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Neoplasms

Teratoma

A teratoma is a germ cell tumor containing tissues derived from more than one of the three embryonic germ layers (ectoderm, mesoderm, endoderm), such as hair, teeth, bone, or neural tissue. It arises most commonly in the ovary, testis, sacrococcygeal region, or mediastinum, and ranges from entirely benign (mature cystic teratoma) to frankly malignant (immature teratoma, teratoma with malignant transformation). The single most testable fact: a mature cystic teratoma (dermoid cyst) of the ovary is the most common benign ovarian germ cell tumor in reproductive-age women and classically shows fat/calcification on imaging.

Practice questionsHigh-yield facts
ICD-10C62.9 (testicular, malignant); site-specific codes vary
Typical patientYoung woman (ovarian) or infant/young man (testicular)
Key findingHeterogeneous mass with fat, calcification, or hair on imaging
First-line treatmentSurgical excision; chemotherapy if malignant/immature
6 min readFor medical studentsUpdated 2026-10-14

Definition and epidemiology

A teratoma is a neoplasm composed of tissues from multiple germ layers, reflecting its origin from a totipotent germ cell. Teratomas are classified by:

  • Maturity: mature (fully differentiated, adult-type tissue) vs immature (contains embryonic/fetal-type tissue, usually neuroectodermal)
  • Behavior: benign vs malignant
  • Site: gonadal (ovary, testis) or extragonadal (sacrococcygeal, mediastinal, retroperitoneal, pineal/CNS)

Coding note: ICD-10 does not have one universal "teratoma" code. Behavior and site determine the code — for example, malignant testicular teratoma falls under C62.x, benign ovarian teratoma under D27, and malignant ovarian teratoma under C56 (the general code for malignant neoplasm of ovary). The code C62.9 specifically refers to an unspecified malignant testicular tumor.

Epidemiology varies greatly by site:

  • Ovarian mature cystic teratoma (dermoid cyst): most common benign ovarian neoplasm, usually diagnosed in women of reproductive age (20s-40s)
  • Testicular teratoma: in adults it is almost always a component of a mixed malignant germ cell tumor; in prepubertal boys it is typically benign
  • Sacrococcygeal teratoma: most common tumor diagnosed in newborns/infants, more frequent in females
  • Mediastinal teratoma: typically anterior mediastinum, most common in young adults
High-yield for exams
  • Mature cystic teratoma (dermoid cyst) is the most common benign ovarian germ cell tumor in reproductive-age women
  • Ultrasound hallmark: heterogeneous mass with a hyperechoic Rokitansky nodule and fat-fluid level
  • Ovarian teratoma is the most common cause of ovarian torsion due to its weight and mobility
  • In postpubertal males, testicular teratoma is treated as malignant regardless of histologic maturity
  • AFP and beta-hCG are typically normal in pure mature teratoma; elevation suggests mixed germ cell tumor
  • Sacrococcygeal teratoma is the most common neonatal tumor and requires coccyx resection to prevent recurrence
  • Malignant transformation (usually squamous cell carcinoma) is a rare long-term risk of ovarian dermoid cysts
  • Growing teratoma syndrome: tumor enlarges despite chemotherapy and normal markers, needs surgical removal

Etiology and risk factors

Teratomas arise from primordial germ cells or totipotent embryonic cells that escape normal differentiation control and begin forming disorganized multi-tissue elements. The precise molecular trigger is not fully defined, but key associations include:

  • Cryptorchidism: increases risk of testicular germ cell tumors, including teratoma components
  • Klinefelter syndrome: associated with mediastinal germ cell tumors
  • Abnormal germ cell migration: thought to explain midline extragonadal locations (sacrococcygeal, pineal, mediastinal) from cells that fail to migrate properly during embryogenesis
  • Age: sacrococcygeal teratoma presents in infancy; ovarian dermoid cysts peak in reproductive years; testicular teratomas have a bimodal distribution (infancy and young adulthood)

There is no strong environmental or lifestyle risk factor comparable to those seen in epithelial cancers; teratomas are primarily a disorder of germ cell biology and embryologic development.

Pathophysiology

Teratomas develop from pluripotent germ cells capable of differentiating along multiple lineages simultaneously, producing a disorganized mixture of mature or immature tissues.

  • Mature teratoma: tissues resemble normal adult structures (skin, hair follicles, sebaceous glands, teeth, cartilage, thyroid tissue, neural tissue). Growth is typically slow and the tumor behaves as benign, though it can enlarge, rupture, torse (ovarian), or rarely undergo malignant transformation (most often squamous cell carcinoma arising within the cyst wall, more common in older women).
  • Immature teratoma: contains primitive, embryonic-appearing tissue, most often immature neuroepithelium. Grading (1-3) is based on the amount and type of immature neural tissue and correlates with malignant potential and metastatic risk.
  • Teratoma with malignant transformation: a somatic-type malignancy (e.g., carcinoma, sarcoma) develops within an otherwise mature teratoma.

In the testis, teratoma is almost always found as one component of a mixed nonseminomatous germ cell tumor alongside embryonal carcinoma, yolk sac tumor, or choriocarcinoma, which drives much of its clinical malignant behavior even when the teratomatous component itself looks mature (teratomas in postpubertal males are considered malignant regardless of histologic maturity, unlike prepubertal boys or ovarian lesions).

Clinical features

Presentation depends heavily on location:

  • Ovarian (mature cystic teratoma): often asymptomatic, found incidentally on pelvic imaging; can cause pelvic pain, pressure, or present acutely with ovarian torsion (sudden severe unilateral pain, nausea, vomiting) due to its heavy, mobile composition
  • Testicular: painless, firm testicular mass; may be noted by the patient or found incidentally; metastatic disease can present with back pain (retroperitoneal lymph nodes) or respiratory symptoms (lung metastases)
  • Sacrococcygeal (infant): visible or palpable mass at the sacrococcygeal region, sometimes detected prenatally on ultrasound; can cause bowel/bladder dysfunction from local mass effect
  • Mediastinal: often asymptomatic until large; may cause chest pain, cough, dyspnea, or superior vena cava syndrome from compression

Rupture of an ovarian dermoid cyst can cause chemical peritonitis from spillage of sebaceous/keratinous material.

Diagnosis

Diagnosis combines imaging, tumor markers, and histopathology.

Imaging

  • Ultrasound (first-line for ovarian and testicular masses): mature cystic teratoma shows a heterogeneous mass with a hyperechoic nodule (Rokitansky protuberance), fat-fluid levels, or acoustic shadowing from calcification/teeth
  • CT: identifies fat density and calcifications, useful for staging and extragonadal sites (mediastinum, sacrococcygeal, retroperitoneum)
  • MRI: best for sacrococcygeal and pelvic masses, especially prenatal/pediatric evaluation and surgical planning

Tumor markers (testicular/malignant germ cell workup)

  • AFP: elevated with yolk sac elements
  • Beta-hCG: elevated with choriocarcinoma elements
  • LDH: nonspecific marker of tumor burden
  • Pure mature teratoma typically does not elevate these markers; elevation suggests a mixed germ cell tumor

Histopathology

Definitive diagnosis requires surgical pathology demonstrating tissue derived from more than one germ layer, with grading of immature elements if present.

Differential diagnosis

  • Other ovarian masses: functional cyst, endometrioma, cystadenoma, malignant epithelial ovarian cancer
  • Other testicular masses: seminoma, epididymal cyst, hydrocele, orchitis, other nonseminomatous germ cell tumors
  • Sacrococcygeal region: meningocele, lipoma, chordoma, neuroblastoma
  • Mediastinal mass: thymoma, lymphoma, germinoma, bronchogenic cyst
  • Dermoid cyst (skin): a distinct, simpler congenital inclusion cyst (not a germ cell tumor) and should not be confused with ovarian dermoid cyst terminology

Management

Management depends on site, maturity, and malignant potential, and follows general oncologic surgical principles supported by major society guidelines (e.g., NCCN for germ cell tumors).

Surgical approach

  • Ovarian mature teratoma: ovarian cystectomy (fertility-sparing) is preferred when feasible; oophorectomy if the cyst is very large, bilateral, or in postmenopausal women
  • Testicular teratoma: radical inguinal orchiectomy is standard, since teratoma typically occurs as part of a mixed germ cell tumor requiring full staging
  • Sacrococcygeal teratoma: complete surgical resection including the coccyx (to reduce recurrence), ideally in infancy; fetal intervention is considered in rare cases of large tumors causing hydrops in utero
  • Mediastinal teratoma: surgical resection, generally curative for mature lesions

Adjuvant therapy

  • Immature teratoma or teratoma with malignant transformation may require chemotherapy (platinum-based regimens, e.g., bleomycin-etoposide-cisplatin) depending on grade, stage, and markers
  • Pure mature teratoma generally does not require chemotherapy or radiation, as it does not respond to these modalities
  • Post-orchiectomy management of mixed testicular germ cell tumors follows risk-stratified protocols (surveillance vs chemotherapy vs retroperitoneal lymph node dissection) based on stage and marker normalization

Long-term surveillance with serial imaging and tumor markers (when applicable) is standard after treatment to detect recurrence.

Complications and prognosis

  • Ovarian torsion or rupture are the main acute complications of ovarian teratoma and require urgent surgical management
  • Malignant transformation (squamous cell carcinoma) occurs in a small percentage of long-standing mature cystic teratomas, more common with increasing age and larger tumor size
  • Growing teratoma syndrome: enlarging mass despite normalized tumor markers and chemotherapy in treated malignant germ cell tumors, requiring surgical resection
  • Metastasis: immature teratoma and mixed germ cell tumors can metastasize; pure mature teratoma essentially does not

Prognosis is excellent for mature teratomas after complete resection. Immature teratoma prognosis correlates with grade and stage but is generally favorable with modern multimodal therapy. Sacrococcygeal teratoma has a good prognosis with early complete resection, though incomplete coccygectomy raises recurrence risk.

Mnemonic

Teratoma tissues = "3 germ layers, 3 classic finds": Teeth/bone (ectoderm/mesoderm), Hair/sebum (ectoderm), Thyroid/gut lining (endoderm) — think 'TOOTH, HAIR, GUT' to recall the mixed-tissue hallmark.

Practice questions

1. A 24-year-old woman presents with sudden-onset severe right lower quadrant pain, nausea, and vomiting. Pelvic ultrasound shows a 7-cm heterogeneous right ovarian mass with a hyperechoic nodule and posterior acoustic shadowing, and absent venous flow on Doppler. Which of the following best explains this clinical picture?

Answer: B. The imaging findings (heterogeneous mass, hyperechoic nodule, acoustic shadowing) are classic for a mature cystic teratoma, and the acute presentation with absent Doppler flow indicates ovarian torsion, a well-known complication due to the tumor's weight and mobility. Ectopic pregnancy and tubo-ovarian abscess do not match this imaging pattern. Endometrioma typically shows homogeneous 'ground-glass' echogenicity, not fat/calcification.

2. A 29-year-old man undergoes radical orchiectomy for a testicular mass. Pathology reveals mature teratoma only, with no other germ cell elements, and serum AFP and beta-hCG were normal preoperatively. Which statement about management is correct?

Answer: B. Unlike ovarian or prepubertal testicular teratomas, postpubertal testicular teratoma is considered to have malignant potential regardless of histologic maturity, so staging workup (imaging, markers) and risk-based management (surveillance or further therapy) are indicated. Radiation is not standard for nonseminomatous germ cell tumors, and prophylactic contralateral orchiectomy is not performed for a unilateral tumor without bilateral disease evidence.

3. A newborn female is noted to have a large mass protruding from the sacrococcygeal region, detected on prenatal ultrasound. After delivery, MRI confirms a predominantly external sacrococcygeal teratoma without intrapelvic extension. What is the most appropriate next step in management?

Answer: C. Sacrococcygeal teratoma is managed with early complete surgical excision, including removal of the coccyx, which is critical to reduce the risk of local recurrence. Chemotherapy and radiation are not first-line for mature lesions, and observation risks tumor growth, rupture, or malignant transformation. Coccygectomy specifically distinguishes definitive treatment from incomplete resection.

Frequently asked questions

What causes teratoma?

Teratomas arise from totipotent germ cells that differentiate abnormally into tissues from multiple embryonic layers instead of forming a single organ. The exact trigger is unclear, but risk is increased by cryptorchidism (testicular tumors) and Klinefelter syndrome (mediastinal tumors). There is no known preventable environmental cause; it reflects abnormal germ cell development rather than lifestyle or external exposure.

What are the first symptoms of teratoma?

Many teratomas are asymptomatic and found incidentally on imaging. When symptomatic, ovarian teratomas cause pelvic pain or pressure, or sudden severe pain if torsion occurs. Testicular teratomas present as a painless testicular lump. Sacrococcygeal teratomas appear as a visible mass at the lower back/buttock in infants, sometimes seen on prenatal ultrasound.

How is teratoma diagnosed?

Diagnosis starts with ultrasound showing a heterogeneous mass with fat, calcification, or a characteristic hyperechoic nodule, followed by CT or MRI for further characterization and staging. Tumor markers (AFP, beta-hCG, LDH) help identify mixed malignant germ cell tumors in testicular cases. Final diagnosis is confirmed by surgical pathology showing multiple tissue types.

Is teratoma curable?

Yes, mature teratomas are generally cured with complete surgical removal and have an excellent prognosis. Immature or malignant teratomas also have good cure rates with surgery plus chemotherapy when needed, though prognosis depends on grade, stage, and completeness of resection. Long-term follow-up imaging is recommended to monitor for recurrence.

Teratoma vs dermoid cyst — what is the difference?

A mature cystic teratoma of the ovary is often informally called a dermoid cyst because it is filled with skin-derived tissue like hair and sebum, but it is a true germ cell tumor containing tissue from all three germ layers. A simple skin dermoid cyst is a different, non-neoplastic congenital inclusion cyst found in the skin, not an ovarian or gonadal tumor.

Key drugs

BleomycinEtoposideCisplatin
DysgerminomaYolk sac tumorChoriocarcinomaEmbryonal carcinomaSeminomaOvarian cystadenomaGrowing teratoma syndromeNeuroblastoma

Sources and further reading

StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: C62.9

Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.