Seen in women of reproductive age, mature cystic ovarian teratomas (dermoid cysts) are the most common germ cell tumour of the ovary, typified by the presence of multiple tissue types and distinctive imaging feature of a Rokitansky nodule or dermoid plug.
Description
Mature cystic ovarian teratoma, also referred to as a dermoid cyst, is a type of benign germ cell tumour derived from totipotent cells and hence capable of differentiating into all three germ layers. It is the most common germ cell tumour in females and is predominantly found during reproductive years. It almost always contains abundant hair and keratinous debris.
Pathogenesis
The pathogenesis of ovarian mature cystic teratoma involves the abnormal differentiation of totipotent germ cells. These cells, which are capable of giving rise to all types of tissues, undergo a process of disorganised development, resulting in the formation of a tumour containing diverse, mature tissue types. The exact mechanisms triggering this abnormal differentiation are not fully understood but are believed to involve genetic and epigenetic factors that disrupt normal germ cell development.
During embryogenesis, primordial germ cells migrate to the gonadal ridges, where they are supposed to differentiate into oocytes in females. In the case of teratomas, some of these cells fail to follow the normal developmental pathway and instead differentiate into various tissue types within the ovary. This process can give rise to a complex structure containing elements from ectoderm (such as skin, hair, and neural tissue), mesoderm (such as muscle, fat, and bone), and endoderm (such as respiratory or gastrointestinal epithelium).
The presence of specific tissue types within the teratoma can influence its clinical behaviour and potential complications. For example, teratomas containing thyroid tissue (struma ovarii) can sometimes produce thyroid hormones, leading to hyperthyroidism. Similarly, those containing neuroendocrine elements (carcinoid tumours) can cause carcinoid syndrome. The genetic basis of teratomas involves aberrations in the processes regulating germ cell differentiation and maturation, but no specific mutations have been consistently identified as causative.
Subtypes
- Typical Mature Cystic Teratoma: Contains diverse tissues from all three germ layers:
- Ectodermal Elements: Skin, hair, sebaceous glands.
- Mesodermal Elements: Muscle, fat, bone, cartilage.
- Endodermal Elements: Respiratory or gastrointestinal epithelium.
- Struma Ovarii: Predominantly thyroid tissue, may secrete thyroid hormones and cause hyperthyroidism.
- Carcinoid Tumour: Contains neuroendocrine tumour, may secrete serotonin and cause carcinoid syndrome.
- Neural Tissue Predominant Teratoma: Predominantly neural elements (e.g. glial tissue), rare.
- .Monodermal Teratoma: Predominantly one type of tissue, either thyroid or neuroendocrine.
Epidemiology, Risk Factors & Associations
- Most common in women of reproductive age (20-40 years).
- No significant identified risk factors or associations.
Clinical Features
Often asymptomatic but may present with abdominal pain due to torsion, rupture, or haemorrhage into the cyst.
Complications
- Torsion
- Rupture
- Malignant transformation, usually to squamous cell carcinoma (adults) or endodermal sinus tumours (paediatrics), is rare
- Hyperparathyroidism (in struma ovarii)
Pathological Features
Histopathology
- Macroscopic: Cystic tumour with a size range from a few cm to >20 cm. Characteristic Rokitansky nodule or dermoid plug (a firm, solid area representing conglomerate of various tissues).
- Microscopic: Depends on subtype but typical teratomas demonstrates variable tissues from all three germ layers. Most commonly skin, hair, and sebaceous material.
Serology
Not typically relevant for diagnosis
Biochemistry
No specific biomarkers
Radiological Features
General Features
- Characteristically demonstrates a cystic lesion with a Rokitansky nodule or dermoid plug, often with calcification and fat-fluid levels.
- Calcification seen in up to 50%, possibly dentiform (‘tooth-like’)
- It demonst
US
- Predominantly cystic with low-level internal echoes
- Echogenic nodules with acoustic shadowing from calcifications (Rokitansky nodule)
- Possible dentiform calcifications
- Usually no internal vascularity (colour score on Doppler = 1)
- Floating balls sign – spherical echogenic structures that move with changes in patient position
- Dermoid mesh sign represents hair in the cyst appearing as a hyperechoic mesh-like structure
- If measures < 10 cm, then is considered an O-RADS 2 lesion (<1 % risk of malignancy, almost certainly benign)
- If measures > 10 cm, then is considered an O-RADS 3 lesion (1 – <10% risk of malignancy, low risk)
CT
- Non-contrast: Demonstrates fat attenuation in cyst or Rokitansky nodule, calcifications, and fat-fluid level.
- Contrast-enhanced: No significant enhancement expected.
MRI
- T1: High signal intensity due to fat content.
- T2: Variable, depending on tissue content.
- T1 C+: No significant enhancement.
- DWI/ADC: Not typically relevant.
- Fat-suppressed: Signal drop in fatty components
- Chemical shift (in/out of phase): Signal drop in out-of-phase images due to microscopic fat component
Grading and Staging
Not applicable as this is a benign condition.
Diagnosis
Typically diagnosed based on characteristic imaging features and clinical history.
Differential Diagnosis
Imaging-based
Other classically benign lesions
- Endometrioma: Ground-glass appearance with homogenous low-level echoes on US. Demonstrates characteristic T2 shading sign and T1 hyperintensity due to blood content on MRI
- Haemorrhagic cyst: Reticular pattern (fine, thin, intersecting lines representing fibrin strands) and a retracting clot (avascular component with angular, straight or concave margins).
- Simple paraovarian cyst: Simple cyst which is separate from ovary (moves independent of ovary with transducer pressure)
- Peritoneal inclusion cyst: Follows contour of adjacent pelvic organs or peritoneum, without exerting mass effect. May be multiseptated. Ovary demonstrate at margin or suspended within lesion.
- Hydrosalpinx: Tubular structure with incomplete septations (short rounded projections from inner wall of fluid-distended fallopian tube) representing endosalpingeal folds
Other ovarian lesions:
- Cystadenoma or cystadenocarcinoma: Typically does not contain fat or calcifications.
Management
Surgical removal is the standard treatment, typically via laparoscopy. Refer to a gynaecologist for surgical evaluation.