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Mature (cystic) ovarian teratoma

Ovarian dermoid cyst and mature cystic teratoma are terms often used interchangeably to refer to the most common ovarian neoplasm 2. Although they have very similar imaging appearances, the two have a fundamental histological difference: dermoids are composed only of dermal and epidermal elements, whereas teratomas have mesodermal and endodermal elements. 

For the sake of simplicity both are discussed in this article, as much of the literature combines the two entities. 

Epidemiology

Mature cystic teratomas account for 10-20% of all ovarian neoplasms. They tend to be identified in young women, typically around the age of 30 years 1 and are also the most common ovarian neoplasm in patients younger than 20 years 8.

Clinical presentation

Uncomplicated ovarian dermoids tend to be asymptomatic and are often discovered incidentally. They do however predispose to ovarian torsion, and may then present with acute pelvic pain. 

Other complications (listed further down in the article) are less common. 

Pathology

Mature cystic teratomas are encapsulated tumours with mature tissue or organ components. They are composed of well-differentiated derivations from at least two of the three germ cell layers (ectoderm, mesoderm, and endoderm). They therefore contain developmentally mature skin complete with hair follicles and sweat glands, sometimes luxuriant clumps of long hair, and often pockets of sebum, blood, fat, bone, nails, teeth, eyes, cartilage, and thyroid tissue. Typically their diameter is smaller than 10 cm, and rarely more than 15 cm. Real organoid structures (teeth, fragments of bone) may be present in ~ 30% of cases.

Location - laterality

They can be bilateral in 10-15% of cases 1-2

Variants

Radiographic features

Plain film

May show calcific and tooth components with the pelvis

Pelvic ultrasound

Ultrasound is the preferred imaging modality. Typically an ovarian dermoid is seen as a cystic adnexal mass with some mural components.  Most lesions are unilocular.

The spectrum of sonographic features includes

  • Rokitansky nodule - dermoid plug
  • diffusely or partially echogenic mass with posterior sound attenuation owing to sebaceous material and hair within the cyst cavity (  echogenic interface at edge of mass that obscures deep structures): the tip of the iceberg sign
  • echogenic, shadowing calcific or dental (tooth) components
  • presence of fluid-fluid levels 5
  • multiple thin, echogenic bands caused by hair in the cyst cavity : the dot-dash pattern
CT

CT has high sensitivity in the diagnosis of cystic teratomas 6, though is not routinely recommended for this purpose in view of ionising radiation.

Typically CT images demonstrate fat (areas with very low Hounsfield values), fat fluid level, calcification (sometimes tooth), Rokitansky protuberance and tufts of hair. The presence of most of the above tissues is diagnostic of ovarian cystic teratomas in 98% of cases 5. Whenever the size exceeds 10cms or soft tissue plugs and cauliflower appearance with irregular borders is seen, malignant transformation should be suspected 5.

When ruptured, the characteristic hypo-attenuating fatty fluid can be found as ante-dependent pockets, typically below the right hemidiaphragm, a pathognomonic finding 2. The escaped cyst content also leads to a chemical peritonitis and the mesentery may be stranded and the peritoneum thickened, which may mimic peritoneal carcinomatosis 2

Pelvic MRI

MR evaluation usually tends tend to be reserved for difficult cases, but is exquisitely sensitive to fat components. Both fat suppression techniques and chemical shift artefact can be used to confirm presence of fat. 

Enhancement is also able identify solid invasive components, and as such can be used to accurately locally stage malignant variants. 

Complications

Recognised complications include

  • ovarian torsion :  ~ 3-16% of ovarian teratomas on general : considered the most common complication
  • rupture : ~ 1-4%
  • malignant transformation : ~ 1-2% : usually into squamous cell carcinoma (adults) or rarely into endodermal sinus tumours (paediatrics).
  • suprimposed infection : 1%
  • autoimmune haemolytic anaemia :  < 1%.

Treatment and prognosis

They are slow growing (1-2 mm a year) and therefore some advocate non surgical management. Larger lesions are often surgically removed. Many recommend initial serial follow for lesions under 7 cm to monitor growth, beyond which a resection is advised.

Differential diagnosis

General differential imaging considerations include :

See also

 


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