Endoscopic ultrasound - A key mode of assessing the gastrointestinal tract

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Endoscopic ultrasound (EUS) is a procedure that combines endoscopy and ultrasound. High frequency transducers are mounted at the end of the endoscope producing clear, detailed images of the gastro intestinal wall layers and surrounding organs (pancreas, liver, kidney, spleen). With the touch of a button the image can switch from endoscopic view to ultrasound view. It is a truly revolutionary tool as no other imaging method can reveal the gut wall from oesophagus to rectum as a series of histological correlates, writes Dr Alina Stoita.

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With EUS frequencies of 5-30 MHz, the intestinal wall is imaged as a multilayered structure, corresponding to mucosa, submucosa, muscularis propria and serosa respectively. This has tremendous relevance to gastrointestinal cancer staging and determining the nature of submucosal lesions. EUS allows fine needle biopsies to be taken through the endoscope in a minimally invasive way to diagnose tumours in the mediastinum, pancreas, liver, lymph nodes. Most of the time the needle tract is within the resection specimen and the risk of complications and tumour seeding is very low.
EUS is performed as an outpatient procedure under conscious sedation. From a patient’s perspective it is similar to having an endoscopy and requires only six hours of fasting prior to the procedure. EUS is usually performed by gastroenterologists who undertook further training in endoscopic ultrasound and are accredited by Gastroenterological Society of Australia (GESA). It is a safe procedure with a safety profile similar to endoscopy.
There are two types of echoendoscopes available depending of the study requited:

• Radial EUS  scanner (7.5- 20 MHz) provides a 360 degree view orientated perpendicular to the tip of the endoscope  similar to the images obtained at computer tomograph (CT). It has Doppler capabilities.


• Linear EUS provides 110 degree scanning in the same plane as the long axis of the endoscope and allows real time EUS guided fine needle aspiration biopsy of the lesions in the gastrointestinal wall, pancreas, liver and lymph nodes. It has Doppler capabilities and is the instrument used in therapeutic procedures such as draining pseudocysts and coeliac plexus block.

EUS is a key investigation in all gastro intestinal malignancies. EUS allows more precise diagnosis of tumours using TNM system as it can clearly see the level of tumour invasion as well as loco regional lymph nodes and vascular involvement.  Accurate staging allows selection of the most appropriate treatment and influences prognosis.
EUS allows delivery of personalised medicine and many times the type of treatment is influenced by the EUS result.  For example, a patient with oesophageal cancer had an EUS that showed an abnormal lymph node away from the tumor. This lymph node was only 8mm and was not seen on CT. The node was biopsied under EUS and proved malignant and as the result the patient underwent radiotherapy with a larger field than anticipated that incorporated the malignant LN.
Indications for EUS (table 1 and 2)
Pancreatic lesions
Pancreatic cancer is usually diagnosed in advanced stages and despite progress in medicine the mortality for pancreatic cancer has not changed for decades, Pancreas is an organ difficult to see on trans-abdominal ultrasound and CT can usually detect only lesions bigger than 1.5 cm. Thus EUS has become the examination of choice for the pancreas and it has been shown to be the best modality to assess smaller lesions when compared to CT and MRI ¹. EUS allows loco regional staging of pancreatic cancer and can assess vascular involvement thus preventing unnecessary surgery. A recent meta-analysis showed that EUS has a sensitivity of 89 per cent and specificity of 96 per cent for pancreatic cancer ². Not all pancreatic masses are cancer and sometimes lymphoma and autoimmune pancreatitis can present as a mass. EUS FNA provides the best modality to diagnose these masses thus preventing surgery in these cases. EUS allows better characterization of incidental pancreatic cysts (some are premalignant), diagnosis of neuroenedocrine tumour and assessing chronic pancreatitis.
In patients with unexplained acute pancreatitis EUS was able to find a cause in 80 per cent of patients, with gallbladder sludge/small stones detected in 40 per cent of patients that otherwise were missed by other modalities.³ A recent study showed that in patients after cholecystectomy the first line of investigation for abdominal pain should be endoscopic ultrasound as 10 per cent of patient were found to have residual stones in cystic duct or common bile duct previously missed by other imaging modalities.⁴ In patients with low or moderate risk of common bile duct stone, EUS has become the standard procedure and is recommended before ERCP is performed.
Endoscopy and EUS are the most accurate imaging modalities for ampullary tumour detection. EUS is more accurate than CT and MRI for staging ampulla cancers but accurancy may be diminished in the presence of a biliary stent.

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“EUS allows delivery of personalised medicine and many times the  type of treatment is influenced  by the EUS result.”  
DR ALINA STOITA

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EUS FNA in non small cell lung cancer is used for posterior mediastinal lymph nodal staging  and  assessment of PET positive lymph nodes. Most importantly EUS allows selection of patients that would benefit from neoadjuvant therapy before surgery.  EUS together with endoscopic bronchial ultrasound (ultrasound at the end of the bronchoscope) allows complete mediastinal nodal staging with a reported 93 per cent sensitivity and 100 per cent specificity   This way we can deliver better care by avoiding unnecessary mediastinoscopies and thracotomies and reducing costs⁵.
In oesophageal cancer, EUS is superior to CT and PET in peritumoral and coeliac axis lymph node detection.⁶ EUS can stage stomach cancer with a sensitivity 85 per cent and specificity of 91 per cent for T staging but this decreases for regional lymph nodes ⁷.If the lesion extends only in the mucosa layer then endoscopic mucosa resection (EMR) is the treatment of choice rather than gastrectomy.
Submucosal lesions is a term used to describe any bulge covered by the normal mucosa  usually found incidentally at endosocopy. EUS is the modality of choice to investigate these lesions as the ultrasound is immediately near the lesion and it can see the layer of origin ( mucosa, submucosa , muscularis) or can tell if it’s an extrinsic compression . The internal echo characteristic give clues to the diagnosis, for example lipomas are ‘bright’ and if larger than 1 cm the submucosal lesion can be biopsied. Some of these submucosal lesions have malignant potential (such as a GIST-gastrointestinal tumour) and is important to establish a diagnosis.  The accuracy of EUS FNA is between 50-93 per cent depending in the size of the lesion, needle size and type.⁸
EUS is a fast evolving field with contrast enhanced EUS ⁹ and Elastography ¹⁰ (to assess tissue stiffness) finding its place more in day-to-day practice to increase the diagnostic accuracy of standard EUS. EUS guided injection of anti tumoral therapy remains promising¹¹ but the key is finding an efficacious and safe agent. EUS can also be used to tattoo small lesions so it’s easier to find them at surgery or place fiducials (radiographic markers) to allow precise delivery of radiotherapy.
EUS should be incorporated in the best clinical practice in staging and diagnosis of gastrointestinal malignancies. Each hospital who treats gastrointestinal malignancy should have streamlined access to an endoscopic ultrasound service to improve CT staging of the disease and provide most appropriate treatment thus improving outcome for their patients. This will be a cost effective process as studies have shown that adding EUS in staging for pancreatic cancer prevents unnecessary surgeries and potential complications and saves money ¹².

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“EUS is a fast evolving field with contrast enhanced EUS   and Elastography  ( to assess tissue stiffness) finding its place more in day-to-day practice to increase the diagnostic accuracy of standard EUS.”  
DR ALINA STOITA

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TABLE 1
MAIN INDICATIONS OF  ENDOSCOPIC ULTRASOUND
PANCREAS

• diagnosis and staging of pancreatic cancer


• assessment of pancreatic cysts


• diagnosis of  neuroendocrine tumours


• evaluate chronic pancreatitis

BILIARY TREE

• diagnosis of gallstones and common bile duct stones


• diagnosis and staging of cholangiocarcinoma


• ampullary lesions

OESOPHAGEAL, STOMACH AND  RECTAL CANCER

• STAGING

SUBMUCOSAL LESIONS  (oesophageal,  gastric and rectal)

•  diagnosis

MEDIASTINUM

• diagnosis of mediastinal mass ( lymphoma, TB)


• staging of lung cancer based on lymph nodes involved

TABLE 2
INTERVENTIONAL EUS

• Pseudo cyst drainage


• Coeliac plexus block and neuroloysis for severe pain


• Hepatico gastrostomy


• Pancreatico gastrostomy


• Abscess drainage

Dr Alina Stoita
MBBS(Hons) FRACP
Gastroenterologist,  St Vincent’s Public and Private Hospital Sydney
Dr Alina Stoita has expertise in endoscopy, colonoscopy, endoscopic ultrasound and capsule endoscopy. Her interests include early detection of bowel cancer, oesophageal, gastric and pancreatic cancer.  She has developed the first Australian pancreatic cancer screening program in high risk individuals using endoscopic ultrasound.

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References

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2. Ge Chen1, Shanglong Liu1, Yupei Zhao, et all. Diagnostic accuracy of endoscopic ultrasound- guided fine-needle aspiration for pancreatic cancer: A meta-analysis. Pancreatology 2013; Vol 13, Issue 3, Pages 298–304.


3. Frossard JL, Sosa-Valencia L, Amouyal G, et all. Usefulness of endoscopic ultrasonography in patients with  “idiopathic “ acute pancreatitis. Am J Med 2000; 109: 196-200.


4. Endoscopy 2014


5. Annema JT, Versteegh MI, Veselic M et al. Endoscopic ultrasound  added to mediastinoscopy for preoperative staging bof patients with lung cancer. JAMA 2005; 294:931-936.


6. Akdamar M, Cerfolio R, Ojha B, et al. A prospective comparison of computerized tomography (CT), 18 fluoro deoxyglucose positron emission tomography (FDG-PET) and endoscopic ultrasonography (EUS)  in the preoperative evaluation of potentially resectable esophageal cancers.  Am J Gastroenterol 2005; 98:s5.


7. Mocellin, S., Marchet, A., and Nitti, D. EUS for the Staging of Gastric Cancer: A Meta-Analysis. Gastrointest. Endosc. 2011; 73: 1122–1134


8. Ioannis S Papanikolaou,Thomas Rösch et all. Endoscopic ultrasonography for gastric submucosal lesion. World J Gastrointest Endosc. May 16, 2011; 3(5): 86–94.


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10. ASGE Technology Committee “ Report on enhanced ultrasound techniques” GASTROINTESTINAL ENDOSCOPY Volume 73,  No. 5 : 2011 857


11. Farrell JJ, Senzer N, Hechy JR , et all.  Longg term data for endoscopic ultrasound percutaneous guided intratumoural  TN-Ferade gene delivery combined with chemoradiation in the treatment of locally advanced pancreatic cancer.Gast Endosc 2006;63: AB93


12. 
    Harewood GC & Wiersema MJ. A cost analysis of endoscopic ultrasound in the evaluation of pancreatic head carcinoma. Am J Gastroenterol 2001;96:2651-6