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EUS Atlas: Normal Anatomy

Ultrasonography is a dynamic process and it is difficult to capture all the relevant information from a study on a few still images. The following images, however, demonstrate examples of normal anatomy and the important landmarks to identify while performing endosonography.

Mediastinum - main bronchi

Mediastinum - main bronchi: The mediastinum is usually imaged by slow withdrawal of the echoendoscope from the gastro-esophageal junction. In this image, at 27cm from the incisors, the left and right mainstem bronchi are seen anteriorly at the 12 o’clock position, with the aorta and spine posteriorly. Inserting the probe 1-2 cm will bring the subcarina into view and it is important to inspect this area carefully for the presence of subcarinal lymphadenopathy (level VII).

Mediastinum - aortic arch

Mediastinum - aortic arch: Upon withdrawing the echoendoscope 2-3cm from the subcarina, the two main bronchi will merge to form the trachea (T) and the aorta will be seen to elongate as it arches. The area between the transducer and the aortic arch is the aortopulmonary window (level V) and must also be examined closely for the presence of enlarged lymph nodes. This image was taken at 25cm from the incisors.


Esophagus and stomach
Esophageal wall

Esophageal wall: Catheter probe image (20MHz) showing normal esophageal wall layers. The first layer consists of a hyperechoic interface between lumen and mucosa, beneath which a hypoechoic layer corresponding to mucosa can be seen (2). The submucosa appears hyperechoic (3), while the muscularis can be seen as inner circular and outer longitudinal layers (4 & 5).

Anatomy - gastro-esophageal junction

Anatomy - gastro-esophageal junction: Radial image at the level of the gastro-oesophageal junction, showing aorta and IVC as it runs through the liver.

Gastric wall layers 1
Gastric wall layers 2

Gastric wall layers: Radial image of the water-filled stomach at 7.5MHz. The 5 layer structure can clearly be seen.


Left adrenal gland
Left adrenal gland

Left adrenal gland: The left adrenal gland (arrow) can often be seen lying between the superior pole of the left kidney and the aorta, just proximal to the celiac axis. It appears as a thin triangular or "seagull"- shaped hypoechoic structure. The right adrenal is not usually seen at EUS.


Celiac axis
Celiac axis 1
Celiac axis 2

Celiac axis: The celiac axis is usually best scanned from just inside the GE junction, where it can be identified as it arises anteriorly from the aorta. It bifurcates into hepatic and splenic artery, an appearance often described as the "whale’s tail". It is important to scan carefully in this region for evidence of celiac LN involvement in patients with malignancy.

Celiac axis 3
Celiac axis 4

Celiac axis: The celiac axis is also easily identified using curved linear array echoendoscopes, by following the aorta distally from the GE junction. The SMA is also clearly seen in this image.


Pancreas - body and tail
Pancreas - body

Pancreas - body: The pancreas lies between the splenic artery running along its superior border and the splenic vein inferiorly. This image shows a normal, homogeneous pasncreatic echotexture and a portion of the main PD can be seen at the genu. The confluence of the splenic and superior mesenteric veins ("clubhead") is also seen.

Pancreas - body

Pancreas - body: It is important to trace the main PD as it runs proximally around the genu of the pancreas ("genu follow-through"). The SMA can be seen in cross-section, behind the splenoportal confluence and neck of pancreas.

Pancreas - genu

Pancreas - genu: The pancreatic parenchyma is homogeneous, the main PD is regular and the duct margins are not hyperechoic, as is often the case in chronic pancreatitis. Note the "genu follow-through" as the PD turns round the genu.

Confluence of splenic and superior mesenteric veins

Confluence of splenic and superior mesenteric veins: This image demonstrates the "clubhead" sign formed by the confluence of SV and SMV. Note also the SMA in cross-section, lying posterior to the confluence.

Pancreas - tail

Pancreas - tail: Because the pancreatic tail lies more cephalad than the pancreatic head, it is necessary to withdraw the transducer slowly while rotating slightly to the patient’s left in order to follow the pancreas out towards the tail. This can be seen close to the splenic hilum , which is at the bottom right of the image.


Biliary tree & pancreatic head
Distal CBD and PD

Distal CBD and PD: Scanning from the apex of the duodenal bulb, it is possible to trace the CBD distally as it runs down to the ampulla. Behind this the main PD can also be seen.

Apical view

Apical view: In this image, the CBD and portal vein can be seen in long view. The gallbladder contains considerable sludge. The muscularis of the duodenal wall can also be seen (arrow).

Apical view

Apical view: This image, from the apex of the duodenal bulb, shows a long view of the CBD and a portion of the portal vein behind it. A periampullary diverticulum (D) is also seen. This may impede adequate visualisation of the ampullary segment of the CBD. The portal vein is usually larger in calibre than the CBD and lies caudal to the CBD. It is seen best by insertion of the echoendoscope slightly beyond the CBD.

"Stack sign"

"Stack sign": In 70-80% of patients it is possible to visualise the CBD, PD and PV in the same echo plane, from the duodenal bulb. This is referred to as the "stack sign" and is an important landmark as it ensures that the echo plane is passing through the pancreatic head, distal CBD and portal vein - making it less likely to miss small lesions in this area.


Gallbladder: The gallbladder is usually best seen from the gastric antrum or, less often, the duodenal apex. The echogenic wall consists of 3 layes. It is important to scan carefully over the gallbladder to look for calculi (with acoustic shadowing), sludge or hyperechoic ‘floaters’.


Pancreas - uncinate and ampulla of Vater

Ampulla: Good visualisation of the ampulla may be difficult to obtain. It is often best seen by inserting the endoscope into the second or third part of duodenum, then slowly withdrawing. The uncinate process will come into view and then, with further withdrawal of the probe, the ampullary region. This image shows both PD and CBD in cross-section through the ampulla.


Ampulla: This image demonstrates a slightly thickened but otherwise normal ampullary sphincter around the distal CBD (arrow).

Pancreas - ventral anlage
Pancreas - ventral anlage

Pancreas - ventral anlage: The ventral portion of the pancreas (V) contains relatively less fat than the larger dorsal portion (D) and therefore appears darker on EUS. This appearance is seen in up to 75% of normal people and should not be mistaken for a mass. It is seen upon withdrawing the probe proximally through the duodenal sweep. This distinctive pattern may be lost in patients with chronic pancreatitis or pancreatic cancer, when it is seen in 40% approximately.

Anatomy - distal duodenum

Anatomy - distal duodenum: By placing the transducer in the duodenal sweep beyond the ampulla, a longitudinal view of the aorta can be obtained as well as the SMA arising from it.

Pancreas - uncinate process
Pancreas - uncinate process

Pancreas - uncinate process: As the scope is withdrawn the aorta will ‘round up’ and the uncinate process of the pancreas will come into view. The SMA will also appear in cross section and, lateral to this, a portion of SMV can be seen. Upon further withdrawal, the splenoportal confluence ("clubhead" view) will appear.


Rectum and anal canal

Rectum: As well as rectal wall layers, it is possible to identify seminal vesicles (SV) which appear as tortuous, paired hypoechoic structures on either side of the bladder base. Orientation of structures is best performed by rotating the image until the bladder (B) lies at the 12 o’clock position.

Prostate gland

Prostate gland: The prostate is seen inferior to the bladder base. This image shows a normal-looking prostate (Pr). In asymptomatic, elderly men, calcification within the gland is often noted.

Endoanal ultrasound - puborectalis

Endoanal ultrasound - puborectalis: On withdrawing the probe through the anal canal, the puborectalis sling, extenal anal sphincter and internal anal sphincter progressively come into view. The puborectalis sling of the levator ani muscle is seen in this image as a hyperechoic (striated muscle) sling running anteroposteriorly around the upper anal canal (arrows). The external anal sphincter, also composed of striated muscle, is hyperechoic and separates into three distinct bands in the lower canal. The internal anal sphincter (smooth muscle) is seen as a concentric 2-3mm hypoechoic zone internal to the external sphincter and visible in the lower 2cm of the anal canal.

Endoanal ultrasound - anal sphincters

Endoanal ultrasound - anal sphincters: This image (B&K rigid rectal probe) shows normal internal (hypoechoic concentric ring) and external (hyperechoic) anal sphincters.

Endoanal ultrasound - anal sphincters

Endoanal ultrasound - anal sphincters: In contrast, this image (B&K rigid rectal probe) shows a large, wedge-shaped anterior defect involving both sphincters (arrow), in a middle-aged woman with a history of obstetric trauma and fecal incontinence.