Predictive Patterns of Pediatric PTLD on PET/MRI

Introduction: A wide variety of transplantations, including multi-visceral solid organ and bone marrow, are performed in our institution. This results in a large number of patients diagnosed with Post Transplant Lymphoproliferative Disorder (PTLD). The aim of this study is to describe the predictive value of unique patterns of Whole-Body 18F-FDG PET/MRI metabolic activity in pediatric patients with PTLD.

Methods: Upon reviewing our database of 700 body 18F-FDG PET/MRI (PET/MRI) studies since 2018, 38 children (age less than 20 years) were identified with a diagnosis of PTLD; M24: F14. We have retrospectively analyzed Whole-Body 18F-FDG PET/MRI examinations at presentation of suspected PTLD in these patients. PTLD imaging and non-imaging parameters for classification included: symmetric vs. asymmetric disease, localized vs. generalized involvement, involvement of the lymph nodes, solid organs, bone and bone marrow, and reviewed type of transplant, pathology, cytogenetics, and EBV status.

Results: 18F-FDG PET/MRI examinations were abnormal in N=29 and normal in N=9. Lymphoma transformation occurred in N=10 patients and included: DLBCL, B cell lymphoma, Burkitt lymphoma, MALT lymphoma, marginal zone lymphoma, pleomorphic T cell lymphoma. PET/MRI was abnormal in 8/10 (80%) with lymphoma transformation (N=2 had normal PET/MRI). Characteristic pattern in this group was asymmetric focal disease with possible involvement of the nodes, solid organs, bowel, or bone (N=6, 67%). 6/8 (75%) of the patients with lymphoma and abnormal PET/MRI scan were EBV positive.

In 17/21(81%) patients with PTLD without transformation to lymphoma and abnormal PET/MRI, a characteristic pattern of diffuse and symmetric uptake with involvement of symmetric lymph node stations that may be present throughout the body was identified (EBV+ N=8, EBV - N=9). The two additional patients with lymphoma with this symmetric pattern had MALT and T Cell lymphoma.

Conclusions: Symmetric diffuse nodal uptake pattern of 18F-FDG is most often seen in PTLD patients that have not transformed to lymphoma. EBV+ lymphoma transformed patients are more likely to have a focal / asymmetric abnormal pattern of 18F-FDG uptake. These findings may help the clinician in patient management to determine need for biopsy and therapy versus continued observation.

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