Endoscopic ultrasound-guided tissue acquisition: does the needle make the difference?

Endoscopic ultrasound (EUS)-guided tissue acquisition is a widespread technique used to obtain tissue samples for histological diagnosis in patients suffering from intraintestinal and extraintestinal lesions, such as pancreatic tumors, lymph node enlargement, or subepithelial masses [1] [2]. However, the diagnostic capability of EUS-guided fine-needle aspiration (FNA) is limited if on-site cytopathological evaluation, which is associated with greater sample adequacy and diagnostic accuracy, is not available [3]. Rapid on-site cytological evaluation is very demanding, requiring a high level of expertise from pathologists who often have very scant tissue material to work with. Nonetheless, in the published literature, the diagnostic accuracy of EUS-FNA has reached sensitivity rates of over 90 % [2]. However, these data relate to “perfect conditions” – a very experienced endonosographer working with an expert pathologist in the setting of rapid on-site evaluation. In not-so-perfect conditions, the diagnostic sensitivity can decrease to 70 % – 75 % [4].

One option to overcome these diagnostic limitations is to obtain a real tissue biopsy, from which histological evaluation can be carried out. A tissue core biopsy with preserved architecture is considered to be essential for the diagnosis and characterization of certain neoplasms and benign lesions [5] [6]. In addition, the acquisition of a tissue core allows the following methods to be applied: immunostaining, thus increasing the diagnostic capability; specific diagnosis of benign lesions, such as tuberculosis or autoimmune pancreatitis; and tissue profiling, such as the use of molecular markers, thus guiding individualized treatment, especially for patients with cancer, the so-called personalized medicine [7] [8].

Over the years, several techniques of tissue acquisition for histological analysis have been described. The Tru-cut biopsy needle (Quick-Core; Cook Medical, Winston-Salem, North Carolina, USA) was designed for EUS-guided fine-needle biopsy. However, this biopsy needle has not demonstrated many advantages over standard cytological needles, mainly because of difficulties relating to the firing mechanism and stiffness of the needle, which allow only a single pass in a single axis, making the needle only suitable for use with very straight echoendoscopes [9]. Another option has been to use standard needles and an ordinary technique, but to introduce certain modifications to both the procedure and the management of the sample. This has been successfully utilized to gather tissue biopsy samples in different indications [10] [11]. New needles that have been designed specifically to obtain histological samples have become available in 19 G, 22 G, and 25 G sizes (ProCore; Cook Medical). These needles do not include a firing mechanism, which makes the biopsy procedure much easier and comparable to procedures with standard needles. An increasing number of publications have arisen over recent years, showing the ability of the ProCore needles to obtain core biopsies [12] [13]. A good interobserver agreement among pathologists has been documented with the needles [14] [15]. After initial studies reported the feasibility and diagnostic capabilities of the ProCore needle, some randomized trials have been published, comparing the diagnostic yield of ProCore needles with that of standard needles, with variable results [16] [17] [18] [19].

In this issue of Endoscopy, a systematic review and meta-analysis by Bang et al. [20], provides very useful information regarding the role of ProCore needles compared with standard needles for EUS-guided tissue acquisition. In their analysis, which included 9 studies and a total of 576 patients, the authors have attempted to define the differences between the standard needles and the ProCore needles, in terms of diagnostic adequacy, diagnostic accuracy, procurement of histological core tissue, and number of needles passes. There was no significant difference in diagnostic adequacy (75.2 % vs. 89.0 %; P = 0.23), diagnostic accuracy (85.8 % vs. 86.2 %; P = 0.53) or rate of histological core specimen acquisition (77.7 % vs. 76.5 %; P = 0.85) between the ProCore and standard needles. However, differences were found in the mean number of needles passes required for diagnosis, which was significantly lower in the ProCore group. Even a subgroup analysis, which separated pancreatic solid lesions from other indications, showed similar results, with no difference in terms of diagnostic yield.

However, there are some considerations that need to be highlighted concerning this meta-analysis. Most of the studies compared smaller-caliber needles (mainly 22 G and 25 G), rather than the larger 19 G needle, which has the highest reported rate of histological tissue acquisition [12]; in fact, this point has been emphasized by the authors in the discussion. Another important point to consider is the role of the pathologist in the world of EUS-guided tissue acquisition. It is well known that an experienced pathologist plays a key role in the work-up of this technique [21]. Even when evaluating the so-called histological needles, different results can be achieved, according to the needle size. In a multicenter study evaluating the 19 G ProCore needle, one of the factors associated with the success of the procedure was the presence of an expert pathologist, who had experience in both cytopathology and the management of diseases evaluated by EUS [12] [14]. However, in another study, which evaluated the interobserver agreement among pathologists and the capability for grading pancreatic cancer, fine-needle biopsy was found to be unreliable [22]. Furthermore, the study authors stated that the results did not support the use of this grading information in clinical practice, mainly because of the suboptimal interobserver agreement between pathologists. In the meta-analysis by Bang et al., information regarding the management of the sample was mentioned but not fully included in the analysis; however, there were differences in the methods of slide preparation and preparation for histological analysis. It would be of great interest to analyze whether the management of the samples may vary the results. However, this is very complex, and it should first be determined whether there is any difference between needle types in terms of the way in which samples are handled and prepared.

Studies comparing needles of similar caliber are of crucial importance to understanding whether or not the ProCore needles are different from standard needles for histological tissue acquisition. In addition, we can fully agree with the conclusions of Bang et al.: we should work to find the best needle – one that is able to provide a complete core biopsy (tissue slice with preserved morphology), is flexible enough for use in any situation, and is big enough to result in adequate tissue yield.

Further multicenter, collaborative studies are needed to establish the best technique for performing EUS-guided tissue acquisition, and also to define the characteristics of the best needle.

• References

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