Imaging abdominalemergencies

RAD Magazine, 41, 486, 24-26

Dr Emily A AherneSpecialist registrar radiology

Dr David P M MitchellSpecialist registrar radiology

Dr Matthew CrockettSpecialist registrar radiology

Dr Peter J MacMahonConsultant radiologist

Department of radiology, Mater Misericordiae Hospital,Dublin, Ireland

IntroductionEvery day in the emergency setting, abdominalpain continues to pose a significant diagnosticchallenge for clinicians. It accounts for approxi-mately 5-6% of all emergency department (ED)attendances.1,2 The ‘acute abdomen’ is a term tra-ditionally used to refer to patients who complainof severe abdominal pain and have a peritonitic,tense abdomen on examination. There are a largenumber of diverse possible causes of an acuteabdomen and clinical examination can often bemisleading. Emergent, life-threatening causes ofan acute abdomen include rupture of an abdom-inal aortic aneurysm, acute bowel obstruction,bowel ischaemia, gastrointestinal perforation,ectopic pregnancy and abdominal trauma. Inemergencies, when critical decisions need to bemade quickly, imaging is often relied upon to pro-vide rapid, accurate assessment. However, it isnot without risk to the patient and it is impera-tive that patients are clinically stabilised prior toany radiologic assessment.Imaging modalitiesPlain radiographyA typical radiographic abdominal series has a very limitedrole for abdominal emergencies. It typically includes ananteroposterior abdomen film (erect position preferred oversupine) and erect chest radiographs. It has the advantagethat it can be performed with minimal patient transporta-tion, low cost, is always available and has the potential todiagnose major pathology such as bowel obstruction or gas-trointestinal perforation (figure 1). Even tiny volumes offree air can be detected on a correctly performed erect chestx-ray (figure 1) but optimal views are often not achievablein critically unwell patients. It is important to rememberthat the absence of findings on abdominal radiographs doesnot exclude significant pathology. Plain radiography is oftenperformed and can be helpful in evaluating for radiopaqueforeign bodies.

UltrasoundSonographic assessment is a real-time, dynamic imagingmodality which plays a limited role in imaging abdominalemergencies. Reduced cost and absence of radiation are themain advantages of ultrasound. Access to immediate bedsideultrasound is variable in the ED. In larger centres, it iswidely available and accessible but less so in rural orsmaller departments with fewer staff.3

Findings can be correlated easily with the maximumpoint of tenderness and this can be a very useful indicatorof disease. FAST (focussed assessment with sonography fortrauma) scanning is increasingly being employed as ascreening tool within the ED by non-radiologists. Four areasare typically assessed for the presence of free fluid: The peri-cardium, the hepatorenal recess, the perisplenic space andthe pelvis. It has a wide variation in sensitivity from42-94% and patients with negative studies often proceed tomore accurate radiologic assessment.4-6

For suspected ectopic pregnancy or ovarian torsion, ultra-sound is the initial imaging modality of choice.7-9

Transabdominal imaging is often supplemented with trans-vaginal imaging in assessment of acute pelvic pathology. Itis also first line for assessment for testicular torsion.10,11

Colour flow and power Doppler imaging are useful, althoughnot always reliable in assessment for testicular ischaemia.10-14

Abdominal ultrasound is very frequently used in the assess-ment of acute cholecystitis where it is equal to or more sen-sitive than CT. It is certainly more sensitive than CT in thedetection of gallbladder calculi.15-17 Another role for ultra-sound is in the assessment of acute hydronephrosis whichcan be an important diagnosis in patients complaining ofrenal colic or who have acute renal failure.

Computed tomographyComputed tomography (CT) is the cornerstone of imagingfor abdominal emergencies.18 Evolution of multidetector CTscanners has significantly reduced scan acquisition time anditerative reconstruction techniques can be used to signifi-cantly decrease radiation dose. It is now widely available 24hours a day and is the most accurate imaging tool we pos-sess in the setting of abdominal emergencies.19

Multi-phasic dynamic contrast enhanced imaging allowsaccurate, timely assessment of most abdominal emergencies.Non contrast imaging can be used to assess for calcificationand foreign bodies. Free air is also readily apparent. Arterialphase imaging is particularly useful for assessment of theaorta and its branches including the mesenteric arteries. Itis also useful to assess for active haemorrhage20 into theabdominal cavity or its organs including peritoneal haem-orrhage, intra-luminal bowel haemorrhage or solid organhaemorrhage (figure 3). This allows for planning of emboli-sation or ligation procedures.

Traditional portal venous phase imaging is most helpfulfor undifferentiated causes of abdominal pain and in assess-ment of the bowel, liver and spleen. It is also the phase ofabdominal CT that radiologists have the most experience inreviewing and their comfort level is highest. Delayed imag-ing is most helpful when looking for slower bleeds or injuryto the genitourinary system. Multiple phases of delayedimaging can be performed.

Oral contrast can be administered but is not a require-ment and should never delay imaging in the emergency set-ting. It can obscure the lumen of the bowel if assessing forintraluminal haemorrhage and should not be administeredin these cases.

Magnetic resonance imagingMagnetic resonance imaging (MRI) is not yet in commonuse for the assessment of the acute abdomen except in preg-nant women.21-23 MRI is less available out of hours and imag-ing can take considerably longer than an equivalent CTstudy, and thus is not routinely used for imaging of emer-gencies. During pregnancy, anatomical distortion of theabdomen and pelvis with the gravid uterus decreases thesensitivity of ultrasound. The absence of ionising radiationrenders MRI relatively safe in pregnancy. There are someconcerns of the heating effect on the placenta during pro-longed image acquisition24,25 but there has been no docu-mented teratogenic effect. Rapid multi-planar T2 sequencescan be obtained with high soft tissue resolution whichreduces the length of time spent in the scanner.24

Gadolinium based contrast agents cross the placenta andhence its administration is not recommended in pregnantpatients.26 Appendicitis often needs to be excluded as a causeof acute abdominal pain in pregnancy. MRI has been demon-strated to be accurate in the diagnosis of appendicitis, whilealso giving information regarding other relevant structuressuch as the bowel, gallbladder and ovaries.

Common causes of acute abdominal pain withexamples of imaging1. Bowel perforationAn erect chest x-ray is the initial investigation of choice andeven small volumes of free air may be detected. Abdominalradiography may demonstrate free air, eg Rigler’s sign orthe football sign, but usually is less sensitive. Multi-planarCT post oral and IV contrast is the gold standard for docu-menting free air and for locating the source of perforationpreoperatively (figure 1).

2. Bowel ischaemiaThere are many causes of bowel ischaemia and it is notori-ously difficult to diagnose at an early, treatable stage clini-cally, biochemically or radiologically.27 CT is the imagingmodality of choice for evaluation. Definite signs of bowelischaemia on CT are commonly late findings and typicallyindicate dead bowel. They include thickened loops of bowelwith altered pre-contrast density or reduced enhancement,gas within the bowel wall (pneumatosis), mesenteric venousgas, and portal venous gas (figure 2). Arterial occlusionwith thrombus or embolic material can sometimes also bedetected.

3. Solid organ traumaSolid organ laceration can occur with blunt or penetratingtrauma and requires rapid characterisation and timely man-agement in the emergency setting. Multiphasic contrastenhanced CT is most useful to grade the organ injury, toassess for active haemorrhage and to guide management,eg conservative, interventional or open surgical (figure 3).

4. AppendicitisAppendicitis is one of the commonest causes of acute abdom-inal pain to present to the ED. Ultrasound is often employedin initial evaluation, particularly in slim, young patients. Anon-compressible, blind ending tubular structure with athickened wall can be identified by the experienced sonog-rapher. CT is commonly used for the evaluation of right iliacfossa pain, particularly where the history and clinical signsare less certain. The appendix can be directly visualised andassessment can be made of morphology, location, presenceof appendicolith, drainable collection or perforation. Otherless common causes of right iliac fossa pain such as diver-ticulitis, epiploic appendagitis and terminal ileitis are readilyapparent on CT. MRI is occasionally used, particularly inpregnant patients (figure 4).

5. Bowel obstructionSmall or large bowel obstruction is a common diagnosis inthe ED. Initially abdominal radiography and more defini-tively CT are most commonly used for assessment.Abdominal radiograph may demonstrate abnormally dilatedloops of small or large bowel. CT is then employed to deter-mine the nature and cause of the obstruction which willguide the surgical management. Closed loop bowel obstruc-tion is an emergency due to the risk of bowel ischaemia.Mechanical causes of obstruction should be identified anddescribed to enable targeted surgical therapy (figure 5).

6. Ectopic pregnancyEctopic pregnancy is a life threatening gynaecologic emer-gency which can cause torrential haemorrhage. Ultrasoundis most useful for initial evaluation and transvaginal imag-ing should be performed in all suspected cases. Most com-monly an ectopic pregnancy is demonstrated as ahypervascular mass in the adnexa and complex (haemor-rhagic) fluid in the pelvis. There will usually be no gesta-tional sac in the uterus. Correlation with serum beta HCGshould be performed for all patients with indeterminateexaminations. Ectopic pregnancies are occasionally imagedon CT, but this is uncommon (figure 6).

ConclusionAbdominal emergencies continue to present a significantchallenge to clinicians. Radiologic imaging modalities enablerapid, accurate assessments and appropriate decision-makingfor critical patients with abdominal pain. CT is the corner-stone of imaging of abdominal emergencies but plainradiography, ultrasound and MRI continue to have impor-tant roles.

References1, Hastings R S, Powers R D. Abdominal pain in the ED: A 35 year retro-

spective. Am J Emerg Med 2011;29(7):711-16.2, Kamin R A et al. Pearls and pitfalls in the emergency department evalu-

ation of abdominal pain. Emerg Med Clin North Am 2003;21(1):61-72, vi.3, Talley B E et al. Variable access to immediate bedside ultrasound in the

emergency department. West J Emerg Med 2011;12(1):96-99.4, Lingawi S S, Buckley A R. Focused abdominal US in patients with

trauma. Radiology 2000;217(2):426-29.5, Dolich M O et al. 2,576 ultrasounds for blunt abdominal trauma.

J Trauma 2001;50(1):108-12.6, Miller M T et al. Not so FAST. J Trauma 2003;54(1):52-59. Discussion;59-

60.7, Potter A W, Chandrasekhar C A. US and CT evaluation of acute pelvic

pain of gynecologic origin in nonpregnant premenopausal patients.Radiographics 2008;28(6):1645-59.

8, Duigenan S, Oliva E, Lee S I. Ovarian torsion: Diagnostic features on CTand MRI with pathologic correlation. AJR Am J Roentgenol 2012;198(2):W122-31.

9, Chang H C, Bhatt S, Dogra V S. Pearls and pitfalls in diagnosis of ovar-ian torsion. Radiographics 2008;28(5):1355-68.

10, Bhatt S, Dogra V S. Role of US in testicular and scrotal trauma.Radiographics 2008;28(6):1617-29.

11, Vijayaraghavan S B. Sonographic differential diagnosis of acute scrotum:Real-time whirlpool sign, a key sign of torsion. J Ultrasound Med2006:25(5):563-74.

12, Albayram F, Hamper U M. Ovarian and adnexal torsion: Spectrum ofsonographic findings with pathologic correlation. J Ultrasound Med2001;20(10):1083-89.

13, Pena J E et al. Usefulness of Doppler sonography in the diagnosis of ovar-ian torsion. Fertil Steril 2000;73(5):1047-50.

14, Fleischer A C et al. Color Doppler sonography of adnexal torsion. J Ultrasound Med 1995;14(7):523-28.

15, Pinto A et al. Accuracy of ultrasonography in the diagnosis of acute cal-culous cholecystitis: Review of the literature. Crit Ultrasound J 2013;5Suppl 1:S11.

16, McIntosh D M, Penney H F. Grayscale ultrasonography as a screeningprocedure in the detection of gallbladder disease. Radiology1980;136(3):725-27.

17, Bortoff G A et al. Gallbladder stones: Imaging and intervention.Radiographics 2000;20(3):751-66.

18, Stoker J et al. Imaging patients with acute abdominal pain. Radiology2009;253(1):31-46.

19, Peitzman A B et al. Prospective study of computed tomography in initialmanagement of blunt abdominal trauma. J Trauma 1986;26(7):585-92.

20, Lubner M et al. Blood in the belly: CT findings of hemoperitoneum.RadioGraphics 2007;27(1):109-25.

21, Furey E A, Bailey A A, Pedrosa I. Magnetic resonance imaging of acuteabdominal and pelvic pain in pregnancy. Top Magn Reson Imaging2014;23(4):225-42.

22, Spalluto L B et al. MR imaging evaluation of abdominal pain duringpregnancy: Appendicitis and other nonobstetric causes. Radiographics2012;32(2):317-34.

23, Birchard K R et al. MRI of acute abdominal and pelvic pain in pregnantpatients. AJR Am J Roentgenol 2005;184(2):452-58.

24, Hand J W et al. Prediction of specific absorption rate in mother and fetus

Figure 1Initial erect chest radio-graph demonstrated a tiny volume of free air under the right hemi-diaphragmwhich can be seen on the coronal CT image. The air was from a perforated sigmoid diverticulitis, seen inthe axial CT image.

Figure 2Selected axial and coronal CT images demonstrating some of the features of advanced bowel ischaemiaincluding: (A) pneumatosis; (B) and (C) portal venous gas and liver infarct; (D) gas within the mesentericveins.

associated with MRI examinations during pregnancy. Magn Reson Med2006;55(4):883-93.

25, Gowland P A, De Wilde J. Temperature increase in the fetus due to radio-frequency exposure during magnetic resonance scanning. Phys Med Biol2008;53(21):L15-18.

26, Kanal E et al. ACR guidance document for safe MR practices: 2007. AJRAm J Roentgenol 2007;188(6):1447-74.

27, Wiesner W et al. CT of acute bowel ischemia. Radiology 2003;226(3):635-50.

Figure 5Contrast enhanced coro-nal and axial CT imagesdemonstrate a fluid-filledtubular structure with athickened enhancingwall with adjacentmesenteric strandingand reactive adenopathycompatible with acuteappendicitis. Ultrasounddemonstrates a blindending, non compressibleloop of bowel with athickened wall. Selectedcoronal and sagittal T2weighted MRI imagesdemonstrate a normalappendix in a differentpregnant patient withright iliac fossa pain.

Figure 4Selected coronal CT images ofsmall bowel obstruction inthree different patients. (A)Dilated air filled loops of smallbowel post-operatively sec-ondary to an incarcerated smallbowel hernia through a laparo-scopic port site. (B) Dilated,fluid-filled loops of small bowelsecondary to an incarceratedright femoral hernia. (C)Dilated fluid filled small bowelloop with swirling compatiblewith closed loop obstructionsecondary to malrotation. Thisis the most emergent type ofsmall bowel obstruction due tothe risk of bowel ischaemia.

Figure 3Dynamic multiphasic CT imaging of acute haemorr-hage into a liver laceration from penetratingtrauma: (A) non contrast; (B) arterial phase;(C) portal venous phase; (D) delayed phase.

Figure 6Selected sagittal, coronaland axial CT imagesdemonstrating a left cor-nual ectopic pregnancy.Simple cyst in the leftadnexa. Selected longitu-dinal ultrasound imageswith colour flow demon-strating a tubal ectopicpregnancy in a differentpatient. There is somefree fluid in the pelvis,likely haemorrhage.