Small "indeterminate" lesions on CT of the liver: a follow-up study of stability

Distinguishing between small benign malformations in the liver and early metastatic disease remains difficult. We identified a group of 115 patients with known or suspected malignant disease who had "indeterminate" small liver lesions and who underwent 2-16 CT examinations (median 5) over a follow up period of 6-60 months (median 16). The size, shape, edge, homogeneity and attenuation of each of these lesions was assessed. The lesions were classified by their behaviour on follow up CT as either stable (79%) or unstable (21%). The unstable lesions (n=62) included 37 that grew larger and 25 that became smaller or disappeared in patients undergoing anti-tumour therapy. Image features predictive of stable behaviour were small size and sharp edge. Heterogeneity and soft tissue attenuation were significantly associated with unstable behaviour, but these features were seen in only a small minority of cases. Shape had no predictive value. A logistic regression model was constructed based on size and edge to allow an estimate to be made of the likelihood of an individual lesion being unstable. In patients with known or suspected malignant disease, the majority of isolated small liver lesions found on CT are benign. Although size under 5 mm and a sharp margin are favourable features, this appearance does not exclude malignancy.