This case is designed to encourage you to keep an open mind. Given the patient's history of immunosuppression, the presence of a single new cystic lesion in the liver was definitively called an abscess on an earlier study. The patient was sent to ultrasound-guided biopsy to determine the infectious agent for targeted antibiotic therapy. The pathology report from the FNA smears and core biopsy told a different story, however:
"Metastatic, poorly-differentiated adenocarcinoma in a background of extensive necrosis and mixed inflammation."
The primary was consistent with an upper GI or pancreatic source, although this could not be seen on the available imaging.
In the differential for a new cystic lesion in an adult liver, one should always consider both infectious and metastatic etiologies. With multiple lesions, a metastatic etiology is much more likely (~98%), but lack of multiple lesions is more ambiguous.