Liver Metastases : Diagnosis
Diagnostic Work-up of Liver Metastases: A tissue diagnosis has to be established before therapy can be initiated. This is accomplished by FNA and needle core biopsies (NCB) obtained via transabdominal ultrasound, endoscopic ultrasound, or CT-guided procedures. The choice of procedure depends upon the size and location of the lesion, the suspected diagnosis, the risk of complications, and the experience of the radiologist performing the procedure. In addition to an adequate FNA sample, a well-prepared cellblock and/or needle core biopsy is essential to provide material for immunohistochemical studies. This allows the pathologist to establish the diagnosis of malignancy, distinguish metastases from primary hepatocellular carcinoma or cholangiocarcinoma, and determine the site of primary tumor. Accurate diagnosis depends upon correct interpretation of FNA/NCB findings in the light of history of previous cancer, radiologic findings and serum tumor marker levels (where applicable). Once the diagnosis of malignancy is confirmed, the first step is to recognize the general tumor type, i.e. whether is a carcinoma, sarcoma, lymphoma, or melanoma, followed by distinction between primary vs. metastases. A basic panel consisting of epithelial markers (pankeratin AE1/AE3, CAM5.2), mesenchymal marker (vimentin), lymphoid marker (CD45), and melanocytic marker (S-100 protein) can help narrow down differential diagnosis. Additional more specific immunohistochemical stains can be performed based on the initial results. Microscopic Features: The microscopic features of liver metastases, including the extent of stromal reaction, mirror those of the primary tumor. There is usually clear demarcation between the metastatic deposit and the surrounding liver parenchyma. Invasion of portal and hepatic veins is seen less frequently than with hepatocellular carcinoma. Metastatic adenocarcinomas may invade bile ducts and show intrabiliary growth pattern mimicking cholangiocarcinoma. This photomicrograph of a CT-guided needle core biopsy of a liver mass shows metastatic neuroendocrine carcinoma. The primary site was pancreas.