False-Positive Bony FDG Accumulations Due to Fractures in a Patient with Lung Cancer: the Value of Integrated Information of PET/CT

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1 False-Positive Bony FDG Accumulations Due to Fractures in a Patient with Lung Cancer: the Value of Integrated Information of PET/CT Hon-Ki Hsu 1, Cheng-Kai Huang 2, Yu-Lin Bai 3, Kai-Yuan Cheng 4, Guang-Uei Hung 2 1 Department of Chest Surgery, Chang-Bing Show Chwan Memorial Hospital, Changhua, Taiwan 2 Department of Nuclear Medicine, Chang-Bing Show Chwan Memorial Hospital, Changhua, Taiwan 3 Department of Radiology, Chang-Bing Show Chwan Memorial Hospital, Changhua, Taiwan 4 Institute of Radiological Science, Central Taiwan University of Science and Technology, Taichung, Taiwan Received 4/14/2009; revised 4/23/2009; accepted 4/30/2009. For correspondence and reprints contact: Guang-Uei Hung, M.D., Department of Nuclear Medicine, Chang-Bing Show Chwan Hospital. 6 Lugong Road, Lukang Township, Changhua 500, Taiwan. Tel: (886) ext , @gmail.com Fluorine--fluorodeoxyglocose ( F-FDG) positron emission tomography (PET) or PET/computed tomography (CT) is a powerful modality in the staging, follow-up and therapeutic evaluation of oncologic patients, including lung cancer. However, FDG is not a specific tracer for cancer and false-positive uptake occasionally occurred. Here, we present a 78-year-old male with history of lung cancer underwent F-FDG PET/CT for follow-up. The PET images showed multiple FDG-avid foci in the bony structures, including ribs, distal and proximal portions of right clavicle and L2 vertebra, and were initially considered as bony metastases. But the co-registered CT images showed typical evidences of fractures and history of recent traffic accident with direct impaction to the chest was traced. Follow-up images, including PET/CT and bone scan, revealed complete resolution of the rib lesions. The bony lesions were finally considered as traumatic fractures. The presented case demonstrates the value of the co-registered CT images in PET/CT study not only in attenuation correction and anatomical localization but also morphological characterization of the FDG-avid lesions to avoid falsepositive interpretation due to traumatic fractures. Key words: F-FDG, PET/CT, false-positive, traumatic fractures Ann Nucl Med Sci 2009;22:3-7 Introduction The high F-FDG uptake may associate malignant neoplasm relative to the level of F-FDG distributed [1,2]. However, localization of F-FDG is not specific for malignancy, and distinguishing malignant neoplasm from normal variants and benign pathologic sources of F-FDG uptake are important works. Nowadays, CT-integrated PET (PET/CT) has become a standard tool in PET laboratory. Co-registered CT images of PET/CT examination provide not only attenuation correction but also anatomical information for the correlative PET images, and may help avoid potential pitfalls related non-malignant processes. In the presented case, a patient with lung cancer showed multiple FDG-avid lesions in bony structures, which had typical appearance of fractures on the corresponding CT images. The traced history and follow-up studies with whole body bone scan also concluded with traumatic fractures. Case Report A 78-year-old male with squamous cell carcinoma at

2 Hsu HK et al left upper lobe (LUL) of lung who was initially staged as T2N0M0 was referred for F-FDG PET/CT study for follow-up 2 years after resection of LUL. The PET/CT was performed on a GE Discovery PET/CT (GE Medical System, Waukesha, Wisconsin, USA) with multiple bed position acquisitions ranging from approximately the mid thighs to the top of skull, head-in bed-out direction in PET protocol. In CT protocol, head-in bed-in direction with 140 kv, 210 ma, pitch 1.75 and 3.75 mm slice. Reconstructed re-sliced into coronal, sagittal and transaxial images were performed. No CT-contrast medium was used. The PET images showed multiple FDG-avid foci in bony structures, including ribs (SUVmax = 2.5), right sternoclavicular area (SUVmax = 4.2), right shoulder area (SUVmax = 3.5) and L2 vertebra (SUVmax = 3.3), and were initially considered as bony metastases (Figure 1). However, there were typical appearances of fractures at ribs, proximal and distal ends of right clavicle, and L2 vertebra on the coregistered CT images (Figure 2). Besides, recent traffic accident with direct impaction to the chest was traced subsequently from the patient s history. A follow-up PET/CT performed 5 months later revealed complete resolution of the FDG-avid lesions in ribs and L3 (not shown). Serial whole Figure 1. The maximum intensity projection (MIP) images of PET reveal multiple foci with increased FDG uptake in the bony structures, including ribs (SUVmax = 2.5), right sternoclavicular area (SUVmax = 4.2), right shoulder area (SUVmax = 3.5) and L-spine (SUVmax = 3.3). These lesions were initially considered as bony metastases. Figure 2. The 2-D PET, CT (bone window) and PET/CT fusion images with transaxial views localize the FDG-avid lesion at the ribs (A) proximal (B) and distal (C) ends of right clavicle and L2 vertebra (D), and show typical appearance of fracture line on the CT images. Ann Nucl Med Sci 2009;22:3-7 Vol. 22 No. 3 September

3 Զጱ ᐪ Њ ว FDG PET False-positive bony FDG PET due to fractures Figure 3. (A) The bone scan performed 2 weeks after the initial PET/CT study shows multiple foci with increased uptake of 99mTcMDP in the right-side rib cages, distal portion of right clavicle, right sternoclavicular area, right-side costovertebral junctions of ribs, and L2 vertebra. (B) The follow-up bone scan performed 11 months after initial PET/CT scan shows complete resolution of the rib, costovertebral junction lesions and L2 vertebra, and partial resolution of the right distal clavicle lesion, which were consistent with healing processes of the traumatic fractures. There was no apparent change demonstrated for the lesion at proximal end of right clavicle, which was considered due to non-union of fracture as evidenced by the follow-up CT scan (not shown). body bone scans performed 2 weeks and 1 year after the carefully differentiated. As our presented case, benign born PET/CT study were also arranged for follow-up, and the fractures might also accumulate F-FDG and cause false- findings were consistent with healing processes of traumatic positive results [7-9]. fractures for the FDG-avid lesions in ribs, distal clavicle and The SUVmax essentially compares the concentration of L3 (Figure 3). Up to present, the patient has been considered to be free of recurrent or metastatic disease. centration of F-FDG in the body, and represents the meta- F-FDG in the suspected tumor site with the average con- bolic activity of target lesion. In general, the higher the Discussion F-FDG PET has been shown to have high sensitivity, specificity, and accuracy for the diagnosis, staging, and follow-up of pulmonary malignancy [3,4]. In addition, several studies have indicated that the degree of F-FDG uptake in primary lung cancer can be used as an independent prognostic factor [5]. Therefore, FDG PET has become an important tool for the management of lung cancer [6]. However, FFDG is not a specific tracer for malignancy; and potential false-positive uptake related to physiologic variants, inflammation/infection or certain benign processes should also be ८ ᗁᄫ 2009;22:3-7 SUVmax, the higher possibility of malignancy is considered for the lesion. Many authors use the cut off value of 2.5 for thoracic lesions, such as solitary nodules. However, it is well published that small lesions and low metabolic rate tumors may have SUVmax less than 2.5 [10]. Additionally, many benign lesions (e.g., granulomas, inflammatory foci, and etc.) have SUVmax greater than 2.5 [11,12]. For bony lesions, other authors had suggested of a higher cut-off value of SUVmax of 4.7 to distinguish malignancy and benign fractures [13]. Healing fractures has been found to cause increased 2009ѐ9 22 ס 3ഇ 5

4 Hsu HK et al F-FDG uptake in bone mimicking osseous metastasis disease [7]. The time interval of positive FDG uptake after fracture might rang from 17 days to 8 weeks, with higher FDG intensity in earlier phases [8]. However, the other authors believed the time interval between fracture and PET/CT did not significantly influence FDG uptake at the fracture site [13]. Integrated PET/CT scanners are able to produce the identical corresponding PET and CT slices of the body within the single examination. The CT portion of combined PET/CT provides not only fast and accurate attenuation correction of the PET emission data but also anatomic information [14,15]. The morphologic characteristics of a PET positive lesion can be easily examined, and by doing so some false-positive studies encountered on PET imaging, including benign bony fractures, can be accurately differentiated, as occurred in our case. Therefore, the CT data, even noncontrast enhanced and/or low-dose, can provide important diagnostic information [16], and should not be used for anatomic localization of PET abnormalities only. In conclusion, CT characteristics of an FDG-positive bone lesion should be carefully examined with PET/CT imaging to avoid a possibly false-positive result such as traumatic fracture. References 1. Strauss LG, Conti PS. The application of FDG PET in clinical onchology. J Nucl Med 1991;32: Delbeke D, Martin WH. Position emission tomography imaging in onchology. Radiol Clin North Am 2001;39: Higashi K, Ueda Y, Sakuma T, et al. Comparison of F- FDG PET and 201 Tl SPECT in evaluation of pulmonary nodules. J Nucl Med 2001;42: Coleman RE. PET in lung cancer. J Nucl Med 1999;40: Yap CS, Czernin J, Fishbein MC, et al. Evaluation of thoracic tumors with F-fluorothymidine and F-fluorodeoxyglucose-positron emission tomography. Chest 2006;129: Higashi K, Matsunari I, Ueda Y, et al. Value of wholebody FDG PET in management of lung cancer. Ann Nucl Med 2003;17: Meyer M, Gast T, Raja S, et al. Increased F-FDG accumulation in acute fracture. Clin Nucl Med 1994;19: Shon IH, Fogelman I. F- FDG positron emission tomography and benign fractures. Clin Nucl Med 2003;28: Fayad LM, Cohade, Wahl RL, et al. Sacral fractures: a potential pitfall of FDG positron emission tomography. AJR Am J Rogentgenol 2003;1: Gordon BA, Flanagan FL, Dehdashti F. Whole body positron emission tomography: normal variations, pitfalls, and technical considerations. AJR Am J Rogentgenol 1997;169: Cook GJR, Fogelman MN. Normal physiologic and benign pathological variants of F-FDG positron emission tomography scanning: potential for error in interpretation. Semi Nucl Med 1996;26: Bakneet SM, Powe J. Benign cause of F-FDG uptake on whole-body imaging. Semi Nucl Med 1998;28: Shin DS, Shon OJ, Byun SJ, Choi JH, Chun KA, Cho IH. Differentiation between malignant and benign pathologic fractures with F--fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography. Skeletal Radiol 2008;37: Nakamoto Y, Osman M, Cohade C, et al. PET/CT: comparison of quantitative tracer uptake between germanium and CT transmission attenuation-corrected images. J Nucl Med 2002;43: Kamel E, Hany TF, Burger C, et al. CT vs 68 Ge attenuation correction in a combined PET/CT system: evaluation of the effect of lowering the CT tube current. Eur J Nucl Med Mol Imaging 2002;29: Osman MM, Cohade C, Fishman EK, Wahl RL. Clinically significant incidental findings on the unenhanced-ct portion of PET/CT studies: frequency in 250 patients. J Nucl Med 2005;46: Ann Nucl Med Sci 2009;22:3-7 Vol. 22 No. 3 September

5 FDG PET False-positive bony FDG PET due to fractures ( ) ;22: (04) @gmail.com 2009;22: