According to the WHO classification 2014,
ovarian epithelial carcinoma is classified into seven types of serous carcinoma,
mucinous carcinoma,
endometrioid carcinoma,
clear cell carcinoma,
malignant Brenner tumor,
seromucinous carcinoma and undifferentiated carcinoma (Fig.1) [1].
Clear cell carcinoma (CCC) of the ovary accounts for 5-10% of surface epithelial carcinoma but for 20% in Japan and is known as the most frequently associated with ovarian and pelvic endometriosis in 50-70% of cases.
As the background of endometriosis,
the mean age is 55years in contrast to 63 years for serous carcinoma.
Clinically,
it is also associated with paraneoplastic hypercalcemia (2-10%) and venous thromboembolism (18-46%).
As for FIGO stage of CCC,
about 56% is stage I in contrast to19% of serous carcinoma.
Moreover,
stage IC is more common at the rate of 55-74% than the other type of carcinoma probable associated with of tumor rupture(Fig.2) [1-3].
The most important criteria were established to differentiate malignant from benign tumors of the ovary with MRI.
Using the five primary criteria with contrast enhancement was reported to improve the accuracy of making the diagnosis of ovarian tumors.
The five criteria are known as (a) size greater than 4cm,
(b) solid mass or large component,
(c) wall thickness greater than 3mm,
(d) septal thickness greater than 3mm and/or vegetations or nodularity,
and (e) necrosis [4].
To distinguish benign from malignant tumors,
it was said that evaluating enhancement patterns on the dynamic contrast MRI was available because benign tumors showed gradual increasing but malignant tumors showed plateau following rapid increase (Fig.3) [5].
Concerning high association of endometriotic cyst,
it was sometimes difficult to indicate benign or malignant tumor on MRI because solid components showed various signal intensities on T2WI and the presence or absence of enhancement [6].
However,
it was presented that evaluating enhancement on dynamic subtraction image was available in order to exclude hemorrhagic high signal intensity surrounded solid components on T1WI [7].
As for morphology of solid components,
it was reported to become one of diagnostic factors to make differentiate ovarian cancer associated endometriosis from benign endometriotic cyst [8].
On focused the growth pattern of solid components,
it was mentioned that eccentric pattern was predominant at the rate of 77.8% of CCC compared to 40.0% of endometrioid carcinoma [9].
As a common appearance of CCCs on MRI,
cystic tumor with solid protrusions (83%) at the mean size of 13cm,
typically unilocular large cystic tumor (90%),
and round solid protrusions (67%) were reported [10].
The shape of CCCs was also reported oval (75%) and unilocular (79%) with large papillary protrusions at the size of 5.13±0.4cm.
On T1WI,
hyperintensity of the cystic component was seen at the rate of 62% (Fig.4) [11].
Recently some reports presented that the combination of DWI and measurement ADC values were useful for differentiating benign from malignant tumors or useful for differentiating borderline from malignant tumors [12-14].
On the other hand,
other reports presented some limitations that measuring ADC values was not available in differentiating benign from malignant tumors because complexity of edematous change and dense fibrous stroma of benign tumors demonstrated some overlap between benign or not benign,
although the presence of low signal intensity on DWI and low signal intensity within the solid component indicate always benign (Fig.5) [15-17].
There is no previous analysis performed for evaluating the combination of DWI and ADC values in the large population of CCCs (Fig.6) [12,15].
Therefore,
we attempt to clarify specific MRI findings of CCCs focused on many aspects such as age,
FIGO stage,
CA125 value,
maximum tumor size,
protrusions appearance within the tumor and pathological features.
To make an accurate diagnosis preoperatively,
radiologists must be familiar with the spectrum of appearance of CCCs on MRI.