Efficacy of FDG-PET/CT Imaging To Guide Biopsies in the Detection of Richter’s Syndrome.

Introduction: Most lymphomas show a good FDG uptake, with significant difference in intensity according to different histopathological subtypes. Richter’s syndrome </DEL> (RS) is defined as the development of aggressive lymphoma in patients with low grade histopathological subtypes. Diagnosis requires histological findings. The aim of our study was to investigate prospectively FDG-PET/CT to guide biopsy in the diagnosis of aggressive transformation of low grade lymphomas.

Material and methods: Thirty-eight patients, presenting clinical and/or biological signs of aggressive transformation were included. The 38 underwent FDG-PET/CT. FDG-PET/CT scans were analysed visually and semi-quantitatively with maximal standardised uptake value (SUVmax) normalised for body mass. Guided-biopsy was performed 4 weeks after FDG-PET/CT, in the abnormal focus showing the highest SUVmax and histopathological analysis was performed.

Results: Histopathological analysis concluded to aggressive transformations in 17 cases (15 NHL and 2 Hodgkin diseases included one composite lymphoma) and low grade lymphomas in 21 cases. Size of lesions on CT was not predictive of RS (p=0.094). FDG-PET/CT images showed abnormal FDG uptake in the 38 included patients. SUVmax ranged from 11.7 to 41.2 in patients with Richter’s syndrome and from 1.7 to 17.0 in patients with no sign of transformation(p<0.0001). Gradient of SUVmax was significantly higher in patients with Richter’s syndrome (p<0.0001). A SUVmax threshold of 14.0 gave the better balance with sensitivity, specificity, predictive positive and negative values around 95.0%. This threshold of 14.0 correctly classified as transformed or not transformed 36/38 patients (94.7%).

Conclusion: FDG-PET/CT imaging is a very relevant tools to detect aggressive transformation of low grade lymphomas and to guide biopsy.