The sensitivity and specificity of FDG-PET for the detection of recurrent disease have been reported as approximately 95% (95% CL 95 – 99%) and 76% (95% CL 64 – 88%) respectively (1). Sensitivity varies according to the anatomic location of the metastatic focus. It has been reported as very high for the liver (9) but, as with CT, is notoriously low for nodal disease (2,5). PET is reported to be more sensitive than CT for all regions except the lungs where it is equal. PET is also reported to be more specific than CT for all regions except the retroperitoneum (9). However, in this and several other published papers there have been sources of bias that could have favored PET over CT including the interval between CT and PET imaging, unequal skill in test performance, variation in CT technology and bias in test interpretation. It should also be noted that the sensitivity of FDG PET for metastatic liver lesions varies significantly with lesion size (10). Ruers et al demonstrated in patients with colorectal cancer metastases to liver, that the sensitivity of FDG-PET for liver metastases was 14% for lesions < 1.5 cm, 84% for those between 1.5 cm and 3 cm, and 100% for those >3 cm (11).
The high sensitivity of FDG-PET for liver involvement takes on added importance due to the high incidence of isolated colorectal metastases to this organ (approximately 14,000 cases per year) and the potential for curative resection. In this situation FDG PET can be used to establish the extent of disease in order to maximize the potential for a curative resection or to spare the patient unnecessary surgery should disease be too extensive. FDG-PET is also important to rule out additional extra hepatic involvement which is presently considered nonsurgical.
FDG-PET is also useful to distinguish postoperative scar versus residual or recurrent disease. In this capacity FDG PET generally yields significantly higher sensitivity than contrast enhanced CT. However, in the postoperative period, relatively higher FDG activity may be observed for several months at the site of surgery. This is typically due to post-surgical inflammation or granulation tissue that can masquerade as tumor recurrence on FDG-PET (12). Fused PET/CT can be particularly useful in this setting for the precise localization of FDG uptake. Figure 3 provides an example of such a case and illustrates the localization advantage of fused PET/CT. In this study a small focus of abnormal FDG uptake correlates with a perianastomic mass on CT and is consistent with recurrent or residual disease. However this same case demonstrates a recognized weakness of PET alone in the assessment of mucinous tumors (13). Several surgically proven mucinous metastases showed no FDG activity but were clearly evident on the CT component of the exam (for example projecting from the anterior abdominal wall on the images below). This case illustrates well the powerful strengths of the combined PET/CT examination in the evaluation of metastases from colorectal cancer.
2. Abdel-Nabi, Doerr RJ, Lamonica DM, Cronin VR, Galantowicz PH, Carbone GM, and Spaulding MB.. Staging of primary colorectal carcinomas with fluorine-18 fluorodeoxyglucose whole-body PET: correlation with histopathologic and CT findings. Radiology. 1999; 206: 755-760.
3. Delbeke D, Vitola JF, Sandler MP, Arildsen RC, Powers TA, Wright Jr JK, Chapman WC, and Pinson CW.. Staging recurrent metastatic colorectal carcinoma with PET. J Nucl Med 1997; 38: 1196-1201.
4. Wahl RJ. Why Nearly All PET of Abdominal and Pelvic Cancers Will be Performed as PET/CT. J. Nucl Med 2004; 45: (1suppl) 82S-95S.
5. Kantorova I, Lipska L, Belohlavek O, Visokai V, Trubac M and Schneiderova M.. Routine 18FDG PET Preoperative Staging of Colorectal Cancer: Comparison with Conventional Staging and Its Impact on Treatment Decision Making. J Nucl Med 2003; 44: 1784-1788.
6. Meta J, Seltzer, M, Schiepers C, Silverman DH, Ariannejad M, Gamghir S, Phelps M, Valk P and Czernin J. Impact of 18F-FDG PET on Managing Patients with Colorectal Cancer; The Referring Physician’s Perspective. J Nucl Med 2001; 42: 586-590.
7. Cohade C, Osman M, Leal J, and Wahl RL. Direct Comparison of 18F-FDG PET and PET/CT in Patients with Colorectal Carcinoma. J Nucl Med 2003; 44: 1797-1803.
8. Bar-Shalom R, Yefremov J, Guralnik L, Gaitini D, Frenkel A, Kuten A, Altman H, Keidar Z, and Israel O. Clinical Performance of PET/CT in Evaluation of Cancer: Additional Value for Diagnostic Imaging and Patient Management. J. Nucl Med 2003; 44: 1200-1209.
9. Valk P, Abella-Columna E, Haseman, M, Pounds T, Tesar R, Myers R, Greiss H, and Hofer G. Whole-Body PET Imaging With [(18)F]Fluorodeoxyglucose in Management of Recurrent Colorectal Cancer. Arch Surg. 1999; 134(5): 503-511.
10. Frohlich, A., Diederichs, C. G., Staib, L., Vogel, J., Beger, H. G., Reske, S. N. Detection of liver metastases from pancreatic cancer using FDG PET. J. Nucl. Med. 1999;40:250-255.
11. Ruers TJ, Langenhoff BS, Neeleman N, Jager GJ, Strijk S, Wobbes T, Corstens FH, Oyen WJ. Value of positron emission tomography with [F-18] fluorodeoxyglucose in patients with colorectal liver metastases: a prospective study. J Clin Oncol 2002; 20: 388-395.
12. Delbeke D. Oncological applications of FDG PET imaging: Brain tumors, colorectal cancer, lymphoma, and melanoma. J Nucl Med 1999;40:591-603.
13. Berger KL, Nicholson SA, Dehdashti F, Siegel BA. FDG-PET evaluation of mucinous neoplasm: correlation of FDG uptake with histopathologic features. AJR 2000;174:1005-1008.
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