Vasculature cast sign on F-FDG PET/CT: a specific imaging marker for pediatric T-lymphoblastic lymphoma.

[PURPOSE] To evaluate the diagnostic performance of F-FDG PET/CT parameters for T-lymphoblastic lymphoma (T-LBL), with particular emphasis on the "vasculature cast" sign, for distinguishing T-LBL from other pediatric anterior mediastinal malignancies.

[METHODS] Pretreatment F-FDG PET/CT scan of 60 patients (≤ 21 years) with anterior mediastinal tumors were retrospectively analyzed. Diagnostic performance of the imaging parameters was compared between T-LBL and nonT-LBL groups. Intra- and interobserver agreement for vasculature cast sign was assessed.

[RESULTS] The vasculature cast sign was present in 15/24 T-LBL cases, with high specificity (97.2%) and positive predictive value (93.8%) but moderate sensitivity (62.5%). Intra- and interobserver agreement were 0.91 and 0.83, respectively. T-LBL had significantly larger tumor dimension (Dmax), lower SUVmax of the tumor or the spleen, higher total or mediastinal tumor metabolic tumor volume with a threshold of 41% of SUVmax and more frequent aortic arch encasement compared to nonT-LBL. Multivariable logistic regression identified the vasculature cast sign (odds ratio [OR], 37.45, 95% CI: 1.83-767.64, p = 0.019), tumor SUVmax (OR, 0.82, 95% CI: 0.69-0.97, p = 0.023) and Dmax > 6.85 cm (OR, 16.67; 95% CI: 1.76-158.21, p = 0.014) as independent imaging markers for T-LBL. Model combining these parameters yielded an area under the curve of 0.943 (p < 0.001), and a simplified scoring system was developed based on the three parameters, yielding the diagnostic rates of 0% (0/8), 14.3% (3/21), 40% (6/15), and 100% (15/15) for scores of 0, 1, 2, and 3, respectively.

[CONCLUSION] The vasculature cast sign is a specific and reproducible PET/CT marker of T-LBL.