Whole body ¹⁸F-FDG-PET/CT for the detection of metastases in sarcomas: is routine scanning of the upper and lower extremities necessary?

Objectives: ¹⁸F-FDG-PET/CT is commonly used for the staging of patients with sarcomas and many centers routinely include the upper and lower extremities in the field of view of the PET/CT study. Imaging of the extremities significantly increase the duration of the PET/CT study, and the CT component results in a non-trivial additional radiation dose. But the clinical value of routinely imaging the extremities is not well established. The aim of this study was therefore to investigate in a large series of patients how frequently new, clinically relevant information is obtained from ¹⁸F-FDG-PET/CT images of the upper and lower extremities.

Methods: The hospital database was searched for patients with sarcomas who underwent ¹⁸F-FDG-PET/CT between 2012-2016. Scan reports were analyzed to determine in how many cases findings were described in the extremities that were not included in “skull base to mid thighs” field of view which is routinely used for ¹⁸F-FDG-PET/CT in most other malignancies. In the clinical reports of ¹⁸F-FDG-PET/CT studies all findings are classified by a certainty lexicon which grades the likelihood of malignancy on a 5 point scale. Findings in the extremities with a low likelihood of malignancy (< 20%) were considered as not clinically relevant because they generally do not cause further workup in our center. Findings that were related to the primary tumor in an extremity or its treatment were also considered as not clinically relevant for this analysis.

Results: A total of 2040 PET/CT scans in 1013 patients were identified. Histopathologic diagnoses comprised Ewing sarcoma (n=138), rhabdomyosarcoma (n=133), leiomyosarcoma (n=84), osteosarcoma sarcoma (n=56), angiosarcoma (n=55), synovial sarcoma (n=49), liposarcoma (n=46), chondrosarcoma (n=35) and other/unspecified sarcoma (n=417). In 1381 scans there were findings in the extremities with 9.2% (127/1381) considered as metastases. The majority (97%, 123/127) of the patients with metastases in the extremities presented with disseminated disease. In only 0.2% of the scans (4/2040) there were metastases in an extremity that would not have been covered by the “eyes-to-thighs” PET/CT or a scan of the extremity involved by the primary tumor.

Conclusion: In this large retrospective series, solitary metastases in an extremity other than the origin of primary were detected in only 0.2% of the scans. Whole body ¹⁸F-FDG-PET/CT almost exclusively detected metastases in the extremities in patients with disseminated disease or in the extremity involved by the primary tumor. Routine imaging of the extremities in all patients with sarcoma may therefore not be necessary. Research Support: None