A diagnostic marriage

Endoscopic ultrasound (EUS) has become an important diagnostic method for evaluating and staging a multiplicity of cancers of the GI tract. Staging of a tumor in the GI tract is determined by following standardized criteria that include assessing the depth of penetration of a tumor through the gastrointestinal wall, the involvement of adjacent lymph nodes, and spread of the tumor to distant organs, such as the liver. Many cancers, including those of the GI tract, are staged via the TNM Classification of cancer, formulated by the American Joint Committee on Cancer. Staging ranges from 0 to 4, with Stage 0 being a precancerous condition and Stage 4 being metastatic disease.¹

EUS is the combination of two medically diagnostic techniques — endoscopy and ultrasound. The marriage of these two techniques, an imaging of the body’s inner wall layers combined with an endoscope’s maneuverability, enhances the physician’s ability to accurately stage gastrointestinal tumors by as much as 89% to 90%.² Ultrasound enables the endoscopist to use sound waves to generate an image of the transmural anatomy on a monitor. It allows the placement of high-frequency transducers close to the intestinal wall and adjacent structures.³ The procedure generates images of the individual layers of the walls of the digestive tract, as well as pictures of the underlying blood vessels, lymph nodes, pancreas, liver, gallbladder, and bile ducts, during a relatively noninvasive procedure. In essence, the EUS technique involves manipulating sound waves to view the inside of the body. In this way it is like an X-ray, but one with no radiation.

The technique used in an EUS is comparable to the one used in an upper endoscopy. In both, a flexible scope, either an endoscope or an echoendoscope, is passed through the oral cavity into the esophagus and the stomach. While the endoscope, which has a camera at its tip, generates a visual view of the gastrointestinal tract from the inside out, the echoendoscope uses sound waves to create a picture of the inside of the body.

This combination of endoscopic ultrasound and FNA to visualize and biopsy tumors enables physicians to see beyond the structures that historically limited their view. A diagnosis that in the past would have required conventional surgery can now be performed on an outpatient basis. The results: reduced pain and recovery time for the patient. At the same time, it allows for considerable cost savings to both the institution and the patient for a much less invasive diagnostic procedure.

EUS can be used to detect small pancreatic tumors and to stage esophageal, gastric, pancreatic, rectal, and lung cancers, as well as tumors of the extrahepatic bile ducts and the ampulla of Vater, the dilatation formed by the junction of the common bile duct and the pancreatic duct proximal to their opening into the duodenum. In addition, EUS can be used to aid in the assessment of benign gastric wall tumors and to evaluate inflammatory pancreatic diseases and cysts, gallbladder stones, and liver tumors.

In its third decade of use, EUS is becoming an important diagnostic tool in the evaluation of such benign diseases as chronic pancreatitis and submucosal masses (nodules in the GI wall covered by normal intestinal tract lining) and in the evaluation of the muscles of the lower rectum and anal canal to determine causes of fecal incontinence.

Esophageal cancer is diagnosed in about 12,300 patients yearly in the United States.⁶ Five-year survival rates are low because the disease is frequently diagnosed at an advanced stage. EUS becomes important in tumor staging at an early stage and may help determine appropriate treatment options for the stage of the cancer at the time of its diagnosis. Historically, staging has been performed via CT scans, but historically their accuracy rate in assessing the depth of tumor invasion has been poor. The overall accuracy of EUS in locoregional staging has exceeded 80% compared to slightly more than 40% with CT scan.⁷

Because ultrasound waves do not penetrate deeply into tissues, an EUS cannot give in-depth information about a tumor’s spread to distant organs. However, it is extremely accurate in evaluating the tumor involvement, or lack of it, through the layers of the gut wall and the surrounding lymph nodes. It can provide detailed information about whether the tumor has spread into nearby blood vessels and is a determining factor in planning treatment options for patients with esophageal, gastric, and rectal cancers.

EUS has been found to be an accurate diagnostic tool in evaluating and staging pancreatic cancers and pancreatic neuroendocrine tumors. Pancreatic cancer is extremely aggressive and ranks among the leading causes of cancer-related deaths. EUS has been shown to be superior to CT scan and MRI in the diagnosis and staging of early pancreatic cancer. An EUS-guided biopsy has been shown to be safer and more definitive than a CT scan-guided biopsy.⁸ The most important factor to determine after the diagnosis itself is whether the cancer is surgically resectable. This can be done by determining the involvement of adjacent vascular or retroperitoneal structures, as well as the presence of distant metastases. All of the above generally are considered to constitute unresectability and to preclude an operation. Although this is readily done with EUS, at present this information is being provided by high-quality CT scanning.

The rectum is the site of about one-third of all colorectal malignancies .⁹ Staging provides information to determine the optimal type of surgery and coordinating therapies, such as chemotherapy and radiation. EUS has become a useful tool in the pretreatment staging of rectal cancers. Tumors that appear to be superficial can be removed with transanal excision. Deeper tumors and those with suspected lymph node metastases can be treated with presurgical chemotherapy and radiation.

EUS also has been used to guide endoscopic drainage of pancreatic pseudocysts, helping the endoscopist to determine the best puncture site, delineating vessels along the path of the needle and solid material within the cyst itself. Additionally, in patients with severe and chronic abdominal pain secondary to pancreatitis, it is sometimes possible to perform a nerve block (neurolysis) under EUS guidance for pain management.

An EUS also can assist in accurately staging lung cancer, again as an alternative to more invasive diagnostic modalities such as surgery. This has been documented via EUS-guided FNAs of adrenal and periesophageal nodes and nodules. It is an important tool in determining the course of treatment.

Meet the echoendoscope

Endoscopes used in the endoscopic ultrasound procedure (echoendoscopes) fall into three major categories — radial echoendoscopes, linear array echoendoscopes, and endoscopic probes. All use sound waves to image tissue consistency and the interfaces between tissue planes.¹⁰ The frequencies used in these scopes are higher than those used in conventional ultrasound technologies (transabdominal). The higher the frequency of the sound waves, the better the definition of the anatomy being analyzed, but the lower the penetration, and vice versa. Therefore, the echoendoscope gives the physician a high level of accuracy in determining the depth of local invasion of a cancerous tumor (T stage).⁶

The radial echoendoscope has a rotating ultrasound probe at its tip. Images are obtained in 270 degrees or 360 degrees of a circumference perpendicular to the endoscopic tip. However, in the radial scope, guidance for a needle aspiration is not available.¹⁰

The linear array echoendoscope also has an ultrasound probe at its tip, and images are obtained along a plane parallel to the endoscope axis. It has a channel that allows the passage of a needle for FNA. This additional capability allows the scope to increase the specificity of the diagnosis. These scopes have Doppler ultrasound capability as well, providing guidance to prevent the needle from injuring vascular structures during FNAs.¹¹

Ultrasound probes are thin and must be advanced through the channel of a regular endoscope. These probes generally provide a high-resolution circumferential view along the same plane as the radial echoendoscope.⁶

The needs of the patient

From the patient’s viewpoint, an EUS is much like an upper endoscopy although an EUS can take longer. Preparation is the same. Patients receive IV sedation/analgesia and must be NPO after midnight or, at a minimum, for six hours before the exam. They will be asked to take any medications they usually take for hypertension, cardiac disease, pain, or seizures in the morning with a sip of water. They must have a family member or friend with them who will be able to bring them home.

If there is a possibility that the physician will do an FNA during the procedure, bloodwork will be drawn for coagulation studies. Blood thinners such as warfarin sodium (Coumadin) and heparin sodium (Heparin) as well as aspirin and aspirin-type products must be stopped several days before the procedure because they all can cause a potential bleeding hazard during an FNA.

The facilitator — the role of the nurse

The primary role of the nurse during an endoscopic ultrasound procedure is to build a communication bridge between the patient, the physician, and the other health care professionals present. Preprocedure, the nurse discusses the procedure with patients, assesses their expectations, and addresses their concerns. During the procedure, the nurse monitors the vital signs as he or she is assessing the patient for comfort and stability — this imperative function being the nurse’s only priority and responsibility intraprocedurally. Postprocedure, the nurse reports patient- and procedure-oriented events to the recovery room nurse at the time of transfer of care in order to ensure continuity of care.

A procedure nurse or technician assists the physician with all of the technical aspects of the procedure. The procedure nurse or technician is responsible for setting up the room, preparing and cleaning the scopes, assembling the accessories required for the procedure, and assisting the physician during the procedure as required. He or she is also responsible for specimen collection and disposition. This becomes especially important during an FNA as many hands are required to manipulate the scope, the ultrasound image, and the long-aspiration needle.

The risks and drawbacks

Much the same as other endoscopic procedures, EUS is a relatively safe procedure and well tolerated by most patients. However, it is not without risk. A patient might have a reaction to the sedating medication, which could cause reactions ranging from nausea and vomiting to a rash and hives. An IV may infiltrate and cause local swelling and pain at the site of insertion, not to mention interfering with safe and appropriate sedation levels.

For patients having an EUS without an FNA or other invasive intervention, specific complications attributable to the procedure are about one in 2,000 (0.05%) cases, similar to the complication rate of upper endoscopy and flexible sigmoidoscopies.¹² The most significant complication is perforation of the esophagus or the stomach, which can occur during endoscopic manipulation of the echoendoscope. Perforations can be treated medically or surgically, but all require hospital admission. Medical treatment includes antibiotics and IV fluids, but most perforations require surgical repair. Perforation, however, is extremely rare. Some patients — such as those with large obstructing tumors of the esophagus requiring dilation (stretching) before or during the procedure — have a predisposition for the possibility of a perforation.

When an FNA is performed, complications may occur more often, but are still rare (0.5% to 1%).¹² Passing the needle into the targeted tissue may cause bleeding. Infection is another rare complication. This is more likely in patients who have an aspiration of a cystic lesion (fluid-filled), such as those in the pancreas. On rare occasions, acute pancreatitis will develop after a biopsy of the pancreas. Acute pancreatitis may require a hospital admission for observation, IV fluids, and pain relief and resolves spontaneously in several days.

It takes time and practice for physicians to master the EUS/FNA procedure. Despite the introduction of the technique into the United States decades ago, relatively few institutions across the country perform it on a large scale. The reasons include the high cost of the equipment, the long learning curve, the lack of sufficient training for physicians, and a multiple number of competing technologies for the diagnostic outcome — extracorporeal ultrasound, CT scan, and MRI.⁴ As one gastroenterologist explained, “It’s not something that you can take a weekend workshop and go and do.”⁴

Recent advances

EUS has become the most accurate means of staging GI, retroperitoneal, and mediastinal malignancies in recent years. Primarily used as a passive imaging device in the past, it’s now evolving into an interventional technique as well. A dramatic evolution in endoscopic design has occurred, which provides both high-quality ultrasound imaging and allows for EUS-guided needle biopsy. This has expanded the scope of the technique, most notably to the pancreas and the extrahepatic biliary system.¹³ It has also increased the use of FNA as a mean of obtaining specimens for cytology and tissue diagnosis, primarily in the diagnosis and staging of pancreatic cancer, and in the nodal staging of gastrointestinal and pulmonary malignancies. Recently introduced therapeutic EUS is based primarily upon precise endoscopic needle placement under EUS guidance. Therapeutic EUS can be used for pseudocyst drainage, the injection of botulinum toxin in the treatment of achalasia (an esophageal motility disorder), and celiac nerve block.¹⁴

A look into the future

Advances in endoscopic technology have transformed diagnostics and therapeutics in gastroenterology. As the technology continues to evolve, EUS will become a more mainstream diagnostic tool, ultimately leading to improved patient outcomes. The first of these innovations may be the development of an echoendoscope that combines the functions of radial imaging views, linear imaging views, FNA, and interventional techniques. Now, different equipment, is required for each diagnostic or therapeutic technique. Although the radially oriented image is the easiest one to interpret and provides the best orientation for imaging, the radial echoendoscope cannot support such diagnostic techniques as FNA. The linear array echoendoscope is the best scope with which to perform an FNA, but affords a limited field of view, making it time-consuming and more difficult to interpret results. Additionally, the EUS procedure is essentially restricted at the present to large tertiary centers, primarily due to its prohibitively long learning curve and the high cost of equipment. With increasing refinements to echoendoscopes and the development of more training programs, endoscopic ultrasound will become a major diagnostic and therapeutic technique in the treatment of patients diagnosed with cancer and, perhaps, for noncancer applications as well.