¹⁸F FDG PET/CT clearly showed a case of lymphoma involving kidneys & bones without morphological abnormality

A 31 yr old male† presented to the Infectious Diseases Department of Yichang Central People’s Hospital, Hubei province, P.R. China, in June 2017, with a fever of unknown origin for over three weeks. The positive laboratory results mainly included erythrocytopenia (3.62×10¹²/l; normal range: 4.3-5.8), leukopenia (3.21×10⁹/l; normal range: 3.5-9.5), thrombocytopenia (118×10⁹/l; normal range: 125-350) and a marked increase in the level of lactate dehydrogenase (1208 IU/l; normal range: 120-250).

However, imaging examinations, including non-enhanced chest and abdominal computed tomography (CT) and abdominal ultrasound were unremarkable (Fig. 1). A whole-body ¹⁸Fluorine labelled fluorodeoxyglucose positron-emission computed tomography/CT (¹⁸F-FDG PET/CT) was done to look for occult infection or malignancy. PET/CT images (Fig. 2) showed abnormally elevated FDG uptake in bilateral kidneys and humerus, left femoral neck and retroperitoneal lymph nodes (all <1 cm in diameter) with a maximum standardized uptake value (SUV_max) of 18.1. No obvious morphological abnormalities were observed in these hypermetabolic lesions on non-enhanced CT. Subsequently, non-Hodgkin’s cytotoxic T-cell lymphoma was confirmed by immunohistochemistry (Fig. 3) through left femoral neck puncture biopsy under the guidance of PET/CT and the patient was transferred from the infectious diseases to the haematology department for treatment. After two cycles of chemotherapy, a repeat PET/CT revealed that the metabolic activity returned to the normal level with a SUV_max of 3.0 (Fig. 4).

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Fig. 1 Renal ultrasound before treatment indicated that there were no obvious abnormalities in the size, shape and sonographic manifestations of both kidneys. Panel A and B show the left kidney and C and D represent the right kidney.

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Fig. 2 PET/CT images before chemotherapy. Panel A-C show renal PET, CT and PET/CT fusion images, respectively. Panel D-F show PET, CT and fused PET/CT images of the left femoral neck, respectively. (G) MIP image shows abnormal FDG uptake in the bilateral kidneys and humerus, left femoral neck and retroperitoneal lymph nodes. The SUV_max of kidney and bone lesions were 18.1 and 17.0, respectively. Arrows indicate lesions. FDG PET/CT, flurodeoxyglucose positron-emission computed tomography, MIP, maximum intensity projection; SUV_max, maximum standardized uptake value.

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Fig. 3 The left femur neck lesion biopsy under the guidance of PET/CT. (A) Haematoxylin and eosin staining showing normal bone marrow structural destruction, with small remnants of adipose tissue and proliferating fibrous connective tissue and atypical lymphocyte infiltration. Immunohistochemical results: (B) MPO (−), CD235 (erythrocyte +), CD61 (−), CD3 (+), (C) CD20 (−), GranzB (scattered +), (D) ki-67 (hot spot LI about 20%+), CD56 (−), CD30 (−), ALK(ALK1), CD138 (−), EBER-CISH (−). Combined with clinical data, it was considered that non-Hodgkin’s cytotoxic T-cell lymphoma involves bone marrow. (A-D, ×20).

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Fig. 4 After two cycles of chemotherapy, a repeat PET/CT showed that all previous hypermetabolic lesions disappeared. Panel A-C showed PET, CT, and PET/CT fusion images of both kidneys, respectively. Panel D-F showed PET, CT and PET/CT fusion images of the left femoral neck, respectively. (G) displayed MIP image of the whole body.

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Lymphoma can involve a variety of tissues and organs outside the lymph nodes. When there is no obvious morphological abnormality, traditional imaging may not pick up abnormal lesions. However, an ¹⁸F-FDG PET/CT can be invaluable in diagnosing an occult malignancy and for subsequent evaluation for the remission of disease.

Acknowledgment: The authors would like to thank pathology expert Yu-fei Liu, haematology expert Jing-ming Guo and oncology expert Xin-hua Xu, The First Clinical Medical College of Three Gorges University, Yichang, China, for providing professional advice.