Key points

Videos of the fanning technique and the uncinate process accompany this article

Introduction

Since its introduction, endoscopic ultrasound (EUS) has been increasingly used for the diagnosis and management of a variety of gastrointestinal (GI) and extraintestinal disorders. Due to its minimally invasive nature and the low morbidity associated with it, EUS-guided fine needle aspiration (EUS-FNA) became the technique of choice for sampling lesions within or in close proximity to the GI tract, with a high diagnostic accuracy exceeding 80% in malignant and benign lesions according to most studies.

Several factors influence the diagnostic yield of EUS-FNA, including the experience of the endosonographer, the availability of onsite cytopathology review, the method of cytopathology preparation, the location and physical characteristics of the lesion, and the size of the needle. Refinements made to sampling techniques and devices have been the focus of several studies published in the last decade, such as needle size, use of suction during FNA, method of sample expression and processing, and the presence of stylet during puncture. Among all these factors, needle size continues to receive the most attention as an independent factor that could increase the diagnostic yield of EUS-FNA.

The most commonly used commercially available EUS-FNA needle sizes are 19, 22, and 25 gauge (G). Choosing a particular size depends on factors such as the type and site of the lesion to be sampled, whether the lesion is solid or cystic, and whether a transgastric or transduodenal approach is required. Needle size also is also determined by whether a cytologic or histologic sample is required, which in turn depends on the nature of the lesion sampled. Smaller needles provide better accessibility due to flexibility in locations where the tip of the scope is angulated and, therefore, are preferred when transduodenal sampling of the pancreatic head or uncinate process is desired.

Traditionally, 22-G needles have been the most commonly used and are considered the “default” needles by many endosonographers. A recent change in this trend has been noticeable in many centers, where 25-G needles are increasingly used particularly for transduodenal access.

In the following sections of this review, the authors focus on comparing the different EUS-guided aspiration needles and techniques used to improve the quality of the sample based on the site and type of the lesion to be sampled. The authors critically evaluate needle size as the determinant of diagnostic accuracy as supported by the literature.

Introduction

Since its introduction, endoscopic ultrasound (EUS) has been increasingly used for the diagnosis and management of a variety of gastrointestinal (GI) and extraintestinal disorders. Due to its minimally invasive nature and the low morbidity associated with it, EUS-guided fine needle aspiration (EUS-FNA) became the technique of choice for sampling lesions within or in close proximity to the GI tract, with a high diagnostic accuracy exceeding 80% in malignant and benign lesions according to most studies.

Several factors influence the diagnostic yield of EUS-FNA, including the experience of the endosonographer, the availability of onsite cytopathology review, the method of cytopathology preparation, the location and physical characteristics of the lesion, and the size of the needle. Refinements made to sampling techniques and devices have been the focus of several studies published in the last decade, such as needle size, use of suction during FNA, method of sample expression and processing, and the presence of stylet during puncture. Among all these factors, needle size continues to receive the most attention as an independent factor that could increase the diagnostic yield of EUS-FNA.

The most commonly used commercially available EUS-FNA needle sizes are 19, 22, and 25 gauge (G). Choosing a particular size depends on factors such as the type and site of the lesion to be sampled, whether the lesion is solid or cystic, and whether a transgastric or transduodenal approach is required. Needle size also is also determined by whether a cytologic or histologic sample is required, which in turn depends on the nature of the lesion sampled. Smaller needles provide better accessibility due to flexibility in locations where the tip of the scope is angulated and, therefore, are preferred when transduodenal sampling of the pancreatic head or uncinate process is desired.

Traditionally, 22-G needles have been the most commonly used and are considered the “default” needles by many endosonographers. A recent change in this trend has been noticeable in many centers, where 25-G needles are increasingly used particularly for transduodenal access.

In the following sections of this review, the authors focus on comparing the different EUS-guided aspiration needles and techniques used to improve the quality of the sample based on the site and type of the lesion to be sampled. The authors critically evaluate needle size as the determinant of diagnostic accuracy as supported by the literature.

Size of needle

The diagnostic yield of EUS-FNA is directly related to the cytologic quality of the sample. Good sample quality increases the diagnostic accuracy and reduces the need for multiple passes or repeat procedures. To examine the effect of needle size, Lee and colleagues compared the quality of samples obtained by 22-G and 25-G needles in a blinded prospective study. Twelve patients with pancreatic or peripancreatic lesions were enrolled, and each lesion was sampled randomly using 22- and 25-G needles by the same endoscopist. There was no statistically significant difference in the cellular yield of the samples accrued by the 2 needles. However, the endoscopist reported less resistance with the 25-G needle. In a larger study involving the same size needles, Siddiqui and colleagues reported on 131 patients with solid pancreatic masses in a prospective randomized trial. No significant difference in diagnostic yield was observed between 22- and 25-G needles (87.5% vs 95.5%, respectively; P = .18). In another study by Fabbri and colleagues, both needles demonstrated 100% technical success and similar diagnostic accuracy for pancreatic lesions; however, an advantage of the 25-G over the 22-G needle was noted in cytologic diagnosis for malignancy (80% vs 68%). Comparing diagnostic yield from the same lesion sampled consecutively by 22- and 25-G needles, Imazu and colleagues found a trend for numerically higher diagnostic accuracy of the 22-G needle in gastric submucosal tumors compared with the 25-G needle (80% vs 60%), although the difference was not statistically significant. In the same study, a higher diagnostic accuracy was observed in 12 patients with pancreatic masses using the 25-G needle (91.5% vs 75%), although the difference was not statistically significant ( Table 1 ). In a large prospective randomized study, Camellini and colleagues compared 22-G with 25-G needles in 127 solid lesions with salvage crossover after 5 inadequate passes or on failure of puncturing the lesion. The number of passes made and specimen adequacy were no different between the 2 groups. More crossover from 22- to 25-G needles was observed in uncinate process masses due to puncture failure. This study suggested a superiority of the 25-G needle in obtaining samples from the pancreatic head. A similar outcome was reported by Sakamoto and colleagues, who reported a higher success rate for reaching a lesion in the uncinate process of the pancreas using the 25-G needle compared with the 22-G needle (see Table 1 ). However, the diagnostic yield for both needles was comparable in technically successful cases.

A meta-analysis by Madhoun and colleagues evaluated 8 studies involving 1292 patients who underwent EUS-FNA with either a 22- or 25-G needle, using surgical histopathology or at least 6 months follow-up as the reference standard for the diagnosis. The sensitivity of the 25-G needle was superior to the 22-G needle (93% vs 85%; P = .0003), although their specificity was not different (97% and 100%, respectively).

Fewer studies compared 19-G needle with 22-G and/or 25-G needles. Song and colleagues compared 19-G with 22-G needles for pancreatic and peripancreatic masses in 117 patients. Technical failure occurred in 5 of 60 patients randomized to the 19-G needle, all of which arose in pancreatic head or uncinate process masses and were successfully sampled once crossed over to 22-G needles. Excluding those technical failures, the overall diagnostic accuracy was higher in the 19-G group (94.5% vs 78.9%; P = .015). Sample quality was also superior in the 19-G needle group ( P = .033).

Sampling methods and technical factors

FNA technique can affect the quality of samples, and endosonographers vary in the techniques they routinely use to biopsy lesions. Common examples to such variability include the use of suction, performing the fanning technique, and expressing samples using air flushing or by reinserting the stylet. Lee and colleagues compared the quality and diagnostic yield of samples obtained with and without suction in 81 patients with pancreatic masses. Samples expressed by reinserting the stylet and those air flushed were also compared in this study. The number of diagnostic samples, cellularity, and accuracy were higher in the suction group. However, no difference in accuracy, sensitivity, or specificity was found between the stylet versus air-flushed groups, although bloodiness was lower in the air-flushed group. In another trial assessing the effect of suction, 52 solid lesions were randomized to FNA with either suction or no suction. Sensitivity and negative predictive values were higher in the suction group compared with the nonsuction group.

From a practical standpoint, the decision to use suction should also be driven by the nature of the lesion to be sampled. In a vascular target like a lymph node, a nonsuction technique may deliver a better, less bloody sample for the on-site pathologist to render a diagnosis. On the other hand, applying suction in aspirating a fibrotic tumor in the setting of chronic pancreatitis may provide a better result.

The fanning technique, in which the trajectory of the needle is altered during FNA using the up/down dial and/or the elevator, was introduced to maximize sampling of various parts of the lesion of interest ( [CR] ). Bang and colleagues compared this technique with the standard one to sample solid pancreatic masses. The fanning technique was found to be superior, establishing the diagnosis in a fewer number of passes, and resulting in higher first-pass diagnostic rate (85.7% vs 57.7%; P = .02). In sampling larger pancreatic masses, this technique provides tissue from the viable peripheral parts of the mass rather than the central part only, which could be necrotic.

The goal of FNA is to provide a confirmatory diagnosis using the least number of passes, which depends largely on the presence of an on-site cytopathologist, who assesses specimen adequacy and provides feedback about the need for further sampling. The optimal number of passes to be performed in the absence of on-site cytopathology services depends on the type of lesion. For example, in solid pancreatic masses, 7 passes have been shown to provide a sensitivity and specificity of 83% and 100%, respectively, whereas in the case of lymph nodes, 5 passes yielded sensitivity and specificity of 77% and 100%, respectively. It is generally recommended that 5 to 7 passes be obtained from pancreatic masses and 3 passes from lymph nodes when an on-site cytopathologist is not available. In this situation, 2 dedicated passes must always be performed and submitted entirely in cell block whenever possible to increase the diagnostic yield, which also allows immunocytochemistry studies ( Fig. 1 ).

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  Expression technique may affect the quality of a specimen. Application of suction during FNA followed by air flushing to express the sample seems to provide a better quality specimen, but data remain limited.

  
  
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  Sampling various parts of the target lesion using the fanning technique has been shown to provide a cytologically superior specimen compared with the standard technique.

  
  
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  On-site cytopathology offers immediate feedback about the quality of EUS-FNA specimens obtained, and therefore helps improve the diagnostic certainty and minimize the need for repeat procedures.

  
  
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  It is recommended that 5 to 7 passes be obtained from pancreatic masses and 3 passes from lymph nodes when an on-site cytopathologist is not available.

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