Consideraciones prácticas

Although complete cardiac ultrasonography can provide a plethora of information, it does require multiple transducer positions, and some emergency practitioners favor a more limited examination for the sake of expediency. One such examination involves the subcostal approach. This technique allows a quick examination in those individuals who cannot be positioned for a complete examination and identification of such maladies as impairment of ventricular function, assessment of the right heart, and detection of pericardial effusion.

In the emergency setting, echocardiography is most useful in detection and elaboration of ischemic heart disease. It provides significant information on overall left ventricular function. Localized or segmental wall motion abnormalities signify prior regions of myocardial infarction or acute ischemia and are evident even in the face of normal electrocardiograms (ECG). It is extremely important to assess overall left ventricular function in the setting of acute myocardial infarction as prognosis is inversely related to degree of impairment. As such, echocardiography is a superior prognostic tool compared with ECG and clinical assessment by Killip classification in predicting morbidity and mortality following acute myocardial infarction. The sensitivity of echocardiography in detecting myocardial infarction is approximately 90%.

It does more poorly with smaller infarctions and with non-Q wave infarctions, but it must be bore in mind that these entities have inherently better prognosis than large transmural infarctions.

Ultrasonography of the heart could prove to be a vital screening tool for determining, not only admission, but also appropriate intervention for possible reperfusion. In our current setting of managed health care, whatever we can do as emergency physicians to defray costs while still practicing quality medicine would be a major improvement in the quality and cost-effectiveness of our health care delivery. ED echocardiography should provide us a valuable adjunct to our current diagnostic regimen in the near future.

Complications of acute myocardial infarction such as mural thrombi, acute ventricular septal rupture, mitral regurgitation, right ventricular infarction, and pump failure are all readily detected by echocardiographic and Doppler examinations. It is also possible to distinguish between the hypotension of decreased intravascular volume and cardiogenic shock using cardiac ultrasound.

The proximal ascending aorta can be seen satisfactorily using transthoracic echocardiography. Unfortunately, the transverse and descending thoracic aorta are not seen clearly using this approach. As discussed in the section on traumatic aortic transection, TEE is effective for assessing acute aortic dissection. It is done at the bedside, which is of paramount importance to the patient's monitoring and to the emergency physician's ability to provide ongoing resuscitative efforts in these most critical patients without having to leave the department as would be the case with angiography or CT scan. Although theoretically the patient could be spared injection of dye for angiography, it is the author's experience that most vascular surgeons still prefer obtaining an angiogram prior to performing surgical repair. In the setting of cardiac tamponade, the most reliable echocardiographic evidence of its presence is diastolic collapse of the right ventricle (or atria) with associated pericardial fluid.

Echocardiographic demonstration of a pericardial effusion can then guide the needle insertion site for pericardiocentesis.

Acute Right Upper Quadrant Pain

The emergency physician is frequently called upon to assess a patient who presents with acute right upper quadrant pain. Because early cholecystectomy is now the accepted standard of treatment of acute cholecystitis, it is important for the emergency physician to establish this diagnosis as accurately and expeditiously as

possible. Various pathologic processes can mimic the clinical presentation of acute cholecystitis, including hepatitis, pancreatitis, gastritis, and nephrolithiasis. With the development of technetium Tc-99m iminodiacetic acid derivatives as radionuclide imaging agents for the biliary system and with the improved resolution of real-time ultrasound, the radiologic assessment of acute right upper quadrant pain has changed dramatically over the past few years.

Many investigators recommend real-time ultrasonography as the screening procedure of choice in the patient with acute right upper quadrant pain. The diagnosis of acute cholecystitis by ultrasonography depends on several sonographic criteria, including:

1. Gallstones.

7. Nonvisualization of gallbladder with acoustic shadowing from gallbladder fossa.

Overall, with these criteria, only 50% of patients with clinically suspected acute cholecystitis had the diagnosis confirmed by ultrasonography. A normal gallbladder ultrasound examination ensures the absence of gallbladder disease in 95% of patients.

Ultrasonography has certain limitations. The quality and clinical utility of the examination depend heavily on the expertise of the operator. Sonograms tell little about the functioning of the biliary system except the size of the common duct and frequently do not show stones in the cystic duct.

Hepatobiliary scintigraphy with technetium Tc-99m iminodiacetic acid derivatives is an easy examination to interpret and is not operator-dependent. It is highly sensitive in determining cystic duct patency; therefore, visualization of the gallbladder within 1 hour virtually excludes the diagnosis of acute cholecystitis.

False-negative results occur in less than 5% of patients. False-positive results occur in alcoholic patients, patients on total parenteral nutrition, and patients with severe intercurrent illness.

The disadvantages of hepatobiliary scintigraphy are many. It exposes the patient to radiation, takes longer to perform than ultrasonography, and cannot detect pathologic conditions in other organs of the right upper quadrant.

Included in the differential diagnosis of the patient with acute right upper quadrant pain is acute pancreatitis. Usually, the disease is of mild to moderate severity and the diagnosis is established clinically by history, physical examination, and laboratory studies. Radiologic intervention on an emergency basis is not needed.

However, a small percentage of patients with pancreatitis present with fulminant, necrotizing disease with the inherent complications of hemorrhage, pseudocyst, abscess, or phlegmon. It is these patients who require rapid and accurate radiologic assessment of the pancreas to determine appropriate medical or surgical management.

CT is considered the single best radiologic modality for the evaluation of pancreatitis and its complications. It provides superb anatomic detail of the pancreas and surrounding structures. Ultrasonography provides technically inadequate visualization of the pancreas in 20 to 38% of cases because of overlying bowel gas. A normal CT or sonogram of the pancreas and retroperitoneal space can reliably exclude clinically significant pancreatic inflammation. CT and ultrasonography are used to evaluate kidney problems. Both modalities are extremely useful in evaluating patients with acute renal failure, acute unilateral urinary tract obstruction, or acute renal infection.

Sonography is the imaging modality of choice in excluding acute bilateral renal obstruction as a cause of acute renal failure. It is comparable with intravenous urography in detecting bilateral renal obstruction, with a sensitivity of 93 to 98%. Ultrasonography has some limitations because it often cannot detect the level or nature of the obstruction, and it has a false-positive rate of about 20%. CT may be of value in elucidating the cause of bilateral ureteral obstruction and may demonstrate periureteral neoplasms or inflammatory masses, uroepithelial tumors, or retroperitoneal fibrosis.

In acute unilateral renal obstruction with normal renal function, intravenous urography is the initial imaging modality of choice because it demonstrates the level of obstruction.

In the patient with uncomplicated acute pyelonephritis, radiologic imaging of any kind is not indicated on an emergency basis. In patients presenting with urosepsis, however, or those who fail to respond to antibiotic therapy, pyonephrosis, renal abscess, or perinephric abscess must be excluded. Both CT and ultrasonography are effective methods of demonstrating acute focal interstitial nephritis, intrarenal abscess, pyonephrosis and perinephric abscess. Although ultrasonography is probably the best screening method in the patient with urosepsis, CT offers several advantages:

1. Its resolution is slightly better than that of ultrasonography in distinguishing focal interstitial nephritis from organized renal abscesses.

2. It is slightly more sensitive in detecting perirenal extension of abscess by revealing increased attenuation of perirenal fat or thickening of renal fascia.

3. It can also distinguish gas within the renal collecting system from gas within the renal cortex or perinephric space—an important distinction because the former is treated medically and the latter requires surgical intervention.

Abdominal Aorta

Ultrasonography has close to a 100% sensitivity in determining the presence of an abdominal aortic aneurysm (AAA). It is insensitive in determining the presence of a ruptured AAA. Whereas as many as 80% of abdominal aortic aneurysms are palpable on physical examination, this percentage drops significantly in individuals who are hypotensive from leakage or rupture. It is clear that rapid diagnosis and treatment are instrumental in optimizing outcomes in individuals afflicted with aortic rupture. Time should not be wasted in diagnostics for patients who are unstable as definitive diagnosis and treatment awaits in the operating room!

The abdominal aorta begins at the diaphragm and ends at the aortic bifurcation, which is roughly at the level of the umbilicus. The normal external diameter in males is 2.1 cm and in females 1.8 cm with tapering occurring distally. Any dilatation of the aorta exceeding 1.5 times normal is considered aneurysmal until proven

otherwise. Thus, an aorta in excess of 3.0 cm in diameter is aneurysmal. Sometimes the only evidence of AAA is lack of distal tapering.

CT scanning is useful in detecting AAA. It is also sensitive and specific for the diagnosis of ruptured AAA. It is the imaging procedure of choice in individuals with chronic, contained rupture. In cases of acute rupture, time should not be wasted performing diagnostics as these patients require emergent surgical intervention.

Many times rupture of an AAA occurs in the radiologic suite during the scanning process. So the question arises: Who should be scanned from the ED when the diagnosis of AAA is suspected? It would appear that there are only three indications for such an action:

1. Patients suspected of having chronic, contained rupture. These patients, by definition, are hemodynamically stable.

2. Stable patients known to have aneurysms, but thought to have acute surgical conditions of the abdomen other than rupture.

3. Patients who have been examined by the surgeon responsible for the surgical component of management who requests CT scanning in preparation for surgical planning. These patients must never be left unattended in the x-ray suite!

Angiography is useful in preoperative planning for elective surgical resection of AAA, but has no place in the management of ruptured AAA as it is time consuming (to the point of being fatally so) and the rupture might even be missed as layers of clot might hide the leak of contrast.

Gynecologic and Obstetric Conditions

Ultrasonography is often used in evaluating problems relative to the female pelvis. The most common gynecologic presenting complaint in the ED is that of acute pelvic pain and vaginal bleeding. The differential diagnosis of pelvic pain is legion, but the most important factor to determine is if the patient is pregnant. Fortunately, the use of b-human chorionic gonadotropin (b-HCG) has simplified this determination.

In the nonpregnant patient, ultrasound is of value in determining the cause of the pelvic pain, whether it is from pelvic inflammatory disease, tubo-ovarian abscess, adnexal torsion, functional cysts, endometriosis, ovarian neoplasms, or uterine myomas.

In the pregnant patient, the role of ultrasonography in the diagnosis of ectopic pregnancy has changed over the past few years. Initially, the ultrasonographic findings of ectopic gestational sac, enlarged nongravid uterus, and fluid in the cul-de-sac were thought to be common and specific findings for ectopic pregnancy. Experience, however, has shown that at least 20% of ectopic pregnancies are not detected with these criteria. The most reliable method of diagnosis of ectopic pregnancy is the failure of normal increase in serial b-HCG levels. Ultrasonography can exclude the diagnosis only if a definite intrauterine pregnancy is demonstrated.

Simultaneous intrauterine and ectopic pregnancies are rare (about one in 30,000 pregnancies). Other causes of nonviable pregnancies, such as missed abortion, incomplete abortion, gestational trophoblastic disease, and blighted ovum, may have similar ultrasonographic appearances. Sonographically, two criteria have been established to identify nonviable pregnancies:

1. A gestational sac of more than 3 cm in diameter should have a fetal pole with a crown-rump length of at least 15 mm to exclude abnormal pregnancy.

2. A fetal pole with a crown-rump length of 25 mm should show fetal movement and fetal heart activity to diagnose normal intrauterine pregnancy.

With these criteria, 85% of nonviable pregnancies are identified on ultrasound examination. Another ultrasonographic criterion has been established for the diagnosis of normal intrauterine pregnancy; it identifies a normal gestational sac before a fetal pole is seen. This is the double decidual sac sign and represents the two layers of the decidua (decidua vera and decidua capsularis) separated by the uterine cavity. This may be seen as early as 4 weeks after the last normal menstrual period.

This criterion is especially helpful in differentiating the decidual cast of ectopic pregnancy from the early normal gestational sac.

In late pregnancy, bleeding occurs in 2 to 3% of patients. The differential diagnosis includes placental abruption and placenta previa. Ultrasonography is 90%

accurate in the diagnosis of placenta previa but has limited value in the diagnosis of placental abruption. The classic ultrasonographic appearance of a retroplacental or extrachorionic fluid collection is often difficult to distinguish from that of normal venous structures.

Suggested Readings

Alker GJ, Oh JS, Leslie EV, et al: Postmortem radiology of head and neck injuries in fatal traffic accidents. Radiology 1975;114:611.

Ang JGP, Hanslits MC, Clark RA, et al: Computed tomography of abdominal and pelvic trauma. J Emerg Med 1985;3:311.

Bernstein EF: Vascular diagnosis. 4th ed. St. Louis, MO: Mosby, 1993

Bilazarian SD, Mittal S, Mills R: Recognizing the extrarenal hazards of intravascular contrast agents. J Crit Illness 1991;6:859.

Bosniak MA, Megibow AJ, Ambos MA, et al: Computed tomography of ureteral obstruction. AJR 1982;138:1107.

Bradley WG, Fiske CE, Filly RA: The double sac sign of early intrauterine pregnancy. Use in exclusion of ectopic pregnancy. Radiology 1982;143:223.

Braffman BH, Coleman BG, Ramchandani P, et al: Emergency department screening for ectopic pregnancy: a prospective US study. Radiology 1994;90(3):797–802.

Brantz-Zawadzki M, Miller EM, Federle MP: CT in the evaluation of spine trauma. AJR 1981;136:369.

Cales RH: Trauma mortality in Orange County: the effect of implementation of a regional trauma system. Ann Emerg Med 1984;13:1.

Chang T, Lapanto L: Ultrasonography in the emergency setting. Emerg Med Clin North Am 1992;1.

Dalinka MK: Emergency department radiology. Emerg Med Clin North Am 1985;3(3).

Earnest F, Baker HL, Kispert DB, et al: Magnetic resonance imaging vs computed tomography: advantages and disadvantages. Clin Neurosurg 1985;32:540.

Eisenberg RL, Heineken P, Hedgcock MW, et al: Evaluation of plain abdominal radiographs in the diagnosis of abdominal pain. Ann Intern Med 1982;97:257.

Erbel R, et al: European cooperative study for echocardiography: echocardiography in the diagnosis of aortic dissection. Lancet 1989;1:457.

Federle MP: Abdominal trauma: the role and impact of computed tomography. Invest Radiol 1981;16:260.

Fordham S: Emergency radiology. Top Emerg Med 1983;5(3).

Gaubert JY, Moulin G, Mesana T, et al: Type A dissection of the thoracic aorta: use of MR imaging for long term follow-up. Radiology 1995;196(2):363–369.

Hammerschlag SB, Hughes S, O'Reilly GV, et al: Blow-out fractures of the orbit: a comparison of computed tomography and conventional radiography with anatomical correlation. Radiology

1982;143:487.

Hauser AM: The emerging role of echocardiography in the emergency department. Ann Emerg Med 1989;18:1298.

Heller M, Crocco T, Patterson J, et al: Emergency ultrasound services as perceived by directors of radiology and emergency departments. Am J Emerg Med 1995;3(4):430.

Koch D, Wakhloo AK, van Velthoven V: Magnetic resonance imaging in spinal emergency. Acta Neurochir 1995;134(1–2):100–107.

Kremkau FW: Doppler ultrasound—principles and instruments. Philadelphia, PA: WB Saunders, 1990.

Laasonen EM, Penttila A, Sumovuoni H: Acute lethal trauma of the trunk: clinical, radiologic, and pathologic findings. J Trauma 1982;20:657.

Lamki N, Raval B: The role of computed tomography in abdominal and pelvic trauma. J Comput Tomogr 1982;6:113.

Marx JA: The role of computed tomography in the management of acute abdominal trauma. J Emerg Med 1985;3:309.

Mateer J, Plummer D, Heller M, et al: Model curriculum for physician training in emergency ultrasonography. Ann Emerg Med 1994;23:95.

McCook TA, Ravin CE, Rice RP: Abdominal radiography in the emergency department: a prospective analysis. Ann Emerg Med 1982;11:23.

McLoughlin RF, Mathieson JR: Imaging and intervention in abdominal emergencies. Baillieres Clin Gastroenterol 1995;9(1):1–19.

Merritt CRB: Doppler color imaging. New York, NY: Churchill Livingstone, 1992.

Orrison WW, Gentry LR, Stimac GK, et al: Blinded comparison of cranial CT and MR in closed head injury evaluation. Am J Neuroradiol 1994;5(2):35–36.

Rowe LD, Miller EM, Brantz-Zawadski MN: Computerized tomography in maxillofacial trauma. Laryngoscope 1981;91:745.

Rubin SZ, Martin DG: Ultrasonography in the management of possible appendicitis in childhood. J Pediatr Surg 1990;25:737.

Sandler CM, Toombs BD: Computed tomographic evaluation of blunt renal injuries. Radiology 1981;141:461.

Shuman WP, Mack LA, Rudd TG, et al: Evaluation of acute right upper quadrant pain: sonography and 99mTc-PIPIDA cholescintigraphy. AJR 1982;139:61.

Siegel MJ, Carel C, Surratt S: Ultrasonography of acute abdominal pain in children. JAMA 1991;266:1987.

Sosna J, Slasky BS, Bar-Ziv J: Computed tomography in the emergency department. Am J Emerg Med 1997;15:244–248.

Stark DD, Bradley WG, Jr: Magnetic resonance imaging. 2nd ed. St. Louis, MO: Mosby, 1992.

Vignault F, Filitarault D, Brandt ML, et al: Acute appendicitis in children: evaluation with ultrasound. Radiology 1990;176:501.

Chapter 11.3 What Test for Blunt Abdominal Trauma—CT, DPL, or Ultrasound?

Principles and Practice of Emergency Medicine

CHAPTER 11 IMAGING