Cytology primer for endosonographers

Preliminary planning

Ideally, an interested pathologist should be involved in the development of the EUS FNA(B) service from the earliest stages of the planning process. This includes such crucial factors as the location of the endosonography suite, the type of instrument and needle used, the personnel involved, the scheduling of FNA, the type of preparation, the transport medium, the need for immediate cytologic evaluation (ICE) or rapid onsite specimen evaluation (ROSE) for determination of adequacy and diagnosis, utilization of real-time telepathology analysis, the need for performing ancillary studies, and the role of the procedure in the patient management algorithm ( Table 20.1 ). Further planning should also involve ordering of supplies, stocking and provision of the FNA cart or cabinet, or maintenance of a permanent small space for supplies in the endoscopy suite area.

The type of tissue specimen preparation (direct smear, liquid-based cytologic preparation, cell block, core biopsy, or a combination) depends on institutional practice, staffing issues, and the physical distance between the pathologist and the endoscopy suite, in addition to the relative sensitivity, specificity, and diagnostic accuracy of the various choices. Developing adequate skills for accurate interpretation of EUS samples not only depends on an experienced cytopathologist but may also require additional specific experience in interpreting these samples in a high-volume services. Experience indicates that cytopathologists who are specifically interested in gastrointestinal diseases tend to be more effective in providing accurate diagnoses. For the pathologist and laboratory staff, a comprehensive understanding of their direct role in the EUS procedure and the patient care algorithm ensures appropriate support. Diagnostic strategies depend on whether the procedure is a screening test, a diagnostic test in a patient who may not undergo further diagnostic workup, or a test to procure material for performance of ancillary studies including molecular analysis to enhance patient management decisions.

A further preliminary planning step is consideration of database archives of cytology and diagnostic data. In combination with the EUS characteristics of lesions and other clinical information, these data can provide valuable feedback regarding diagnostic accuracy, individual practitioner competency, utility of ICE, and other quality assurance measures.

Professional staff should be properly trained and should understand the limitations of their expertise and of the technique. In the United States, both the technical and the interpretive services in the cytology laboratory are regulated at state and federal levels by the provisions of the Clinical Laboratory Improvement Amendments of 1988 (CLIA 1988), the Laboratory Accreditation Program of the College of American Pathologists (CAP), and others. Such mandatory and voluntary standards ensure high-quality laboratories.

The following sections discuss technical factors that may improve diagnostic yield for EUS FNA procedures, including needle type and size, suction or “capillary” aspiration, number of passes, and direction of passes. These factors are listed in Table 20.2 .

Fine-needle aspirates

Fine-needle aspirates/biopsies are used widely for EUS, computed tomography (CT), and other image-guided biopsy techniques, as well as for percutaneous biopsies of palpable masses. The material contained within a fine-needle aspirate is usually smeared onto slides, and the resulting monolayer of cells is immediately fixed or dried and stained. Material obtained from a fine needle is generally dispersed as single and small groups of cells, rather than intact tissue cores. As the preparation is not sectioned, the cells represented on an aspirate smear are intact. Thus cells round up or splay out depending on how they are treated in further processing steps. The monolayer smear created from a fine-needle aspirate is very important to decipher details of the nucleus and cytoplasm that is superior to many other modalities.

Recently new developments have allowed acquisition of core biopsies utilizing endoscopy ultrasound-guided route. These samples have the advantage of providing tissue architecture.

Choice of needles

Fine needles are defined as needles which have 22-G or smaller bore. Varying sizes of EUS instruments and needles are available on the market, and the choice of needle may also influence cytology findings. The cutting edge of the needle plays a role in obtaining samples; for example, a beveled edge requires less force in comparison with circular edges. Similarly, needle sizes also have an impact on the procurement of tissue samples. In current practice, EUS needles range from 19 to 25 G. Contrary to intuitive thinking that larger size is always better for FNA samples, sometimes the smaller-bore needle provides better sampling.

Several prospective studies and meta-analysis of published literature have been attempted to determine the impact on cell yield and diagnostic performance of samples obtained by the various EUS FNA needle types. Some of these investigators suggested that needle aspirates from 25-G needles provide less hypocellular or acellular and bloody specimens, have better diagnostic performance, and perhaps induce less tissue injury in comparison with samples from a 22-G needle. ^{, ,} Other investigators, however, could not independently confirm this finding and found either no or minimal difference between 22- and 25-G needles with regard to the ability to render a diagnosis. ^,

FNA samples are also increasingly used for ancillary studies. In a study designed to determine the optimum needle size and number of passes to obtain material for RNA quantitation, the number of cells obtained from needles of varying sizes was counted. With 10 needle excursions into a tumor, 32,000 cells were obtained with a 25-G needle. Although large numbers of cells are important for molecular tests, such as RNA extraction, it is generally accepted that diagnoses can be made on smears containing fewer than 100 cells. Investigators have suggested that a larger needle (e.g., 22 G) may be useful for lesions associated with less risk of complication or that require large numbers of cells for classification. Unraveling of underlying molecular targets that may affect diagnosis, prognosis, or therapeutic predictions are increasingly being characterized. This has resulted in increased utilization of small tissue samples in performance of molecular tests such as fluorescence in situ hybridization (FISH) analysis, pyrosequencing, and newer platforms to generate high-throughput molecular mutational profiles utilizing techniques such as next-generation sequencing. ^{, ,} As a unique technique, the authors have also de-stained Diff-Quik–stained smears and performed FISH analysis to detect specific chromosomal translocations in lymphomas to improve diagnostic performance. This method has the clear advantage of making a morphologic determination and then using the same cells for detection of characteristic chromosomal translocations to clinch the diagnosis.

Given the tradeoff between more cells and more complications with larger fine needles, the choice of needle size should be based on the site and type of lesion to be aspirated. Indications for a smaller needle (e.g., 25 G) include patients with coagulopathy, organs in which leakage of fluid or air may occur, organs in which tissue trauma may increase complications (e.g., pancreas), and vascular organs or lesions. A smaller needle size decreases potential complications such as bleeding into the tissue and hemodilution or obscuring of the cytology sample by excessive blood. Smaller needles also cause less tissue damage and thus possibly less risk of pancreatitis.

Needle core biopsy versus fine-needle aspiration

Unlike many cytopathologists, for several reasons, some clinicians and surgical pathologists believe that a tissue core yields unequivocally better diagnostic material. This belief perhaps stems from the concept that tissue cores will result in adequate samples with fewer needle passes, they do not involve onsite specimen assessment, they reduce procedure times, they provide architecture, and ancillary studies can be performed on these samples. It is also true that needle core biopsies (14 to 19 G) have been used for a long time to obtain tissue samples. Sections made from these core biopsies are sliced at 3 to 5 μm and when stained and viewed microscopically, show cells or portions of cells within their intact tissue stroma. Most histopathologists are very familiar with this method of tissue-based assessment and therefore promote use of core needle biopsy samples.

Conversely, however, one should also be aware that analysis of tissue core may not always provide adequate diagnostic clues. Tru-Cut biopsy also induces greater tissue injury and complications than an FNB and is more invasive. Such considerations could deter clinicians from using large-bore Tru-Cut needles. It is also true that needle core biopsies can pose greater challenges for diagnosing well-differentiated carcinomas of the pancreas in comparison with FNA samples. In preliminary analyses, the success of FNA sampling using EUS guidance led to a sharp decline in performance of percutaneous needle core biopsies and CT-guided FNA. Such a change dramatically altered practice management decisions for pancreatic neoplasms.

A possible explanation for the failure of core needles to sample the lesion may be the attributes of the lesion itself, given that a larger needle may deflect from the surface of a firm or rubbery lesion. In addition, a Tru-Cut biopsy represents a single pass into the tissue and is not able to sample the lesion widely without further passes into the tissue. The use of larger needles increases the risk of bleeding and complications, although these risks remain very low.

The use of EUS-guided needle core biopsies has recently demonstrated a significant promise in review of lymphadenopathy as well as from other solid organs. These needles utilize thin bores and have been found to be useful not only to establish the diagnosis of lymphoma but also to characterize cellular architecture, which is more important in disorders such as follicular center cell lymphomas. EUS FNB also may be more useful in cases in which flow cytometry results can provide false-negative results, such as large B-cell lymphomas. EUS-guided biopsy may also be helpful in establishing the difficult diagnosis of Hodgkin lymphoma in which morphology is varied and often challenging to identify.

Recently, newer biopsy needles have been introduced to procure samples with minimal fragmentation thereby retaining architecture. Histologically, an ideal core has uninterrupted structure or architecture, whereby cell groups maintain their interface with extracellular matrix or stroma. Architecture can be crucial to the definitive diagnosis and/or staging. Three needles are being utilized more frequently in today’s practice which include reverse bevel needle (Procore, Cook Endoscopy, Winston Salem, NC), fork tip needles (Shark Core, Medtronic Corp., Boston, MA), and Franseen tip needle (Acquire, Boston Scientific, Marlborough, MA). Initial assessment of Procore needles, 25-, 22-, 19-G fork-tip needles (Shark Core, Medtronic Corp., Boston, MA) and the 22-G Franseen tip needle (Acquire, Boston Scientific, Marlborough, MA) have demonstrated a strong promise in tissue acquisition studies. Fork tip and Franseen needles show superior performance in acquiring tissue samples and reducing number of passes over reverse bevel needles to obtain core tissue and shows that they are noninferior to EUS FNB tissue acquisition with ROSE. ^{, ,} Increasing studies also demonstrate value of new EUS FNB needles to procure samples for assessments of medical liver conditions. The samples from these needles are, however, fragmented, and are more expensive. EUS FNB offers several advantages of reduced number of passes, alleviates need for onsite assessments, and reduces procedure times. This, however, needs to be balanced against losing critical communication between endosonographes and cytologists as well as losing possibility to adequately triage tissues for ancillary studies (see Table 20.3 ).

The decision to obtain cores instead of, or in addition to, aspirates rests on certain factors, including the available equipment and personnel, the training and expertise of the pathologists and staff, and the endoscopist’s preference. Each type of biopsy has advantages and disadvantages that must be considered for individual lesions or patients. Overall, FNA smear and cell block preparations assessment is considered a more sensitive diagnostic method, and it can be complemented by core biopsy.

To apply or not to apply suction

For many fine-needle aspirates, suction is applied to the needle to attempt to increase cell yield. This is the origin of the term fine-needle aspirate . The purpose of suction is not to draw cells into the needle, but rather to “hole” the tissue against the cutting edge of the needle. Suction should be turned off before the needle is withdrawn.

In another technique, the cells are obtained without applying suction. The lumen is filled with cells by the direct cutting action of the needle through the tissue or capillary action. A study of 670 superficial and deep lesions sampled by biopsy with a fine needle without suction showed that diagnostic material was obtained in more than 90% of the cases. Specific to EUS FNA, a study by Wallace and colleagues found no difference in suction versus no suction in terms of overall diagnostic yield for lymph nodes, but these investigators noted excess blood in the specimens to which suction was applied. Another study demonstrated that EUS-guided fine-needle sampling with suction increased the number of slides (17.8 ± 7.1 slides) needed to be prepared as compared with a significantly ( P < .0001) reduced number of slides to be prepared for samples in which no suction was applied.

In general, applying suction to the needle increases cellular yield but potentially increases artifact and blood, especially in vascular organs and lesions. Suction is commonly used because the increased cellular yield of specimens often outweighs the disadvantages. Some clinicians attempt up to three passes without suction and add further passes with suction if the cellular yield is low. While no suction improves analysis, the choice to use or not to use suction should be dictated by the type of lesion.

When a large amount of blood is aspirated and the specimen clots, a less desirable but useful salvage of material is with gentle microdissection of the clot or fragment with a small scalpel blade or separate needle tip. The fragments are then lifted from the slide and are placed in formalin for subsequent cell block preparation. Forceful smearing of the clot to disperse the cells may cause significant crush artifact and may render the cells uninterruptible.

Number of passes

A pass usually comprises 10 or more needle excursions or movements of the needle to-and-fro once the needle is within the lesion. The number of passes needed to obtain diagnostic material depends on multiple factors, including experience of the endosonographer, location of the lesion, type of lesion, cellularity of the lesion, and risk of complications. Many investigators suggest that after a certain number of passes, the procedure reaches a state of diminishing returns for obtaining diagnostic cellularity.

The landmark study was performed earlier where issue of number of passes and specimen adequacy rates were more carefully investigated in 204 cases. In this early analysis of more than 204 cases, diagnostic cellularity was obtained after 5 passes in more than 90% of cases. It also emerged in this study that the rate of diminishing returns was reached earlier for lymph nodes and later for the pancreas. For solid pancreatic lesions, adequate cellularity was achieved with fewer numbers of passes when the lesion was smaller (≤25 mm) compared with larger lesions. This study also demonstrated that after five passes, lymph nodes offered little benefit in obtaining diagnostic cells. It was also evident that for lymph nodes, a mean of only three passes was needed for obtaining diagnostic cellularity. In recent years, better technique and experience and fellowships in advanced endoscopies have led to reduction in the number of passes needed to procure adequate diagnostic cellularity.

A well-known advantage of real-time image-guided biopsies, especially EUS, is the ability to direct the needle to a small point of interest. Selection of the exact site of biopsy may influence the cytologic yield. Biopsy of the necrotic center of a tumor may be nondiagnostic, whereas the edge may contain viable tumor cells. Conversely, biopsy of the edge of a pancreatic carcinoma may show only chronic pancreatitis, a common reactive change in the surrounding pancreatic tissue.

Depending on the anatomic site, directing the needle to specific portions of the lesion may be advantageous. Metastatic tumor in lymph nodes may be histologically more apparent in the subcapsular sinus, but in lymph node aspirates evaluated by EUS FNA, aspiration of the edge of the node did not increase the likelihood of a correct diagnosis. Nonetheless, because EUS allows visualization of the lesion, biopsy of a necrotic area can be avoided, and, as discussed later, onsite evaluation of the specimen can provide guidance to another location if the first site is necrotic.

A main advantage of the FNA technique is the wide sampling of a lesion by maneuvering the needle in different directions with each back-and-forth movement. Small redirections of the needle to make a fan shape will result in sampling of new areas of the lesion each time. Utilization of the fanning technique as described in another chapter in comparison to the standard multiple-pass technique to obtain cells helps reduce the number of passes and improves diagnostic cellularity rates. Repeated needle excursions in the same direction, along the same needle tract, result in biopsy of the blood or fluid that can fill the area with blood.

Immediate cytologic evaluation

One way to ensure adequate material from an FNA procedure is the use of ICE ( Video 20.1 ). The goal of ICE is to provide real-time feedback about the content and quality of the smears, to reduce the number of nondiagnostic or atypical biopsies, and to maximize the efficiency of the procedure. We as well as other investigators have demonstrated that ICE yields increased highly reliable preliminary diagnosis and will also help triage the specimen for performing ancillary studies. Other investigators have demonstrated that specimen adequacy is more than 90% when a cytopathologist is present in the endoscopy suite for ICE. Such high specimen adequacy rates drop when cytopathologists are not present in the endoscopy suite for ICE. In a direct comparison of EUS FNA procedures performed by the same endoscopist at two institutions, with and without a pathologist present during the procedure, ICE was more likely to result in a definitive diagnosis and less likely to involve an inadequate specimen. Most false-negative EUS results are caused by inadequate sampling, which may necessitate a second procedure. It is also true that the most effective way to reduce sampling error is ICE.

A retrospective analysis was conducted of changes noted after the transition from CT-guided FNA to EUS-guided FNA sampling from the pancreas. Cytopathologists were present to provide ICE in an endoscopy suite, whereas this practice was not in place for samples obtained under CT guidance. The results demonstrated that EUS FNA provided more definitive diagnoses and fewer unsatisfactory or equivocal diagnoses. The investigators were also able to procure additional samples for ancillary studies. Such efforts at other institutions have also seen greater than 90% specimen adequacy rates and reductions in equivocal diagnosis. When ICE is performed, selected air-dried slides are stained in the endoscopy suite or an adjacent room and are reviewed immediately by the pathologist, so that feedback can be given to the endoscopist regarding the adequacy of the pass. If diagnostic material is present, additional passes are not made, and the procedure is stopped. If the smears are nondiagnostic, further passes are made. If there are no cells or only necrosis, the needle can be redirected for the next pass, and the procedure can be continued until adequate material for diagnosis is obtained.

In addition to minimizing the number of passes needed to obtain diagnostic material, another advantage of ICE is the triage of specimens for special studies. Such a practice may allow procurement of samples for ancillary studies such as lymphoma workup or for cell block when the initial smears show a tumor that may need classification by immunohistochemistry, in situ hybridization, or molecular studies for better patient management. Thus, obtaining additional directed passes is encouraged for making an adequate cell block.

Although ICE clearly improves diagnostic yield, this practice is variable throughout the world. The use of ICE is influenced by the physical location of the laboratory and gastrointestinal suite, personnel, and cost issues. Reluctance of a pathologist to attend EUS FNA procedures may relate to lack of time and inadequate reimbursement for the time investment required.

Unfortunately, however, lack of will on the part of consumers of these services has not helped to change the conventional stance on reimbursements in the United States. Instead, the reimbursement rates are increasingly becoming more cost prohibitive. All institutions and regions of any country are different, and they need to develop their own cost-effective strategies for the sake of providing optimal health care for their patients.

In an attempt to minimize the impact of the lack of ICE, different investigators, with variable success, have investigated alternatives. These alternatives include assessment of cellularity by visual inspection, performance of smears and evaluation by endosonography personnel, and the use of services of advanced cytotechnologists following adequate training or advanced trainees in cytopathology. In this context, the use of dynamic telecytology for adequacy assessment provides a powerful alternative and is successfully used in daily practices at many institutions. ^,

Regardless of whether ICE is used or not, an adequate sample is the foundation of the diagnosis. The needle must be placed into the lesion, and the technical aspects of the sampling must be optimized to obtain cells for evaluation, and the smears must be free of crush, drying, staining, or other artifact and obscuring blood, inflammation, or necrosis.

Cytology smears and cell block

A smear slide is the standard method of preparing cells obtained from an FNB for viewing. As in a blood smear, the biopsy material is dispersed or “smeared” onto a glass slide, stained, and viewed as individual cells. For EUS FNA, after the needle is removed from the endoscope, the tip is placed near the frosted end of a labeled slide, and a single small drop is expressed onto the slide by slowly advancing the stylet into the needle. Dropping the material from a distance, squirting, or spraying it onto the slide can result in drying of the specimen and unwanted artifact. A second slide is then drawn over the drop of material, to pull the material into a monolayer. The technique requires practice. If the smear is too thick, the cells are obscured by one another or by background cells; if too much pressure is applied, the cells are artificially disrupted from their normal microarchitecture or are lysed. Imperfect smears may reduce the diagnostic yield. Another technique is also called “butterfly technique” where a drop is placed in the center of the slide and two slides are placed at right angles such that the material spreads between two slides by capillary action. One slide is then air-dried and the counterpart is immediately fixed in alcohol for additional stains. No pressure is applied. This technique requires less technical expertise without compromising quality of diagnosis.

Should one acquire tissue core biopsies, then one should firmly touch the core tissue to transfer cells on the slides. Firmly applying pressure to the core may result in squashing the tissue which may or may not provide optimal information.

In contrast to smears, a cell block is a preparation in which the aspirated cells are placed into a liquid medium or fixative, transported to the laboratory, spun into a pellet, formalin fixed, paraffin embedded, and selected for standard hematoxylin and eosin (H&E) staining. This routine formalin fixation and paraffin embedding is not optimal for preserving cytologic detail. A cell block is often made from leftover material rinsed from the needle. Its value as an adjunct to diagnosis can improve if an additional directed pass is obtained at the end of the procedure. This technique is highly recommended, especially for lesions that may require special stains.

Many institutions place EUS FNB samples in formalin and transport it for surgical pathology assessment. It is authors’ strong recommendation that EUS FNB samples should be prepared like the process for cell block preparation to ascertain higher cellular yield.

Air-dried or alcohol-fixed smears

In general, smears prepared from FNA material are either air dried or alcohol fixed. Air-dried smears are stained rapidly (using a modified Romanowsky stain [e.g., Diff-Quik]) and are typically used for ICE. Some institutions use H&E or rapid Papanicolaou (Pap) stains for ICE.

Diff-Quik–stained, air-dried smear preparations highlight intracytoplasmic material and extracellular substances. Alcohol fixation causes cells to shrink and round up but it preserves nuclear features and is followed by Pap or H&E staining. The Pap stain highlights nuclear detail and chromatin quality, as well as demonstrating keratinization of squamous cells. The cytoplasm appears more transparent in Pap-stained slides. Slides can be fixed in preparation for a Pap stain by immersing or spraying them with alcohol. The Pap and Diff-Quik stains are complementary, and optimal cytologic detail is provided when both alcohol-fixed and air-dried smears are prepared from the FNA.

Transport media and liquid-based preparations

Samples are frequently collected in transport media for subsequent preparations. Although many media are available, Hank’s balanced salt solution is preferred. This medium allows for preparation of cytospins and cell blocks, and should one require lymphoma consideration later, this medium can also be used for flow cytometric analysis. For consideration of any lymphoma workup, many institutions also collect their samples in RPMI 1640. This is also a useful medium to collect for cytogenetic analysis, as well as gene rearrangement studies.

Liquid-based cytology is now firmly embedded in clinical practices. Often times when ICE/ROSE is not possible these samples can be placed in the transport medium for cytologic interpretation. Several studies have suggested that this can obviate the need for ICE/ROSE. It is also becoming more evident that for pancreatic cysts utilizing this approach is more beneficial. increasingly being investigated. Currently, two methods have been approved by the Food and Drug Administration: ThinPrep (Cytyc Co, Marlborough, MA) and SurePath (TriPath Inc., Burlington, NC). There are slight differences between the two methods but both offer advantages of monolayer cell dispersion, elimination of obscuring mucus and blood, and consistent cell preparation without artifacts of preparation, as noted with smear preparations.

These techniques, however, increase the cost of preparation and cannot be used for ICE. Because the preparations may disaggregate cells (loss of architecture) and alter some cytologic details, they offer challenges to interpretation. Some of the proprietary liquid fixatives contain methanol, a coagulative fixative (rather than a protein cross-linking fixative such as formalin), which may lead to suboptimal fixation for immunohistochemistry. Liquid-based cytology preparations do not fare as well as direct smear preparations. However, liquid-based cytology offers a viable alternative when ICE is not a consideration. Samples from pancreas prepared using liquid-based cytology preparations demonstrated smaller cell clusters, smaller cell size in comparison with air-dried smears, better nuclear characteristics, and diminished or absent mucin. Furthermore, these samples could not be used at a later time for flow cytometry analysis. Such considerations should be taken into account during selection of transport media and preparations. A brief overview of a general process of EUS FNA procedure is shown in Table 20.4 .

Cytology interpretation

Evaluation of the biopsy begins the moment material is expressed from the needle onto a slide or into a fixative. An adequate aspirate, or one that is likely to yield a diagnosis, is cellular, so that when placed on the slides and smeared out, a finely granular quality is apparent. In contrast, in a hypocellular or purely bloody smear, the thin sheen of material is smooth. When the material is placed in fixative, visible particulate matter or cloudiness is usually present. Mucus, pus, and necrosis may also be grossly apparent.

Diagnostic evaluation of the slide

Whether onsite or in the laboratory, the cytotechnologist or pathologist begins the slide evaluation by assessing the cell types, cell arrangement, and cellular features on the smear. Central to a cytology diagnosis is the appearance of the nuclear and cytoplasmic features of individual cells; these are quite distinct, depending on the lesion sampled. No single feature is diagnostic of malignancy, but rather the composite picture of cell type, microarchitecture, and nuclear and cytoplasmic characteristics determines the diagnosis. It is useful to know the common pathologic diagnoses accessioned from various sampled sites ( Table 20.5 and Fig. 20.1 ).

Normal components from GI tract also get aspirated on endoscopically guided FNA and should be recognized. The appearance and composition of a benign aspirate may also resemble various cell populations in normal tissue. Epithelial cells are round to oval, have moderate to abundant cytoplasm, and are cohesive. Benign epithelial cells show evidence of differentiation. Squamous cells acquire keratin as they mature, whereas their nuclei become progressively smaller and darker (pyknotic). A benign superficial squamous cell exfoliated from the esophagus has a large, polyhedral shape, with a small, uniformly dark, nucleus described as an “ink dot” ( Fig. 20.2 ). The cytoplasm is orange-pink to blue, depending on the degree of keratin accumulation. Benign, mature squamous cells appear single, unless they are from the deeper layers of the epithelium, in which case they may remain together as large sheets of cells with less keratinization of the cytoplasm. Benign glandular epithelium from the stomach ( Fig. 20.3 ), intestine, and pancreas also demonstrates an orderly arrangement of differentiated cells with organ-specific variations. In smears, duodenal epithelium consists of folded or draped sheets of columnar cells, with interspersed goblet cells appearing as clear spaces among the absorptive cells ( Fig. 20.4 ). Glandular cells are polarized, with the nucleus present at one end of each cell in the sheet of epithelium. The cytoplasm may be filled with a single mucin droplet (the goblet cell), smaller more finely divided vacuoles, or other secretory products such as zymogen granules. Classically, benign columnar epithelium has a honeycomb pattern. Changing the microscope plane to focus reveals the hexagonal borders of the apical cytoplasm and polarized, orderly nuclei at the base of the honeycomb sheet. In contrast, benign stromal or mesenchymal cells have elongated nuclei and usually abundant cytoplasm. Occasionally, small vascular structures are visible in smears of benign tissue.

The cells represented in an aspirate of normal tissue are proportionate to their mixture in the organ. For example, benign pancreatic tissue is composed mostly of acini, with relatively few ductal structures (see Fig. 20.5 ) and islets usually represented on FNA smears. A benign reactive lymph node ( Fig. 20.6 ) contains a polymorphic mixture of cell types, with large and small lymphocytes, macrophages, and sometimes identifiable germinal centers, whereas lymphoid malignancy is usually monomorphic. In contrast to the order inherent in benign tissue, malignant cells deviate in their organization and demonstrate predictable unpredictability in architecture.

Normal epithelial cells exhibit cohesion, whereas malignant epithelial cells are loosely aggregated or single cells. The degree of dyshesion is relative and is an important criterion in the overall assessment of malignancy. In contrast to epithelial cells, some tissue types are normally dyshesive. Unlike carcinomas, which reveal cohesive cell clusters and many single cells, FNA from noncarcinoid tumors and melanoma are usually noted as single cells. An overzealous smearing technique may artificially separate epithelial cells and may lead to overestimation of dyshesion.

Malignant cells also exhibit disorganization of their normal arrangement of polarity. The loss of polarity is a particular diagnostic feature in lesions arising in columnar epithelium. An important EUS FNA example is the diagnosis of atypia or malignancy in mucinous neoplasms. Once the low-power assessment of the general characteristic of the smear has been evaluated for cell types, overall organization, cohesion, and detailed analysis of the nucleus and cytoplasm allow characterization of a cell as benign or malignant. Specific nuclear features determine malignancy, whereas cytoplasmic features and microarchitecture demonstrate differentiation of the cell.

Pancreas

EUS is, in itself, a highly effective modality for detecting, staging, and determining respectability of pancreatic carcinomas. FNA was documented to be as accurate as frozen section diagnosis and is less invasive, faster, and more cost effective for the diagnosis of both resectable as well as nonresectable pancreatic carcinomas. Investigators also showed that EUS FNA is better than percutaneous FNA for obtaining accurate preoperative diagnosis. The objectives of EUS FNA of lesions of the pancreas are to obtain the initial diagnosis of a clinically suspicious malignant neoplasm, to obviate the need for surgery for the purpose of obtaining tissue for diagnosis, and to obtain tissue confirmation of the diagnosis before surgical resection with curative intent or initiating adjuvant chemotherapy. As a result, this modality has now found its rightful place as a preferred technique for obtaining tissue diagnosis and confirmation by the members of the National Comprehensive Cancer Network.