© Pol J Radiol, 2011; 76(3): 38-48 Werewka-Maczuga A et al – Characteristics of computed tomography… Figure 18. Axial CT scans of the abdomen. Another case of lowering of density of liver metastasis during chemotherapy (picture on the right) with concomitant increase in size. Figure 19. Axial CT scans of the abdomen. Two examples of GIST metastases with pseudocystic appearance due to the fibromyxoid transformation induced by Imatinib treatment. The density of these lesions is usually slightly higher than of simple cysts. Figure 20. Axial CT scans of the abdomen. A case of pseudocystic liver metastases increasing in size and density – failure of Imatinib treatment and tumor progression. Figure 21. Axial CT scans of the abdomen. A case of small liver metastases that initially were not visible. After several months of treatment, they appeared in CT images due to the lowering of their density. Such lesions may be incorrectly reported as new lesions. • unexpected changes in size and contrasting of tumors, such as: concomitant reductions and increases in sizes of different lesions, decrease in tumor size despite disease progression, seeming increase in lesion density, • picture of a very slow progression, which sometimes lasts for years, • a unique pattern of disease progression in the form of so- called ‘nodules within tumors’. Figures 19 and 20 show hepatic ‘cysts’ that were formed as a result of treatment but always contain a live neo- plastic tissue despite the lack of contrast enhancement. In some situations, when initial CT images and medical 45