Continuing Education Activity

Ultrasound is an imaging modality that has been in clinical use for approximately 50 years, though its utility and efficacy have dramatically improved since its introduction. Ultrasound is portable, cost-effective, and does not require radiation or contrast. This activity reviews the use of ultrasound in detecting many abdominal pathologies, with a particular focus on indications, contraindications, and the technique involved in performing a transabdominal ultrasound. This activity highlights the role of the interprofessional team in the care of patients undergoing this procedure.

Objectives:

• Identify the indications for an abdominal ultrasound.
• Describe the technique involved in performing an abdominal ultrasound.
• Outline the limitations of an abdominal ultrasound.
• Communicate interprofessional team strategies for improving care coordination and communication to enhance the utilization of abdominal ultrasound and improve patient outcomes.

Introduction

Ultrasound is an imaging modality that has been in clinical use for approximately 50 years. Sokolov first described the potential for using this technology to produce low-resolution images in 1939. Later understanding of the piezoelectric effect and further technological refinements have led to advancements in machines. We have seen machine sizes decrease dramatically; some of the earliest machines were the size of refrigerators, while more recently, we have seen the introduction of transducers compatible with smartphones. Although ultrasound technology can be used in a variety of settings and body locations, the focus of this article will be on transabdominal ultrasound, including its definition, indications, and diagnostic pearls and pitfalls.[1][2]

Transabdominal ultrasound was initially used in its most common setting, pregnancy, in the 1960s.[3][4] It is now used to visualize multiple abdominal organs, both intraperitoneal and retroperitoneal. By definition, any evaluation with an ultrasound transducer overlying the abdominal wall can be considered a transabdominal ultrasound. Transabdominal ultrasound can be used to visualize the liver, gallbladder , kidneys, pancreas, small and large intestines, appendix, bladder, uterus, adnexa, spleen, stomach, aorta, and IVC. In the setting of obstetrics and gynecology (OBGYN), the transabdominal approach is usually performed to evaluate for possible pelvic pathology or pregnancy in a less invasive manner. In the emergency department (ED) a transabdominal ultrasound is most commonly utilized to evaluate for intrauterine pregnancy[5], cholelithiasis, intraabdominal free fluid, abdominal aortic aneurysm, and hydronephrosis. 

Emergency physicians (EPs) perform limited point-of-care ultrasound (POCUS) compared with formal radiology transabdominal ultrasound. The EP performs the former, whereas a trained sonographer performs a thorough and complete examination of the organ. ED POCUS focuses on binary questions that are rapidly evaluated at the bedside and directly impact patient care. For example: “Is there an intrauterine pregnancy?” In most cases, when an intrauterine pregnancy is identified, the examination is complete. While both EPs and sonographers perform transabdominal ultrasound, their performance characteristics and goals differ.[6]

Anatomy and Physiology

Sonographic anatomy, similar to gross anatomy, recognizes landmarks and scanning conventions that were originally defined by specialties like obstetrics and radiology. For example, the gallbladder is located under the liver and has great variability with its location. The sonographic cystic pedicle (SCP) is a landmark utilized to ensure correct identification of the gallbladder.[7] Originally this was called the main lobar fissure (MLF), which was thought to correlate to the main portal fissure. Cadaveric dissection later found this to be an extrahepatic structure paralleling the rim of the main lobar fissure and was re-named the SCP, which includes the cystic duct, ensheathing fat and blood vessels. Each organ of interest has its varying anatomy and ultrasound scanning convention to acquire the desired image or measurements needed to identify pathology.

Indications

Abdominal Pain

Right Upper Quadrant [8]: Evaluation for free fluid, cholelithiasis, choledocholithiasis, hepatic abscess mass, and hydronephrosis

Right Lower Quadrant: Evaluation for appendicitis[9], intussusception, psoas abscess

Left Upper Quadrant: Evaluation for free fluid, splenic pathology (laceration or fracture), stomach, and hydronephrosis

Left Lower Quadrant: Evaluation for diverticulitis, small bowel obstruction[10]

Epigastric: Evaluation for pancreatic mass, abdominal aortic aneurysm

Pelvic: Evaluation for free fluid, urinary retention, pregnancy, ectopic pregnancy, pelvic mass

Blunt or Penetrating Abdominal Trauma

• Evaluation of free fluid[11]

Vaginal Bleeding

• Evaluation for pregnancy, ectopic pregnancy, uterine pathology, abortion (fetal parts)

Hypotension:

• Evaluation for infectious sources listed above, vascular assessment of the inferior vena cava as a surrogate marker for volume status or volume loss from hemorrhage, and abdominal aortic aneurysm [12]

Hematuria

• Evaluation for genitourinary mass, nephrolithiasis, and hydronephrosis

Contraindications

There are no absolute contraindications to performing a transabdominal ultrasound. One should take care not to scan over a wound or incision to avoid contamination and infection. Color and pulsed Doppler should not be applied to a fetus because of the theoretical radiation risk to the fetus.[13]

Equipment

Transabdominal ultrasound should be performed with a low-frequency probe, ideally with a large convex footprint. The most commonly used probes are the curvilinear and phased-array probes. Disinfectant wipes and cleaning equipment are institution-specific and usually determined by the infectious disease department.

Personnel

A trained provider can perform a transabdominal ultrasound. Registered diagnostic medical sonographers (RDMS) have different requirements and certification than most primary providers performing a point-of-care ultrasound at the bedside. For example, emergency physicians are required to perform and interpret a minimum of 25 to 50 cardiac ultrasound exams upon graduation from residency.

Preparation

Ensure that the probe and machine are cleaned before entering a patient's room. The correct probes should be connected to the machine. The patient is ideally lying in a supine position on a stretcher with his or her abdomen exposed. Care should be taken to avoid unnecessary exposure by tucking towels around the gown and undergarment edges. This will also help keep unexposed areas free of ultrasound gel.

For dominant right-hand operators, the ultrasound machine should be positioned at the patient’s anatomic right near the head of the bed, plugged in (if applicable), and turned on. The lights should be dimmed if possible. For gallbladder evaluation, fasting aids gallbladder engorgement and improves visualization. When evaluating the uterus, instructing the patient to maintain a full bladder will aid visualization by providing an acoustic window to deeper structures.

Technique or Treatment

A low-frequency convex probe is best for a transabdominal ultrasound. Alternatively, a phased-array probe can be used if a convex probe is unavailable. The ultrasound machine settings should be adjusted to the desired exam being performed, for example, abdominal, FAST, or vascular. The machine's settings optimize image quality for the scan being performed. Generally, the probe indicator is always aimed cephalad (toward the patient’s head) or to the patient’s right side. A specific scanning technique is utilized depending on the organ or pathology being evaluated. For example, when evaluating the gallbladder, the probe is placed in a sagittal plane (with the indicator cephalad) in the right upper quadrant just inferior to the costal margin. The operator then slides the probe medially and laterally along the costal margin while maintaining the sagittal plane (cephalad), evaluating the optimal sonographic window for image acquisition. Asking the patient to take a deep breath and hold it causes the diaphragm to contract, displacing the liver and gallbladder inferiorly, and aiding in image acquisition. A coronal scan of the right upper quadrant is another technique that can be used to evaluate the gallbladder. With the probe placed on the patient’s right, in the mid-axillary line, indicator cephalad, the operator can then fan the probe anteriorly and posteriorly through the liver to acquire an optimal window for evaluating the gallbladder. The gallbladder is then evaluated for (1) stones or sludge, (2) wall thickening (normal less than 3 mm), (3) presence of a sonographic Murphy's sign, and (4) pericholecystic fluid.[14] The presence of all four is very sensitive and specific for cholecystitis. This is an example of one specific area of transabdominal ultrasound. There are specific techniques for evaluating most abdominal organs and underlying pathologies using ultrasound.

Complications

Transabdominal ultrasound, like most diagnostic ultrasound applications, is associated with little if any risk. There may be some associated discomfort when pressure is applied.

Clinical Significance

Transabdominal ultrasound is an inexpensive, safe, and rapid way to assess multiple pathologies. It can be used to effectively rule in or out specific pathologies, such as cholecystitis, without the need for further imaging in many cases. This can lead to an expedited diagnosis and treatment, and a reduction in ionizing radiation.

Enhancing Healthcare Team Outcomes

It is the healthcare provider's responsibility to decrease the harm caused by ionizing radiation. ALARA principle supported by the US-Nuclear Regulatory Commission and the Centers for Disease Control and Prevention (CDC).[15][16]

Review Questions

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References

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2.

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Benson CB, Doubilet PM. The history of imaging in obstetrics. Radiology. 2014 Nov;273(2 Suppl):S92-110. [PubMed: 25340440]

4.

Schillinger H, Müller R, Kretzschmar M, Wode J. [Estimation of fetal weight by ultrasound (author's transl)]. Geburtshilfe Frauenheilkd. 1975 Nov;35(11):858-65. [PubMed: 1193357]

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Hall MK, Mirjalili SA, Moore CL, Rizzolo LJ. The student's dilemma, liver edition: incorporating the sonographer's language into clinical anatomy education. Anat Sci Educ. 2015 May-Jun;8(3):283-8. [PubMed: 25573229]

8.

Joshi G, Crawford KA, Hanna TN, Herr KD, Dahiya N, Menias CO. US of Right Upper Quadrant Pain in the Emergency Department: Diagnosing beyond Gallbladder and Biliary Disease. Radiographics. 2018 May-Jun;38(3):766-793. [PubMed: 29757718]

9.

Matthew Fields J, Davis J, Alsup C, Bates A, Au A, Adhikari S, Farrell I. Accuracy of Point-of-care Ultrasonography for Diagnosing Acute Appendicitis: A Systematic Review and Meta-analysis. Acad Emerg Med. 2017 Sep;24(9):1124-1136. [PubMed: 28464459]

10.

Taylor MR, Lalani N. Adult small bowel obstruction. Acad Emerg Med. 2013 Jun;20(6):528-44. [PubMed: 23758299]

11.

Williams SR, Perera P, Gharahbaghian L. The FAST and E-FAST in 2013: trauma ultrasonography: overview, practical techniques, controversies, and new frontiers. Crit Care Clin. 2014 Jan;30(1):119-50, vi. [PubMed: 24295843]

12.

Ciozda W, Kedan I, Kehl DW, Zimmer R, Khandwalla R, Kimchi A. The efficacy of sonographic measurement of inferior vena cava diameter as an estimate of central venous pressure. Cardiovasc Ultrasound. 2016 Aug 20;14(1):33. [PMC free article: PMC4992235] [PubMed: 27542597]

13.

Kurjak A. Are color and pulsed Doppler sonography safe in early pregnancy? J Perinat Med. 1999;27(6):423-30. [PubMed: 10732300]

14.

Woo MY, Taylor M, Loubani O, Bowra J, Atkinson P. My patient has got abdominal pain: identifying biliary problems. Ultrasound. 2014 Nov;22(4):223-8. [PMC free article: PMC4760551] [PubMed: 27433223]

15.

Shah NB, Platt SL. ALARA: is there a cause for alarm? Reducing radiation risks from computed tomography scanning in children. Curr Opin Pediatr. 2008 Jun;20(3):243-7. [PubMed: 18475090]

16.

Bello SO, Ekele BA. On the safety of diagnostic ultrasound in pregnancy: have we handled the available data correctly? Ann Afr Med. 2012 Jan-Mar;11(1):1-4. [PubMed: 22199039]

Disclosure: Ami Kurzweil declares no relevant financial relationships with ineligible companies.

Disclosure: Jennifer Martin declares no relevant financial relationships with ineligible companies.