Extensive FDG uptake and its modification with corticosteroid in a granuloma rat model: an experimental study for differentiating granuloma from tumors.
BACKGROUND
Increased (18)F-fluorodeoxyglucose (FDG) uptake in inflammatory lesions, particularly in granulomatous inflammation (e.g., sarcoidosis), makes it difficult to differentiate malignant tumors from benign lesions and is the main source of false-positive FDG-PET findings in oncology. Here, we developed a rat granuloma model and examined FDG uptake in the granuloma. The effects of corticosteroid on FDG uptake in the granuloma were compared with those in a malignant tumor.


METHODS
Rats were inoculated with Mycobacterium bovis bacillus Calmette-Guérin (BCG) or allogenic hepatoma cells, and subdivided into control and pretreated (methylprednisolone acetate, 8 mg/kg i.m.) groups. Radioactivity in tissues was determined 1 h after the FDG injection. FDG-PET was performed in rats bearing BCG granulomas or tumors before and after prednisolone treatment.


RESULTS
Mature epithelioid cell granuloma-formation and massive lymphocyte-infiltration were observed in the control group of granuloma, histologically similar to sarcoidosis. The mean FDG uptake in the granuloma was comparable to that in the hepatoma. Prednisolone reduced epithelioid cell granuloma-formation and lymphocyte-infiltration. Prednisolone significantly decreased the level of FDG uptake in the granuloma (52% of control), but not in the hepatoma. The FDG uptake levels in the granulomas and tumors were clearly imaged with PET.


CONCLUSIONS
We developed an intramuscular granuloma rat model that showed a high FDG uptake comparable to that of the tumor. The effect of prednisolone pretreatment on FDG uptake was greater in the granuloma than in the tumor. These results suggest that BCG-induced granuloma may be a valuable model and may provide a biological basis for FDG studies.
Zhao
Songji
S
Department of Nuclear Medicine, Graduate School of Medicine, Hokkaido University, Kita 15 Nishi 7, Kita-ku, Sapporo, Japan.
Kuge
Yuji
Y
Kohanawa
Masashi
M
Takahashi
Toshiyuki
T
Kawashima
Hidekazu
H
Temma
Takashi
T
Takei
Toshiki
T
Zhao
Yan
Y
Seki
Koh-ichi
K
Tamaki
Nagara
N
D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000000981:diagnostic imaging* / Q000378:metabolism*; D045744:Cell Line, Tumor; D003937:Diagnosis, Differential; D004195:Disease Models, Animal; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D005938:Glucocorticoids / Q000008:administration & dosage; D006099:Granuloma; D008113:Liver Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D011239:Prednisolone / Q000008:administration & dosage; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D051381:Rats; D017208:Rats, Wistar
D005938:Glucocorticoids; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D011239:Prednisolone