Keywords
endosonography - pancreas - anatomy - education - diagnostic imaging
Introduction
Endoscopic ultrasound (EUS) can be performed by a radial or linear echoendoscope.
The radial echoendoscope provides a 360-degree view, while the scanning range of a
curved linear array echoendoscope varies from 120 to 180 degrees.[1] Therefore, a curved linear array echoendoscope should be rotated either in a clockwise
or an anticlockwise direction to obtain a complete view of the structure.
A thorough understanding of the anatomy is vital when performing an EUS. Initially,
it can be quite challenging to understand the anatomy; however, some basic steps should
be followed before and during EUS training to master the techniques of EUS ([Table 1]).[2]
[3]
Table 1
Beginner's guide for starting endoscopic ultrasound (EUS)
|
1
|
Be well acquainted with cross-sectional imaging
|
|
2
|
Read and watch educational materials on the basics of EUS
|
|
3
|
Participate in EUS hands-on training program on animal or simulator models
|
|
4
|
Learn how to handle the scope and understand the knob movements
|
|
5
|
Understand the terminology used in EUS; clockwise and anticlockwise movements, and
big knob movements (terminologies used here are downward big knob movements—toward
you; upward—away from you)
|
|
6
|
Understand the orientation during EUS examination
|
|
7
|
The first step is identification of structures
|
|
8
|
Focus on easily accessible structures, such as the aorta and the left lobe of the
liver
|
|
9
|
Find a homebase at a particular station
|
|
10
|
Learn about one structure and one station at a time
|
|
11
|
Record your own videos and label the structures within them, and later confirm the
labeling with mentors or collogues
|
|
12
|
Identify what is normal first, and then know and focus on abnormal pathology
|
|
13
|
Discuss difficulties with peer group and mentor, and try to resolve them
|
|
14
|
Practice daily and repeat all the above-mentioned steps. This is the key to mastering
EUS
|
Basic Principles of EUS Examination
Basic Principles of EUS Examination
It is imperative to understand the orientation during a linear EUS examination, and
for that it is essential to follow the station-wise approach. It is pivotal to carefully
observe and interpret the EUS image. The position and direction of the transducer
can be determined by the EUS image. For instance, when the descending aorta or pancreas
is visible on the screen, it means the transducer is facing posteriorly. Conversely,
when the left lobe of the liver or the heart is seen on the screen, it means the transducer
is facing anteriorly.[4] Once the orientation and position of the transducer are comprehended, the specific
maneuvers required to locate the organ of interest can be determined automatically.
Different terminologies are used during EUS maneuvering ([Fig. 1]) and it is essential for the endoscopist to know these terminologies while performing
an EUS. In conjunction with clockwise and anticlockwise torquing of the scope, minimal
push and pull movements of the scope are required to precisely locate a specific organ.
For instance, at the gastroesophageal (GE) junction when aorta and celiac artery (CA)
are visible, the echoendoscope should be pushed down minimally to locate the pancreas.
But why is it necessary to push down the scope? As the pancreas is located below the
origin of the CA, the scope must be pushed down to view the pancreas. Another way
to learn is by conducting “trial and error” exercises, such as which structures can
be viewed and why, based on specific movements at particular stations. This way, you
can learn the specific movements required to obtain the desired images.
Fig. 1 Terminology used while performing endoscopic ultrasound (EUS). (A) Big knob down (toward you) and big knob up (away from you). (B) Clockwise rotation (along the clock direction) and anticlockwise rotation (against
the clock direction).
In the beginning, an endoscopist may have difficulty in handling the scope, removing
the artifacts, and obtaining good images at a particular station. Here are a few steps
to overcome these difficulties:
-
Familiarize yourself with the scope: Learn the proper grip and movements to obtain optimal imaging. Hold the scope straight
and avoid excessive twisting of the scope and pushing against resistance while maneuvering.
-
Do not rely on the measurement numbers on the scope to determine the position of the
scope; use the EUS image instead. From the beginning, make a practice of predicting
the location by observing the EUS image. For example, if you see the left atria and
the right pulmonary artery (subcarinal space) on the EUS image, it means the echoendoscope
is in the mid-esophagus.
-
The endoscopic view and EUS image do not corelate. The EUS transducer is placed distal
to the camera (∼1–1.5 cm). If you see the pyloric ring on the endoscopic view, it
means the transducer has already crossed the pylorus and it is in the duodenal bulb.
Endoscopic vision should be used to navigate the scope from one place to another to
avoid untoward complications.
-
Artifacts recognition and reduction: Air is the enemy of ultrasound and can interfere in imaging. Air artifacts can be
removed by suctioning the air, keeping mucosal tissue and transducer approximation
by using the big knob, and water immersion. Avoid unnecessary air insufflation of
the lumen while scanning.
-
Rule of 360 degrees: Linear EUS scanning range varies from 120 to 180 degrees. To get the complete image,
an extra 180-degree rotation is required and this can be achieved by a clockwise and
an anticlockwise rotation. To see the structure from one particular point, do either
a 270-degree clockwise rotation or a 90-degree anticlockwise rotation ([Fig. 2]). For example, from the GE junction, the spleen can be visualized on clockwise rotation
while tracing the pancreas (270 degrees); however, it can also be seen from the left
lobe of the liver on anticlockwise rotation (90 degrees).
-
Tracing of structure: To trace a structure, first bring it to the center of the screen (around the 6 o'clock
position) and then perform a clockwise or anticlockwise rotation to trace it ([Fig. 3]). If the structure is located at the extreme right or left of the screen, tracing
it can be challenging. In such instances, utilize a combination of movements along
with minimal pull/push movements to bring the structure into the center of the screen.
-
Vessels: Identifying vessels (with name) has diagnostic and therapeutic importance. Vessels
must be traced from the origin until the end or it branches. Veins (oval shaped) change
their shape during the course and on compression, while arteries (usually round/tubular)
maintain their shape.
-
Imaging from stomach: Suck all the air out of the stomach until its wall gets collapsed onto the transducer,
and follow a station-wise approach. In the stomach, on clockwise rotation the left-sided
structures are visible, and on anticlockwise rotation, the right-sided structures
are visible. While scanning from the GE junction, sometimes resistance can be felt
on clockwise movement. It is typically due to the echoendoscope hitting the lesser
curvature. At that point, switch to the endoscopic view, torque the scope in an anticlockwise
direction, and push the scope into the proximal body.
-
Imaging from the duodenal bulb: Duodenal intubation should be done under endoscopic visualization. If crossing the
pylorus is difficult, the scope should be pulled/pushed two to three times from the
body-antrum. With this maneuver, the stomach remodels and allows smooth entry into
the duodenal bulb. The duodenal bulb is a compact space and many structures are visualized.
These structures easily get compressed with the transducer. To improve visualization
of these structures, it is advisable to instill some water, release the pressure on
the big knob, and trace the structure with fine clockwise and anticlockwise movements.
-
Duodenal part 2: Unlike the shortening of a duodenoscope during endoscopic retrograde cholangiopancreatography,
shortening of an echoendoscope should be started from the bulb to facilitate entry
of the scope into D2 under endoscopic vision. Never push the scope against the resistance
at the D1–D2 junction. To shorten the scope, rotate the small wheel to the right and
torque the shaft of the scope in a clockwise direction. In D2, suck out the air and
fill it with water as water helps in better acoustic coupling and also helps in stabilization
of the scope.
-
Image optimization: It is an important part of an EUS examination. Understand the different controls
and settings on the ultrasound machine to optimize image quality. Adjust parameters
such as gain, contrast, depth, frequency, and focus to obtain a clear and detailed
image.
Fig. 2 Schematic diagram explaining the rotation required during linear endoscopic ultrasound
(EUS) examination: point B can be traced from point A by a 270-degree clockwise rotation
or a 90-degree anticlockwise rotation.
Fig. 3 Tracing structures during endoscopic ultrasound (EUS) examination. (A) Schematic diagram showing vessels on the left side of the screen. (B) The echoendoscope must be pushed down to bring the vessels into the center of the
screen. From here, the vessels can be traced back and forth. (C) A representative EUS image showing splenic vessels and pancreas are seen on left
of the screen. (D) A representative EUS image shows that the pancreas was brought into the center of
the image by pushing the echoendoscope down. From this point, tracing the entire pancreas
will be easier.
Station-Wise Approach for Pancreas Examination
Station-Wise Approach for Pancreas Examination
The pancreas can be visualized from the stomach, duodenal bulb, and descending duodenum
([Fig. 4;]
[Video 1]).[5]
[6]
[7]
[8] Although the entire pancreas can be visualized from the stomach, it is essential
to scan from all stations.[9]
[10] Finding the homebase at a particular station to trace the pancreas is crucial.[11] The normal pancreas echotexture on EUS is described as “salt and pepper” appearance.
Embryological variation makes the echotexture of the pancreas different for the ventral
pancreas (hypoechoic) and dorsal pancreas (hyperechoic). The ventral pancreas forms
the posterior part of the head and uncinate process, while the dorsal pancreas forms
the anterior part of the head, genu, body, and tail ([Fig. 5]).[12] Although slight variation in anatomy and echotexture can occur from person to person,
a station-wise approach should be followed for a complete examination.
Fig. 4 A station-wise approach for complete pancreas examination and parts of pancreas seen
from different stations.
Video 1 Station-wise examination of the pancreas with curved linear array echoendoscope
Fig. 5 Parts of the pancreas with embryological variation in echotexture. (A) Schematic diagram showing different parts of the pancreas with embryological variation.
(B) A representative endoscopic ultrasound (EUS) image showing hypoechoic ventral pancreas
and hyperechoic dorsal pancreas.
Examination of the Pancreas from the Stomach
Examination of the Pancreas from the Stomach
The pancreas can be located from the stomach using two methods: (1) from the GE junction
by locating the CA or the liver hilum using the push method and (2) from the body
of the stomach by finding the portal vein confluence (PVC) using the pull method.[7]
[11]
GE Junction (the Push Method)
GE Junction (the Push Method)
By Locating the Celiac Artery
The aorta is the homebase to locate the pancreas from the GE junction. At the GE junction,
the left lobe of the liver is visible on the EUS view in the neutral position. Once
the left lobe of the liver is visible, rotate the scope in clockwise direction to
visualize the umbilical portion of the left portal vein (LPV). On further clockwise
rotation (>45 degrees) from the LPV, the intrahepatic inferior vena cava (IVC) will
be seen. Once the IVC is seen, rotate the scope again in clockwise direction to see
the aorta. At the GE junction, anterior to the aorta, a hypoechoic linear structure
can be observed, which corresponds to the crus of the diaphragm. Once the aorta is
visible, push the echoendoscope slightly to see the CA ([Fig. 6]). In the same plane, the splenic artery (SA) and the splenic vein (SV) with some
part of the pancreatic parenchyma can be seen on the extreme left upper quadrant of
the image. Push the echoendoscope down to bring the pancreas into the center of the
screen ([Fig. 7]). Once the pancreas is in the center of the screen, the position of the transducer
is facing posteriorly. From this point, perform a clockwise and anticlockwise rotation
to trace the whole pancreas back (toward the tail) and forth (toward genu), respectively.
Fig. 6 Locating the celiac artery from the gastroesophageal (GE) junction on endoscopic
ultrasound (EUS). (A) At the GE junction on EUS, the left lobe of the liver is seen. (B) On clockwise rotation from the left lobe, the umbilical portion of the left portal
vein (UPV) along with the ligamentum teres (LT) and ligamentum venosum (LV) is seen.
(C) On further clockwise rotation, the intrahepatic inferior vena cava (IVC) is visualized.
(D) Further clockwise rotation, the aorta can be visualized along with the celiac artery
(CA). If the CA is not seen after visualizing the aorta, push down the echoendoscope
slightly. SA, splenic artery.
Fig. 7 Locating the pancreas after visualization of the celiac artery (CA). (A) Schematic diagram showing the position of the transducer when the CA is seen, with
an arrow indicating to push down the echoendoscope to see the pancreas. (B) Schematic diagram showing structures seen on endoscopic ultrasound (EUS) from the
gastroesophageal (GE) junction after locating the CA. (C) A representative EUS image showing the aorta, CA, splenic artery (SA), and pancreas
body (PB) in the left corner of the screen. (D) The pancreas body is visualized after pushing down the echoendoscope after locating
the celiac artery. SMA, superior mesenteric artery; SV, splenic vein.
As the pancreas is placed in a slanting position, clockwise movements and minimal
withdrawal are required to visualize the pancreas tail ([Fig. 8]) and similarly, anticlockwise rotation and pushing of the scope are required to
visualize the genu and the head of the pancreas ([Fig. 9]).[13]
Fig. 8 Tracing the pancreas body and tail from the stomach. (A) Schematic diagram showing the pancreas placed in the slanting position. To image
the pancreas body and tail, a clockwise rotation and minimal withdrawal of the scope
is required as the tail is placed higher up compared with the head-body. (B) Endoscopic ultrasound (EUS) image showing the pancreatic body, splenic vessels,
left renal vein (LRV), and aorta in the same plane. (C) On further clockwise rotation, the pancreas body, splenic artery (SA), splenic vein
(SV), LRV, and left renal artery (LRA) are seen. (D) On further clockwise rotation, the pancreas body, splenic vessels, left renal vessels
are seen entering the left kidney and the left adrenal gland. (E) On further clockwise rotation, the pancreatic tail can be seen along with the left
kidney and spleen. (F) Complete examination of the pancreas by viewing the splenic hilum by clockwise rotation.
Fig. 9 Tracing the pancreas genu from the pancreatic tail. (A) Schematic diagram showing anticlockwise rotation and push movements are required
while tracing the pancreas from the tail to the genu. (B) On anticlockwise rotation from the tail, the left adrenal gland and the pancreatic
body are seen. (C) On further anticlockwise rotation, the splenic vessels, left renal vessels, and
pancreas body are seen (the image will be similar to a clockwise rotation image).
(D) On further anticlockwise rotation, the pancreas genu can be seen, and the splenic
vein (SV) can also be seen joining the portal vein confluence (PVC) along with the
superior mesenteric vein (SMV). In addition, common bile duct (CBD) and common hepatic
artery (CHA) can also be seen. (E) Pushing down the scope further and keeping an anticlockwise torque, the SMV is seen
running horizontally between the pancreas head and body. (F) From the SMV on anticlockwise torque, the pancreas genu can be seen clearly with
dropping pancreatic duct (PD) in the head region. LRA, left renal artery; LRV, left
renal vein; SA, splenic artery.
On clockwise rotation when tracing the pancreas body and tail, the splenic vessels,
left renal vessels, left kidney, left adrenal gland, and spleen are visualized. The
spleen and the left kidney are hallmarks of the pancreas tail. Always trace the pancreas
till the splenic hilum to avoid missing of any pancreatic tail pathology ([Fig. 8F]).
In case of obese patients, identifying the pancreas can be challenging. Therefore,
it is advisable to develop the habit of tracing the splenic vessels, which run parallel
to the pancreas ([Fig. 8B–D]). Tracing splenic vessels serves as a reliable method to locate the pancreas. The
left renal vessels are also seen in close proximity to the splenic vessels and should
be separately identified.
On anticlockwise rotation, the pancreas can be traced from the tail to the head. While
performing anticlockwise rotation, the SV will be seen joining the PVC. On further
pushing the scope down from the PVC, the superior mesenteric vein (SMV) will be seen
dividing the body and head of the pancreas and on continuing minimal anticlockwise
rotation the pancreas genu will be seen ([Fig. 9]).[11] In the same plane of the PVC, distal intrapancreatic part of the common bile duct
(CBD) can also be seen ([Fig. 9D]). The CBD should be confirmed by color Doppler.[9]
Once the SMV is visible from the stomach, the superior mesenteric artery (SMA) can
be visualized by slight clockwise rotation. From this point, the SMA can be traced
up to the aorta, and the uncinate process can be examined ([Fig. 10]).[9] This way the whole pancreas can be scanned from the stomach.[9]
Fig. 10 Visualization of the uncinate process on endoscopic ultrasound (EUS) from the stomach.
(A) Schematic diagram showing the uncinate process located between the superior mesenteric
vessels (SMVs) and the aorta. (B) A representative EUS image of the uncinate process from the stomach. SMA, superior
mesenteric artery.
The pancreatic duct (PD) is a small, tubular, anechoic structure running within the
center of the pancreas. Therefore, tracing the PD does not require any special maneuvers.
During PD examination, it is important to assess for PD dilatation, wall echogenicity,
intraductal filling defect (such as calculi), and any anatomical variation. The diameter
of normal PD is 4 mm in the head, 3 mm in the body, and 2 mm in the tail. Physiological
dilatation of the PD may be seen in elderly people.[12] Pancreas divisum is the most common congenital anomaly of the PD and can be found
in 10% of the general population.[14] Diagnosing pancreas divisum is essential, especially in idiopathic recurrent acute
pancreatitis. EUS has been reported as a safe and effective modality for diagnosing
pancreas divisum with moderate sensitivity (51–95%) and high diagnostic accuracy (97%).[14]
[15]
[16] Pancreas divisum can be precisely diagnosed from the duodenal bulb.
By Locating the Hilum of the Liver
By Locating the Hilum of the Liver
This is another method of locating the pancreas from the GE junction. At the GE junction
once the left lobe of the liver is seen, do a clockwise rotation to see the umbilical
portion of the LPV. On further slight clockwise rotation (<45 degrees), the LPV will
become round, and the middle hepatic vein (MHV) will also be visible. Once the LPV
becomes round, push down the echoendoscope to see the liver hilum. At the liver hilum,
the main portal vein (MPV), right hepatic artery (RHA), and common hepatic duct are
visible. On pushing the scope further down, the common hepatic artery (CHA), MPV,
and CBD can be seen stacked on top of each other. Follow the MPV to the PVC while
keeping a clockwise torque. As you proceed in this manner, the pancreas will begin
to appear. At the PVC, SV, SMV, and occasionally inferior mesenteric vein (IMV) are
visible. The SA is seen running adjacent to the SV. By rotating scope in an anticlockwise
direction from the PVC, the pancreas genu will be visualized along with the dropping
PD ([Fig. 11]), and by clockwise rotation the pancreas can be traced to the tail as explained
earlier.
Fig. 11 Locating the pancreas by identifying the liver hilum on endoscopic ultrasound (EUS).
(A) At the gastroesophageal (GE) junction on EUS, the left lobe of the liver is seen.
(B) On clockwise rotation, from the left lobe of the liver, the umbilical portion of
the left portal vein (LPV) along with the ligamentum teres and ligamentum venosum
is seen. (C) On slight clockwise rotation, the LPV becomes round shaped. (D) When the LPV becomes round, push down the scope to see the liver hilum. At the liver
hilum, the common hepatic duct (CHD), main portal vein (MPV), and right hepatic artery
(RHA) are seen. (E) Trace the MPV by minimally pushing the scope and maintaining a clockwise torque.
The common hepatic artery, MPV, and suprapancreatic common bile duct (CBD) are seen.
(F) Schematic diagram showing the pancreatic head, genu, portal vein confluence (PVC)
along with the splenic vein (SV), superior mesenteric vein (SMV), and CBD. (G) A representative EUS image showing PVC, SMV, SV, inferior mesenteric vein (IMV),
CBD, pancreas head, and genu. After identifying the PVC, the maneuvers are the same
to trace the pancreas back and forth by clockwise and anticlockwise rotation, respectively.
(H) EUS image showing the pancreas genu with dropping pancreatic duct (PD), on anticlockwise
rotation from the PVC. Seg 2: segment 2, LHV: Left hepatic vein, seg 3: segment3,
LT: Ligamentum teres, UPV: Umbilical portion of left portal vein, LPV: Left portal
vein, MPV: main portal vein, Seg 4: segment 4, CHD: Common hepatic duct, RHA: Right
hepatic artery, MPV: main portal vein, CHA: common hepatic artery, CBD: Common bile
duct, HOP:head of pancreas, GB: Gall bladder, SA:Splenic artery, SV: Splenic vein,
PVC: portal vein confluence, SMV: Superior mesenteric vein, PH : pancreatic head,
IMV:inferior mesenteric vein, p head: pancreatic head, P genu: Pancreatic genu.
From the Distal Body of the Stomach (the Pull Method)
From the Distal Body of the Stomach (the Pull Method)
Another way to find the pancreas is to insert the scope into the distal body of the
stomach/duodenal bulb and gradually withdrawing it while scanning. This method is
not commonly used because it is not as easy to find the pancreas as it is from the
GE junction initially. As the majority of the pancreatobiliary pathology lies in the
head of the pancreas and can be detected from the duodenal bulb, it may be a good
practice to start from the duodenal bulb. After the scanning from bulb, the scope
is gradually withdrawn while maintaining a clockwise torque until the PVC/pancreas
is identified. The advantage of this method is that resistance will not be encountered
like in the push method; however, finding the pancreas can be difficult without a
homebase.
Examination of the Pancreas from the Duodenal Bulb
Examination of the Pancreas from the Duodenal Bulb
The duodenal bulb is a small and compact place. The echoendoscope will be in a long
position with the transducer facing posteriorly and toward the left. From the duodenal
bulb, major vessels and organs like the PV, IVC, aorta, CBD, pancreas head and neck,
PD, right kidney, and liver (right lobe) can be visualized ([Fig. 12]).
Fig. 12 Pancreas examination from the duodenal bulb. (A) The main portal vein (MPV) is the home base in the duodenal bulb. On endoscopic
ultrasound (EUS) image, an anechoic common bile duct (CBD) is seen, then main portal
vein (MPV) and common hepatic artery (CHA) are visualized in sequence. This is the
reverse order of the stomach examination. (B) On slight clockwise rotation, the portal vein confluence (PVC), splenic vein (SV),
superior mesenteric vein (SMV), inferior mesenteric vein (IMV), CBD, and pancreas
head (PH) along with the pancreatic duct (PD) are visualized. (C) A representative EUS image depicting the same. (D) On slight clockwise rotation, the CBD, PH, SMV, and superior mesenteric artery (SMA)
are visualized. (E) On further clockwise rotation, the intrapancreatic CBD, pancreas head (PH), PD,
and inferior vena cava (IVC) along the right renal vein (RRV) are seen. (F) On clockwise rotation, the IVC, RRV, aorta, and distal-most part of the CBD seen.
(G) On further clockwise rotation, the distal-most part of the CBD and PD along with
the right kidney can be seen. (H) Further on fine clockwise rotation, the ampulla can be seen from the duodenal bulb
along with the terminal part of the CBD and PD.
The homebase in the duodenal bulb is the PV, and it should not be confused with the
IVC. The echoendoscope should be wedged in the bulb in a long position. If the scope
is not wedged properly and crosses the D1–D2 junction, the right kidney may be visible.
In this case, the echoendoscope should be withdrawn slightly to see the PV. Once the
PV is visualized, visualizing the CBD and pancreas becomes easier. If the CBD is not
visualized, it may be compressed by the transducer. In this case, releasing the big
knob and instilling some water may help in visualizing the CBD.
On EUS view from the duodenal bulb, the CBD, MPV, and CHA will be seen placed in sequence,
which is the reverse order of the image seen from the stomach ([Fig. 11E] and [Fig. 12A]). The pancreas head is very well seen from the bulb on clockwise rotation and a
part of the uncinate process can also be visualized. To visualize the pancreas neck
from the bulb, minimal anticlockwise rotation is required from the PVC. The PD is
stacked behind the CBD (stack sign), and by clockwise rotation, the CBD, PD, and pancreas
head are traced up to the ampulla ([Fig. 12]).[17] Absence of the “stack sign” and presence of the “crossed duct sign” (PD crossing
the CBD) indicates pancreas divisum on EUS.[14] From the ampulla, on anticlockwise rotation, the CBD can be traced till the liver
hilum, and the cystic duct and gallbladder can also be visualized while tracing the
CBD.
Duodenum Part 2
The aorta is the homebase in the descending duodenum. The ampulla, pancreatic head,
uncinate process, proximal PD, intrapancreatic CBD, and mesenteric vessels can be
visualized from D2. In the deep descending duodenum, the transducer faces posteriorly
so parts of the IVC and aorta are visible, and on anticlockwise rotation, the right-sided
structures (right to the aorta) such as the infrarenal IVC and right kidney are visible,
while on clockwise rotation, the aorta and pancreas are visible.
Once the aorta is seen, slowly withdraw the scope while maintaining a clockwise torque
until the pancreas head comes into view. Along with the pancreas head, the uncinate
process and mesenteric vessels (SMV is closer to the transducer) can also be seen.
On further withdrawal and clockwise rotation, the CBD and PD will be seen joining
the ampulla. At the ampullary level, release the big knob, and instill some water
to push away the ampulla. This is to ensure that small stones or lesions at the ampulla
are not missed. At the ampullary level, if either of the ducts is not visualized,
slight maneuvering of the scope is required. When CBD is visualized, a slight clockwise
rotation is required to see the PD. Conversely, when PD is visualized, minimal anticlockwise
rotation should be done to visualize the CBD ([Fig. 13]).[12]
[17]
Fig. 13 Pancreas examination from the duodenum part 2. (A) The homebase in descending duodenum is the abdominal aorta. Schematic diagram showing
inferior vena cava (IVC) and aorta from D2. (B) A representative endoscopic ultrasound (EUS) image showing the IVC and aorta from
D2. (C) Once aorta is seen, withdraw the scope slowly and maintain clockwise torque. The
pancreas and mesenteric vessels will start appearing. A schematic diagram showing
the pancreas head, uncinate process, and superior mesenteric vessels (SMV; it is closer
to the transducer). (D) A representative EUS image of the pancreas head, uncinate process, and SMVs. (E) Schematic diagram showing the position of the transducer in D2 along with the scanning
range. (F) On further withdrawal, the ampulla will start appearing along with the pancreatic
duct (PD). (G) A slight anticlockwise rotation is required to see the common bile duct (CBD) from
the PD; similarly a clockwise rotation is required to see the PD when the CBD is visualized
at the ampulla. An EUS image showing the ampulla with both the PD and CBD. (H) An EUS image showing the CBD with stones and the abdominal aorta. From the ampulla,
the CBD can be traced to the liver hilum by slow withdrawal and keeping an anticlockwise
torque. For tracing the PD from the major papilla to the body, gradual withdrawal
and clockwise torque is required.
From the ampulla, the PD and CBD can be traced until the pancreas body and liver hilum,
respectively. To trace the PD from the ampulla, gently withdraw the scope while maintaining
a clockwise torque. During this maneuver, the scope may slip into the stomach and
directly lie on the genu/body of the pancreas. This allows tracing of the PD from
the ampulla to the body of the pancreas. The inability to trace the PD from the major
papilla to the pancreatic body is also suggestive of pancreas divisum.[14] A similar maneuver is performed to trace the CBD from the ampulla to the liver hilum,
but with an anticlockwise torque.
Understanding the orientation from the descending duodenum can be difficult, and stabilizing
the scope can be quite challenging at first. Therefore, it is advisable to learn this
station once you feel confident in other station examinations.
Conclusion
Understanding the anatomy with the linear EUS is crucial in mastering the technique.
A station-wise approach can be helpful in comprehending the orientation of the pancreas.
For complete examination of the pancreas, a station-wise approach should be followed,
and examination of the pancreas should be repeated multiple times until you feel comfortable
with your performance. It is good practice to examine the pancreas during every EUS
examination. The best way to learn EUS is to read about it, watch videos of experts
performing the procedure, observe their body movements, record your own videos, label
the structure, discuss the difficulties encountered during EUS examination, and repeat
these steps over and over again. Mastering basic anatomy will undoubtedly aid in advanced
therapeutic EUS and to master EUS, what one can do is practice, practice, and practice.
