
Fetal MRI of Stage III Twin-to-Twin Transfusion – Case courtesy of Dr Alexandra Stanislavsky, Radiopaedia.org. Case: rID: 51114

Hannah from Daytrips & Diapers has graciously given me permission to discuss/link her in this post. She is pregnant with monochorionic – diamniotic twins and was diagnosed with twin-twin transfusion syndrome (TTTS) at 16 weeks. She recently traveled to the nearest fetal surgery center, >8 hours from her home, and underwent a procedure aimed at decreasing placental connections and improving blood flow (and hopefully, outcomes) for both babies.

She then experienced a known complication of the surgery, however at the time of my writing is still joyfully pregnant with both of her twins. Hop over to her blog or Instagram and follow her story for the human side of medicine. Read on below if you’re interested in the medical side – I’ll discuss diagnosis, pathophysiology, and treatment of TTTS below.


What is Twin-Twin-Transfusion Syndrome?

  • A complication isolated to monochorionic (one placenta) twin pregnancies where vascular connections on the shared placenta develop pressure/flow gradients. This allows one twin (“donor”) to become anemic and the other (“recipient”) to become plethoric and begins a cascade of physiologic changes which can become catastrophic.

How Often Does This Occur?

  • The incidence in mo/di pregnancies is about 10-15% and bout 6% in mo/mo twins develop TTTS. Dichorionic twins cannot develop twin-twin transfusion syndrome, as they have two placentas.

How Is Twin Twin Transfusion Syndrome Diagnosed?

  • The diagnosis is made clinically by ultrasound. It is classically identified by “Poly-Oli Sequence”
    • !! This will be how it’s presented on USMLE-type exams. !!
      • Refers to polyhydramnios of recipient twin and oligohydramnios of donor twin.
    • Occasionally, there will be such severe oligo in the donor twin that it develops “Stuck Twin,” which is essentially the ultrasound appearance of a donor twin being stuck to the placenta. Anatomically, this results from such severe oligohydramnios that the amniotic sac is lying directly against the fetus.

What’s The Pathophysiology?

Basic overview of donor and recipient pathophysiology in TTTS.
Basic TTTS Pathophysiology
  • DONOR: Relative Hypovolemia –> Kidney Injury –> Hypertension
  • RECIPIENT: Relative Hypervolemia –> Vasodilation/Diuresis –> Polyhydramnios –> Hypertension
  • BOTH: Hypertension –> Cardiac Dysfunction –> Hydrops Fetalis
  • Click Flow Chart to enlarge for more detail

How Bad Is It?

  • It depends on the stage.
  • Quintero Staging
    • I: Poly-Oli Sequence (Visible Donor Bladder + Normal Doppler Flow)
    • II: Poly-Oli Sequence + Collapsed Donor Bladder (Normal Doppler Flow)
    • III: Poly-Oli Sequence + Non-Visualized Bladder + Abnormal Doppler Flow
    • IV: Hydrops Fetalis in one or both twins
    • V: Fetal Death in One or Both Twins

How Is It Treated?

  • The treatment course depends on gestational age at diagnosis and severity/stage, however there are basically 3 options:
    • Expectant Management (i.e. No intervention, just watch)
    • Fetoscopic Laser Ablation
    • Amnioreduction (removing the “Poly” of the poly-oli sequence)
Fetoscopic Laser Ablation - Edited by me, click for original source from Japan Fetal Therapy Group
Fetoscopic Laser Ablation – Edited by me, click image for detail. For original source – Japan Fetal Therapy Group

What is Fetoscopic Laser Ablation?

  • This is a surgical procedure which is performed by fetal surgeons. It involved laser cauterization of superficial anastomotic placental connections through minimally invasive fetoscopes.
  • Maternal preparation includes complete ob ultrasound (including placental location, distance between umbilical cord insertions, and fetal locations/presentation/sizes) and medications (antibiotic + tocolytic +/- steroid for fetal lung maturity depending on gestational age). The procedure is enerally performed with local or regional anesthesia + sedation

Fetoscopic Laser Ablation Procedure Steps

  • Skin incision with scalpel (site determined by placental and fetal locations)
  • Entry Options
    • 18g hollow-needle introduced through maternal abdominal wall and placenta
      • J-Wire guide placed –> Needle removed –> Catheter placed over guidewire with US guidance
      • Metal trocar placed through cannula to allow for uterine entry
    • 2-3mm Fetoscope (with or without angled scope, depending on entry-technique and surgeon preference) inserted
  • Identify all fetal extremities to avoid injury
  • Identify vascular equator
    • Typically in recipient amniotic sac (parallel to “stuck twin” if present)
  • Anastomoses are mapped out and typed
    • Types include arterial-venous (AV), venous-arterial (VA), arterial-arterial (AA), and venous-venous (VV)
  • Visible connections are coagulated using laser ablation
    • Sequential selective ablation (AV –> VA –> AA –> VV) reduces intrauterine fetal death rates
  • Vascular equator re-identified and coagulated

What are the Complications and Outcome?

  • Complications of the Procedure
    • Preterm Labor
    • Preterm Delivery (Avg. gestational age is 31-33w)
    • Preterm Premature Rupture of Membranes (PPROM)
    • Intertwin Membrane Rupture
      • Essentially bringing all the risks of monoamniotic twins into play (like cord-entanglement)
    • Pseudo-Amniotic Band Syndrome
    • Fetal Demise
      • Perinatal Survival Rates: 65%
        • Still with long-term neurodevelopmental, cardiac, & renal morbidities associated with survival.
        • 50% both survive
        • 33% one survivor/one fetal demise
        • 33% both with fetal demise

Wow, Those Odds Look Bad…

  • They are daunting, for sure. However, TTTS severe enough to warrant laser-intervention which is left completely un-treated will result in fetal death of one twin in nearly 100% cases and both twins in >90%. These outcomes, when appropriate candidates are selected, are far superior to no treatment.


That’s a brief overview of TTTS and fetoscopic laser ablation. I’ve done a few LIVE Q&As on Twins, I’ll try to round those up to get on YouTube for a more thorough discussion of the pathophysiology and also the different types of twins.

It’s so important when learning about things like this that we don’t forget there’s a human (or, in this case 3) on the other side of our text books. Hop over to the blog and/or IG linked in the intro paragraph for a view into how this looks from a patient perspective.