Validation of 18F-FDG PET/MRI and diffusion-weighted MRI for estimating the extent of peritoneal carcinomatosis in ovarian and endometrial cancer -a pilot study

Abstract

Background: The extent of peritoneal carcinomatosis is difficult to estimate preoperatively, but a valid measure would be important in identifying operable patients. The present study set out to validate the usefulness of integrated ¹⁸F-FDG PET/MRI, in comparison with diffusion-weighted MRI (DW-MRI), for estimation of the extent of peritoneal carcinomatosis in patients with gynaecological cancer.

Methods: Whole-body PET/MRI was performed on 34 patients with presumed carcinomatosis of gynaecological origin, all scheduled for surgery. Two radiologists evaluated the peritoneal cancer index (PCI) on PET/MRI and DW-MRI scans in consensus. The surgeon estimated PCI intraoperatively, which was used as the gold standard.

Results: Median total PCI for PET/MRI (21.5) was closer to surgical PCI (24.5) (p = 0.6), than DW-MRI (median PCI 20.0, p = 0.007). However, both methods were highly correlated with the surgical PCI (PET/MRI: β = 0.94 p < 0.01, DW-MRI: β = 0.86, p < 0.01). PET/MRI was more accurate (p = 0.3) than DW-MRI (p = 0.001) when evaluating patients at primary diagnosis but no difference was noted in patients treated with chemotherapy. PET/MRI was superior in evaluating high tumour burden in inoperable patients. In the small bowel regions, there was a tendency of higher sensitivity but lower specificity in PET/MRI compared to DW-MRI.

Conclusions: Our results suggest that FDG PET/MRI is superior to DW-MRI in estimating total spread of carcinomatosis in gynaecological cancer. Further, the greatest advantage of PET/MRI seems to be in patients at primary diagnosis and with high tumour burden, which suggest that it could be a useful tool when deciding about operability in gynaecological cancer.

Keywords: Carcinomatosis; DW-MRI; Ovarian cancer; PET/MRI; Peritoneal cancer index (PCI).

Fig. 1

Correlations between surgical total PCI index and MRI PCI (a) and PET/MRI (b) and between surgical small bowel (region 9–12) PCI index and MRI small bowel PCI (a) and PET/MRI small bowel PCI index (b)

Fig. 2

Bland-Altman plots comparing PCI index of DW-MRI (a) and PET/MRI (b) with surgical PCI index. DW-MRI bias was 2.91 ± 7.49, regression b = − 0.15 ± 0.13, p = 0.24. PET/MRI bias was 0.41 ± 6.24, regression b = − 0.14 ± 0.11, p = 0.19

Fig. 3

This FSE T2-w image (a) illustrates the difficulty in discriminating the different structures that contribute to form the complex image seen in the center of the pelvis. There are areas of restricted diffusion in DWI b = 1000 (b) which do not correspond to areas of increased FDG uptake as showed in this fused PET/MR image (c). The image was interpreted as being formed by a cystic ovarian tumor (solid black arrow), bowel loops (open arrows), peritoneal carcinomatosis (encircled) and fundus uteri (solid white arrow) (d). The exact localization of peritoneal implants, if they were on bowel surface or on the surface of pelvic peritoneum, was very difficult, as was to say if the loops corresponded to ileum or sigmoid colon. PCI for “Pelvis”, or “region 7”, was 3 for surgery, 0 for MRI alone (DWI) and 3 for PET/MR, thus a false negative for MRI and true positive for PET/MRI

Fig. 4

a FSE T2-w image: Ascites helped to correctly localize a peritoneal implant on the surface of pelvic peritoneum (arrow) by displacing adjacent bowel loops. The lesion was easily diagnosed either by MRI alone or by PET/MRI because of clear restriction of diffusion in DWI (b) and marked FDG uptake (c)