1. Endosonography
Tarek Almouradi, MD

2. Introduction
Diagnostic ultrasonography is a relatively recently developed technology
Initial reports began to appear in the late 1950s
Ultrasonography rapidly gained acceptance in the 1970s
As with any technology, diagnostic ultrasound has advantages and disadvantages
Reasonable portability
Relatively low cost
Lack of a need for ionizing radiation
Ability to perform real time imaging during both diagnostic and therapeutic interventions

3. Introduction
Soon after its introduction, several limitations of standard ultrasound became apparent
Ultrasound is unable to image deep to air-filled structures
Ultrasound is unable to image deep to extremely dense structures such as bone or calculi
As such, ultrasound is of little value in imaging the mediastinum due to the overlying, ribs, sternum, and adjacent lungs
Imaging of the pancreas and distal common bile duct is also greatly limited

4. Introduction
Another limitation occurs due to a basic principle of sound transmission
Higher resolution imaging requires the use of relatively high frequency sound energy
Unfortunately, higher frequency sound travels poorly through tissue (as evidenced by the booming bass sound coming from passing cars with loud stereos without audible treble tones)
In order to image structures far from the body surface, standard ultrasound requires the use of relatively low frequency energy (3.5–5 MHz), which as a result produces lower resolution images

5. Introduction
In an effort to overcome these limitations, endoscopic ultrasound and transesophageal echocardiography were developed in the early 1980s
By placing the ultrasound transducer within the body, it is possible to avoid air- filled or bony structures and reduce the distance between the transducer and the region of interest
As an example, a transducer placed in contact with the duodenal wall will be within 5 mm of the intrapancreatic portion of the distal common bile duct and avoids the interference caused by air in the duodenum, small bowel and colon.

6. The basics of Sonography
Ultrasound imaging relies upon the use of crystalline material with a unique property called the piezoelectric effect
These crystals vibrate in response to electrical stimulation and, as a result, produce sound
Different crystals produce sound of different frequencies
As important is the reverse phenomenon in which sound energy contacting the crystal will result in the production of electrical current
As a result, the crystals can simultaneously produce a sound beam and “listen” for the portions of this sound energy, which are reflected back to the surface of the crystal.

7. The basics of Sonography
Measurement of the time taken for energy to return allows a calculation of the distance to a given reflecting object
A computer can then display on a map the different locations which produced echoes
Regions which reflect a greater percentage of sound energy is displayed as brighter spots on the map.
Imaging with a single crystal will allow probing of a thin line (like a beam from a flashlight) extending from the crystal
By arranging hundreds to thousands of these crystals in an array, a wider region of tissue may be simultaneously imaged.

8. Echoendoscope design
Ultrasound imaging is currently available in two primary imaging planes determined by the orientation in which the individual crystals are arrayed on the echoendoscope.
Radial
Curved linear array

9. Echoendoscope design
Linear array imaging has one major advantage compared to radial array
A therapeutic device, such as a biopsy needle, will remain within the imaging beam
As a result, the entire length of a biopsy needle can be followed continuously as it is advanced through the bowel wall and into structures of interest
This degree of visualization is simply not possible with radial devices. A biopsy needle will pass through the imaging beam at roughly a right angle – resulting in a small echogenic spot on the ultrasound image

10. Echoendoscope design

11. Echoendoscope design
Radial array imaging may allow more expeditious screening of large portions of the GI tract wall
Linear imaging does not provide a 360° cross-section of the bowel wall surrounding the endoscope
The resulting blind-spot may be difficult to overcome in some locations without pressing on and distorting the
The blind spot also makes complete evaluation of the entire surface of circumferential GI tract tumors such as esophageal carcinoma somewhat limited with a linear device

12. Indications
Since the introduction of EUS in 1980, its indications and role have continued to expand
Diagnostic Imaging
Tumor Staging
Tissue Acquisition
Therapy

13. Diagnostic imaging
The endosonographic appearance alone may provide a confident diagnosis for certain lesions such as
Gut duplication cysts
Lipomas
Bile duct stones
Side branch intraductal papillary mucinous neoplasias (IPMN)
Follow-up imaging may be indicated when EUS demonstrates a benign-appearing lesion, to identify interval growth or other signs suggestive of malignancy

14. Chronic pancreatitis
The diagnosis of chronic pancreatitis can be challenging
Non specific symptoms
Causes both ductal and parenchymal changes, that can be difficult to detect using conventional imaging
CT and MRI rely mainly on main pancreatic duct dilation, moderate-sized cysts and calcifications, all of which are markers of severe disease
MRCP can make some further inferences regarding main pancreatic duct irregularity and the presence of dilated side branches; However, the resolution is often too poor to be accurate in this assessment when the ducts are not dilated

15. Chronic pancreatitis
In contrast, EUS can use parenchymal criteria in addition to ductal criteria to make a diagnosis of chronic pancreatitis
Smaller cysts and more subtly dilated or clubbed side branches are more reliably identified
Even calcifications a few millimeters in size can be readily identified as shadowing hyperechoic reflections.

16. Proposed Histologic Correlate
Rosemont criteria
EUS finding
Proposed Histologic Correlate
Hyperechoic duct margin
Periductal fibrosis
Irregular duct contour
Irregularity resulting from fibrosis
Hyperechoic foci and strands
Interlobular fibrosis, may also represent small calcifications not dense enough to cause an acoustic shadow
Hypoechoic lobules
Groupings of anatomic lobules with focal edema, inflammation, or atrophy, often encapsulated by
interlobular fibrosis
Shadowing hyperechoic foci
Stones and parenchymal calcifications

17. Chronic pancreatitis Normal (salt and pepper) Honeycombing lobularity
Shadowing and non shadowing hyperechoic foci

18. Tumor staging
Accurate staging is necessary to determine prognosis, to guide administration of chemo-radiation, and to select the ideal means and extent of resection when appropriate
Staging usually begins with noninvasive imaging such as computed tomography (CT), magnetic resonance imaging (MRI), which are generally superior to EUS for excluding distant metastases
In the absence of metastases, EUS is performed for T (tumor) and N (nodal) staging

19. T2 tumor invades into but not thru MP
Tumor staging
Normal gastric wall
T1 tumor invades SM
T2 tumor invades into but not thru MP
T3 tumor breaches MP

20. Nodal staging EUS provides important nodal staging information
The typical EUS characteristics of malignant lymph nodes are echo-poor appearance, round shape, smooth border, and size greater than 1 cm
Overlap in appearance between benign reactive and malignant lymph nodes makes nodal staging problematic, leading to over-staging of tumors
The addition of FNA improves nodal staging accuracy

21. Tumor staging
EUS has a limited role in establishing the presence or absence of distant metastasis (M stage)
Occasionally, a suspicious lesion is best approached for aspiration through EUS
A previously unsuspected metastasis is diagnosed during EUS performed for local staging (e.g., a liver lesion in a patient with pancreatic cancer)

22. Role of EUS in pancreatic tumors
EUS retains a key role in the evaluation of pancreatic masses for two reasons:
Its ability to detect abnormalities missed by CT (can identify small pancreatic tumors, small metastatic lesions that were not identified on CT, including left lobe liver metastases, perivascular cuffing by tumor, and malignant involvement of celiac ganglia)
Its capability to obtain tissue specimens during the examination, to differentiate adenocarcinoma from other neoplasms such as neuro-endocrine tumors or metastases, or benign conditions such as autoimmune pancreatitis, as these lesions cannot always be differentiated by clinical findings, imaging, and laboratory tests

23. Tissue acquisition
EUS often provides the least invasive and most successful route to obtaining tissue specimens
Compared to transabdominal ultrasound or CT-guided biopsy, EUS is favorable
Because of their poor sensitivity in the diagnosis of small lesions
Concern for potential tumor seeding of the biopsy needle tract
EUS is indicated for other reasons such as for loco-regional staging or celiac plexus neurolysis, FNA can be performed during the same examination, offering a cost-effective approach and simplified patient care

24. Therapy
The ability to pass a hollow needle under ultrasound guidance has expanded the applications of EUS
Celiac plexus neurolysis or block
Pseudocyst/Walled of necrosis drainage/Cyst-gastrostomy
Fine- needle injection to deliver therapeutic agents into solid pancreatic cancer
Drainage of other- wise inaccessible biliary and pancreatic ducts
embolization of bleeding gastric varices
Placement of fiducials to guide radiation therapy of pancreatic cancer
Trans-duodenal gallbladder drainage (Cholecystitis patients who are poor surgical candidates)

25. Contraindications Contraindications to EUS are very few
Unacceptable sedation risk
EUS FNA is generally contraindicated in the presence of
Coagulopathy (INR >1.5)
Thrombocytopenia (platelets <50,000)
Intervening structures prohibiting biopsy

26. Patient preparation
Initial planning and preparation for EUS of the upper and lower GI tract are similar to those for routine endoscopy and colonoscopy
Upper EUS is ideally performed following an overnight fast
At a minimum, patients should avoid solid foods for 6 hours and liquids for 4 hours before the procedure
When there is concern for incomplete gastric emptying as a result of dysmotility or obstruction, a 1 to 2 day of clear liquids may be advised
Retained gastric contents increase the risk of aspiration, may compromise acoustic coupling, produce image artifacts, and impair the overall examination quality

27. Patient preparation
Although some endosonographers perform rectal EUS after administering enemas alone, a full colon preparation is preferred
To optimize acoustic coupling
Minimize image artifacts
Rreduce infectious complications associated with FNA by decreasing intraluminal contents
More intense or prolonged efforts at cleansing the colon may be required in patients with chronic constipation or a recent barium examination

28. Patient preparation
Heavier sedation is often required for EUS compared to routine endoscopic procedures
longer examination time
Need to minimize movement of the patient while performing FNA

29. Laboratory studies
Current recommendations are based on extrapolation of surgical data
Demonstrated a lack of utility of routine preoperative studies such as hemoglobin level, blood crossmatching, routine chemistry, coagulation parameters, urinalysis, chest radiograph, and electrocardiogram for patients without evidence of relevant underlying disorders
Routine preoperative testing in healthy patients rarely identifies abnormal findings and does not predict or correlate with patient outcomes
An exception is women of childbearing age

30. Medications
Patients are instructed to continue their cardiac, antihypertensive, pulmonary, antiepileptic, psychiatric, and contraceptive medications.
These medications are ingested with sips of water early on the day of the procedure.
Diabetic patients are advised to take half of their morning insulin dose at the usual time and the remaining dose with a postprocedure meal.
Oral hypoglycemic agents are withheld the morning of the procedure and until resumption of a normal diet

31. Anticoagulants and antiplatelet agents
The ASGE classified procedures as either high risk or low risk depending on the likelihood of inducing bleeding
EUS without FNA is regarded as a low- risk procedure
Although patients undergoing EUS FNA are not believed to be at increased risk of bleeding, EUS FNA is considered a high-risk procedure because resulting bleeding is inaccessible or uncontrollable by endoscopic means
Patients’ conditions are classified as high risk or low risk based on the likelihood of developing a thromboembolic event

32. Anticoagulants and antiplatelet agents
High risk
Low risk
Atrial fibrillation (with valve disease)
Atrial fibrillation (without valve disease)
Mechanical valve
Bio prosthetic valve
Deep venous thrombosis

33. Anticoagulants and antiplatelet agents
Warfarin:
low risk patients: Hold 5 days before procedure, resume after
High risk patients: Consider heparin drip
Aspirin: Do not stop
Clopidogrel: Stop 7 days prior if FNA is planned
Low molecular weight heparin: Stop at least 8 hours before procedure

34. Risks and complications
EUS shares the risks and complications of other endoscopic procedures
Cardiovascular events
Complications of conscious sedation
Allergic reactions to medications

35. Perforation Reported risk is around 0.4%
The increased risk is related to echoendoscope design, which combines oblique or side-viewing optics with a relatively long rigid tip that extends well beyond the optical lens
The tip of the endoscope may cause luminal perforation during advancement, particularly in areas of angulation (oropharynx or apex of duodenal bulb), stenosis (esophageal cancer), or a blind lumen (pharyngeal or esophageal diverticula)
High risk patients include age >65 years, history of swallowing difficulties, known cervical osteophytes, kyphosis of the spine, or hyperextension of the neck

36. Bleeding
Mainly related to the performance of FNA, with reported risk around 0.4%
A small amount of luminal bleeding is often seen endoscopically at FNA puncture sites, but it is generally without sequelae
Bleeding may also occur in the gut wall, adjacent tissue, or target structure undergoing aspiration
EUS-induced extraluminal bleeding is seldom associated with clinically important sequelae such as need for transfusion, angiography, or surgical intervention
Bleeding usually occurs from small vessels since endosonographers are trained to avoid sonographically visible vessels when selecting a needle path for FNA

37. Infection
Reported risk is about 0.3% and it includes infections associated with the endoscopy itself (aspiration pneumonia) or with FNA
9% rate of infection has been reported after EUS FNA of cysts
Risk is markedly decreased by antibiotic administration before and after EUS FNA
Increased risk with multiple needle passes into a cyst, failure to completely aspirate the cyst fluid

38. Pancreatitis
The risk of pancreatitis after EUS FNA of solid pancreatic lesions is 0.3%-0.6%
Aspiration of cystic lesions has been associated with pancreatitis in 1% to 2%
The risk of pancreatitis may be reduced by
limiting the number of needle passes
Minimizing the amount of "normal" pancreatic parenchyma that must be traversed
Avoiding the pancreatic duct during EUS FNA procedures

39. Other complications Tumor seeding along the needle tract
This risk is of minimal concern for pancreatic lesions because of inclusion of the needle tract site within the field of resection
Bile peritonitis from traversal of bile duct of gallbladder of especially in the presence of an obstructed biliary system
Missed or miss taged lesions

40. In conclusion
Endoscopic ultrasound is a safe procedure with evolving diagnostic and therapeutic applications, helping new generation endoscopists push the former boundaries of endoscopy

41. Questions