Ultrasound abdomen general
This course provides general information about ultrasound examination of the abdomen, with details on how it can and cannot be used.
- Abdominal pain (including appendicitis, bile stones, kidney stones), herniation, umbilical hernia, inguinal hernia.
- Abdominal aneurysm
- Abnormal blood test results (liver and renal impairment)
- Unexplained fever
- Trauma (internal bleeding screening)
- Oncology (liver metastases screening)
The Ultrasound Technique course provides a basic understanding of ultrasound technique; it is recommended to read this course also.
By way of repetition: location and direction of the transducer on the patient's skin determine anterior/posterior and left/right in the image.
As a general rule, in the transversal plane:
- The top of the ultrasound image is the anterior (ventral) side and the bottom is the posterior (dorsal) side.
- Left on the image is actually right and vice versa. The body is seen from below as it were (as in a transversal section of a CT scan).
Figure 1a. Left kidney in the transversal plane.
As a general rule, in the sagittal plane:
- The top of the ultrasound image is the anterior side and the bottom is the posterior side.
- Right on the image is towards the feet (= caudal) and left is towards the head (= cranial).
Figure 1b. Left kidney in the sagittal plane.
Orientation tip during examination: up is always the skin side, irrespective of position and tipping.
As a general rule, each organ and each abnormality is imaged in two directions; in most cases the transversal and sagittal directions.
Posterior sound transmission and acoustic shadowing are ultrasound characteristics that are frequently used in abdominal ultrasound examinations. See also the Ultrasound Technique course under Artefacts.
The normal anatomy or organs imaged in a standard abdominal examination is explained below.
Note: for the sake of brevity, the various organs will be not discussed in detail.
The liver allows for effective ultrasound imaging. A healthy liver has a homogeneous echo reflection pattern and smooth contours. The echo reflection pattern of the liver is similar to or slightly higher than that of the renal cortex. The echo reflection pattern and smooth contours of the liver are best evaluated by imaging the right kidney and the right liver lobe together (see fig. 2).
Figure 2. Technique for sagittal direction of the liver and right kidney. Note that liver parenchyma has virtually the same echogenicity as the cortex of the right kidney.
Liver vessels include the portal vein, hepatic artery and hepatic veins (fig. 3).
Figure 3. Hepatic vasculature.
1. The main branch of the portal vein can be seen clearly in the hepatic hilum. The portal vein can be identified by its echogenic fibrous wall and has a left and right branch at the center of the liver.
The direction of flow in the portal vein is into the liver (= hepatopetal) with a monophasic Doppler signal (fig. 4).
Figure 4. A normal portal vein with hepatopetal flow.
2. The hepatic artery carries oxygen-rich blood to the liver. The main arterial branch is also located in the hepatic hilum. There it (in most cases) passes between the portal vein (anterior) and choledochal duct (posterior) and then branches into the left and right hepatic arteries (fig. 5).
The direction of flow is into the liver (=hepatopetal) with a triphasic Doppler signal.
Figure 5. The common hepatic artery.
3. The hepatic veins originate in the inferior caval vein and normally have three main branches: right, middle and left branch. The hepatic veins have hypoechogenic walls, making them easily distinguishable from the portal vessels (fig. 6).
The direction of flow is out of the liver (= hepatofugal) with a triphasic Doppler signal.
Figure 6a. Normal hepatic veins (in the sagittal plane) with hepatofugal flow.
Figure 6b. The hepatic veins have a rabbit ear configuration in the transversal plane (at the level of the basis) – the so-called (playboy) bunny sign.
The gallbladder is best evaluated when the patient is in the fasting state, when the gallbladder is filled with hypoechogenic bile. The gallbladder wall thickness is usually < 2 mm. When the patient inhales deeply, the gallbladder will appear from under the rib cage (fig. 7a). The gallbladder now lies against the abdominal wall, enabling you to use your echo transducer to push into the gallbladder and evaluate its compressibility. A filled gallbladder will be partially compressible when you push against it (fig. 7b).
Figure 7a. Technique for ultrasound examination of the gallbladder.
Figure 7b. Gallbladder with normal compressibility; visible as a flattening of the rounded contour when extra compression is applied.
The choledochal duct is located in the liver hilum. Here it passes anterior/ventral of the portal vein (fig. 8). The choledochal duct usually has a diameter < 7 mm. The diameter may increase in elderly patients or patients who are stable after cholecystectomy.
Figure 8. Ultrasound examination of the choledochal duct.
The intrahepatic bile ducts are too small for ultrasound evaluation. However, dilated intrahepatic bile ducts (in bile duct obstruction) will become visible (see Pathology section).
The right kidney can be imaged effectively using the right liver lobe as acoustic window (fig. 9/10). For the left kidney, the spleen can act (partially) as acoustic window. When the patient inhales deeply, the kidneys will move in the caudal direction, which may facilitate evaluation of the kidneys.
Figure 9. Ultrasound examination of the right kidney.
Figure 10. Normal right kidney. Note the kidney moves during relaxed breathing. The passing black (hypoechogenic) vertical bands are the ribs.
As in each organ, the kidneys are always imaged in two directions; sagittal and transversal (fig. 11). As stated previously, renal parenchyma has the same echogenicity or is somewhat more hypoechogenic than hepatic parenchyma. The renal medullary pyramids are triangular and hypoechogenic. The pyelocaliceal system has an echogenic appearance (fig. 11). The average dimension of the kidneys in adult patients is about 12 cm (craniocaudal dimension).
Figure 11. The right kidney in sagittal and transversal directions.
The adrenal glands are not good identifiable in adult patients; however, the adrenal region should always be evaluated with ultrasound for the presence of abnormalities. In neonates, the adrenal glands can be seen clearly. The adrenal glands have a V-shape with a hypoechogenic rim and echogenic center (fig. 12).
Figure 12. A normal right adrenal gland in a neonate of a few days old.
The bladder must be filled for adequate evaluation. A filled bladder has thin walls with hypoechogenic content (fig. 13). A filled bladder creates a perfect acoustic window for evaluation of the distal ureteral orifices in the bladder posterior wall.
Figure 13. Ultrasound examination of the bladder in the transversal plane.
A healthy spleen has a homogeneous reflection pattern, smooth contours and a craniocaudal length of about 12 cm at adult age (fig. 14). The echo reflection pattern is similar to that of the liver in most patients. The spleen may also act as an acoustic window for evaluation of the pancreatic tail.
Figure 14. Ultrasound examination of the spleen in sagittal direction.
The pancreas cannot be imaged effectively when there is significant air content in the stomach/duodenum or transversal colon.
The lienal vein may help localize the pancreas as the pancreas is draped, as it were, over the lienal vein (fig. 15). It may also help to ask the patient to make a round tummy (Valsalva), which will move the pancreas towards the abdominal wall and increase visibility. The spleen may act as an acoustic window for evaluation of the pancreatic tail. The pancreatic duct has a diameter of 2-3 mm in most cases.
Figure 15. Ultrasound examination of the pancreas in the transversal direction.
Because of its position, the pancreas is not always fully visible in any plane (fig. 16); angulating the echotransducer and/or moving it in the craniocaudal direction will allow for evaluation of as much of the pancreatic parenchyma as possible.
Note: air content in the stomach/duodenum or transversal colon may reduce visibility of the pancreas (the tail in particular!).
Figure 16a. Ultrasound examination of a normal pancreas in the sagittal direction. Note that the tail tip cannot be evaluated due to intestinal gas. SMA = superior mesenteric artery/
Figure 16b. The CT examination illustrates that the pancreas is not entirely in the horizontal plane and that the pancreatic head has a caudal orientation from the corpus. A = aorta, SMA = superior mesenteric artery, SMV = superior mesenteric vein, arteria mesenterica superior.
The echo reflection pattern of the pancreas may differ between patient/age categories. The echo reflection pattern will become more echogenic with age.
The abdominal aorta is located centrally in the abdomen (fig. 17). It can be difficult to image it effectively, particularly with significant obesity and extensive intestinal gas. Adequate compression is necessary.
Figure 17. Ultrasound examination of the abdominal aorta in the transversal plane.
Abdominal aorta dimensions (fig. 18):
- Normal < 2.5 cm
- Dilatation > 2.5 cm
- Aneurysm > 3 cm
Figure 18. Ultrasound examination of a normal aorta in the transversal plane.
The (small) intestines can never be imaged in their entirety by ultrasound. However, ultrasound may be very helpful in common intestinal pathologies.
The intestinal wall appearance changes markedly from the small intestine (Kerkring folds) to the colon (haustrations). Intestinal gas is a limiting factor in reliable evaluation of the intestinal wall (fig. 19).
Figure 19. Extensive intestinal gas prevents continued evaluation.
In some cases, intestinal compression may improve imaging. When compression does not help, evaluation of the intestinal anterior wall will have to suffice.
Figures 20/21 show a number of ultrasound images of normal intestinal loops.
Figure 20. Normal peristalsis of a number of intestinal loops.
Figure 21. Examples of normal intestinal loops.
For the purpose of evaluating the duodenum or pylorus, it may be very helpful to have the patient drink a few cups of water prior to or during the examination. A fluid-filled lumen creates the ideal acoustic window for evaluation of the entire intestinal wall.
We are frequently asked to assess patients with abdominal pain for appendicitis. The appendix is in the right lower quadrant. The appendix is compressible and normally has a diameter of under 7 mm (fig. 22/23).
Figure 22. Ultrasound examination of the appendix.
Figure 23a. Normal appendix.
Figure 23b. A healthy appendix is compressible. Compressibility can be evaluated effectively by imaging the appendix in the transversal plane.
Figure 23c. Healthy appendix. The appendix lies close to the surface and has a winding course, originating at the medial side of the cecum. The air-filled cecum (acoustic shadowing!) is at the left side in the illustration.
Each radiologist will have his or her personal preferences for imaging abdominal organs. A common sequence of a full abdominal ultrasound examination is aorta - pancreas - liver/gallbladder - kidneys - bladder region - intestines.
As a general rule, each organ and abnormality is imaged in two directions; in most cases the transversal and sagittal directions.
Tips for viewing stored ultrasound images:
- Top is always the skin side
- Use the marker on the screen to see in which region and which direction (sagittal or transversal) the structures have been imaged.
- Fluid does not reflect sound waves, making it anechogenic (=black). If you therefore see an anechogenic structure, this could be a fluid-filled organ or fluid-filled abnormality (e.g. gallbladder, bladder, vessels, cysts, ascites).
- Calcified structures (such as bile stones and kidney stones) may cause acoustic shadowing.
- Compare the echo reflection pattern of the liver parenchyma with the cortex of the right kidney in order to evaluate for the presence of liver steatosis (see Pathology section).
- Comparison with normal anatomy is useful and can help improve the identification of pathology. Examples: do the kidneys appear symmetrical or is there (mild) hydronephrosis? Intestinal wall thickening versus normal intestinal wall (see Pathology section).
- Liver pathology (steatosis, liver lesions)
- Gallbladder/bile ducts (bile stones, cholecystitis, dilated bile ducts)
- Renal pathology (hydronephrosis, kidney stones, kidney lesions)
- Bladder pathology (clot, bladder tumor)
- Spleen (splenomegaly)
- Pancreas (pancreatic tumor)
- Aorta (aneurysm)
- Intestines (appendicitis, diverticulitis, intestinal wall thickening)
Fatty liver degeneration will make the liver parenchyma echogenic as compared to the kidney parenchyma (fig. 24). This is termed liver steatosis. Causes of steatosis include alcohol abuse, diabetes and obesity.
Figure 24. Liver steatosis; the liver parenchyma is highly echogenic vs the right kidney cortex.
In liver cirrhosis patients, the liver surface will have an uneven/nodular aspect. In advanced stages, liver volume will decrease and the liver parenchyma will have a coarse-grain echo reflection pattern (fig. 25).
Figure 25. Liver cirrhosis versus normal liver parenchyma.
Multiple focal abnormalities may be found in the liver.
In patients with a steatotic liver, anechogenic areas are frequently seen in the gallbladder bed or around the falciform ligament; in most cases, there will be areas without fatty degeneration or “focal non-steatosis” (fig. 26).
Figure 26. Focal non-steatosis in the gallbladder bed.
Another frequent finding in the liver is a liver cyst. A cyst is a benign, thin-walled fluid vesicle. Cysts have anechogenic (black) content. In order to distinguish cysts from anechogenic solid lesions, two artifacts are used: posterior wall enhancement and increased sound transmission (fig. 27). For additional information on ultrasound artifacts, see the Ultrasound Technique course.
Small liver cysts are usually asymptomatic and aspecific. Large cysts can in some cases exert a mass effect on the surrounding structures and thereby induce symptoms.
Figure 27. Liver cyst vs solid liver lesion.
Another frequent benign abnormality in the liver is the hemangioma.
Most hemangiomas are asymptomatic, sharply delineated echogenic small lesions (fig. 28). Perfusion in hemangiomas is slow, frequently preventing the use of color Doppler to demonstrate flow.
In some cases, hemangiomas have an aspecific echo reflection pattern, making them indistinguishable from other liver abnormalities (e.g. metastases); additional diagnostics are then indicated.
Figure 28. A hemangioma in the liver parenchyma. The hemangioma has no color Doppler signal.
Other benign liver lesions include granuloma, focal nodular hyperplasia (FNH) and adenoma; they will be discussed in more detail in a subsequent course.
Metastases are the most common malignant liver abnormalities. In most cases, these patients have an oncologic history. Depending on the primary tumor, metastases may have either an anechogenic or echogenic reflection pattern (fig. 29). Usually they are mostly anechogenic. Metastases are frequently solid and vaguely delineated; flow cannot be demonstrated using color Doppler.
Figure 29. Multiple liver metastases. Note also increased echogenicity of the liver parenchyma (as compared to the cortex of the right kidney), consistent with steatosis.
In patients with liver cirrhosis, hepatocellular carcinoma (HCC) is a common malignant abnormality. The echo reflection pattern varies from anechogenic to echogenic or a mix. Flow may be imaged using color Doppler in HCC, making it distinguishable from a metastasis or hemangioma.
Gallbladder/bile duct pathology
When the gallbladder contains bile stones, they can be imaged effectively using ultrasound. Bile stones are echogenic and opaque, causing “acoustic shadowing” immediately behind the stone (fig. 30).
Figure 30. Bile stone with acoustic shadowing in the gallbladder.
In order to evaluate bile stone mobility, you can ask the patient to lie on his or her left side or stand if possible. The bile stones will move to the bottom with gravity. An immobile echogenic nodular lesion in close correlation with the gallbladder wall without acoustic shadowing is termed a gallbladder polyp, frequently consisting of cholesterol (fig. 31). The polyps will not move with gravity.
Figure 31. Small gallbladder polyps vs a bile stone with acoustic shadowing.
If there is a bile stone in the gallbladder neck that does not move with gravity, this is termed a “lodged stone”. It causes biliary outflow obstruction, putting pressure on the gallbladder. The gallbladder base will no longer be compressible and the patient will also indicate pain when you press on the gallbladder: this is a “hydropic gallbladder” or “Murphy’s sign". When the bile stone has been lodged chronically with associated bile stone colic, the gallbladder wall will thicken and have a layered aspect: the wall has become edematous (fig. 32/33).
Figure 32. A lodged stone (with acoustic shadowing) in the gallbladder neck with localized wall thickening.
Figure 33. Edematous gallbladder wall thickening in cholecystitis.
Dilated bile ducts
The choledochal duct can be evaluated by localizing the portal vein in the liver hilum; the choledochal duct is ventral of the portal vein. The choledochal duct usually has a diameter < 7 mm. A stone in the choledochal duct may cause obstruction and dilatation.
Figure 34. Dilated choledochal duct vs a normal choledochal duct.
The intrahepatic bile ducts are too small for ultrasound evaluation. In the event of bile duct obstruction, the intrahepatic bile ducts will become visible (fig. 35a/b). This is termed the tram track sign (fig. 35a).
Figure 35a. Dilated peripheral intrahepatic bile ducts with the tram track sign. Color Doppler reveals flow in the portal branches (as opposed to the bile ducts).
Figure 35b. Markedly dilated central bile ducts. Color Doppler reveals flow in the portal branches (as opposed to the bile ducts).
Urinary outflow obstruction will cause the pyelocaliceal system to dilate: this is termed hydronephrosis (fig. 36).
Figure 36. Left kidney with hydronephrosis in sagittal direction.
Hydronephrosis may have several causes, e.g. a lodged kidney stone, UPJ stenosis (fig. 37), or a lump exerting a mass effect on the ureter, or bladder retention (in reflux).
Figure 37. Hydronephrosis of the left kidney secondary to UPJ stenosis.
Like bile stones, kidney stones cause acoustic shadowing (fig. 38). Very small renal concrements of a few millimeters may be missed in ultrasound examination as the acoustic shadowing is invisible. The gold standard to demonstrate or exclude nephrolithiasis is an abdominal CT examination without contrast.
Figure 38. Left kidney in the sagittal plane. A large concrement in the pyelum with proximal dilatation of the renal collecting system.
One of the most common abnormalities in the kidneys are cysts (fluid-filled sacs). Cysts are generally asymptomatic. Uncomplicated cysts are thin-walled, have anechogenic content and posterior wall enhancement & increased sound transmission (fig. 39). For additional information on ultrasound artifacts, see the Ultrasound Technique course.
Figure 39. An uncomplicated kidney cyst with posterior wall enhancement and increased sound transmission.
Cysts may vary markedly in size. It is important to carefully evaluate the cyst wall and exclude any solid components. In the event of solid components or multiple septations, additional characterization using abdominal CT is indicated (fig. 40).
Figure 40. A complex cortical cyst with multiple echogenic septations.
One of the most common malignant lesions in the kidney is renal cell carcinoma (RCC). This is usually a solid mass with a heterogeneous reflection pattern and vascularization (fig. 41).
Figure 41. Spherical heterogeneous mass in the right kidney lower pole (PA: renal cell carcinoma).
The bladder must be filled for adequate bladder wall evaluation. The bladder usually has anechogenic content without wall irregularities.
In the event of trauma, blood clots may add mobile echogenic content to the bladder (fig. 42).
Figure 42. Blood clots in the bladder in diagnosed kidney laceration
Wall irregularities may signify a bladder tumor (fig. 43). It is helpful to have the patient turn to his/her left/right side during the examination in order to evaluate the mobility of the abnormality. A parietal tumor will obviously not move, sludge/stones and clots will. In practice, it is not always clear whether tissue is solid; cystoscopy is indicated for additional evaluation.
Figure 43. Irregular mass originating in the bladder wall, consistent with a bladder tumor.
The spleen usually has a craniocaudal dimension of 12 cm and a triangular shape. The spleen may increase in size in the event of e.g. portal hypertension (fig. 44), lymphoma or after infection. This will give the spleen a plump aspect with rounded rims.
Figure 44. Patient with liver cirrhosis and portal hypertension with splenomegaly (craniocaudal length 18 cm). Note also collateral vessel formation in the splenic hilum.
Cysts and hemangiomas may also develop in the spleen. The most common malignant abnormality is lymphoma.
Pancreatic imaging may be complicated by air content in the stomach or interfering intestinal gas in the transversal colon.
When asked to confirm or exclude pancreatitis, the origin of symptoms and the ability of ultrasound to demonstrate abnormalities should be taken into account. Despite abnormal blood chemistry, there will be no or few abnormalities on ultrasound over the first days.
When a pancreatic mass or unexplained dilatation of the pancreatic duct is suspected, CT or MRI examination is indicated for additional analysis.
Signs that are highly suspicious for pancreatic head carcinoma during ultrasound:
- Mass in the hepatic hilum / pancreatic head region.
- Dilatation of both the choledochal duct and the pancreatic duct (= double duct sign).
- Clinically a painless icterus will also be found.
Ultrasound is an effective and convenient way to confirm or exclude an abdominal aortic aneurysm (fig. 45).
Dimensions of the abdominal aorta:
- Normal < 2.5 cm
- Dilatation > 2.5 cm
- Aneurysm > 3 cm
In the event of abdominal aortic aneurysm, a CTA examination may be performed for additional evaluation.
Figure 45. Abdominal aortic aneurysm with extensive mural thrombus.
We are frequently asked to confirm or exclude appendicitis in patients with abdominal pain. The appendix is located in the right lower abdomen, usually has a diameter of less than 7 mm and is compressible. When the appendix is infected, the diameter will increase and the appendix will no longer be compressible. There will also be fatty infiltration around the inflamed appendix and increased flow will be visible around the appendix using color Doppler. There may also be a trace of free fluid (fig. 46).
Figure 46. Appendicitis with thickening of a non-compressible appendix (appendix was imaged transversally) with fatty infiltration, surrounded by a trace of free fluid.
At times an echogenic structure with acoustic shadowing may be found in the appendix lumen secondary to appendicitis; the appendicolith (fig. 47). The etiology of this calcified structure has not been elucidated yet. It is thought that an appendicolith obstructs outflow, enabling bacteria to replicate and cause infection.
Figure 47. Appendicitis with appendicolith (with acoustic shadowing) in the tip.
Thickened intestinal wall
Full and reliable evaluation of the entire small intestine is never possible. But in most cases the terminal ileum can be evaluated, which is important when confirming or excluding Crohn's disease (fig. 48).
Figure 48. Terminal ileitis with abscess formation in a patient with Crohn's disease.
Marked colonic wall thickening can also be imaged (fig. 49).
Figure 49. Colonic wall thickening consistent with colitis vs normal fluid-filled intestinal loop.
When asked to confirm or exclude diverticulitis, abdominal ultrasound is a suitable initial test. Depending on location (colon/sigmoid) and the patient's build (slender vs obese), an infected diverticulum may or may not be visible.
Figure 50. Diverticulitis. A prominent diverticulum at the dorsal side of the intestine is visible at the level of focal pain symptoms, surrounded by echogenic (= inflamed) fat tissue.
Ultrasound examination may be used in the trauma room to exclude posttraumatic damage. This is also termed the FAST echo (FAST = Focused assessment with sonography for trauma).
The presence of intra-abdominal fluid can be assessed (fig. 51). The fluid (in this case blood) is often found around the spleen, surrounding the liver and in Morrison's pouch (= space between the liver and right kidney).
Figure 51. Free fluid in Morrison's pouch (= space between the right kidney and the liver).
Focal abnormalities in the abdominal organs are also evaluated, particularly in the liver and spleen. Splenic lacerations have poor visibility with ultrasound. After trauma and in the presence of free intra-abdominal fluid, a laceration of the spleen or other parenchymal organ should always be excluded using abdominal CT.
- B. Block. Abdominal Ultrasound: Step by Step (2004).
- W.D. Middleton et al. The Requisites – Ultrasound (2004).
Text & cases:
drs. M.P.M. Kop (abdominal radiologist AMC)
dr. A. Srámek (chief residents & abdominal radiologist LUMC)
drs. A. van der Plas (MSK radiologist Maastricht UMC+)
31/07/2016 (translated 08/02/2018)
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