In several studies, Japanese researchers investigated the diagnostic value of pancreatic juice, which is collected with or without papillotomy of the opening of the pancreatic ducts into the common bile duct. Their results were encouraging. Cytologic studies of the juice allowed for a better classification of mucin-producing tumors of the pancreas (Uehara et al, 1994), and for the occasional discovery of noninvasive intraductal carcinoma (Shimizu et al, 1999).

The principal indication for FNA is the identification of a space-occupying solid or cystic lesion of the pancreas. In the latter situation, aspiration may serve as both a diagnostic and a therapeutic procedure. FNA is more likely to provide an accurate diagnosis compared to intraoperative core needle or wedge biopsy of the pancreas (Moossa et al, 1982; Saez et al, 1995).

There are three principal approaches to performing diagnostic FNA of the pancreas:

Intraoperative aspirations are probably more efficient and accurate than intraoperative wedge or needle core tissue biopsies with intraoperative consultation with frozen sections, which is occasionally done during exploratory laparotomies for pancreatic tumors, particularly when resection of the head of the pancreas is contemplated (Whipple procedure) (Saez et al, 1995; Robins et al, 1995). However, even the small, direct tissue biopsies are not free of the risk of significant morbidity and mortality, and they are not always easy to interpret (Ferucci et al, 1979; Beazley, 1981). The fear of causing acute pancreatitis and peritonitis resulting from the leakage of enzymes, and the difficulty in differentiating chronic pancreatitis from pancreatic carcinoma by gross examination at surgery often results in the acquisition of inadequate tissue samples. Crushing of the small biopsy sample may also create problems in interpretation.

Benign ductal cells of the pancreas appear as sheets of uniform cuboidal cells forming monolayers of various sizes with centrally placed small nuclei (see Fig. 39-1C). At the edge of clusters derived from large ducts, the cells may be columnar in configuration, parallel to each other, with basally placed nuclei. The cytoplasmic borders are well demarcated and the cytoplasm is transparent in fixed smears stained with Papanicolaou stain, accounting for the honeycomb pattern of the flat clusters (Fig. 39-2B). Cytoplasmic vacuoles or goblet cells are very rarely seen. The nuclei are round or slightly ovoid, and equally spaced, and there are no nuclear contour abnormalities. The chromatin is finely granular and uniformly distributed. Tiny nucleoli may be visible.

Occasionally, large areas of the ductal epithelium are aspirated (Fig. 39-2A). The smear may show very large flat sheets of benign glandular cells that may fold at the edges. Occasionally, the ductal cells form thick, multilayered sheets with crowding of nuclei. Such clusters may be a cause for concern because this may represent a well-differentiated ductal adenocarcinoma. Examination of the edges of such thick clusters usually allows for a close examination of the nuclei that fail to show the nucleolar abnormalities characteristic
of cancer. The absence of single cancer cells is another reason to regard such clusters as benign.

The acinar cells usually form small, tightly knit clusters, often arranged in spherical, three-dimensional structures. Higher magnification reveals the pyramidal shape of cells arranged around a central narrow lumen, resembling rosettes, with the nuclei aligned at the periphery of the cells (Fig. 39-2C,D). The cytoplasm is relatively abundant, and in air-dried or well-fixed cells it may show prominent coarse cytoplasmic granularity imparted by the zymogen granules, which are precursors of digestive enzymes. In most cases, however, the granules are lost, and the cytoplasm of the acinar cells appears clear or vacuolated (Hastrup, 1977). The nuclei are uniform and small and round, with a smooth membrane, and are located away from the acinar lumen. The chromatin is granular and evenly distributed, and the nucleoli are inconspicuous.

In general, the islet cells cannot be recognized in FNA smears without the use of immunohistochemical markers for endocrine function. In a fortuitous case of pancreatic FNA performed in a young male patient with sclerosing cholangitis and total atrophy of the exocrine pancreas, the aspirated islet cells formed loose, approximately spherical or oval aggregates of cells with eosinophilic cytoplasm (Fig. 39-3A). The cell borders were indistinct, and in this material cytoplasmic granules were not visible. The regular round nuclei with minimal pleomorphism were similar in size to the acinar cell nuclei. The nuclear chromatin may show an endocrine “salt and pepper” granularity, with a visible nucleolus. In this particular case, the identity of the cells was confirmed at autopsy (Fig. 39-3B). It must be reemphasized that this presentation of islet cells is exceptional and is not likely to be duplicated in practice.

Large sheets of benign glandular cells may be aspirated from gastric or intestinal (mainly colonic) mucosa. However, benign gastric mucosal cells are identical to pancreatic ductal epithelium (Fig. 39-4A). The origin of the sample can be identified if parietal gastric cells, which have a finely granular and intensely eosinophilic cytoplasm, are present. The presence of goblet cells identifies intestinal epithelium (Fig. 39-4B).

The mesothelial cells of peritoneal origin typically occur in monolayer sheets, in which the cells are separated from each other by wide spaces or windows. These cells have notoriously large, readily visible nucleoli, and therefore may be confused with cancer cells (see Fig. 38-1D; for further discussion and illustrations of these cells, see Chap. 25). Large hepatocytes, occurring singly or in small sheets, may be present in smears if on its way to the pancreas the needle passes through the left liver lobe (see Fig. 39-4C). Their morphology is described in Chapter 38. Capillary vessels, connective tissue cells, and sometimes striated muscle and fat cells may also occur in pancreatic FNA smears. Exceptionally, when the needle penetrates beyond the pancreas and reaches sympathetic ganglia, ganglion cells may be observed (Fig. 39-4D).

In tissue sections, chronic pancreatitis is characterized by variable degrees of fibrosis, acinar atrophy, and ductal hyperplasia. As a result of atrophy of the exocrine pancreas, the islets of Langerhans are readily visible and appear larger than normal. The stroma shows an infiltrate composed of lymphocytes and plasma cells. The epithelium of the dilated and distorted ducts may show hyperplasia with some atypia, and, rarely, squamous metaplasia in the smaller ducts. The duct lumens may be filled with protein plugs. In the end stage of the disease, the ducts may be distorted by diffuse fibrosis and may show mucinous metaplasia, thus mimicking a well-differentiated adenocarcinoma of the scirrhous type (Fig. 39-5A). Fat necrosis with calcium deposits is commonly observed at the periphery of the pancreatic tissue. At laparotomy, the pancreas may be rock-hard on palpation, grossly mimicking infiltrating carcinoma. It can be a formidable problem to correctly interpret needle core biopsies by frozen sections. Cytologic studies may help in difficult situations.

The FNA smears of subacute and chronic pancreatitis vary in cellularity and cell composition, but, contrary to panorcetic cancer, are usually scanty. On screening magnification, the smears typically reveal a polymorphous picture of variably sized and configured clusters of ductal cells, occasional acinar cells, macrophages and other inflammatory cells, connective tissue fragments, granulation tissue, mucus, calcification, and debris (Fig. 39-5B,C). Not all of these components are seen in a given case. The number and type of inflammatory cells present depend on the stage of the disease: In subacute pancreatitis, neutrophils and macrophages predominate. In chronic pancreatitis, lymphocytes, macrophages, and plasma cells predominate. In chronic fibrosing pancreatitis, the FNA smears may have a relatively clean background.

Problems with interpreting pancreatic material in pancreatitis are related to the presence of hyperplastic and atypical ductal cells, which may occur singly or form disorderly clusters (Fig. 39-5D). In some (fortunately very uncommon) cases, nuclear atypia in the form of nuclear enlargement and clearly visible but not very large nucleoli makes it extremely difficult to differentiate chronic pancreatitis from well-differentiated adenocarcinoma. The presence of an inflammatory infiltrate in the background of the smear should strongly suggest the use of caution before interpreting such smears as malignant. The
important factors in the differential diagnosis of inflammatory atypia of ductal cells versus well-differentiated ductal carcinoma are discussed below in reference to carcinoma, and are summarized in Table 39-3 (see below). An additional confounding factor is that ductal carcinoma and chronic fibrosing pancreatitis may coexist and may account for at least some of the false-negative diagnoses on FNA of this organ.

The most common type of acquired nonneoplastic cysts is the pancreatic pseudocyst, which follows the destruction and necrosis of pancreatic tissue secondary to pancreatitis. Patients usually present with jaundice, pain, weight loss, nausea, and vomiting. Pseudocysts are usually solitary and unilocular, and while their cystic nature may be determined by CT or US, it is not possible to exclude a cystic neoplasm based on imaging alone. Therefore, the nature of the cyst should be determined by cytologic examination of the cyst contents.

The cysts are lined by a single layer of uniform cuboidal or flattened epithelial cells with clear glycogen-containing cytoplasm, and may show intracystic papillation, usually without a fibrovascular core (Fig. 39-7D). The central stellate scar is formed by fibrous, hyalinized tissue with a few clusters of tiny cysts.

The aspirate yields small amounts of clear, watery fluid. The cellularity of the smear is variable and may be abundant in a vigorous aspirate (Fig. 39-7A-C). At low magnification, the smear gives the impression of numerous, tightly cohesive normal acini, which actually represent the microcysts and small intracystic papillae. At high magnification, the small papillary groups are made up of uniform small cells with transparent, well-delineated cytoplasm. Some flat sheets of epithelial cells of variable sizes may be encountered; however, a perfect honeycomb pattern, as found in sheets of benign ductal cells, is not seen. Periodic acid-Schiff (PAS) stain is positive. The nuclei are spherical and show very little, if any, pleomorphism or atypia. Similar findings, with slight variations in cytologic presentation, were reported by Hittmair et al (1991) and Nguyen and Vogelsang (1993).

A malignant counterpart—serous cystadenocarcinoma—has been reported (George et al, 1989). We have
no first-hand experience with such a lesion in aspiration smears.

Mucinous cystic tumors are uncommon pancreatic neoplasms, representing approximately 2% to 5% of all exocrine pancreatic tumors (Thompson et al, 1999). More than 500 cases of this tumor have been reported (Compagno and Oertel, 1978b; Zamboni et al, 1999). The tumors are composed of cysts lined by columnar, mucin-producing epithelium supported by ovarian-type stroma. They are subclassified as adenoma, borderline malignant, or noninvasive or invasive carcinoma according to the level of abnormality of the epithelium, which may form single or multiple layers or papillary projections (Fig. 39-8D). There are many similarities between this pancreatic tumor and its ovarian equivalent (see Chap. 15). Mucinous cystic tumors of pancreas occur almost exclusively in middle-aged women (Zamboni, 1999) in the body or tail of the pancreas. The smaller tumors may be an incidental finding, whereas larger tumors may produce nonspecific symptoms of pressure and diabetes mellitus. Malignant mucinous cystic tumors are often slow-growing and have a much better prognosis than pancreatic ductal carcinoma (Warshaw, 1990). No deaths from cancer have been observed in patients classified as benign or borderline malignant (Warshaw et al, 2003). Thus, the recognition and accurate classification of the cystic tumors is of great clinical value.

The characteristic feature of fine-needle aspirates of mucinous cystic tumors is the presence of a grossly obvious clear mucoid material that forms the background of the smears. Mucus is much easier to recognize as a stringy, purple substance in air-dried smears, stained with hematologic stains, than as a faintly pink background in fixed smears processed with Papanicolaou’s stain. If the cyst is large, the cell content of the smear may be very low. Smaller cysts yield numerous epithelial cells. In the benign and borderline mucinous cystic tumors, the cells form flat sheets with a “honeycomb” pattern closely resembling normal duct epithelium in a background of mucus (Fig. 38-8A). In other cases, sheets of goblet cells, floating in mucin, may be observed (Fig. 39-8B). As a point of differential diagnosis, occasional goblet cells may occur in aspirates from chronic pancreatitis, but they are never numerous and the smears do not have a mucinous background. In borderline tumors, small clusters and single cells with visible nucleoli are common (Fig. 39-8C). Furthermore,
careful scrutiny of smears from high-grade mucinous cystic tumors reveals papillary or three-dimensional groups with obvious nuclear atypia. Frankly malignant tumors of this category are classified as mucinous adenocarcinoma (see Fig. 39-16A,B) and are cytologically identical to colloid (mucinous noncystic carcinoma; see below). A positive mucin stain excludes serous cystadenoma (Table 39-2). Rubin et al (1994) reported that benign and malignant mucinous cystic neoplasms can be differentiated by the level of the tumor marker CA 15.3 in the cyst fluid.