Although endoscopic ultrasonography (EUS) is considered superior to MRI and CT in detecting pancreatic masses, it is the ability to target and place a needle into suspicious lesions that has made EUS indispensible in the evaluation of patients with solid pancreatic tumors. Endoscopic ultrasound-guided-fine-needle aspiration (EUS-FNA) is an accurate and safe technique to confirm the diagnosis of pancreatic cancer. EUS-FNA is now the principal technique applied to obtain the diagnosis of malignancy. We have designed this article to address a number of the key technical aspects of EUS-FNA of solid pancreatic masses.
Introduction
Over the past 2 decades, endoscopic ultrasonography (EUS) has evolved to become an indispensible tool for the evaluation of the pancreas. EUS plays a critical role in the evaluation of the patient with a known or suspected pancreatic mass. Published literature supports the superiority of EUS compared with cross-sectional imaging for tumor detection, with the greatest advantage seen with tumors smaller than 2 to 3 cm. Although the sensitivity for tumor detection is high, it is also important to note that it has a very high negative predictive value (NPV). This has important implications for the clinician because it means that EUS can reliably exclude pancreatic cancer, especially in the setting of a low or indeterminate pretest probability. Although EUS is not 100% accurate, it is the single best choice to detect a pancreatic neoplasm. It should be noted, however, that cross-sectional imaging techniques (magnetic resonance imaging [MRI] and computed tomography [CT]) are well-standardized procedures, and operator skill is an important factor when performing EUS. As a result, published studies comparing cross-sectional imaging techniques with EUS may not translate into all situations, and in clinical practice, the role of CT, MRI, and EUS should be considered complementary.
Although EUS is considered superior to MRI and CT in detecting pancreatic masses, it is the ability to target and place a needle into suspicious lesions ( Fig. 1 ) that has made EUS indispensible in the evaluation of patients with solid pancreatic tumors. Endoscopic ultrasound-guided–fine-needle aspiration (EUS-FNA) is an accurate and safe technique to confirm the diagnosis of pancreatic cancer. With the advent of neoadjuvant therapies for pancreatic cancer, most patients with this disease require a tissue diagnosis before initiating treatment. EUS-FNA is now the principal technique applied to obtain the diagnosis of malignancy. We have designed this article to address a number of the key technical aspects of EUS-FNA of solid pancreatic masses.
Is there an optimal-gauge needle?
EUS-FNA is a well-established modality for cytologic evaluation of solid pancreatic lesions. A principal advantage of EUS compared with CT is the ability to perform FNA at the index examination rather than having to schedule a second examination, as is the case with CT. The precision and safety of EUS-FNA is well established and the overall accuracy in establishing a diagnosis of cancer is high. In a study by Eloubeidi and colleagues, 101 patients with solid pancreatic masses underwent a median of 4 needle passes with EUS-FNA, resulting in a sensitivity of 95%, specificity of 100%, positive predictive value (PPV) of 100%, and NPV of 85.2%.
EUS-FNA can be performed with 25-gauge, 22-gauge, or 19-gauge needles. Recently, 22-gauge and 19-gauge needles have become available designed with a specially designed side hole, and preliminary studies suggest that they are capable of obtaining a core of tissue suitable for histologic examination (ProCore, Cook Endoscopy, Winston-Salem, NC, USA) ( Fig. 2 ). Endosonographers have also had the option of a 19-gauge trucut needle (Cook Endoscopy). This needle is designed with an inner stylet that has a space (tray) cut into it at the distal end. The needle is passed into the mass, the stylet is advanced farther into the mass, and then a spring-fired mechanism is activated that advances the needle over the stylet. The needle is designed to obtain a “core” of tissue, similar to a liver biopsy. Although a larger number of cells are required for certain tests, such as RNA extraction, a diagnosis can usually be made on smears containing fewer than 100 cells. When choosing a particular gauge needle, there are several considerations: (1) which will provide the optimal yield of cells, (2) which will minimize contamination with blood, (3) how much flexibility is required to access the lesion, and (4) which will minimize complications? A smaller-gauge needle may decrease contamination with blood, generally has greater flexibility, and may decrease the potential for bleeding. Historically, the 22-gauge needle has been the needle of choice for FNA of pancreatic lesions. Thinner needles have the disadvantage of not being able to obtain a core specimen for histopathological diagnosis. Having increased flexibility in the needle is particularly important when accessing a lesion in the uncinate process or other positions in the duodenum, when significant tip deflection and maximum elevator are required to pass the needle into the lesion. A prospective study by Sakamoto and colleagues showed that the 25-gauge needle was significantly superior in terms of technical success rate and overall diagnostic accuracy, especially for the lesions in the head and uncinate process of the pancreas, when compared with the standard 22-gauge and the 19-gauge trucut needles. They concluded that the 25-gauge needle was the “best choice” needle for cytologic diagnosis of solid pancreatic lesions. In cases in which a histologic diagnosis is desired, the 22-gauge FNA needle and 19-gauge trucut needle may be at an advantage in head/uncinate and body/tail lesions, respectively. The overall accuracy for the 25-gauge, 22-gauge, and 19-gauge trucut needle in the previously cited study was 91.7%, 79.7%, and 54.1%, respectively. Accuracy for cytologic diagnosis irrespective of the site of lesions with 25-gauge, 22-gauge, and trucut needles was 91.7%, 75.0%, and 45.8%, respectively. For uncinate masses, it was 100.0%, 33.3%, and 0.0%, respectively. With regard to accuracy for histologic diagnosis, the 25-gauge needle was significantly inferior ( P <.05) to the 22-gauge and trucut needles.
A recently published study compared the rates of diagnostic accuracy, technical success, and complications of EUS-FNA performed with 22-gauge and 25-gauge needles on the same solid pancreatic lesion. Fifty patients underwent EUS-FNA with both 22-gauge and 25-gauge needles with randomization of the needle sequence. The accuracy of the EUS-FNA was determined by comparing the cytologic results with the final surgical pathologic diagnoses or with the results of a clinical follow-up. Technical success was 100% and no complications occurred. Diagnostic accuracy of EUS-FNA was 94% and 86% for the 25-gauge and 22-gauge needles, respectively. Analysis of the cytologic score showed a tendency toward the 25-gauge needle, although the difference was not statistically significant.
In studies that have looked primarily at cytologic yield, some have demonstrated no difference in diagnostic yield, number of passes required, and safety when 25-gauge and 22-gauge needles were compared.
In case an on-site cytopathologist is not available, EUS-FNA with a 19-gauge aspiration needle may be a valuable method for the diagnosis of pancreatic/peripancreatic masses. The amount of cellular material obtained by a 19-gauge needle is higher as compared with a smaller-caliber needle. The problem with the use of the standard 19-gauge needle in lesions in the head of the pancreas is that it is often too stiff to allow complete access to the mass. Recently, a new 19-gauge aspiration needle ( Fig. 3 ) has been introduced (Flex 19, Boston Scientific, Natick, MA, USA). This needle is made of nitinol and, as a result, is more flexible and does not become distorted after passing over the elevator. More experience will be required to determine its efficacy in accessing lesions in the head of pancreas, safety, and cellular yield, as well as its ability to obtain a core sample for histopathologic analysis.
Given the trade-offs between the different-gauge needles, the clinician’s choice of needle should be based on (1) the location of the lesion (head vs body/tail), (2) the nature of the lesion (pancreatic mass vs peripancreatic lymph node), and (3) whether cytology is sufficient or if a core will be needed (solid pancreatic mass vs possible autoimmune pancreatitis). Either 25-gauge or 22-gauge needles can be used for solid masses of the pancreas, but because of its greater flexibility, the 25-gauge needle is the preferred option for lesions in the head of the pancreas, especially the uncinate process. If an on-site cytopathologist is not available or a core specimen may be required, the 22-gauge or 19-gauge Procore or the 19 Flex needle may be better option to obtain a larger sample of tissue.
Is there an optimal-gauge needle?
EUS-FNA is a well-established modality for cytologic evaluation of solid pancreatic lesions. A principal advantage of EUS compared with CT is the ability to perform FNA at the index examination rather than having to schedule a second examination, as is the case with CT. The precision and safety of EUS-FNA is well established and the overall accuracy in establishing a diagnosis of cancer is high. In a study by Eloubeidi and colleagues, 101 patients with solid pancreatic masses underwent a median of 4 needle passes with EUS-FNA, resulting in a sensitivity of 95%, specificity of 100%, positive predictive value (PPV) of 100%, and NPV of 85.2%.
EUS-FNA can be performed with 25-gauge, 22-gauge, or 19-gauge needles. Recently, 22-gauge and 19-gauge needles have become available designed with a specially designed side hole, and preliminary studies suggest that they are capable of obtaining a core of tissue suitable for histologic examination (ProCore, Cook Endoscopy, Winston-Salem, NC, USA) ( Fig. 2 ). Endosonographers have also had the option of a 19-gauge trucut needle (Cook Endoscopy). This needle is designed with an inner stylet that has a space (tray) cut into it at the distal end. The needle is passed into the mass, the stylet is advanced farther into the mass, and then a spring-fired mechanism is activated that advances the needle over the stylet. The needle is designed to obtain a “core” of tissue, similar to a liver biopsy. Although a larger number of cells are required for certain tests, such as RNA extraction, a diagnosis can usually be made on smears containing fewer than 100 cells. When choosing a particular gauge needle, there are several considerations: (1) which will provide the optimal yield of cells, (2) which will minimize contamination with blood, (3) how much flexibility is required to access the lesion, and (4) which will minimize complications? A smaller-gauge needle may decrease contamination with blood, generally has greater flexibility, and may decrease the potential for bleeding. Historically, the 22-gauge needle has been the needle of choice for FNA of pancreatic lesions. Thinner needles have the disadvantage of not being able to obtain a core specimen for histopathological diagnosis. Having increased flexibility in the needle is particularly important when accessing a lesion in the uncinate process or other positions in the duodenum, when significant tip deflection and maximum elevator are required to pass the needle into the lesion. A prospective study by Sakamoto and colleagues showed that the 25-gauge needle was significantly superior in terms of technical success rate and overall diagnostic accuracy, especially for the lesions in the head and uncinate process of the pancreas, when compared with the standard 22-gauge and the 19-gauge trucut needles. They concluded that the 25-gauge needle was the “best choice” needle for cytologic diagnosis of solid pancreatic lesions. In cases in which a histologic diagnosis is desired, the 22-gauge FNA needle and 19-gauge trucut needle may be at an advantage in head/uncinate and body/tail lesions, respectively. The overall accuracy for the 25-gauge, 22-gauge, and 19-gauge trucut needle in the previously cited study was 91.7%, 79.7%, and 54.1%, respectively. Accuracy for cytologic diagnosis irrespective of the site of lesions with 25-gauge, 22-gauge, and trucut needles was 91.7%, 75.0%, and 45.8%, respectively. For uncinate masses, it was 100.0%, 33.3%, and 0.0%, respectively. With regard to accuracy for histologic diagnosis, the 25-gauge needle was significantly inferior ( P <.05) to the 22-gauge and trucut needles.
A recently published study compared the rates of diagnostic accuracy, technical success, and complications of EUS-FNA performed with 22-gauge and 25-gauge needles on the same solid pancreatic lesion. Fifty patients underwent EUS-FNA with both 22-gauge and 25-gauge needles with randomization of the needle sequence. The accuracy of the EUS-FNA was determined by comparing the cytologic results with the final surgical pathologic diagnoses or with the results of a clinical follow-up. Technical success was 100% and no complications occurred. Diagnostic accuracy of EUS-FNA was 94% and 86% for the 25-gauge and 22-gauge needles, respectively. Analysis of the cytologic score showed a tendency toward the 25-gauge needle, although the difference was not statistically significant.
In studies that have looked primarily at cytologic yield, some have demonstrated no difference in diagnostic yield, number of passes required, and safety when 25-gauge and 22-gauge needles were compared.
In case an on-site cytopathologist is not available, EUS-FNA with a 19-gauge aspiration needle may be a valuable method for the diagnosis of pancreatic/peripancreatic masses. The amount of cellular material obtained by a 19-gauge needle is higher as compared with a smaller-caliber needle. The problem with the use of the standard 19-gauge needle in lesions in the head of the pancreas is that it is often too stiff to allow complete access to the mass. Recently, a new 19-gauge aspiration needle ( Fig. 3 ) has been introduced (Flex 19, Boston Scientific, Natick, MA, USA). This needle is made of nitinol and, as a result, is more flexible and does not become distorted after passing over the elevator. More experience will be required to determine its efficacy in accessing lesions in the head of pancreas, safety, and cellular yield, as well as its ability to obtain a core sample for histopathologic analysis.
Given the trade-offs between the different-gauge needles, the clinician’s choice of needle should be based on (1) the location of the lesion (head vs body/tail), (2) the nature of the lesion (pancreatic mass vs peripancreatic lymph node), and (3) whether cytology is sufficient or if a core will be needed (solid pancreatic mass vs possible autoimmune pancreatitis). Either 25-gauge or 22-gauge needles can be used for solid masses of the pancreas, but because of its greater flexibility, the 25-gauge needle is the preferred option for lesions in the head of the pancreas, especially the uncinate process. If an on-site cytopathologist is not available or a core specimen may be required, the 22-gauge or 19-gauge Procore or the 19 Flex needle may be better option to obtain a larger sample of tissue.
How many passes do I make and is there an optimal technique?
The determination of the number of passes to make is dependent on whether or not an experienced cytopathologist is present in the EUS suite to make real-time interpretation of the EUS-FNA specimens. If absent, one has to determine the optimal number of samples required to maximize the chance that an accurate diagnosis can be made. LeBlanc and colleagues concluded that 7 is the optimal number of passes for pancreatic masses (sensitivity and specificity of 83% and 100%), whereas 5 passes are optimal for lymph nodes (LNs) (sensitivity and specificity of 77% and 100%). Wallace and colleagues suggested that 3 samples obtained by back-and-forth needle movement for 30 seconds each is sufficient for diagnosis of all malignant LNs. Erickson and colleagues showed that FNA of liver lesions and LNs requires significantly fewer needle passes to obtain adequate diagnostic material as compared with solid tumors of the pancreas. In this study, the investigators suggested that without a cytopathologist in attendance, 5 to 6 passes should be made for pancreatic masses and 2 to 3 for liver metastases or LNs.
There are as many opinions on the optimal technique for EUS-FNA as there are endosonographers. Accurate evaluation of a specific technique is very difficult without introducing bias and, as a result, it is not possible to recommend one specific technique. Our one recommendation is to move the needle through the lesion in a “fanlike pattern” ( Fig. 4 ). The trajectory of the needle can be altered using either the “up/down” endoscope dial or the elevator. It is likely that after thrusting the needle deeply into a mass, the path fills with blood on withdrawal of the needle. If one passes the needle back and forth in the same trajectory, one suctions blood into the needle rather than diagnostic cells. In addition, if one feels both soft and firm areas within a pancreatic mass, one should confine the needle movement to the firm areas while avoiding the soft ones, which are usually necrotic. It may be difficult to change the trajectory of the needle in masses located in the uncinate process, which highlights the need for the most flexible needle.
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