Benign metastasizing pleomorphic adenoma in liver mimicking synchronic metastatic disease from colorectal cancer: a case report with emphasis on imaging findings

Pleomorphic adenoma of the parotid gland with metastases to the liver is a rare etiology of focal liver lesions, and there are no described pathognomonic imaging features. We report a patient who presented with a newly diagnosed rectal cancer and multiple cystic liver lesions suspicious of mucinous synchronous liver metastases. Following chemotherapy no reduction in the number or size of the liver lesions was observed. The patient was re-evaluated and a biopsy of a lesion was performed. The specimen showed a metastasis from a pleomorphic adenoma of the parotid gland for which the patient had been treated 20 years earlier. The case illustrates how a thorough medical history can be crucial when a standard diagnostic imaging workup for colorectal cancer metastases is uncertain, and how a biopsy, though regarded as contraindicated due to the risk of tumor cell dissemination, can be required to secure a correct diagnosis.