Incidence and significance of small focal liver lesions on MRI.

Purpose: Analysis of the frequency and significance of small focal liver lesions (less than or equal to 2 cm) detected on MRI in the presence or absence of a history of malignancy. Methods: 628 MRI examinations of the liver performed during 1994-1996 were evaluated. The inclusion criterion into the study was the detection of a focal liver lesion with a size less than or equal to 2 cm. The frequency, the size, the diagnostic proof, and the differential diagnosis of the focal liver lesions were analysed with regard to the patients history of a known malignant tumor. Results: Overall, 179 of the 628 patients (28.5%) had focal liver lesions less than or equal to 2cm (n=338) 58.9% of the lesions could be classified based upon follow-up studies by ultrasound, CT or MRI, or by biopsy. The remaining 41.1% of the lesions could not be classified due to the absence of follow-up examinations. 57.3% of all proven lesions were benign and 42.7% were malignant. A history of a malignant tumor was present in 76.7% of all patients with small liver lesions; however, lesions were benign in these patients in 50.6% of the cases. In patients with no known history of a malignancy, 75% of the lesions were benign and 25% were malignant. However, these malignant lesions were in 10/11 cases hepatocellular carcinomas in patients with liver cirrhosis. Conclusion: Even in the presence of a history of a malignant tumor, about 50% of the detected smalt liver lesions on MRI are benign. In the absence of a tumor history the probability of a small malignant liver lesion is very low, if the patients does not have Liver cirrhosis where small hepatocellular carcinomas can be present.