Fine Needle Aspiration Cytology

Liver and Pancreas
Jan F. Silverman, MD and Telma C. Pereira, MD


Fine needle aspiration (FNA) biopsies of the liver or pancreas are common procedures in many medical centers. The usual indication for a fine needle biopsy of either the liver or pancreas is evaluation of a mass lesion. In the past, pathologists have been more familiar with evaluating tissue core biopsies of liver masses, although FNA biopsy has become the standard procedure in the majority of hospitals. FNA of the pancreas, however, is more common than core biopsies due to the potential complication of pancreatitis following a core biopsy. One of the advantages of FNA biopsies of the liver or pancreas is that multiple aspirates can be performed during a single procedure, which can potentially allow a more complete sampling of the mass.

FNA biopsy of liver neoplasms has a sensitivity which ranges from 92 to 96%. FNA biopsy is useful in the workup of metastatic carcinoma, as well as in the diagnosis of primary hepatocellular carcinoma and cholangiocarcinoma [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13] . Critical in the evaluation of the liver aspirate is appreciation of the spectrum of cytomorphologic changes that can be seen with benign hepatocytes. Liver cells can vary from polygonal to round and have well defined cell borders. Usually a moderate amount of uniform, granular dense cytoplasm is present. In Papanicolaou stained ThinPrep® slides, the cytoplasm contains small eosinophilic to deeply basophilic granules, and occasional cells can show evidence of cytoplasmic bile, lipofuscin pigment, lipid and/or glycogen vacuoles. Hepatocytes usually have a single, centrally located, round nucleus possessing evenly distributed, finely granular chromatin and a single round, prominent nucleolus. Hepatocytes can demonstrate variation in nuclear size and be binucleated. However, in contrast to hepatocellular carcinoma, the nuclei maintain relatively low nuclear-to-cytoplasmic (N:C) ratios. Occasional microtissue fragments can also be present having irregular frayed edges in contrast to the sharply demarcated borders seen in hepatocellular carcinoma. Trabeculae usually consist of one to two layers of hepatocytes in contrast to the thick cords of hepatocellular carcinoma. Individually scattered hepatocytes and Kupffer and endothelial cells having spindled nuclei with pale, finely granular chromatin, inconspicuous nucleoli and scanty indistinct cytoplasm can be present. [1, 2]

Occasionally, a dominant nodule in cirrhosis may be aspirated as part of an evaluation of a mass lesion [1, 2] . An important cytologic feature of a cirrhotic nodule is the variable, rather than uniform appearance of the liver cells on ThinPrep slides. Occasionally, atypical features including nuclear enlargement, binucleation and anisonucleosis may be seen, which are helpful in making a diagnosis of cirrhosis, since the polymorphic appearance of the liver cell population is a feature of benign, reactive hepatocytes versus the uniform atypia of hepatocellular carcinoma. Besides the variable cellularity of the liver cells in cirrhosis, thin trabeculae and cords measuring no greater than two cells thick are present and the cells have low nuclear-to-cytoplasmic ratios. Bile ducts may also be seen, along with occasional inflammatory cells and fibrous tissue.[1, 2]

ThinPrep prepared aspirates of hepatocellular carcinoma show cells with uniformly high nuclear-to-cytoplasmic ratios arranged in complex branching, anastomosing thick trabeculae, having sharply demarcated peripheral borders. The trabeculae contain greater than four cells in thickness, and there is peripheral endothelial encirclement, as well as so called "transgressing" endothelial cells present. Scattered single cells and small groups are often present, along with stripped atypical hepatocytic nuclei. Occasionally, bile pigment may be seen [1, 2, 6, 7, 8, 9, 10, 11, 12, 13] .

Occasional variants of hepatocellular carcinoma may be encountered, including fibrolamellar hepatocellular carcinoma, small cell and clear cell subtypes and mixed hepatocellular/cholangiocarcinomas. Cytologic features of these variants are well described in standard textbooks.[1, 2]

Aspirates of benign hepatocellular tumors such as adenoma and focal nodular hyperplasia consist of liver cells indistinct from hepatocytes of the unremarkable surrounding liver on ThinPrep slides.[1, 2] Fragments of fibrous tissue and bile ducts are present in focal nodular hyperplasia but are not appreciated in adenomas.

Due to the lack of atypical findings, a specific diagnosis of adenoma or focal nodular hyperplasia can't be made from fine needle aspiration specimens. Therefore, it is critical to correlate the cytologic findings with the placement of the needle.

Lastly, liver aspirates of metastatic carcinoma are quite common, since the liver is the second most common abdominal site for metastatic malignancy, following lymph nodes. Metastatic carcinomas account for more than 90% of all malignant hepatic neoplasms. Adenocarcinomas from various sites are the main histologic type of metastatic carcinoma to involve the liver, with colorectal carcinoma having an especially high prevalence. Cytomorphologic features of metastatic adenocarcinoma are quite similar to the cytologic features seen in primary cholangiocarcinoma. FNA preparations of adenocarcinomas usually consist of cohesive aggregates of malignant cells in which gland formation may be seen. Cuboidal to columnar-shaped cells having delicate pale cytoplasm and eccentrically placed, round to irregular nuclei with prominent nucleoli are present. Colorectal carcinoma often has an associated "dirty necrosis" in the background, in contrast to the clean background of cholangiocarcinoma. In addition, cancers of other cell types can be encountered including metastatic small cell carcinoma, melanoma, malignant lymphoma and mesenchymal tumors.[1, 2]

Percutaneous, intraoperative and endoscopic ultrasound (EUS)-guided FNA biopsies are increasingly being utilized to evaluate cystic and solid masses of the pancreas[1, 2, 14, 15] . FNA has distinct advantages over large core biopsies and wedge resections of the pancreas, since these latter procedures can potentially lead to pancreatitis and/or peritonitis due to the spillage of exocrine enzymes and bile.[16] FNA biopsy of the pancreas can also be useful for the diagnosis of an inflammatory pancreatic lesion, obviating the need for a surgical procedure. Therefore, the cytopathologist needs to know the cytologic features and spectrum of changes seen in benign ductal and acinar pancreatic epithelium.[1, 2, 17] Characteristically, pancreatic ductal cells are arranged in flat honeycomb sheets with evenly spaced, round to oval nuclei and well-defined cell borders. Acinar cells tend to be arranged in small cohesive aggregates, consisting of cells with small uniform, basally placed nuclei having finely granular to clumpy chromatin with inconspicuous nucleoli surrounded by a moderate amount of granular cytoplasm. Islet cells are generally not appreciated in the aspirates.[1, 2, 14, 18]

Aspirates of pancreatic pseudocysts generally have scant cellularity with few or no epithelial cells, although acute and chronic inflammatory cells, histiocytes, granulation tissue and background debris with fragments of calcification can be present.[1, 2] Cytomorphologic features of acute pancreatitis include moderate to high cellularity consisting predominately of neutrophils in the smears along with a "dirty" background.[1, 2] Ductal and/or acinar cells may show reparative and/or inflammatory atypia, and fat necrosis may be appreciated. In contrast, aspirates of chronic pancreatitis generally have relatively low cellularity with only a few ductal cells that tend not to show the degree of atypical and/or reactive features seen in acute pancreatitis.[1, 2] Chronic inflammatory cells will be present.

It is critical to appreciate the cytomorphologic features of pancreatic adenocarcinoma, since this is a common malignancy, accounting for approximately 3% of all cancers and 5% of cancer mortality.[18, 19] Nearly ¾ of all pancreatic adenocarcinomas are of the ductal type. Cytomorphologic features of ductal adenocarcinomas in ThinPrep slides include high cellularity with atypical cells arranged singly and in groups and clusters.[1, 2] Within the cell groups, a syncytial arrangement of the cells is present along with loss of nuclear polarity. Both nuclear and cytoplasmic enlargement may be seen. The nuclei tend to be hyperchromatic with irregular chromatin and nuclear borders, along with occasional nuclear grooves. Considerable variation in nuclear size can be seen, as well as prominent nucleoli. The background usually contains a tumor diathesis.

Uncommon variants of pancreatic adenocarcinoma include anaplastic carcinoma (pleomorphic giant cell carcinoma), which has a markedly pleomorphic population, including giant and/or spindle shaped malignant cells and the very rare osteoclastic-like giant cell tumor of the pancreas, which consists of scattered multinucleated osteoclastic-like giant cells with centrally clustered nuclei and a moderate amount of surrounding cytoplasm, as well as similar appearing mononucleated cells.[1, 2]

Aspirates of islet cell neoplasms tend to be cellular, consisting of a monomorphic population of uniform small cells arranged predominantly in a discohesive pattern. The tumor cells are small with round to oval nuclei with evenly dispersed, finely to coarsely granular chromatin and inconspicuous nucleoli. The nuclei are eccentrically placed within these cells. In contrast, aspirates of the very uncommon acinar cell carcinoma have cells arranged in a lobular fashion and have hyperchromatic nuclei with clumpy chromatin and prominent nucleoli.[1, 2] Both islet and acinar cells have granular cytoplasm. Cytomorphologic features of papillary-cystic tumor include papillary structures having fibrovascular cores lined by one or more layers of epithelial cells with pale chromatin, delicate nuclear membranes and occasional longitudinal nuclear grooves.[1, 2] Mucinous cystic neoplasms, in contrast, have nuclei that vary from bland, atypical and/or frankly malignant.[1, 2] The cells can be singly arranged, in flat honeycomb groups or three-dimensional clusters associated with abundant intracellular and/or extracellular mucinous material. Other unusual lesions that have been described in the FNA literature include aspirates of serous cystadenoma and pancreatoblastoma. [1, 2, 20] Lastly, FNA of metastatic malignancies to the pancreas can be encountered. [21]

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