There is a new hypodense mass in the liver, which is shown in standard soft tissue (upper image) and liver (lower image) windows.
Liver lesions are classic misses on chest CT exams, especially noncontrast exams. There are predictable reasons why this happens:
- Edge of the film: We know that important findings at the edges of imaging studies are more likely to be missed. This usually happens at the top and bottom slices of CT exams.
- Using appropriate window/level settings: We also know that liver lesions are more conspicuous when using liver windows. This is especially important for noncontrast studies when the inherent difference in contrast between the liver and malignancy/metastasis is less.
- Alliterative bias: Radiologists who read the reports for prior studies can be influenced by the results. When someone opens a follow-up study to evaluate for recurrence and notices that the patient has multiple prior exams without evidence of recurrent or metastatic disease, they are more likely to come to the same conclusion. The mechanism is similar to satisfaction of search, where a thorough search for new findings is terminated prematurely due to the belief that the patient is unlikely to have new recurrent disease given the negative prior exams.
Below are images from a follow-up study 6 months later. It is not surprising that the liver lesion is again missed despite being larger, likely for the same reasons.
