Background and purpose of the study

The assessment of depth of myometrial invasion is important in evaluating endometrial cancer on MRI, because it closely correlates with the prevalence of nodal metastasis and the patient’s prognosis. DWI demonstrates endometrial cancer as a high signal intensity mass, however, detailed evaluation of myometrial invasion on conventional DWI is occasionally difficult due to low spatial resolution and distortion^1-3. Reduced phase direction field-of-view (FOV) technique by using spatially selective phase encoding gradient can offer high quality DWI with improved spatial resolution, without associated phase wrap round artifact, and with less artifacts related to motion and susceptibility which are common in larger FOV images^{4, 5}. The purpose of this study is to compare the diagnostic performance of reduced FOV DWI (rFOV-DWI) with those of T2WI and 3D dynamic contrast-enhanced MRI (DCE-MRI) in evaluating the depth of myometrial invasion.

Materials and methods

25 women with endometrial cancer underwent preoperative MRI including T2WI, conventional DWI and rFOV-DWI (b = 0 and 800 sec/mm²) and 3D-DCE-MRI with 3T MRI units (Discovery MR750, GE Healthcare). The depth of myometrial invasion was evaluated on T2WI, rFOV-DWI (FOCUS: FOV optimized and constrained undistorted single shot, FOV:20-24*8-12cm, Matrix:160*80, thickness:5mm), and 3D-DCE-MRI (3D fast spoiled gradient-recalled echo sequence with fat-suppression; FOV:30cm, Matrix:320*192, thickness:3 mm/1.5 mm overlap; with intravenous administration of 0.1 mmol/kg of gadopentetate dimeglumine). The depth of myometrial invasion evaluated on both sagittal and oblique axial (short axis) images by two radiologists was classified as stage S (superficial invasion: limited in the endometrium or invades less than 50% of the myometrium) and stage D (deep invasion: invades 50% or more of the myometrium). The results were compared with the histologically confirmed depth of myometrial invasion to determine the diagnostic accuracy of T2WI, rFOV-DWI and 3D-DCE-MRI, respectively.

Results

The 25 surgically proven endometrial cancers included 16 stage S and 9 stage D tumors (Table 1). All 25 tumors exhibited high intensity on rFOV-DWI with clear margins (Fig. 1-4). The depth of myometrial invasion was not able to estimate on T2WI in 8 stage D tumors due to poor tumor-to-myometrium contrast (tumor and adjacent myometrium showed similar signal intensity) (Fig. 2), or due to poor tumor-to-coexisting adenomyosis contrast (Fig. 3), and also not able to estimate on 3D-DCE-MRI in 2 stage D tumors due to poor tumor-to-coexisting adenomyosis contrast (Fig. 3). The myometrial invasion was not able to estimate on rFOV-DWI in one stage S tumor due to distortion caused by susceptibility artifact from adjacent rectal gas (Fig. 4). The staging accuracy was 68% (17/25) for T2WI, 92% (23/25) for 3D-DCE-MRI, and 96% (24/25) for rFOV-DWI. Combination of rFOV-DWI reading together with T2WI improved the assessment of myometrial invasion with a diagnostic accuracy of up to 100%.

Discussions

The depth of myometrial invasion strongly correlates with the risk of lymph node metastasis (3% with superficial myometrial invasion and 46% with deep myometrial invasion) and prognosis of the patients with endometrial cancer. Beddy et al. reported that DWI had a higher diagnostic accuracy in assessing the depth of myometrial invasion than did DCE-MRI¹. DWI has a high diagnostic accuracy in detecting deep myometrial invasion, and there is no significant difference between sensitivity and specificity of DWI and DCE-MRI according to a meta-analysis³. However, detailed evaluation of myometrial invasion on conventional DWI is occasionally difficult due to low spatial resolution and distortion caused by susceptibility artifacts^{4, 5}. In this study all 25 tumors were demonstrated as high signal intensity masses with clear margins on rFOV-DWI. The depth of myometrial invasion was correctly diagnosed due to good tumor-to-myometrium contrast except for one lesion with distortion caused by susceptibility artifact from adjacent rectal gas. By referring T2WI, the depth of myometrial invasion was correctly assessed in this patient. The depth of myometrial invasion could not be evaluated both on T2WI and on DCE-MRI in 2 patients with coexisting adenomyosis. Adenomyosis may show heterogeneous signal intensity on T2WI and/or heterogeneous contrast enhancement on DCE-MRI, and the boundaries between the tumor and adenomyosis may be unclear². Our results suggest that rFOV-DWI is helpful for differentiating coexisting adenomyosis and tumor invasion in such cases.

Conclusions

We conclude that addition of rFOV-DWI may improve the staging accuracy of endometrial cancer in assessing the depth of myometrial invasion. Especially rFOV-DWI has an advantage in assessing the depth of myometrial invasion in cases with coexisting adenomyosis. rFOV-DWI can be an alternative to DCE-MRI in evaluating myometrial invasion of endometrial cancer without the use of contrast medium.

Acknowledgements

No acknowledgement found.

References

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