Yield of Endoscopic Ultrasound Guided Fine Needle Aspiration (EUS-FNA) With and Without the Use of a Stylet in the Biopsy Needle

Purpose:

To compare the diagnostic yield of endoscopic ultrasound guided fine needle aspiration biopsy (EUS-FNA) in patient with pancreatic masses with and without the use of a stylet in place within the biopsy needle.

Hypothesis:

In patients undergoing an EUS FNA for pancreatic indications, patients having a fine needle aspiration biopsy (FNA) without the internal stylet will have a greater diagnostic yield compared to those with the internal stylet.

Justification:

EUS-FNA is an increasingly important means of obtaining tissue samples from lesions within the thorax and abdomen. In experienced hands EUS-FNA is a safe alternative to more invasive procedures such as mediastinoscopy or laparoscopy. EUS-FNA can be used for sampling suspected cholangiocarcinoma, pancreatic masses or cysts, submucosal gastric lesions, peripancreatic, perigastric or mediastinal lymph nodes and in some cases adrenal or liver masses. Therefore, it is a powerful tool for both diagnosis and tumour staging. For example, for the diagnosis of pancreatic adenocarcinoma, which is a common indication for EUS-FNA, the sensitivity varies from 75 to >90%, with a specificity of 82-100% and a mean accuracy of 85%. Improving the diagnostic yield may lead to an earlier diagnosis with a reduced number of investigations and earlier institution of treatment for the patient.

The FNA needle system consists of a 22 or 19 gauge needle which is manipulated by a handle piston that attaches to the biopsy channel of the endoscopic ultrasound (EUS) linear scope. The tip of the needle has grooves to disperse ultrasound waves making the tip of the needle easily seen. The sample is taken by inserting a specially designed needle into the area of interest under EUS guidance. Inside the needle is a removable stylet with a rounded or bevelled tip to facilitate the passage of the needle into the tissue. The usual practice is for the stylet to be extracted after the needle has been passed into its optimum position within the tissue and for it to be re-inserted before each pass. However, a recent prospective trial with 111 patients, published in abstract form, found this approach was associated with a significant reduction in the proportion of adequate samples compared to when the stylet was removed before passing the needle. Although there was no significant difference in the diagnostic yield between the two groups this study raises the issue that the stylet left in place is to the detriment of the tissue sample and, ultimately, may reduce the diagnostic yield or increase the number of passes needed to obtain a satisfactory sample.

One limitation to this study includes the heterogenous patient population. Yields of EUS-FNA vary considerably depending on the type of tissue being biopsied. The second limitation is that consecutive patients were randomized to having the stylet removed versus having the stylet not removed at the time of FNA. There is no control group from which to compare the two groups. An improvement in the study design would be to have each patient to be their own control group. Successive passes of the FNA needle can increase the bloodiness of the sample, so randomization of the order in which each group is done will help eliminate potential bias.

It is clear from the current published literature that removing the stylet increases the cellularity of the sample. However, this increased cellularity may be the result of more contamination from the GI tract through which the FNA needle needs to pass in order to get an extra-luminal sample. Blood or a traumatic FNA can also lead to increased cellularity that can compromise diagnostic accuracy.

Diagnostic yield depends on both adequacy of the sample and enough cells from the lesion to interpret. A preliminary result based on an air dried slide often can lead to fewer FNA passes if a diagnosis can be made. If this is not possible, a cell block preparation is made from all the washings from the EUS-FNA needle. No study has examined the diagnostic accuracy of these two types of samples using an EUS-FNA needle with and without the stylet within the same patient.

Objectives:

To determine if the diagnostic yield of EUS-FNA is increased if the stylet is removed from the FNA needle compared with leaving it in place.