Pediatric Abdominal Ultrasound: A Comprehensive Guide to Making the Diagnosis — Part II
August 1, 2018
AUTHORS
Ultrasound is evolving rapidly as the ideal imaging modality for many common pediatric complaints. In the second part of this series, the authors discuss point-of-care use of ultrasound for concerns regarding the kidneys, ovaries, testicles, gallbladder, and small bowel obstruction. The ability to make critical diagnoses safely and rapidly with ultrasound is an invaluable clinical tool to facilitate and improve pediatric care.
— Ann M. Dietrich, MD, FAAP, FACEP, Editor
To avoid ionizing radiation in support of the ALARA (as low as reasonably achievable) concept in pediatric imaging, ultrasound frequently is the preferred imaging modality in the pediatric population.1 Ultrasound is noninvasive, cost-effective, easy to use, portable, and requires no sedation; however, the reliability of ultrasound is highly operator dependent. Point-of-care ultrasound performed and interpreted in the emergency department (ED) can reduce the time to disposition and expedite definitive patient care.2-4 This two-part series reviews the applications of ultrasound to diagnose common pediatric abdominal pathologies, as well as discusses the basic technique for each ultrasound exam. Part I included discussion of pyloric stenosis, acute appendicitis, intussusception, the Pediatric Focused Assessment with Sonography for Trauma (FAST) exam, and imaging of the inferior vena cava and aorta. Part II will include renal, ovarian, testicular, and biliary ultrasound focusing on diagnosing obstructive uropathy, ovarian torsion, testicular torsion, small bowel obstruction, and cholecystitis. Emergency medicine physicians should be proficient in using point-of-care pediatric ultrasound while having a thorough understanding of the limitations and common pitfalls.
Renal, Testicular, and Ovarian Ultrasound: From the Beans to the Groin and Everything in Between
Renal Ultrasound: Time Traveling Back to the Stone Age
A 12-year-old girl presents to the ED with right-sided flank pain and nausea. Her creatinine is within normal limits and her urinalysis is significant for hematuria. There is concern that she may have an obstructing ureteral stone. The incidence of renal colic in the pediatric population is rising and mostly affects adolescents.5 Stone disease is related to one in 685 pediatric hospitalizations in the United States.6 Stones that are more distal in location and 5 mm or less in size have a greater probability of passing and are unlikely to require urologic intervention.7
Unenhanced computed tomography (CT) is the preferred imaging method to detect nephrolithiasis in patients with suspected renal colic; however, ultrasound is a useful alternative in the emergency setting to lower cost and limit exposure to ionizing radiation. Ultrasound can be useful for diagnosing kidney stones either via direct visualization or by evidence of obstructive uropathy, particularly in the setting of a high clinical suspicion for the presence of obstructing stone disease. Point-of-care ultrasound can identify signs of obstruction secondary to urolithiasis, including hydronephrosis, hydroureter, and decreased or absent ureteral jets on the affected side.8 Although ureteral stones often are obscured by bowel gas, ultrasound is best at detecting stones that are either proximal to the ureteropelvic junction or distal to the ureterovesical junction.9 Stones are hyperechoic with associated posterior shadowing. CT is both highly sensitive and specific for diagnosing kidney stones with a sensitivity of 95-98% and specificity of 95-100%.10-12 Authors of one study found that the preferential use of ultrasound as the initial imaging modality vs. CT reduced cumulative radiation exposure; they found no significant difference in complications, hospitalizations, pain scores, serious adverse events, or return ED visits.13
Initiate the exam with the patient in the supine position. The curvilinear or phase-array transducer should be used to perform the exam. The smaller footprint of the phase-array probe may assist in intercostal imaging to avoid rib shadowing. The right kidney typically is found posterior to the right midaxillary line between the ninth and 10th intercostal space. The probe indicator should be directed toward the patient’s head. Adjusting either the angle of the probe to facilitate imaging between the intercostal spaces or directing the probe cephalad or caudal may be necessary to bring the kidney, with its characteristic bean shape, into view. Both the upper and lower poles of the kidney should be visualized.14,15 A thin, linear capsule separates the kidney from the surrounding echogenic perirenal fat. The kidney is divided into the renal parenchyma, which is composed of the cortex and more hypoechoic medullary pyramids, and the hyperechoic renal sinus, which includes the calyces, renal pelvis, and major intrarenal vessels.16 Nomograms exist for estimating pediatric kidney size based on height and weight.17 Fan the probe anteriorly and posteriorly in the coronal plane to evaluate the entire long axis of the kidney. Evaluate the structure of the kidney while looking for evidence of hydronephrosis, stones, masses, cysts, or other pathology. (See Figure 1.)
Figure 1. Ureterovesical Junction Stone |
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A stone (indicated by the arrowheads) is present at the ureterovesical junction (or UVJ). The asterisk denotes the ureteral dilation proximal to the stone. |
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Rotate the probe by 90 degrees to view the kidney in a transverse orientation. Fan the ultrasound probe in the cephalad to caudal direction to view the entire kidney. The left kidney’s anatomical placement differs from that of the right kidney. The left kidney is located more superior and posterior compared to the right kidney. To visualize the left kidney, place the probe, with the probe indicator toward the head of the patient, between the seventh and eighth intercostal spaces at the posterior axillary line. Perform the same movements to obtain the images of the left kidney in both the coronal and transverse planes. Sometimes overlying bowel gas may obscure the view of the kidney. If the kidneys are difficult to visualize, ask the patient to take a deep breath in and hold. The position of the kidney will change with inspiration and may provide a superior imaging window. Furthermore, rotating the patient in the lateral decubitus or prone position may be helpful.14,15
Renal point-of-care ultrasound is used commonly in the ED setting to evaluate for secondary signs of nephrolithiasis, including hydronephrosis. (See Figure 2.) A grading system ranging from mild to severe was created to classify the degree of dilation of the intrarenal collecting system. In a normal kidney or grade 0, no dilatation of the collecting system should be present. Grade I is minimal dilation of the renal pelvis only. Grade II is present when the pelvis and most, but not all, calyces are dilated. Grade III is complete pelvocaliectasis with uniformly dilated calyces with sparing of the parenchyma. Grade IV is significant dilation of the entire collecting system with parenchymal thinning.16,18
Figure 2. Progressive Severity of Hydronephrosis |
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The twinkling artifact is a multicolor, high-intensity signal produced behind highly reflective surfaces, like calculi, when color Doppler is applied. Several studies have shown that the sensitivity of ultrasound for detecting lithiasis increases when this artifact is present compared to using B-mode alone.19,20 The sensitivity, specificity, and accuracy of ultrasound for detecting lithiasis are 90-98.3%, 100%, and 92-98.4%, respectively.21,22 The twinkling artifact may assist in localizing smaller stones and stones positioned in the ureter, often one of the most challenging areas to visualize with ultrasound.22
Ureteral jet flow can provide useful information about the integrity and flow dynamics of the urinary tract system. Studies have shown that the ureteral jet frequency, duration, and peak velocity are decreased in an obstructed ureter when compared to an unobstructed ureter.23 Peak flow velocity is related inversely to stone size, and can be used to predict spontaneous passage.24 Perform the exam by obtaining a transverse image of the bladder that encompasses both of the ureteral orifices at the level of the trigone. Apply color Doppler to view the ureteral jets. Most studies in the literature suggest observing for ureteral jets for 5-10 minutes.23,25
Ovarian Torsion: Twister Warning
A 15-year-old female with a recent diagnosis of polycystic ovarian syndrome enters the ED with a two-day history of right lower pelvic pain. She reports one episode of vomiting. She is afebrile and has right pelvic tenderness to palpation. Laboratory results reveal leukocytosis. A large differential diagnosis exists for pelvic and lower abdominal pain in children; however, ovarian torsion (OT) is a possible suspect. (See Table 1.)
Table 1. Findings on Point-of-care Ultrasound |
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Pathology |
Findings |
Comments |
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Ovarian torsion |
Enlarged peripherally displaced cysts, free fluid, whirlpool sign, medialization of the ovary, absence of color Doppler (typically a late finding) |
Ultrasound is a good indicator, but is not definitive to exclude torsion. Must consult gynecology if there is a high degree of suspicion. |
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Testicular torsion |
Heterogenous appearance, enlarged, lack of color Doppler, whirlpool sign (spermatic cord twisting) |
Ultrasound is a good indicator, but is not definitive to exclude torsion. Must consult urology if there is a high degree of suspicion |
OT is a challenging, time-sensitive, and feared gynecologic emergency to miss among emergency medicine physicians. OT is defined by a partial or complete rotation of the ovary and adnexal components around the ligamentous structures that results in compromised circulation and lymphatic obstruction.26,27 It is referred to as adnexal torsion if the fallopian tube is affected as well.27 Often, children are unable to provide an adequate history, and the presenting symptoms frequently are nonspecific; however, nausea and vomiting are more likely to be reported in OT.28-31 Peritoneal signs are elicited more often in patients with torsion.29
OT is rare, with an estimated incidence of 4.9 per 100,000 females between 1 and 20 years of age, with an average age of 14.5 years.32 Both premenarchal and postmenarchal girls are at risk for OT.27,33 Ultrasound is the primary imaging modality to evaluate pelvic pain, with a sensitivity and specificity of 90.9% and 68.7% for OT, respectively.28 The presence of an ovarian mass, most commonly a functional cyst, mature teratoma, or serous cystadenoma, is associated with OT.28 OT has been found to occur more frequently on the right side.34
Authors of several recent studies have advocated for ovarian detorsion, with the goal to spare the ovary rather than perform definitive operative management with oophorectomy.30,35 Walker et al found that more than 70% of children and adolescents who underwent ovarian-sparing operations had signs of subsequent development of ovarian follicles in the previously torsed ovary.30 Laparoscopy should be considered in children with high clinical suspicion for ovarian torsion, despite a negative ultrasound.36
The most common sonographic finding of OT is an enlarged ovarian mass.28,34 An ovarian mass > 5 cm in the setting of pain is highly determinant for OT.28 The presence of ovarian stromal edema and the peripheral distribution of follicles has been found to be predictive of OT.28 Linam et al found ovarian torsion in menarchal females is unlikely if the adnexal volume is less than 20 mL,37 while Servaes et al found that the median volume of the torsed adnexa was 12 times that of the contralateral normal ovary when both ovaries were visualized.34 Assessment of the contralateral ovary is essential when evaluating for torsion. In torsion, medialization of the affected ovary may occur. That is, when the adnexal structures become twisted, the distance between the ovary and the uterus shortens and the ovary becomes more mid-line.38
A high-frequency or curvilinear probe should be used to perform the exam. The transabdominal approach is preferred in premenarchal children. It is recommended that the patient have a full bladder during the assessment to create an acoustic window to improve visualization of the ovaries.27 Place the probe superior to the pubic symphysis midline on the abdominal wall with the probe angled into the pelvis; the probe indicator should be pointed toward the patient’s head. Assess the uterus, ovaries, and the adnexal structures in both the longitudinal and transverse orientations. A normal ovary should appear as an ellipsoid structure containing hypoechoic follicles; the size of the ovary varies with age, pubertal status, and menstruation.
The ovary has a dual blood supply from both the ovarian and uterine arteries. There is conflicting evidence regarding the ability of color Doppler to predict ovarian vascular compromise in torsion. Several studies have found a poor correlation between actual vascular sufficiency and color Doppler tracings. Color flow, either venous or arterial in origin, was found to be present in 62% of OT cases.34 A Doppler signal in an abnormal ovary does not eliminate the possibility of OT. Likewise, the absence of color Doppler signals as a lone ultrasound finding does not necessarily translate into a diagnosis of torsion every time.27,39
Free fluid in the pelvis may be present, but often is small in quantity and nonspecific.29,34 The “spiral” or “whirlpool” sign is a sonographic finding indicative of adnexal torsion;40 this sign refers to the appearance of the twisted ovarian pedicle together with a characteristic Doppler sign that resembles a whirlpool or spiral.41 To produce this sign, move the probe back and forth along the axis of the ovarian pedicle.40 This sign can be found lateral or medial to the ovary.40 Although it is sensitive for torsion, it is not always present.41,42 Of note, this sign is used in the testicular torsion literature as well. Be aware that hemorrhagic cysts can share a similar appearance to OT and may result in false-positive results.28,38 (See Figure 3.)
Figure 3. Ovarian Ultrasound |
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The first image shows the peripheral distribution of the hypoechoic ovarian follicles, a common finding in ovarian torsion. The second image depicts a longitundinal view of the bladder, uterus, and posterior cul-de-sac. |
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Special consideration must be made with both ovarian and testicular torsion, as these are diagnoses that cannot be excluded with ultrasound alone. A high degree of suspicion for either ovarian or testicular torsion, even with a negative ultrasound, warrants a consultation with a gynecologist or urologist, respectively. While point-of-care ultrasound can serve as an adjunct to a more rapid diagnosis, emergency providers must not rely solely on a negative study to rule out these pathologies if the clinical presentation is supportive of the diagnosis.
Testicular Torsion: Pain and Suffering
A previously healthy, fully immunized 9-year-old male has experienced a two-hour history of acute onset of right-sided scrotal pain and nausea that began during play. No history of trauma is mentioned. He appears uncomfortable during the exam and has right scrotal tenderness. The cremasteric reflex is difficult to elicit on the right, and there is concern for a high-riding right testicle. (See Table 1.)
There is a broad differential diagnosis for acute scrotal pain in children. Epididymitis and torsion of the testicle, appendix testis, and appendix epididymis are common culprits, with varying levels of morbidity (i.e., testicular loss). Testicular torsion is a urological emergency that accounts for approximately 23% of acute scrotums in boys and requires a prompt and accurate diagnosis to guide management to promote testicular salvage.43,44 Torsion occurs when the testis twists around the vascular pedicle, also known as the spermatic cord. Ultrasound is the main diagnostic modality used to differentiate between various scrotal pathologies.45 (See Figure 4.)
Figure 4. Testicular Torsion |
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The first color Doppler image illustrates compromised vascular flow observed in testicular torsion. The second image of the male pelvis demonstrates the bladder and seminal vesicles in the transverse view. |
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Normally, the testes appear as symmetric, oval-shaped, and homogenous structures within the scrotum. The testes are separated by a highly reflective raphe. The tunica albuginea that encases each testicle is easily differentiated from the surrounding structures because of its hyperechoic appearance. The mediastinum testis, rete testis, appendix testis, and the epididymis should be identified. The mediastinum testis can be seen as a linear, thin echogenic band traversing the testis near the midline, whereas the nearby rete testis can be visualized as a collection of hypoechoic tubular structures. The isoechoic oval-shaped appendix testis lies between the epididymis and testis. The epididymis is a curved structure that extends over the posterior border of the testicle.46-49 The head of the epididymis often appears isoechoic or slightly hyperechoic or hypoechoic compared to the testicle, while the body and tail tend to be isoechoic.50 The spermatic cord is highly echogenic and can be found within the testicle extending into the inguinal canal.46-49
Always perform genital exams with a chaperone present. Prior to examination, ensure that the patient is comfortable. Placing a towel under the scrotum provides elevation and support. Use a high-frequency, linear transducer. Ask the patient to locate the point of maximal pain. First, examine both testicles side-by-side in the transverse view to document lie and obtain both static and real-time color Doppler images. Each testis should be scanned in both the longitudinal and transverse orientation. Measure each testicle in three dimensions to calculate the testis volume. Scan the unaffected testicle first to provide a normal reference point to compare against the symptomatic testicle.46,47,51
Assess the flow pattern of each testis using color or power Doppler (calculate a testicular arterial resistive index if possible). Power Doppler often is preferred over color Doppler because of its greater sensitivity.46 Scan the testis thoroughly again in multiple orientations; note the echotexture of the normal testicle, as this should be compared against the abnormal side. Identify and evaluate the orientation and echogenicity of the epididymis. In the longitudinal plane, follow the spermatic cord from its origin through the inguinal canal to the internal ring. Furthermore, survey the testicle and extra-testicular space for additional pathology or incidental findings (e.g., hydrocele, mass, appendages.)46,47,51 Repeat the exam on the affected side documenting any pathology.
Impedance of the venous, arterial, and lymphatic system of both the testis and epididymis may develop. Consequently, this process can lead to ischemia, infarction, and eventually necrosis of the testis, which translates into highly variable sonographic findings.52 Although some studies have demonstrated that color Doppler ultrasound has an ability to detect testicular torsion with a 96-100% sensitivity and 75-95% specificity,53-55 there is evidence in the literature to suggest that color Doppler waveform should not be the sole determinant of the presence or absence of torsion, particularly in the setting of early torsion or partial torsion in which testicular flow still may be present, leading to false-negative results.43,53-62 In the case of complete torsion, arterial and venous flow often are absent or reduced.46,63
The torsed testicle may assume a heterogeneous and hypoechoic or hyperechoic appearance that results from arterial insufficiency and subsequent ischemia.46,64 Concomitantly, the testicle may become enlarged secondary to vascular congestion, and a significant size discrepancy between the affected and unaffected testicle may be notable. A healthy testis typically is positioned in the vertical orientation, while a horizontal or oblique lie is a concerning feature.65 Scrotal edema and reactive hydroceles comprised of anechoic fluid on ultrasound may occur.64
Abnormal morphology and displacement of the epididymis, and/or an enlarged, rotated, redundant, or an abnormal echo texture or compromised vascular flow of the spermatic cord suggests torsion.62,66 The classic “whirlpool sign” signifies a twisting of the spermatic cord creating a spiral-like pattern.67-69 A recent systematic review and meta-analysis found the “whirlpool sign” to be highly prognostic for torsion of the testicle and spermatic cord in children, with the exception of neonates.49 Unfortunately, the “whirlpool sign” is not reliably observed in all cases.70
Small Bowel Obstruction: Blocks Are Not Fun for Children
A 6-year-old female with a past surgical history of appendectomy reports a three-day history of paroxysmal abdominal pain. She has had several episodes of nonbilious emesis. Multiple children have been ill at her school recently. While her symptoms easily could be attributed to gastroenteritis or even constipation, it is important to include small bowel obstruction (SBO) as part of the differential diagnosis. Fifteen percent of hospital admissions for acute abdominal pain are attributable to SBO.71 The common culprits of SBO in children include intestinal adhesions, Meckel’s diverticulum, and internal hernia.72 If not recognized in a timely manner, the complications of SBO, such as ischemia, necrosis, and perforation, could result in significant morbidity and mortality.73
Ultrasound is valuable in the diagnosis of SBO. Most studies in the literature primarily have focused on the adult population, while the existing data in the pediatric population are limited.74,75 Although the diagnosis of SBO occurs less frequently in children compared to adults, the incorporation of point-of-care ultrasound into the assessment of children who present with abdominal pain, vomiting, and/or abdominal distention to identify SBO should be considered. Plain abdominal films often are nondiagnostic and have been found to be inferior to ultrasound in the evaluation of SBO, despite the use of X-ray as a standard initial imaging technique.76-78 X-ray has a sensitivity of 46% and specificity of 67% for SBO.78
In a systematic review and meta-analysis, Gottlieb et al concluded that ultrasound was 92% sensitive and 96% specific for the diagnosis of SBO.74 Although the authors did not exclude the pediatric population from this study, the mean age of participants was 50 years, which raises concerns about the generalizability of using ultrasound to diagnose SBO in children. However, several clinical cases have demonstrated the successful use of point-of-care ultrasound in the ED to diagnose SBO in children.75 Emergency medicine residents are able to diagnose SBO accurately using point-of-care ultrasound, comparable with that of radiology residents, after a brief training period.76,78
Both phase array and curvilinear probes are acceptable to evaluate for SBO.78 The patient should be in the supine position. Scan in the colic gutters, epigastrium, and suprapubic region, observing for fluid-filled dilated bowel, abnormal peristalsis, and collapse of the colonic lumen.76,78 (See Figure 5.) A dilated bowel extending over three bowel loop segments that measures ≥ 25 mm in the jejunum and ≥ 15 mm in the ileum has a sensitivity of 91-94% and specificity of 84-94% for SBO.76,78 The intestinal fold pattern and location of dilated loops should aid in the discernment of the location of the bowel obstruction.76 The jejunum has prominent and numerous valvulae conniventes, also known as plicae circulares, which decrease substantially in the ileum. Abnormal peristalsis has been associated with SBO.78
Figure 5. Small Bowel Obstruction |
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Dilated loops of fluid-filled bowel present in small bowel obstruction. |
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Frequently, abnormal peristalsis is visualized in SBO and has been described as “to-and-fro,” “bounce-back,” or “back and forth” movements with echoes present within the fluid-filled bowel.76 Increased or decreased to absent peristalsis also has been reported in SBO.75,76,78 Decreased peristalsis alone has a sensitivity of 27%, while increased peristalsis has a reported sensitivity of 72%.76,78 Combining both the presence of dilated bowel and decreased peristalsis increased the sensitivity to 94%, improving the sensitivity of either finding alone.78 A collapsed colon is 85% sensitive for SBO.76 Additionally, the presence of ascites in the setting of SBO is suggestive of intestinal strangulation, a complication of SBO with high morbidity.72 An increase in bowel wall thickness and an increase in the intestinal content may be found as well.71
Pediatric Cholecystitis: A Condition Gallingly on the Rise
A 6-year-old, afebrile male is being evaluated for a one-day history of abdominal pain. His mother denies fever, vomiting, diarrhea, constipation, dysuria, or contact with sick individuals. His exam is remarkable for voluntary right-sided abdominal guarding. Labs are normal. After a period of observation and a normal ultrasound of the appendix, his abdominal tenderness remains concerning. Although cholecystitis primarily is considered an adult disease, the prevalence of cholecystitis and biliary tract pathology in the pediatric population has been on the rise.79 The etiology of the increase is not fully understood; however, the rising childhood obesity rate and more widespread use of ultrasound, leading to a higher rate of diagnosis, have been proposed as factors.80
Children of all ages are subject to gallbladder disease.80 Although many cases of pediatric cholelithiasis are idiopathic, there is a wide spectrum of risk factors, including obesity, pregnancy, hemolytic disease, prolonged total parenteral nutrition, and use of oral contraceptives.81-86 In addition, chronic cholecystitis and acute acalculous cholecystitis (ACC) account for a subset of pediatric inflammatory gallbladder disease.87,88 ACC can result in significant morbidity and mortality, and it has been found to be an unfortunate complication of the course of various illnesses, including infectious disease (e.g., hepatitis A, Epstein-Barr virus, human herpes virus-type 6), systemic disease (e.g., systemic lupus erythematosus, Kawasaki disease, cystic fibrosis), critical illness (e.g., sepsis), trauma, and the postoperative period.88-94 ACC can occur in otherwise healthy children.95 In contrast, hemoglobinopathies, such as sickle cell disease, predispose children to gallstones from disproportionate bilirubin production secondary to recurrent hemolysis.85 Ultrasound is the favored imaging modality to identify gallbladder pathology. Detection of cholecystitis by ultrasound by emergency medicine physicians shares similar accuracy to that of radiologists.96
The gallbladder is a hypoechoic, oblong structure surrounded by a thin echogenic wall.93 The normal anterior gallbladder wall thickness is < 3 mm. (See Figure 6.) Gallbladder wall thickening alone is not definitive for cholecystitis; wall thickening can be manifested in multiple other disease processes, including bacterial or viral infections (e.g., hepatitis A), systemic disease (e.g., renal failure, heart failure, liver disease, or systemic lupus erythematosus), and pancreatitis.97-99 The normal common bile duct has a diameter up to 6 mm in older children and adults, while the standard is considered to be < 3.3 mm in children younger than 13 years of age and < 1.2 mm in children younger than 3 months of age.100
Figure 6. Transverse and Longitudinal Views of a Normal Gallbladder |
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Sonographically, cholelithiasis will appear as hyperechoic foci within the gallbladder or ducts.93 Most gallstones will produce a posterior acoustic shadowing artifact, but stones < 5 mm may not.93 The wall-echo-shadow complex, or WES sign, is produced when the gallbladder is collapsed and filled with a large or multiple stones.101 The WES complex is composed of the highly echogenic, thin curvilinear wall of the gallbladder with a subjacent echo formed from the reflective gallstones with the accompanying underlying shadowing.101 Pericholecystic fluid and gallbladder distention are additional secondary findings. (See Figure 7.)
Figure 7. Gallbladder |
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A. Gallbladder wall thickening. B. Pericholecystic fluid. C. Stone in the neck of the gallbladder. D. Multiple stones in the gallbladder. |
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A positive sonographic Murphy sign, a key diagnostic marker, occurs when pain is elicited as downward pressure is placed directly over the gallbladder by the ultrasound probe.93 The sonographic Murphy sign detected by emergency medicine physicians has been shown to have superior sensitivity for diagnosing acute cholecystitis compared to a formal ultrasound by radiology.102 Tsai et al suggested that ultrasound findings described in acute cholecystitis have lower sensitivities and positive predictive values in the pediatric population compared to those reported in adults.103
Perform the examination with the patient in the supine position, starting in either the sagittal or transverse orientation with either the curvilinear or phase array probe.80,93 Ideally, the exam should be performed after the patient has fasted to avoid contraction of the gallbladder, which naturally occurs after meal consumption. Several different techniques can be used to locate the gallbladder, including the “subcostal sweep,” “X-minus 7,” and “flattening the probe.” In the subcostal approach, the probe is oriented in the longitudinal direction with the probe indicator toward the patient’s head subjacent to the xiphoid process. The probe then is swept inferiorly and laterally along the subcostal margin. Alternatively, the probe is placed 7 cm to the right of the xiphoid process in the closest intercostal space in the “X-minus 7” approach. Furthermore, it may be helpful to flatten and direct the probe subcostally while aiming toward the patient’s shoulder and fanning anteriorly and posteriorly.104 Rotating the patient in the left lateral decubitus position, scanning in the oblique plane, and having the patient take a deep breath can improve visualization of the gallbladder.80 The main lobar fissure and portal triad are useful landmarks.80
Obtain images in the longitudinal, oblique, and transverse plane to evaluate the entire gallbladder and portal triad. Scan through the entire gallbladder from the fundus to the narrow neck. The anterior gallbladder wall should be measured from outer-to-outer wall in the transverse plane. Follow the echogenic line of the main hepatic fissure, which extends from the neck of the gallbladder to the portal triad. The gallbladder, hepatic fissure, and portal triad resemble an “exclamation point.” The portal triad consists of the portal vein, common bile duct (CBD), and the hepatic artery. The CBD has a “double-barrel shot-gun” or “tram track” appearance. The CBD is located parallel and anterior to the right of the portal vein in the oblique long axis. The diameter of the CBD should be measured from inner-to-inner wall.93 Color Doppler is beneficial to differentiate the CBD from the hepatic artery, which lies anterior and to the left of the portal vein.93
CONCLUSION
Ultrasound is instrumental in the diagnosis of many pediatric abdominal diseases and may be used to guide patient care. Emergency medicine physicians should have a foundation in the basics of point-of-care ultrasound. Being adept at using ultrasound is an invaluable skill in expediting patient care by providing a quick diagnosis and disposition while avoiding ionizing radiation. Although ultrasound is a very effective and efficient means to diagnose pediatric abdominal pathologies, providers must be attentive to cautions and limitations for each exam. While the diagnostic parameters in this article are widely accepted in the literature, it is important to verify the values used with the guidelines of each institution’s radiology department.
The authors would like to thank Geoffrey E. Hayden, MD, FACEP, for his assistance in creating some of the ultrasound images.
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Ultrasound is evolving rapidly as the ideal imaging modality for many common pediatric complaints. In the second part of this series, the authors discuss point-of-care use of ultrasound for concerns regarding the kidneys, ovaries, testicles, gallbladder, and small bowel obstruction. The ability to make critical diagnoses safely and rapidly with ultrasound is an invaluable clinical tool to facilitate and improve pediatric care.
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