EUS Anatomy and Diseases
Now let’s take a deeper look at why EUS/FNA would be needed for a patient and how the doctor would choose a system. It is best to look at FNA in two different areas: masses and cysts. With a mass or submucosal tumor, we are looking for tissue for diagnosis; with a cyst, we are looking for aspiration, either for evaluation or aspiration alone.
| Masses | Cysts |
|---|---|
|
|
Submucosal Tumors: Esophagus
EUS-FNA in the esophagus is about staging. Imaging gives the doctor a sense of the depth of the tumor invasion. FNA will help validate the diagnosis. Not every EUS in the esophagus will involve FNA. Typically, if it is limited submucosa, doctors won’t do FNA and may go to EMR. A CT scan will often show if there is lymph node involvement, but a doctor may see something suspicious in the lymph nodes on EUS and decide to use FNA on the nodes.
It is important to know that a doctor should never use the same needle for FNA of the nodes that they used for FNA of the tumor itself. So they will always FNA the nodes first, then the tumor. The rationale for this order is the serious concern for the adverse event of tumor seeding where cells from a cancerous mass are passed to another mass at another location via the contaminated needle. Some physicians may want to use a smaller needle for the nodes, and a larger needle for the tumor. Being able to have a catheter in place and the ability to rapidly move needles in and out is efficient.
Submucosal Tumors: Stomach
Gastrointestinal stromal tumors (GIST) are soft tissue sarcomas that can be located in any part of the digestive system, most commonly in the stomach and small intestine. The goal of EUS/FNA is to determine the level of tumor invasion into the wall of the stomach, and to acquire tissue to confirm diagnosis. While there are no recommendations on the number of passes necessary here, certainly the more tissue, the better.
Ideally, a pathologist should be present during the procedure. If the sample is too small, the pathologist would immediately inform the doctor, who in turn would switch to a larger needle. The pathologist may notice that there is too much blood in the sample, in which case the doctor would switch to a smaller needle and use less suction. Additional immunohistochemical staining of suspected GISTs is important for a definitive diagnosis. The adequacy and diagnostic yield of EUS-FNA specimens may be lower for submucosal lesions than those from pancreatic lesions and lymph nodes.
Pancreatobiliary Masses
Retrieving samples from pancreatobiliary masses can be complicated. The torqued scope position makes needle exchanges difficult and forcing a needle through a torqued channel risks scope damage. Repositioning of the scope may be necessary to allow needle exchanges. Typically, it takes about 5-7 passes of the needle to achieve adequate tissue diagnosis.
The physician will position the scope in the third part of the duodenum to obtain images and create the angles necessary to sample the target lesions. It can be challenging to maneuver through the pylorus with a side viewing scope. Remember, you are looking out the side of the scope and trying to move through a sphincter that is straight ahead in your field of vision. Working with the scope in the 3rd section of the duodenum creates torque on the scope, which compromises the integrity of the scope channel. All those twists and bends will flatten the channel, much like crimping a straw. Positioning of the scope is critical to retrieving a good sample and once proper positioning is achieved, the sample is taken.
Typically, after the first sample is taken, a couple things happen. 1. The needle system is withdrawn and reinserted. 2. The scope will need to be repositioned in the stomach to create the straight channel.. 3. Once the needle is removed, the tissue is expelled. 4. The needle is reloaded through the channel and the physician will maneuver back into the duodenum. Fortunately, there are some systems that will allow you to leave the catheter in place and only remove and exchange the needle in a rapid exchange process, not losing time or positioning.
FNB in Solid Pancreatic Lesions
The ability to detect malignancy is reduced in patients with underlying pancreatitis because of the difficulty identifying a discrete mass lesion in this setting. FNB does not improve the diagnostic yield of malignancy compared with FNA. However, the ability to obtain histologic specimens can aid in diagnosing benign conditions such as autoimmune or chronic pancreatitis, in which the assessment of tissue architecture is necessary to achieve a diagnosis. EUS-FNB should be considered in lesions with prior nondiagnostic EUS.
Now let’s take a deeper look at cysts. With a cyst, we are looking for aspiration, either for evaluation or aspiration alone. With cysts, aspiration might be the only objective. In those cases, the doctor will typically only need one pass. But often times, the secretions from a cyst might be very mucinous. The process is typically started with a smaller needle because there is always concern about bleeding when using a larger needle. If the small needle is too small, substitution for a larger needle may be necessary. If multiple needles are needed, a scope which allows the physician to leave the catheter in place and exchange needles in a rapid method would be more efficient.
Scope position is relevant in pancreatic cyst cases. Doing an EUS + CFA [Cyst Fluid Analysis] aids in the differentiation between mucinous and non-mucinous cysts and the identification of specific subtypes and high-risk stigmata for surgical evaluation.
There are several products in the market for doctors to choose from. They need to explore their options and find the product which works best for them.
Next Page: Patient Considerations