Mature teratoma is the most common benign tumor of the ovary.
It is typically found in young women and it may be bilateral in 25% of cases.
It contains mature elements from germ cell layers (ectoderm,
mesoderm,
endoderm).
The cystic form (or dermoid cyst) represents the most frequent form of mature teratoma: it is unilocular and delimited by a thick wall covered by squamous epithelium,
sometimes with intralesional calcification.
It may contain sebaceous material,
fat and elements deriving from the germinal layers.
An endocytic excrescence (Rokitansky nodule) may be often visualized,
in which is not unusual to see dental and bone elements [1].
Because of its different and heterogeneous components,
dermoid cyst may be visualized and correctly diagnosed using almost all conventional imaging techniques.
This clinically silent lesion is often discovered as an occasional finding during radiological exams carried out for other reasons.
Most of these lesions can be visualized on plain radiograph as radiopaque formations in the pelvis,
because of the bone components; since it is not possible to provide an immediate diagnosis of nature (as well as the differential diagnosis with other radiopaque images in pelvic excavation,
i.e.
phlebolis or faecal material),
it is necessary to go on with further imaging modalities.
On US examination,
they have a cystic appearance,
sometimes with sebaceous material or hairs within.
It is not rare to observe small hyperechogenic components with a posterior acoustic shadowing (dental and bone elements).
The Rokitansky nodule appears as a mural,
hyperechoic tubercle and often its visualization in a cystic lesion within the pelvis allows an easy diagnostic orientation.
Integration with Color Doppler shows no intralesional vascularization (this aspect is clearly important for assessing any malignant degeneration,
possible in 1% of cases).
CT has a high sensitivity in the diagnosis of cystic teratoma although it is not recommended as a routine examination due to exposition to ionizing radiation.
Typically,
CT images show cystic lesion in the pelvis containing fat,
fat-fluid levels,
calcifications (sometimes dentiforms),
Rokitansky nodules and hair in different percentages [2],
which allows a diagnosis of nature.
Malignant degeneration of dermoid cysts should be suspected where the size of the lesion exceeds 10 cm or an aspect of the vegetative lesion with irregular shape is observed [3].
Although it’s not used as a routine investigation for the diagnosis of dermoid cyst,
MRI is particularly sensitive to the adipose component of this lesion.
The fat suppression technique and the chemical shift artifact can be effectively used for a correct diagnosis.
Furthermore,
the use of contrast medium allows to identify solid invasive components in case of malignant degeneration.Mature cystic teratoma can be usually remain completely asymptomatic unless it is complicated by ovarian torsion or rupture,
causing acute pelvic pain.
Immature teratoma has a malignant degenerative potential.
It represents 1% of all teratomas and it is mostly found in the second decade of life.
At Imaging,
it appears as a voluminous and heterogeneous mass with a prominent solid component,
sometimes with tumor extension to surrounding tissues due to the invasion of the capsule.
On US,
immature teratoma appears as a heterogeneous,
partially solid,
often calcified lesion; on CT and MRI as a large lesion with calcifications and hemorrhagic areas.
The administration of contrast agent can help to identify malignant lesions and perform local staging.
As well as the benign form,
even the immature teratoma may undergo rupture (due to sudden increase in size) and cause acute pelvic pain.
In monodermal teratoma,
there is only one tissue type.
The most frequent subtype,
struma ovarii,
is composed entirely or predominantly of thyroid tissue and contains follicles of variable size with colloidal material.
It represents 0.3-1% of all ovarian tumors and about 3% of all mature cystic teratomas.
Due to its content of functioning thyroid tissue,
it can show as a hyperthyroidism up to a real thyrotoxicosis (5-8% of cases).
Although the imaging aspect is not highly specific,
on US it has a "complex-mass" appearance due to the alternation of cysts to solid areas.
On CT it appears as a multi-cystic mass with regular margins,
hyperdense on non-contrast scan.
Cysts do not show significant wall enhancement after contrast agent administration [4].
On MRI,
struma ovarii appears as a multiloculated cystic mass,
with solid components.
On T1 and T2 weighed images,
cysts have both high and low signal intensities due to the presence of a gelatinous colloid (the presence of areas with very low signal intensity in T2-weighted images is considered to be pathognomonic for struma ovarii).
Solid components may show enhancement after contrast administration.