Novel PETMR approach improves detection of endometriosis in difficult-to-assess areas

A new PETMR technique that targets fibroblast activation protein (FAP) overexpressed in endometriosis is more effective at identifying lesions than conventional imaging. According to new research published in the August issue of The Journal of Nuclear Medicine, this approach was particularly effective in regions of the pelvis and abdomen that are typically difficult to image. By accurately mapping the extent of endometriosis, FAP-targeted PETMR has the potential to enable more personalised management and improve patient outcomes.

Endometriosis is a chronic inflammatory condition characterised by endometrial tissue growing outside of the uterus, affecting six to 10 per cent of women of childbearing age. It is a leading cause of chronic pelvic pain, infertility, and decreased quality of life, posing significant public health and economic challenges. Diagnosis of endometriosis is difficult and is often delayed by four to 12 years.

Until recently, laparoscopy with histologic confirmation was considered the diagnostic gold standard for endometriosis. However, diagnostic laparoscopy is increasingly abandoned because of advancements in diagnostic imaging. Transvaginal ultrasound and MRI are commonly used in diagnosis; however, they may underestimate the extent of disease, particularly in deep infiltrating endometriosis.

“While MRI shows anatomical changes, FAP-targeted PETMR highlights tissue remodelling and fibrosis, which are important features of endometriosis,” said Philipp Schindler, MD, radiologist and nuclear medicine diagnostic specialist at the University Hospital Münster in Germany. “In light of the established value of diagnostic MRI, combined FAP-targeted PETMR may represent a valuable diagnostic tool for the evaluation of endometriosis by improving diagnostic performance.”

The retrospective study investigated the feasibility of utilizing FAP-targeted PETMR to improve endometriosis detection. Participants included 18 premenopausal women: a test cohort of nine patients with suspected or confirmed endometriosis who had undergone FAP-targeted PETMR or PETCT and a reference cohort of nine patients who had undergone FAP-targeted PETMR or PETCT for initial staging of breast cancer. Lesions were assessed using a segment-based analysis and focal radiopharmaceutical uptake was assessed. Clinical assessments and laparoscopic findings, when available, served as reference standards. 

In the test cohort with available PETMR data, MRI alone identified endometriosis-suspicious findings in 19 per cent of segments. In contrast, combined PETMR identified findings in 49 per cent of segments. In the reference group, lesions with focal uptake of the FAP inhibitor radiopharmaceutical outside of the uterus were identified in 14 (13 per cent) of 108 evaluated segments, compared with 44 (41 per cent) of 108 segments in the test group. Where available, PETMR findings showed substantial concordance with laparoscopic results.

“Not only did the combined examination showed substantially more findings suggestive of endometriosis than MRI alone, but these included findings in areas that are often difficult to assess, such as the peritoneum, ovaries, fallopian tubes and locations outside the pelvis,” noted Schindler. “If our findings are confirmed, FAP-targeted imaging could establish a new application for molecular imaging in endometriosis, and potentially in other diseases involving tissue remodeling and fibrosis.”

Figure: Images from patient T1, who had menstrual cycle–dependent right shoulder pain. (A) Maximum-intensity-projection images show abnormal findings for right diaphragm (arrowhead), bilateral round ligaments, peritoneum around bilateral ovaries, and left fallopian tube. Combined PET/MRI show hyperintense lesion with focal uptake inferior of right diaphragm, indicative of endometriosis (arrowhead, B). Confirmatory laparoscopy demonstrated extensive pelvic disease and implants of right diaphragm (C) that stained intensely positive for FAP (D).

Source: SNMMI.

The authors of “Initial Results of FAPI PET/MRI to Assess the Extent of Endometriosis” include Philipp Schindler, Jonas Brandt, and Tobias Krähling, Department of Radiology, University Hospital Münster, Münster, Germany; Stefanie Bobe, Gerhard-Domagk-Institute of Pathology, University of Münster, Münster, Germany, and European Institute for Molecular Imaging, University of Münster, Münster, Germany; David Ventura, Michael Schäfers, and Philipp Backhaus, European Institute for Molecular Imaging, University of Münster, Münster, Germany, and Department of Nuclear Medicine, University Hospital Münster, Münster, Germany; and Ariana Plasger, Martin Götte, Ludwig Kiesel, Paulina Marie Dorten, Ralf Witteler, Louisa Liehn, Lars Hanker, and Stephanie Eltrop, Department of Gynecology and Obstetrics, University Hospital Münster, Münster, Germany.

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