BACKGROUND AND OBJECTIVEThe colorectum is long and its position is not fixed. The thickness of the colorectal wall is unfixed because it changes following wall contractions. The metabolism of the colorectum is not stable and abnormal metabolism results from smooth muscle movement, gland action, spasm, inflammation, and so on. These anatomic and physiologic factors can bring a few difficulties in correctly judging colorectal information on 18F-FDG positron emission tomography/computed tomography (PET/CT) scans. This study was to discuss the imaging characteristics of colorectal hypermetabolic lesions in 18F-FDG PET/CT and their value to clinical diagnosis.

METHODSAccording the metabolic characteristics and the shape of the lesion, 118 colorectal hypermetabolic lesions of 74 patients were detected by 18F-FDG PET/CT and separated to 6 groups (localized/CT+, localized/CT-, segmented/CT+, segmented/CT-, diffuse/CT+, diffuse/CT-). To contrast groups and the qualitative data, a RxC Chi2 test was performed to judge statistical differences.

RESULTSIn the 118 lesions, 50 were determined to be malignant and 68 nonmalignant. A total of 30 lesions were in the localized/CT+ group (23 malignant, 7 non), 35 to the localized/CT- group (22 malignant, 13 non), 4 to the segmented/CT+ group (4 malignant, 0 non), 35 to the segmented/CT- group (1 malignant, 34 non), 0 to the diffuse/CT+ group, 14 to the diffuse/CT- group (0 malignant, 14 non). The rates of nonmalignant lesions in the segmented/CT- and diffuse/CT- groups (97.1%, 100%) and of malignant lesions in the segmented/CT+ groups (100%) were similar, so these three groups were combined to a nonlocalized group. The group of diffuse/CT+ was deleted. There were significant differences among the three groups of nonlocalized, localized/CT+, and localized/CT-(P < 0.001). The localized/CT+ and localized/CT- groups were combined into one localized group because no significant difference was found between them (P = 0.229). There was a significant difference between the nonlocalized and the localized groups (P < 0.001).

CONCLUSIONSOn 18F-FDG PET/CT, colorectal hypermetabolic lesions in the diffuse/CT- or segmented/CT- groups were highly likely to be nonmalignant and those in the segmented/CT+ group were highly likely to be malignant. Lesions in the localized/CT+ or localized/CT- groups had only a normal likelihood of being malignant. To correctly diagnose colorectal hypermetabolic lesions, it is necessary to analyze the PET of the metabolism and the CT of the anatomy together. Especially for the metabolic lesions of the localized/CT- group, we cannot easily make the judgment of malignant or nonmalignant unless we refer to the relevant clinical data.