Objectives

This case report demonstrates the potential utility of [68Ga]Ga-FAPI-04 Positron Emission Tomography/Computed Tomography (PET/CT) for diagnosing endometriosis.
The scan confirmed a known endometriotic lesion in the sigmoid colon previously identified by Magnetic Resonance Imaging (MRI).
Importantly, [68Ga]Ga-FAPI-04 PET/CT identified additional suspected endometriotic lesions in the left ovary and ligamentum teres uteri bilaterally, which were not detected by MRI.
This is presented as the first confirmed case showing clear and intensive [68Ga]Ga-FAPI-04 uptake in endometriosis, suggesting it could be a promising diagnostic tool alongside its established use in oncology.

Methodology

A 43-year-old female patient with a history of endometriosis and persistent symptoms underwent preoperative imaging.
Imaging included standard MRI (contrast-enhanced T1-weighted fat-saturated sequence) and [68Ga]Ga-FAPI-04 PET/CT.
For the PET/CT scan, 148 MBq of [68Ga]Ga-FAPI-04 was administered, and images were acquired 10 minutes post-injection.
Tracer uptake was assessed visually and quantitatively using the maximum standardized uptake value (SUVmax).
Findings were compared between MRI and PET/CT.
Post-surgical histopathology confirmed deep infiltrating endometriosis extragenitalis.

The known sigmoid colon lesion identified by MRI showed intense tracer uptake on PET/CT (SUVmax 9.8). !Figure[A] !Figure[B]
Additional lesions undetected by MRI were identified by PET/CT in the left ovary (SUVmax 11.3) and bilaterally in the ligamentum teres uteri (SUVmax 7.3 and 5.4).
Surgical intervention followed, and histopathology confirmed the presence of deep infiltrating endometriosis extragenitalis.
The evidence is based on a single case, providing preliminary support for the potential diagnostic value of [68Ga]Ga-FAPI-04 PET/CT in endometriosis.

This case report compellingly illustrates the potential of [68Ga]Ga-FAPI-04 PET/CT to visualize endometriotic lesions with high contrast, potentially identifying sites missed by conventional MRI.
A primary limitation is that the findings are derived from a single patient. While promising, generalization requires systematic investigation in larger cohorts, as acknowledged by the authors mentioning an ongoing prospective study (NCT06792318).
While histopathology confirmed endometriosis, the report lacks explicit confirmation correlating each specific FAPI-avid lesion (especially those newly identified in the ovary and ligaments) with histopathological findings from those exact locations. Future studies should aim for precise site-specific pathological correlation.
The comparison between FAPI-PET/CT and MRI is primarily qualitative. Incorporating standardized, potentially blinded, comparative reading protocols could strengthen the evidence for FAPI-PET/CT's added value in future research.
Investigating the relationship between SUVmax levels and lesion characteristics (e.g., type of endometriosis, inflammatory activity, depth of invasion) could provide further insights into the biological basis of FAPI uptake in this condition.