[18F]FDG-PET/CT in extranodal non Hodgkin lymphoma

Objectives Although lymphoma generally originates from lymph nodes, in up to 40% of HD/NHL (especially NHL), arises at extranodal sites along the gastrointestinal tract, head and neck, orbit, central and peripheral nervous system, thorax, bone, skin, breast, testis, thyroid, and genitourinary tract. We aim to evaluate the role of [18F]FDG-PET/CT in extranodal manifestations of lymphoma.

Methods We retrospectively evaluate 37 patients (M=18; F=19) with NHL who performed from 02/2009 to 10/2015 a [18F]FDG-PET/CT for a total of 87 examinations. Lymphoma originated from gastrointestinal tract in 15 cases (stomach=12; bowel=3), head and neck in 8 cases (orbit=1; pharynx=2; parotid=3; cheek=1; tongue=1), breast in 6 cases, skin in 4 cases, heart in 2 cases, testicle and brain in 1 case each. PET/CT was acquired 1 hour after [18F]FDG injection (median activity=331 MBq; range 245-644 MBq). [18F]FDG-PET/CT was performed to stage (n=25; post-surgery=4), to evaluate treatment response (n=10) or during follow-up (n=52) patients. [18F]FDG-PET/CT results were compared to final diagnosis obtained by follow-up (clinical-radiological, [18F]FDG-PET/CT or histology). We excluded from the present analysis 4 patients (5 scan totally) affected by cardiac, gastric, ileum, and orbital NHL respectively, due to the lack of final diagnosis.

Results Out of the 82 scans evaluated (staging=24, treatment response evaluation=10, follow-up=48), [18F]FDG-PET/CT resulted positive in 34 cases and negative in 48 cases. Based on final diagnosis was classified as true positive (TP), true negative (TN), false positive (FP) and false negative (FN) in 30, 47, 4, and 1 cases, respectively (Table 1). FP results were observed during the follow-up period of a gastric and a rectum NHL patients in which focal [18F]FDG uptake (SUVmax>3.0) was present in stomach (2 scans) and rectum (1 case). In another case focal [18F]FDG uptake was found in some enlarged right inguinal lymph nodes (SUVmax=3.4-4.1) during the follow-up of the patient with testicle NHL. In this case after the radiological confirmation of the suspicious of recurrence, patient underwent lymphadenectomy which excluded the presence of disease (FP) diagnosing follicular hyperplasia. The only case resulted FN was a patient with gastric NHL in which biopsy performed after PET/CT confirmed microscopic residual disease. Considering the clinical purpose, sensitivity and specificity of PET/CT were 95% and 100% in the staging setting, and 100% and 90% in the follow-up (Table 2). In the 10 scans performed to evaluate treatment response PET/CT was TP in 1 case and TN in the remaining 9 patients. Eleven patients who performed PET/CT to stage disease performed additional PET/CT examinations during their follow-up which diagnosed disease recurrence in 2/11 and residual disease in 1/11 case. PET/CT revealed additional site(s) of disease in 19 cases (lymph nodes=17, bone=3, spleen=1, adrenal=1, pharynx=1).

Conclusions As for nodal lymphoma, [18F]FDG-PET/CT presents very good diagnostic performances (sensitivity=97%, specificity=92%, accuracy=94%) also in extranodal NHL resulting very useful in the clinical management of patients.