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| REVIEW ARTICLE |
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| Year : 2016 | Volume
: 14
| Issue : 4 | Page : 113-120 |
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Bedside ultrasound of the abdomen - Part 1
Sudha Kiran Das
Department of Radiodiagnosis, JSS Medical College and Hospital, Mysore, Karnataka, India
| Date of Web Publication | 22-Nov-2016 |
Correspondence Address:
Sudha Kiran Das
Department of Radiodiagnosis, JSS Medical College and Hospital, Mahatma Gandhi Road, Mysore - 570 004, Karnataka
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0973-4651.194476
Ultrasound of the abdomen is a commonly requested investigative procedure. By the use of different probes and varying maneuvers, a remarkable range of views can be obtained. Imaging of the liver is done using four views which can identify most pathological conditions. Being aware of the possible artifacts helps in avoiding a wrong diagnosis. Gallbladder (GB) imaging is useful in detecting gallstones and inflammation of the GB. When inflamed, the pancreas enlarges in size and is bulky, with peripancreatic fluid, which is suggestive of acute pancreatitis. Keywords: Abdomen, liver, ultrasound
How to cite this article:
Das SK. Bedside ultrasound of the abdomen - Part 1. Curr Med Issues 2016;14:113-20 |
| Introduction | |  |
Ultrasound of the abdomen is one of the most commonly requested investigative procedures. It has the advantage of being noninvasive and is relatively inexpensive. It uses sounds at ultrasonic frequencies and their interaction with tissues to visualize intra-abdominal organs and detect abnormalities. For a beginner, it can prove to be intimidating given the different organs involved. Knowledge of the basics can lay the foundation for developing expertise in this procedure. [1],[2],[3] The role of imaging is two-fold - (1) to arrive at a diagnosis and (2) ultrasound-guided intervention if clinically indicated.
A simplified goal can ease the purpose of learning. This article will focus on the basics of "how to do" ultrasound along with a few common pathologies encountered in day-to-day practice. This subsection (Part-1) focuses on basic sonographic views used to evaluate the liver, gallbladder (GB), and pancreas.
| The Probes and Frequencies | | |
For ultrasound of the abdomen, two basic probes are used; one being the curvilinear probe (5-7 MHz) and the other being the linear probe (5-12 MHz). Curvilinear probes generate a wedge-shaped US beam. Straight probes produce a straight US beam and an image with a width equal to the size of the transducer footprint from the surface to the deeper structure. For routine sonography of the abdomen, the curvilinear probe is used. Higher the frequency, greater the attenuation, lesser the penetration, and better the resolution, the linear high-frequency probes are used for evaluation of superficial structures, appendix, and intestine.
| Fundamental Probe Maneuvers | | |
Pressure, alignment, rotation, and tilt are fundamental probe maneuvers that can affect the view (commonly referred by mnemonic "PART") as depicted in [Figure 1]. [4] The amount of pressure applied changes the echogenicity of the tissue under the probe, enables compression of a vein, or pushes an organ out of the way. Alignment or sliding of the probe allows the organ of interest to be identified and placed in the center of the screen. Rotation and tilt of the probe allow the operator to view different sections of the organ (axial, coronal, etc.).
Sonographic terminology
Ultrasound waves are essentially sound waves that have a frequency exceeding 20,000 Hz. These waves interact with body tissues and are attenuated either by absorption, scattering, or beam divergence. The reflected sound waves referred to as echoes are converted to greyscale and displayed as ultrasound images. The intensity of the returning echo determines the echogenicity of a structure [Figure 2]. [5] The following terms are used to classify tissues based on echogenicity.
- Anechoic: No echoes or sonolucent, these appear black on ultrasound (e.g., fluid)
- Hypoechoic: Less reflective and low amount of echoes when compared with neighboring structures, appears as varying shades of darker gray
- Hyperechoic: Highly reflective and echo rich, these appear white on ultrasound
- Isoechoic: Of similar echogenicity as adjacent structures
- Reflective: Complete attenuation of echoes, posterior.
| Sonography of the Liver | | |
Liberal use of the coupling gel is essential in sonography of the liver. Methodical use of the curvilinear probe (fan, angulate, rotate, and translocate) is essential for complete visualization of the organ. Artifacts can be confounding and may lead to misdiagnosis. Being aware of these artifacts can minimize misdiagnosis. Maneuvers such as rotation/translocation of the probe often help differentiate factual images from artifacts.
Four common view stations are utilized:
Epigastric view
This sonographic window [Figure 3][6] is used to evaluate the left lobe of the liver. This view station also clearly delineates the anterior perihepatic space, antropyloric junction of the stomach, and pancreas. For optimal visualization of structures, the patient is asked to drink water before the scan; gas impedes acoustic echoes resulting in poor imaging. Water serves as a window to evaluate deeper structures, namely, pancreas, superior mesenteric vein, and splenic vein confluence. GB and vascular structures are anechoic and are defined by a wall; a lack of echoes within is due to fluid content.
Subcostal view
This sonographic window [Figure 4]6] is used to evaluate the right lobe of the liver. The portal vein, the common bile duct, the intrahepatic veins and hepatocaval confluence, and the diaphragm are best imaged in this window. The patient is asked to take a deep breath and hold it while the sonographer sweeps or fans the probe to visualize the right lobe in its entirety. The lung bases are seen in this window and also pleural effusions. | Figure 4: (a) Subcostal view robe positioning, (b) liver in subcostal view
Click here to view |
One artifact encountered in ths window is the mirror image artifact as depicted in [Figure 5]. This is due to the diaphragm which is a strong reflector of ultrasound echoes resulting in a mirror image of the structure. Artifacts can be confounding and lead to misdiagnosis. Rotation/translocation of the probe often differentiates factual from artifactual.
Parasagittal view
This window [Figure 6][6] is for the right lobe of the liver, namely, segment 6 and 7 (posterior segments). This window aids in visualization of the suprarenal region and the kidney in coronal plane. | Figure 6: (a) Parasagittal view, (b) right lobe of the liver and right kidney
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Intercostal view
The intercostal window [Figure 7] [6] is essentially to evaluate the right lobe. This section depicts the intrahepatic veins and its confluence with IVC. The probe is moved along the intercostal spaces, parallel to the ribs. The lung bases, occurrence of pleural effusion, can be evaluated in this window. | Figure 7: (a) Intercostal view, (b) right lobe of the liver with intrahepatic veins
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Common conditions encountered
In evaluating the liver, the focus is on the uniform echogenicity and texture of the liver. The normal liver parenchyma is of medium echogenicity, usually slightly darker than the spleen and approximately isoechoic to the renal cortex. Its appearance in ultrasound is nearly homogenous except for a characteristic discrete fine-mottled architecture. The liver surface is smooth. It varies very little among individuals and does not change with age. Increased echogenicity is seen in fatty infiltration, and altered echotexture is encountered with cirrhosis of the liver. Focal lesions of the liver can be anechoic (cyst or cystic lesions), hyperechoic (viz, hemangioma), or hypoechoic (infective or neoplastic) [Figure 8] [Figure 9] [Figure 10] [Figure 11]. [6]  | Figure 8: Normal liver and cirrhosis of the liver. Smooth echotexture is lost, surface is no longer smooth, and instead is nodular. Note the free fluid around the liver - ascites
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 | Figure 9: Normal liver (left) and fatty liver (right). Increased echogenicity of the liver in comparison to the renal cortex if kidney is diseased (chronic kidney disease)
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 | Figure 10: Hypoechoic/hyperechoic/anechoic liver lesions. Hypoechoic and hyperechoic - if numerous likely to be metastases. Anechoic lesions are hepatic cysts or cystic lesions
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 | Figure 11: Liver abscess. Two patients with liver abscess, note the lesion with central necrosis. Lack of intrinsic vascularity differentiates this from a necrotic mass
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Liver abscess
Liver abscess is characterized by a lesion with central necrosis and often ragged edges [Figure 11]. Drainage of the liver abscess may be done under ultrasonographic guidance [Figure 12]. [6]  | Figure 12: Ultrasound-guided abscess aspiration. The probe is in the left hand and focuses on the abscess cavity, and the needle is introduced parallel to and alongside the probe under continual guidance as depicted above
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| Sonography of Gallbladder | | |
The GB is visualized using the subcostal and intercostal windows in different positions:
Subcostal window
This may be done in the supine and prone position. Supine subcostal window is commonly performed. Prone subcostal window is done to tip a small GB neck calculus to the fundus for better visualization.
Subcostal and Intercostal windows are also done in the left lateral decubitus position [Figure 13]. [6]
Normal gallbladder
A normal GB should be thin walled (<3 mm) and is anechoic [Figure 14]. It is pear-shaped, saccular structure for bile storage. The size of GB varies depending on the amount of bile. Optimal evaluation of GB is done in a fasting (6 h) state.
Gallstones and acute calculous cholecystitis
Gallstones [Figure 15] are often easily detected using ultrasound and are characterized by dark acoustic "shadows." The wall of the GB is often thickened by inflammation. | Figure 15: Cholelithiasis. Two echogenic foci within the gallbladder lumen with dark shadow posteriorly - gallbladder stones. The last image shows diffuse wall thickening and pericholecystic fluid in a distended gallbladder with calculus suggestive of acute calculous cholecystitis
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| Sonography of the Pancreas | | |
The texture of the pancreas is coarser than that of the liver. The echogenicity of the normal pancreas changes with age. In a child or young person, it may be quite bulky and relatively hypoechoic in comparison to the liver. In adulthood, the pancreas is hyperechoic compared to normal liver. The pancreas does not have a capsule and its margins can appear rather ill-defined, becoming infiltrated with fat in later life. The epigastric window is used for imaging the pancreas [Figure 16]. [6]  | Figure 16: Epigastric window for the pancreas. Often the pancreas is obscured by gastric air. Air impedes sound waves, hence visualization becomes difficult. To overcome this, the patient is made to drink water before the scan and often asked to "blow-out" their abdomen, these two techniques aid in imaging the pancreas
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Age-related changes in the pancreas may be seen with ultrasound [Figure 17]. Acute pancreatitis is characterized by bulky pancreas with peripancreatic fluid and necrosis [Figure 18]. [5] Chronic pancreatitis often presents with calculi with the pancreas or in a dilated pancreatic duct [Figure 19]. | Figure 18: (a) Normal pancreas (left) and acute pancreatitis with peripancreatic fluid (right). (b) Acute pancreatitis with necrosis and pseudocyst formation. When inflamed, pancreas enlarges in size and is bulky with peripancreatic fluid, indicative of acute pancreatitis. Severe pancreatitis can present with necrosis, wherein there is a loss of normal appearance of pancreas, intrapancreatic hypoechoic necrotic areas. Thick-walled collections usually represent a pseudocyst or a walled-off necrosis. Internal contents and debris can help in differentiating the two. The presence of foci of air (hyperechoic foci with comet-tail artifact) is suggestive of superadded infection
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 | Figure 19: Chronic pancreatitis. Multiple echogenic foci with posterior shadow suggestive of calculi. These are seen in the parenchyma as well as along the main duct. The normal caliber of main pancreatic duct is <2 mm; in the images above, the duct is dilated with calculi
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| Conclusion | | |
In closing this section, it is important to remember that practice makes perfect. It is essential to achieve a good hand-eye coordination and acclimatize the eye to the normal appearances before diving in to understand pathology. This can only be mastered by doing several ultrasound procedures rather than wait for the "need of the hour" situation before reaching out for the probe. Systematic and meticulous evaluation is the cornerstone for good detection rates.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | | |
| 1. | Lutz H, Buscarini E. WHO Manual of Diagnostic Ultrasound. 2 nd ed., Vol. 1. WHO in Collaboration with the WFUMB. Geneva, Switzerland. WHO Press. © World Health Organization 2011. Available from: http://www.who.int/diagnosticimaging/publications/en/. [Last accessed on 2016 Sep 29].  |
| 2. | Bates JA. Abdominal Ultrasound: How, Why and When. 2 nd ed. New York, NY: Churchill Livingstone; 2012. |
| 3. | Berthold B. Abdominal Ultrasound: Step by Step. 2 nd ed. Thieme Stuttgart, New York: 2009. |
| 4. | Ihnatsenka B, Boezaart AP. Ultrasound: Basic understanding and learning the language. Int J Shoulder Surg 2010;4:55-62. [ PUBMED]  |
| 5. | |
| 6. | |
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19]
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