The "question-mark" MR anatomy of the cervico-thoracic ganglia complex: can it help to avoid mistaking it for a malignant lesion on 68Ga-PSMA-11 PET/MR?

Background Detectable uptake of 68Ga-PSMA-ligands in sympathetic ganglia may potentially lead to mistaking them for malignant lesions. Our aim was to investigate the anatomy of cervico-thoracic-ganglia-complex (CTG-C) in the MR part of multimodal 68Ga-PSMA-11 PET/MR imaging, in view of PET factors hindering its proper identification. Patients and methods In 106 patients, 212 sites of the CTG-C were retrospectively reviewed to assess the radiotracer uptake (SUVmax), size, shape, position, symmetry of location and visual uptake intensity. Asymmetry of PSMA-ligand uptake and increased uptake were regarded as risk factors of malignancy. Results In 66.0% left (L) and 53.8% right (R) CTG-C we noticed configurations, resembling the shape of an exclamation-mark, a question-mark, or its part (called "typical"). Tumor-like CTG-C shapes (oval, binodular or longitudinal) were detected in 28.3% L-CTG-C and in 40.6% R-CTG-C. When visual assessment of PET suggested malignancy, the recognition of "typical" shape of underlying CTG-C on MR generated a rise in the accuracy of their proper identification (from 34.4% to 75%, χ2(1) = 70.4; p < 0.001). Recognizing the shape of the CTG-C as "typical" in MR allowed us to classify as "not-suspicious" 61.9% of all CTG-C which were treated as "suspicious" after sole PET assessment. Conclusions The characteristic shape of cervico-thoracic-ganglia-complex (resembling a question-mark, or its part) helps in proper recognition of CTG-C on multimodal whole-body 68Ga-PSMA-ligand PET/MR imaging, when detectable uptake might lead to considering pathology.