• Germ cell ovarian tumors
  • Arise from the primordial germ cells (e.g., oocytes)

Here’s a table differentiating mature and immature teratomas:

Feature	Mature Teratoma	Immature Teratoma
Malignancy	Usually benign. Malignant transformation is rare, but possible (most commonly to squamous cell carcinoma).	Often malignant, can metastasize.
Differentiation	Well-differentiated, containing mature tissues from all three germ layers (ectoderm, mesoderm, endoderm). Often contains skin, hair, teeth, bone, muscle, and even complex parts.	Contains immature or embryonic tissues, most commonly neuroectoderm (immature neural tissue). May also have immature cartilage and skeletal muscle.
Age of Onset	Can occur at any age, but they’re most common during reproductive years.	Most frequently in the first two decades of life, rare after menopause.
Common Locations	Most common in ovaries (dermoid cysts) in females and testes in males. Can occur in other midline locations.	Ovaries and testes are common sites, can be found in other locations.
Appearance	Often cystic, containing a variety of mature tissues. The predominant type is cystic (Mature Cystic Teratoma or MCT) and it always contains skin, hair, and neural tissues, along with sebaceous materials.	Typically larger and more solid, with heterogeneous areas, often including coarse calcifications and small foci of fat.
Prognosis	Generally good due to benign nature.	Depends on grade and stage, generally poorer than mature teratomas.
Genetic	Usually a diploid, normal 46, XX karyotype	May have a variety of karyotypes

Dermoid cysts (mature cystic teratoma)

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Epidemiology

• Most common of all germ cell tumors (90% of all cases)
• Most common ovarian tumor in women < 30 years

Clinical features

• Mostly asymptomatic
• Larger tumors may cause:
  • ↑ Abdominal girth
  • Pressure symptoms (e.g., ↑ urinary frequency)
  • Lower abdominal pain
  • Predispose to ovarian torsion

Diagnostics

Ultrasound appearance

• Heterogeneous mass
• Hyperechoic nodule
• Echogenic shadowing
• Absent internal vascularity and/or fluid-fluid levels

Histology

• Contains somatic tissue (e.g., hair, teeth, sebaceous glands) from any of the three embryonic germ layers:
  • Endoderm
  • Mesoderm
  • Ectoderm