Lymph node staging with a combined protocol of ¹⁸F-FDG PET/MRI and sentinel node SPECT/CT: a prospective study in patients with FIGO I/II cervical carcinoma

Abstract

Lymph node metastases (LNM) are present in a minority of patients with early stages of cervical carcinomas. As conventional imaging including PET/CT has shown limited sensitivity, systematic lymphadenectomies are often conducted for staging purposes. Therefore, the aim of this prospective study was to analyze the impact of ¹⁸F-FDG PET/MRI in addition to sentinel node (SLN) biopsy on lymph node status. Methods: 42 women with initial diagnosis of FIGO IA-IIB cervical carcinomas were included between 03/2016–04/2019. Each patient received preoperative whole body ¹⁸F-FDG PET/MRI (Biograph mMR®, Siemens Healthineers) and SLN imaging with SPECT/CT (Discovery 670 Pro®, GE Healthcare) after intracervical injection of ^99mTc-labeled nanocolloid. Systematic Lymphadenectomy and SLN biopsy served as reference standard. Staging in PET/MRI was performed as a consensus of nuclear medicine and radiology experts. Results: One patient was excluded from surgical staging due to newly diagnosed liver metastases in PET/MRI. Overall prevalence of LNM in the remaining 41 patients was 29.3% (12/41). 5/12 patients with LNM solely had small metastases with maximum diameter ≤5mm. Interpretation of PET/MRI as a consensus of experts showed a specificity of 100% (29/29, 95%CI: 88.3-100%) for LNM-staging, but a low sensitivity of 33.3% (4/12, 95%CI: 12.8-60.9%). LN size was the most important factor for the detectability of metastases, since only LNM >5mm could be identified by PET/MRI (sensitivity >5mm: 57.1%; ≤5mm: 0%). Paraaortic LNM were evaluated accurately in 3/4 cases (16 patients with paraaortic LN removal). SLNs were detectable by SPECT/CT in 82.9% of the patients or 69.0% of hemipelvis. In cases with undetectable SLN in SPEC/TCT, malignancy rate was considerably higher (31.2% vs. 19.3%). The combination of PET/MRI and SLN SPECT/CT improved the detection of pelvic LNM from 33.3% to 75%. Conclusion: ¹⁸F-FDG PET/MRI is a highly specific N-staging method and improves LNM detection. Due to the limited sensitivity in frequently occurring small LNM, PET/MRI should be combined with sentinel node mapping. The proposed combined protocol helps to decide whether extensive surgical staging is necessary in patients with FIGO I/II cervical cancer.