Endometriosis is a benign and chronic gynecologic disorder, where there is ectopic implantation of endometrial glands and stroma outside the uterine cavity. It has been shown to cause various symptoms, including chronic pelvic pain, dysmenorrhea, dyspareunia, and/or infertility .
Endometriomas can occur unilaterally or bilaterally, and approximately 28% of endometrioma patients have bilateral endometriomas .
In our study, bilaterality was observed in 35% of endometriomas. However, as mentioned by Lee et al. , bilaterality cannot be used to reliably differentiate endometriomas from other cystic lesions.
There is a range of imaging features in endometriosis, but the hemorrhagic character of lesions markedly aids in their characterization .
Shading sign in T2-weighted MRI images is typical of endometriomas that helps differentiate it from other hemorrhagic ovarian lesions. Menstrual bleeding over time and long term produce high iron concentration, protein, and methemoglobin with consequent T2 shortening . Lee et al.  reported that the shading sign had a sensitivity and specificity of 90–98% for the diagnosis of endometriomas; however, his study included more than 80% of the lesion endometriomas. Outwater and Dunton  conducted a study, where the sensitivity and specificity of T2 shading were only 68% and 83%, respectively. In our study, conventional MRI with high T1-weighted images and shading sign in T2-weighted images exhibited a sensitivity of 65.4% and a specificity of 71.4%. We believe that the shading is not a reliable MRI sign for differentiating endometriomas from hemorrhagic cysts.
Blood or hemosiderin within endometriomas shortens T1, causing a consequent reduction in ADC values; therefore, DWI may distinguish endometriomas from other cystic lesions . In our study, 42 out of 52 pathologically proven endometriotic lesions and 4 non-endometrial hemorrhagic cysts showed restricted diffusion, with SE, SP, PPV, and NPP of 80.7%, 71.4%, 91.3%, and 50%, respectively. Thus, DWI has shown an increase in sensitivity, PPV, and NPV yet similar specificity, when compared to conventional MRI. This is comparable to Abd El-Dayem et al.’s  study where 11 out of 14 cases were restricted in DWI representing 78.57% sensitivity.
However, due to the presence of overlap between the ADC values of endometriomas and hemorrhagic cysts, the diagnosis should be based upon the combination of clinical history and conventional MRI together with DWI findings and should not be based on DWI alone.
In 2002, it was suggested by Moteki et al.  that endometriomas had lower ADC values (0.91 ± 0.47 × 10−3 mm2/s) than other pelvic cysts (2.82 ± 0.80 × 10−3 mm2/s). Busard et al . reported that ADC values of endometriomas are 1.10 ± 0.38 × 10−3 mm2/s), and Lee et al. . calculated ADC values for endometriomas to be 1.06 ± 0.38 × 10−3 mm2. These studies’ results are comparable to our study, which had mean ADC values for endometriomas of 1.03 ± 0.51 × 10−3 mm2/s.
Methemoglobin and hemosiderin are especially well visualized on T2*-weighted image that is a MR sequence that is sensitive to blood by-products. The visualization of signal voids is caused by the local heterogenicity of the magnetic field, resulting from hemorrhagic products .
Takeuchi et al.  reported that T2* improved the characterization of endometrioma by detecting signal void along the cyst wall as hemosiderin deposition. Later in 2015, Takeuchi et al.  proved that signal voids as hemorrhagic components on T2* were also observed in extra-ovarian endometriosis.
Moreover, Pin et al.  suggested that T2* might be useful and added as a sequence for treatment planning of endometriosis. Pin et al . in their study stated that the overall diagnostic performances of MRI with T2* were improved regarding the evaluation of adnexal and deep infiltrating endometriosis with an increase of the sensitivity from 88.2 to 94.1% and specificity from 68.8 to 73.3%.
In our study, with the addition of T2*WI, 50 out of 52 endometriomas/adenomyosis showed signal voids. Thus, the sensitivity improved from 65.4% by conventional imaging to 96.15% with the addition of T2*. Also, the specificity improved from 71.4% by conventional imaging to 85.7% with the addition of T2*.
So, in cases with doubtful ultrasound and conventional MRI findings in confirming the diagnosis of endometriosis, DWI and T2* can represent an additional diagnostic tool in order to differentiate endometriomas from other cystic lesions.
Our study had few limitations. Although the study was originally done on 120 cases, yet only 66 lesions were included in the study as we considered the pathology is our gold standard; so, a larger sample size is needed. Susceptibility artifacts caused by intestinal gas may camouflage the detection of signal voids resulting from the presence of blood by-products within especially in cases of ultra-small and deep endometriotic foci. One of our patients was excluded from the study due to susceptibility artifacts caused by colonic overdistension, which limited the visibility of the pelvis. Two lesions were re-evaluated by two radiologists to sort out the discrepancies resulting from susceptibility artifacts.