Small hypoattenuating lesions in the liver on single-phase helical CT in preoperative patients with gastric and colorectal cancer: Prevalence, significance, and differentiating features

Purpose: The purpose of this study was to determine the prevalence and significance of small low attenuating hepatic lesions (SLAHs) seen on helical CT in preoperative patients with gastric and colorectal cancers and to find differentiating features of benign from malignant SLAH. Subjects and Methods: By the retrospective review of preoperative helical CT scans in 1,133 consecutive patients with proved gastric and colorectal cancers, 289 patients (25.5%) with 947 SLAHs (less than or equal to 15 mm) were selected. Among them, 66 SLAHs in 21 patients without final diagnosis were excluded. The size, margin, shape, attenuation, and enhancement features of the lesions were evaluated. For 200 randomly selected SLAHs, interobserver agreement for each parameter was assessed. Results: Among 881 SLAHs in 268 patients, 693 (78.3%) in 248 patients (92.5%) were benign, and 188 (21.2%) in 30 patients (11.2%) were metastases; 10 patients (3.7%) had both. Among SLAHs in patients who had SLAHs only, 14 lesions (1.6%) in 6 patients (2.2%) were metastases. Benign SLAHs were smaller (6.4 +/- 3.1 mm; P < 0.001) and more frequently had discrete margin (P < 0.001) and markedly low attenuation (P < 0.001) than metastases (9.3 +/- 2.7 mm). Target-enhancement was far more frequent in metastases (64.4%) than benign SLAHs (1.2%; P < 0.001). Excellent interobserver agreement (kappa > 0.60) was found for all parameters in SLAHs larger than 5 mm. Conclusion: The prevalence (25.5%) of SLAH on helical CT was higher than that reported on conventional CT; however, metastases only presenting as SLAH were rare (2.2%). For SLAHs larger than 5 mm, careful analysis of CT findings can be helpful to differentiate benign from malignant SLAH.