Heather Alison Jacene MD, Abstract Co-Author: Nothing to Disclose

Kent P. Friedman MD, Presenter: Nothing to Disclose

Christian Cohade MD, Abstract Co-Author: Nothing to Disclose

Richard Leo Wahl MD, Abstract Co-Author: Nothing to Disclose

The purpose of this study is to evaluate the imaging characteristics of primary and metastatic gastrointestinal stromal tumors (GIST) by FDG PET and PET/CT.

15 patients (6 males, 9 females; mean age 58 ± 13 y; range 39-91) underwent FDG PET/CT imaging for evaluation of malignant GIST between June 2001 and December 2003. Two nuclear medicine physicians retrospectively and independently reviewed the PET and the fused PET/CT data on separate occasions. The two sets of data were compared for diagnostic certainty and lesion localization. SUVmax and SUVmean were obtained for the primary and metastatic tumors. Scan findings were compared to follow-up diagnostic imaging studies and pathology when available.

The referral population included 1 patient with an untreated primary tumor (8 cm), 3 with Imatinib-treated primary tumors (mean size 7.3 ± 3.1 cm), 9 status post primary tumor resection alone, and 2 status post primary tumor resection and Imatinib. The untreated tumor and 2/3 Imatinib-treated tumors demonstrated heterogeneous and intense FDG uptake with central photopenia. SUVmax and SUVmean were 4.38 and 1.42 for the untreated primary tumor and 6.15 ± 3.9 and 1.96 ± 1.08 for the 3 Imatinib-treated tumors. One gastric primary was equivocal on PET alone due to adjacent physiologic gastric activity, but PET/CT clearly identified the abnormality. Untreated and biopsy-proven liver metastases in one patient had isointense FDG uptake compared to liver parenchyma, and was considered a false negative on PET. Six treated liver and peritoneal metastases had FDG uptake equivalent to background (SUVmax and SUVmean = 2.78 ± 1.26 and 1.58 ± 0.31). PET/CT improved localization of 17 lesions compared to PET alone; 8 equivocal lesions on PET were interpreted as benign on PET/CT and one equivocal interpretation was changed to definitely malignant.

While PET is useful in GIST, false negatives can occur on PET alone due to low uptake tumors appearing isotense to normal bowel. The anatomic data provided by PET/CT can allow detection of these tumors and enhance image interpretation. Longer term follow-up is necessary to determine the prognostic value of FDG PET/CT in GIST.

R.L.W.: Research support and an honoraria from GE Medical Systems.Honoraria from CTMI, Varian, and Cardinal Health.

Jacene, H, Friedman, K, Cohade, C, Wahl, R, Characterization of Gastrointestinal Stromal Tumors by FDG PET/CT: Initial Experience.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4416224.html