Diffusion-weighted (DW) MR imaging has a higher diagnostic accuracy in assessing the depth of myometrial invasion and the overall staging of endometrial cancer than dynamic contrast-enhanced (DCE) MR imaging, and this was confirmed by Beddy et al. [10]. Yamada et al. [11, 12] proved that DTI had a role in evaluation of the depth of invasion in esophageal and gastric carcinomas.
Only few articles were published about using DTI parameters in the evaluation of myometrial invasion and grading of endometrial carcinoma. The current study was designed to investigate the role of both DW-ADC and diffusion tensor parameters (mainly DT-FA and DT-MD) in the detection of myometrial infiltration and grading of endometrial carcinoma with the most common malignant pathology were endometrioid adenocarcinoma. Similar findings were detected by Toba et al. [1], Zhang et al. [13] and Yamada et al. [14], as the most common pathology was endometrioid adenocarcinoma.
Tian et al. [15] concluded that diffusion-weighted and diffusion tensor imaging could help in the differentiation of endometrioid adenocarcinoma and serous adenocarcinoma. Also, the results of the current study showed that mean DT-FA and DT-MD values of endometrioid adenocarcinoma (0.35 ± 0.13 and 0.907 ± 0.19, respectively) were more than that of papillary serous carcinoma (0.187 ± 0.01 and 0.509 ± 0.04, respectively).
As accurate diagnosis of myometrial invasion is essential in the preoperative assessment of endometrial cancer, Deng et al. [16] reported that diffusion and ADC value could aid in the prediction of deep myometrial invasion. Also, Gil et al. [17] stated that the conjunction of diffusion-weighted imaging with T2WI had better results than the dynamic contrast study and T2WI in the evaluation of myometrial invasion. Similar findings were detected in the current study, and there was a significant statistical difference considering mean DW-ADC values between intact (1.260 ± 0.17) and invaded areas of the myometrium (0.870 ± 0.16) (P value ˂0.001).
In this study, there was a significant statistical difference regarding DT-FA mean values between intact (0.450 ± 0.07) and invaded areas of myometrium (0.260 ± 0.07) (P value ≤ 0.001).
Also, there was a significant statistical difference regarding DT-MD mean values between intact (1.310 ± 0.15) and infiltrated regions of myometrium (0.650 ± 0.16) (P value ˂0.001).
This is compatible with Zhang et al. [13], who stated that DT-FA mean values showed significant differences between cancerous (0.41) versus non-cancerous areas (0.27) within the superficial myometrium (P value ˂ 0.001). Also, they reported that mean DT-MD could distinguish cancerous (1.16) from non-cancerous areas (1.48) within the superficial myometrium (P value ˂ 0.001).
Also, Toba et al. [1] and Yamada et al. [14] concluded that DTI might be a useful tool for diagnosing myometrial invasion of uterine endometrial cancer, both ex vivo and in vivo, respectively.
Previous studies by Zhang et al. [13] and Yamada et al. [14] confirmed that the DTI parameters were superior to the ADC in the assessment of myometrial invasion of endometrial carcinoma. This is in agreement with the results of this study, as the accuracy of DT-MD (98.0%) and DT-FA (90.0%) was superior to the accuracy of DW-ADC (86.0%) in the prediction of myometrial infiltration.
For grading of endometrial carcinoma, Nakamura et al. [18], Inoue et al. [19] and Habib et al. [20] reported that DW-ADC may have a value in differentiation of endometrioid adenocarcinoma pathologic grades and the lower ADC value is associated with the higher grade of the tumor.
The results of this study are matching with the previous studies, and there was a significant statistical difference regarding DW-ADC mean values in different endometrioid adenocarcinoma grades (G1 = 1.03 ± 0.12; G2 = 0.892 ± 0.062 and G3 = 0.824 ± 0.072) (P value ≤ 0.001).
Diffusion tensor imaging proved to have a role in grading of breast, renal cancers and brain gliomas [21,22,23,24,25,26], especially DT-FA parameter which is decreased with a higher grade of the tumor and this is mostly due to packed cells and heterogeneity [22].
Yamada et al. [14] reported that the mean DT-FA and DT-MD values of endometrioid adenocarcinoma G1, G2, and G3 were statistically different with significant (P value ≤ 0.001).
Similar findings were detected in the current study: there was a significant statistical difference between DT-FA mean values and the pathological grade of endometrioid adenocarcinoma as G1 = 0.463 ± 0.085, G2 (0.296 ± 0.058) and G3 (0.225 ± 0.042). Also, the mean DT-MD values of endometrioid adenocarcinoma G1 = 1.042 ± 0.16, G2 = 0.861 ± 0.12 and G3 = 0.731 ± 0.094 with significant (P value ≤ 0.001).
The results of this study confirmed that there is an inverse correlation between the mean values of DW-ADC, DT-MD and DT-FA; and the pathological grade of endometrioid adenocarcinoma (the higher the grade, the lower the value, and vice versa) (P value ≤ 0.001). This is in accordance with Habib et al. [20] with (P value = 0.03 for DW-ADC) and in harmony with Yamada et al. [14] who stated that there was a significant inverse correlation between DT-FA and DT-MD values and histo-pathologic grades (P value < 0.001).
The analysis of the ROC curve showed that DW-ADC, DT-FA and DT-MD were useful for grading of endometrioid adenocarcinoma with DT-FA had more accuracy than DT-MD and DW-ADC for differentiation of G3 from G1 or 2 (94.9%) and also differentiation of G1 from G 2 or 3 endometrioid adenocarcinoma (90.0%). This is in agreement with Yamada et al. [14] who stated that DT-FA had the largest area under curve for differentiation of Grade 1 from G2 or 3 and for differentiation of Grade 3 from G1 or G2 endometrioid adenocarcinoma. They added that the use of DTI parameters, especially FA values, is useful for evaluating the degree of aggressiveness of endometrial carcinoma.
Lastly, a preliminary recent study done by Ghosh et al. [27] used the whole tumor histogram texture for defining the ROI to measure the DTI parameters in evaluation of myoinvasion and type of endometrial carcinoma. They assumed that this texture approach will have more reproducibility and make the results more confident than subjective drawing the region of interests (ROIs) and added that more future extensive studies are needed for better results.
Limitation
This study pays attention to endometrioid subtype of endometrial carcinoma and its histopathological grades with small numbers of other subtypes of endometrial cancer.
Also, the relatively small numbers of overall patients participated in the study.
Further studies with a large scale of patients and adding DTI and DWI to conventional pelvic MRI with more standardization of the protocols are recommended in the evaluation of endometrial cancer patients. Also, more detailed inter-observer agreement studies are recommended.