Prepared by Dr. D.R. Petty, Radiology Registrar, St. James'
University Hospital; and Dr. J.A. Spencer, Consultant
Radiologist, St. James' University Hospital, Leeds, United
A 28-year-old woman presented to her primary care physician with
an 8-year history of primary subfertility. Pelvic ultrasound
performed as part of the investigation of this condition
demonstrated a left ovarian mass (Figure 1). A pelvic magnetic
resonance (MR) scan was subsequently performed to further
characterize this lesion (Figures 2 and 3). A left
salpingo-oophrectomy was performed.
What was the diagnosis?
The transvaginal ultrasound demonstrated a 4.4 * 6.0 cm cystic
mass containing a solid component, some of which was hyperechoic,
suggesting the presence of fat. One area demonstrated acoustic
shadowing, in keeping with a focus of fat or calcification.
The pelvic MR demonstrated a complex 8.0 * 5.0 * 5.0 cm left
ovarian mass (Figure 2), parts of which demonstrated significant T1
signal loss with fat suppression (Figure 3). In addition, there was
a small focus that returned low signal on all sequences. These
characteristics are in keeping with mature fat and calcification,
The specimen consisted of a soft, smooth-surfaced mass attached
to the left fallopian tube. Pathologic examination revealed that it
was a cystic mass containing hair, sebaceous material, fat, and
Left ovarian mature teratoma
Mature cystic teratomas (MCT), also known as dermoid cysts, are
the most common form of ovarian teratoma (which also includes
monodermal teratomas, such as struma ovarii and immature
These entities contain well-differentiated cell lines from at least
two of the germ-cell layers.
They account for 25% of all ovarian tumors and are bilateral in 10%
to 25% of cases.
Ovarian MCT affect a younger age group than ovarian epithelial
tumors with a mean age of 30. They are usually asymptomatic,
although complications, such as torsion, can occur. Malignant
degeneration occurs in approximately 2% of cases, usually in
Occasionally, the cyst can rupture, which produces granulomatous
peritonitis; this is said to occur in <1% of cases.
The diagnosis of ovarian MCT can sometimes be made on a plain
abdominal radiograph if a radiolucent pelvic mass containing a
tooth is demonstrated.
Ultrasound appearances are often characteristic due to the
presence of a highly reflective dermoid plug (Rokitansky nodule)
that is the solid element within the cyst. This contains hair
follicles, sebaceous glands, fat, and calcified or ossified
elements. It usually forms an acute angle with the wall of the
and can produce acoustic shadowing due to the presence of hair,
calcium, or bone. A fluid-fluid level may be detected due to sebum
floating on an aqueous, more echogenic, layer.
Echogenic lines and dots may be seen within the fluid, caused by
strands of hair in the cyst, although fibrinous strands in
can also cause this appearance.
Tubo-ovarian abscesses can also contain fluid-fluid levels and
echogenic pus and produce acoustic shadowing due to gas. Ectopic
pregnancies also demonstrate shadowing from bones and contain
echogenic hemorrhage, which may separate to give fluid-fluid
levels. Therefore, these conditions can mimic ovarian MCT
sonographically, although the clinical setting should allow
accurate diagnosis in the majority of these cases.
Hemorrhagic cysts can also cause diagnostic difficulty; however,
the echogenic focus produced by fresh hemorrhage displays through
transmission rather than acoustic shadowing.
Ovarian MCTs are the most commonly missed ovarian neoplasm on
sonography, often due to the tip of the iceberg sign, in which the
back wall of the cyst is obscured by acoustic shadowing, causing
the echogenic Rokitansky plug to be misinterpreted as bowel gas.
Computed tomography (CT) and MR are more sensitive to the
presence of fat and calcium than is ultrasound, thus making the
diagnosis using these modalities more straightforward.
On CT, the demon-stration of fat within an adenexal mass is highly
suggestive of an ovarian MCT.
It was present in 93% of cases in one series, with teeth or other
calcifications present in 56%.
Contrast enhancement is unusual in benign MCT and is suggestive of
The presence of malignancy should also be considered if the solid
element within the cyst measures >5 cm.
With MR, the intracystic sebum and the adipose tissue usually
present in the Rokitansky nodule typically have signal
characteristics of high signal on T1-weighted images and
intermediate signal on T2-weighted images. These findings are not
diagnostic of ovarian MCT, as they can also occur in intracyst
hemorrhage, eg, in endometriomas. Hemorrhagic products in an
endo-metrioma can also produce a layered appearance on T2-weighted
images or sometimes a gradated signal loss called shading, a
finding that is not seen in MCT.
The loss of high signal on T1-weighted images with fat
suppression is diagnostic of MCT, allowing it to be differentiated
from hemorrhagic lesions. Occasionally nondependant spheres of
intracyst lipid are demonstrated within the MCT.
Areas of calcification and ossification are of low signal on all
sequences on MR. A salt-and-pepper speckled appearance can
sometimes be seen within an MCT, which is thought to be due to
multiple chemical shift artifacts at fat/water interfaces.
The diagnosis of ovarian MCT can often be made confidently on
ultrasound; in one study, experienced observers were able to
achieve 100% positive predictive value in cases in which two or
more characteristic sonographic features were present.
In uncertain cases, MR and CT will increase diagnostic accuracy due
to their high sensitivity for fat and calcium content. MR is the
more sensitive of the two modalities,
and has the added advantage of not involving ionizing radiation in
the young-adult age group.
Due to the potential for complications, such as torsion and
rupture, MCTs are usually resected. Therefore, gynecological
referral is recommended upon their diagnosis.