Dr. LeBedis is an Assistant Professor, Dr. Penn is a Radiology Resident, Dr. Gupta is an Associate Professor, Dr. Tkacz is an Associate Professor, and Dr. Soto is a Professor of Radiology, Boston University Medical Center in Boston, MA; and Dr. Broder is a Radiologist, Lahey Clinic, Burlington, MA.
widespread availability and diagnostic capabilities of ultrasound (US)
and computed tomography (CT) have made these tools invaluable in
triaging patients with abdominal pain in busy emergency departments.
Given the variety of diagnostic possibilities in patients with abdominal
pain and their sometimes urgent ensuing treatments, a rapid and
accurate diagnosis is of paramount importance. For example, emergent
abdominal surgical procedures account for approximately 53% of all
nontrauma-related surgical interventions performed in the acute care
The American College of Radiology (ACR) rates
US and CT with a high priority score of 6 to 9 for acute abdominal and
pelvic conditions in nonpregnant adults (1=least appropriate; 9=most
appropriate). However, in pregnant or young patients, the
appropriateness of CT drops to 4 to 6, depending on the indication.2
Although US yields high sensitivities and specificities in abdominal
and pelvic pathology in the hands of an expert, it is highly operator
and patient dependent. For example, obesity can
affect the ability of the ultrasound beam to penetrate the soft tissues,
and patient motion and bowel gas can prevent visualization of
underlying organs.3 The main disadvantage of CT is exposure of the patient to ionizing radiation.4 In younger patients, the radiation dose considerably increases the risk of developing a radiation-induced cancer.5
advances in magnetic resonance imaging (MRI) sequences, protocols, and
coil technology, as well as growing familiarity with the modality on
both the part of technologists and radiologists, MRI has become a viable
alternative to CT. MRI can assess the entire abdomen within minutes,
yielding diagnostic sensitivities and specificities similar to those of
CT and without the operator dependence encountered in US. Acute
abdominal and pelvic conditions that can be rapidly diagnosed with MRI
include choledocholithiasis, acute cholecystitis, acute pancreatitis,
bowel inflammation in the setting of inflammatory bowel disease (Crohn’s
disease and ulcerative colitis) and appendicitis.6,7 In addition, MRI is critical in the characterization of indeterminate CT and US findings.7
The ACR, however, rates MR imaging of nonpregnant patients in acute
abdominal and pelvic conditions with a medium appropriateness score of 4
to 6 because of its limited availability, longer acquisition times,
higher cost and lack of incremental diagnostic gain compared with CT.
The appropriateness score for evaluation of a pregnant woman with fever,
leukocytosis and suspected appendicitis jumps to 7, just below the
appropriateness score of 8 for US.2
several notable advantages over US and CT in the assessment of abdominal
pathologies. The first is its lack of ionizing radiation. This feature
is of particular benefit to pediatric patients and, by extension, to
pregnant women.5,8 Another subset of patients who undergo
numerous CT scans for recurring abdominal pain are patients with
inflammatory bowel disease. A second advantage of MRI is the ability to
image patients who have allergies to CT contrast agents. Third, MRI can
delineate certain disease entities better than US or CT, such as
choledocholithiasis, where bowel gas and patient body habitus can
obscure acoustic windows on US exams and many stones can go undetected
on CT. Last, MRI provides superior contrast resolution and excellent
characterization of pathologic tissue.9
of MR imaging in evaluating acute gastrointestinal conditions include
its high cost, limited availability, longer examination times compared
to US and CT, and its incompatibility with equipment used for intensive
care and patient monitoring.7 In addition, MR imaging also has poorer spatial resolution and higher sensitivity to motion-related artifacts than does CT.10
MR imaging acquisition times by tailoring protocols to the clinical
question at hand is of paramount importance in the emergent setting.
clinical indication for the study determines the choice of oral
contrast. For MR cholangiopancreatography (MRCP), we prefer a negative
oral contrast to minimize background bowel signal on the heavily
T2-weighted MRCP sequences, allowing unobstructed visualization of the
pancreaticobiliary tree. Similarly, for patients being evaluated for
acute appendicitis, we prefer a negative oral contrast, which renders
normal bowel dark, as compared with an obstructed appendix which can be
filled with T2 hyperintense fluid. At our institution, a 50/50 vol/vol
combination of ferumoxsil (Gastromark; Mallinckrodt Medical, St. Louis,
MO) and barium sulfate suspension is utilized as the negative oral
contrast for MRCP and acute appendicitis studies. It is particularly
useful if the MR image is nondiagnostic for appendicitis, as the patient
is simultaneously prepared to undergo a CT examination, without any
additional delay for appropriate opacification of bowel. For imaging of
inflammatory bowel disease, we prefer a neutral oral contrast agent,
such as Volumen, which has improved bowel distention given the presence
of 2% sorbitol. This oral contrast preparation has the added benefit of
demonstrating maximal tissue contrast against the bowel wall on
T1-weighted, gadolinium-enhanced sequences, where the bowel lumen is
hypointense and the wall is hyperintense, and vice versa on T2-weighted
If the patient is
capable, breath-hold sequences are ideal, given their short acquisition
times. Otherwise, lengthier free breathing or respiratory-triggered
imaging protocols may be employed. Two-dimensional T1-weighted,
gradient-recalled echo (GRE) sequences may be helpful in the workup of
acute appendicitis, as gas or negative oral contrast within the appendix
(suggesting luminal patency), will demonstrate susceptibility artifact
on these sequences. Intravenous gadolinium-based contrast agent use is
useful for detecting acute inflammation of the bowel wall, but is
contraindicated in early pregnancy.
T2-weighted turbo spin-echo sequences (SSFSE, SSTSE, or HASTE, based on
the vendor) are particularly useful for bowel imaging with a neutral
oral contrast agent, given their excellent spatial resolution,
T2-weighting and rapid scan times. But they may demonstrate dark signal
voids in fluid-filled bowel. Balanced steady-state free precession
sequences, (TrueFISP, FIESTA and balanced FFE, based on the vendor), are
also useful for bowel imaging, given their rapid acquisition time and
lack of bowel signal voids, but they are prone to susceptibility
artifacts that can be created in the presence of Gastromark. Balanced
gradient echo techniques have the added benefit of creating “white
blood” noncontrast MR angiographic images. Short tau inversion-recovery
(STIR) and respiratory-triggered, T2-weighted, chemically fat-suppressed
turbo SE sequences can be helpful, but scan times are inherently longer
due to their multi-shot image techniques and longer TR.
studies, we use heavily T2-weighted 2D SSTSE (20 mm thick) slabs,
obtaining 5 radial slices in approximately 10-15 seconds. In addition, a
coronal 3D, respiratory-triggered TSE sequence (1.6 mm slice thickness)
is acquired, providing improved signal-to-noise ratio (SNR) compared
with 2D techniques, and the ability to perform multiplanar reformatted
images. Scan times, however, may be up to 5 minutes.
3D T1-weighted sequences (such as THRIVE, VIBE, LAVA and FAME,
depending on the MR vendor) can be useful in detecting active bowel
inflammation, particularly in inflammatory bowel disease. These
sequences provide high-resolution interpolated sections (2-3 mm thick)
while allowing acquisition of dynamic phases after administration of
intravenous gadolinium-based contrast (rate, 2 mL/sec; volume, 20 mL).
To evaluate suspected inflammatory bowel disease, we add 3-plane SSTSE
sequences and balanced gradient echo and coronal T1 dynamic, 3D
fat-suppressed gradient echo sequences with and without gadolinium,
using a neutral oral contrast. The examination is typically 20-30
To evaluate suspected appendicitis,
usually in the setting of pregnancy, our imaging protocol consists of
3-plane SSTSE sequences with and without chemical fat suppression, and
axial T1-weighted, in-phase and opposed-phase GRE sequences with a
negative oral contrast agent. Gadolinium is avoided in pregnant
patients. Although the safety of MRI for the fetus has not been proven
according to U.S. Food and Drug Administration guidelines, no human
teratogenic or carcinogenic effects of MRI have been described in the
literature.9 The effects of fetal exposure to high magnetic
fields, gradient shifts and radiofrequency energy deposition remain
largely unknown.7 At our institution, these facts are discussed with our pregnant patients, and written informed consent is obtained.
presence of an obstructing stone in the CBD either from the passage of a
gallbladder stone through the cystic duct, or primary formation of
stones within the common bile duct, can lead to acute biliary
obstruction with resultant pain, jaundice, fever, cholangitis,
pancreatitis or sepsis.
Choledocholithiasis is encountered in 10% to 15% of the cholecystectomies performed each year,13,14
confounding the diagnosis and management of patients with right upper
quadrant pain. Most patients presenting with right upper quadrant pain
will undergo sonographic evaluation of the biliary tree for
cholecystitis, given the high sensitivity and specificity of US for
diagnosing this entity.15
suspected dilation of the common bile duct (>8 mm) is present on US
or CT. However, visualization of the distal common bile duct with these
modalities can be limited. On US, overlying bowel gas can obscure the
distal common bile duct and make stones difficult to visualize,15
and CT has inherent limitations for detecting choledocholithiasis.
Thus, MRCP is typically performed when there is clinical suspicion for
common bile duct stones given its high sensitivity and specificity (97%
to 99% and 95%to 99%, respectively) for detecting common bile duct
abnormalities. On MRCP, calculi appear as low signal intensity filling
defects in the biliary tree against the high signal intensity bile
(Figure 1). The differential diagnosis for a biliary tree filling defect
includes air, neoplasm, blood clot and sludge.
MRCP plays a
crucial role in management of patients with cholecystitis in whom
choledocholithiasis is suspected since it can accurately triage patients
to endoscopic retrograde cholangiopancreatography (ERCP) and direct the
appropriate surgical intervention. Although MRI is not used as a
screening test for cholecystitis, the condition can be depicted on MR as
pericholecystitic fluid, gallbladder wall thickening, and gallbladder
wall edema on T2-weighted images. Transient hyperenhancement of the
adjacent hepatic parenchyma can also be seen (Figure 2). Complications
of acute cholecystitis such as gangrenous cholecystitis and Mirizzi
syndrome can be diagnosed with MRCP.7 Gangrenous
cholecystitis manifests as segmental absence of mucosal enhancement on
contrast-enhanced MR images (Figure 3) or it can be visualized as air
within the wall of the gallbladder, best seen as a focus of blooming
artifact on opposed-phase, T1-weighted images (Figure 4). Mirizzi
syndrome is the mechanical obstruction of the hepatic duct by a stone
impacted in the adjacent cystic duct (Figure 5).
Gallstones are the inciting factor in 50% of patients with acute pancreatitis,16
as stones that migrate into the distal common bile duct can obstruct
the pancreatic duct. Patients typically manifest with persistent
epigastric pain, nausea and vomiting. Elevation of serum lipase and
amylase is common. MRCP has been shown to be comparable to
contrast-enhanced CT in the diagnosis of equivocal cases acute
pancreatitis and for assessment of disease severity.17 Acute
pancreatitis manifests as glandular enlargement (edema), periglandular
inflammatory changes, and intra- and peri-pancreatic fluid collections
on MR, particularly on fluid-sensitive sequences with fat suppression
(Figure 6). Pancreatic necrosis is a complication of severe pancreatitis
in which there are regions of nonviable pancreatic parenchyma (Figure
7); it carries higher morbidity and mortality rates relative to
uncomplicated pancreatitis.18 The advantage of MRCP lies in
its ability to identify choledocholithiasis as the cause of acute
pancreatitis and to triage the appropriate patients to ERCP where
sphincterotomy and retrieval of impacted stones can be performed. A
potentially fatal complication of acute pancreatitis is hemorrhagic
pancreatitis, where severe inflammation and regional necrosis cause
vessel erosion with resultant hemorrhage into the pancreatic bed,
retroperitoneum, peritoneal cavity or gastrointestinal tract.19 Hemorrhagic
pancreatitis is depicted on T1-weighted sequences as a region of high
signal intensity within the pancreas or adjacent structures (Figure 8).
enterography (MRE) is beneficial in the emergent setting to evaluate
pregnant patients with suspected acute appendicitis and patients with
acute symptoms with inflammatory bowel disease (IBD). Pregnant patients
benefit from MRE by obtaining imaging of the appendix without the
hazards of fetal ionizing radiation. In patients with IBD, MRE can
assess for active inflammation and its related complications without
The prevalence of appendicitis does not
change during pregnancy and acute appendicitis is the most common cause
of emergent gastrointestinal surgery in a pregnant patient.20
The diagnosis of acute appendicitis in pregnancy is challenging due to
displacement of the appendix by the uterus. In addition, during
pregnancy the classic signs of appendicitis (leukocytosis, fever, and
right lower quadrant pain) are nonspecific, as leukocytosis can be
normal in pregnancy.
At our institution, an algorithm based on
the ACR Appropriateness Criteria was developed to assess pregnant
patients with potential appendicitis. All pregnant patients with
suspected appendicitis are initially evaluated with a directed abdominal
ultrasound study. Prior to being transported to the ultrasound suite,
the patient drinks a negative oral contrast agent as detailed above. In
our experience, ultrasound visualization of the appendix is poor. If the
ultrasound is nondiagnostic, MR imaging without intravenous gadolinium
is performed 2 hours after oral contrast ingestion. If the appendix is
not visualized on MR imaging, then the patient undergoes CT with
intravenous noniodinated contrast agent. The dual oral contrast mixture
provided in the emergency room prepares the patient for MR and CT
The MR imaging findings of acute appendicitis
include appendiceal diameter of >7 mm (Figure 9) and a wall thickness
of >2 mm, which are both best visualized on T2-weighted sequences.9
Periappendiceal and appendiceal inflammation and edema are best imaged
on STIR sequences; they appear as hyperintense signal within the
appendiceal wall or the surrounding tissue (Figure 9).12, 21-23
MR imaging can demonstrate fluid signal within the appendix, which can
also suggest acute appendicitis. Overall, MR imaging demonstrates high
sensitivity (97% to 100%) and specificity (92% to 93%) in acute
A growing number of patients with IBD present to the emergency room with acute complaints;24
MRE can facilitate diagnosis of acute flares and/or complications.
Crohn’s disease is a chronic granulomatous inflammatory process of the
gastrointestinal tract that affects approximately 400,000 to 600,000
people in North America.25 The etiology of Crohn’s disease is
complex and likely involves immunologic, genetic, infectious, vascular,
dietary and environmental factors.26, 27
Crohn’s disease usually involves the small bowel (80%), but it can affect any portion of the gastrointestinal tract.26 Gastrointestinal involvement can be separated by uninvolved bowel termed “skip lesions”.26,27
Crohn’s disease consists of superficial mucosal ulcerations (aphthous
ulcers) and deep fissuring ulcers. The deep fissuring ulcers can
penetrate the mucosa and result in submucosal inflammation, edema, and
bowel wall thickening. The submucosal edema results in increased
T2-weighted signal intensity of the submucosa.27 The
enhancing mucosa and serosa, combined with the submucosal edema on
contrast-enhanced T1-weighted, fat-suppressed sequences, produces a
“target” or “trilaminar” appearance of the bowel. Transmural
inflammation and ulcerations in Crohn’s disease can result in sinus
tracts, fistulas, and abscesses, while the chronic inflammatory changes
can result in strictures and bowel obstruction (Figure 10).
with ulcerative colitis also benefit from MRE. For example, ulcerative
colitis patients who are status post-ileal pouch-anal anastamosis can
obtain MRE to accurately diagnose complications such as “pouchitis”
(Figure 11), abscess, fistulas, strictures, and venous thrombi.28
MR and CT enterography in Crohn’s disease demonstrate equivalent rates of detecting active disease and complications.29
The cumulative radiation doses associated with CT scans for patients
with Crohn’s disease is substantial, and MRE can significantly reduce
their overall radiation exposure.30, 31
imaging can be used to accurately and rapidly diagnose and triage
patients with acute abdominal pain presenting to the emergency
department. MR imaging of the abdomen is particularly advantageous in
subsets of patients who are at higher risk for radiation-related
cancers, such as pediatric patients, pregnant women and patients who are
serially imaged, and in patients with allergies to iodinated CT
contrast agents. The relatively lengthy examination times and higher
cost compared to CT, lack of availability, and its incompatibility with
patient monitoring devices currently hinders the use of MR. As MR
imaging techniques continue to evolve and attempts grow to reduce
patient exposure to imaging-related radiation, this modality may play a
larger role in delivering health care to patients with abdominal pain in
the emergent setting.
- Ciesla DJ, Moore EE, Moore JB, et al. The academic trauma center is a model for the future trauma and acute care surgeon. J Trauma. 2005;58:657-662.
- Rosen MP, Ding A, Blake MA, et al. ACR Appropriateness Criteria®
2010. American College of Radiology Web site. http://www.acr.org/.
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- Hanbidge AE, Buckler PM, O’Malley ME, Wilson SR. From the RSNA
refresher courses: Imaging evaluation for acute pain in the right upper
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- Aldrich JE, Bilawich AM, Mayo JR. Radiation doses to patients
receiving computed tomography examinations in British Columbia. Can
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- Heverhagen JT, Klose KJ. MR Imaging for acute lower abdominal and pelvic pain. Radiographics. 2009;29:1781-1796.
- Patel SJ, Reede DL, Katz DS, et al. Imaging the pregnant patient for
nonobstetric conditions: Algorithms and radiation dose considerations. Radiographics. 2007;27:1705–1722.
- Tkacz JN, Anderson SA, Soto J. MR imaging in gastrointestinal emergencies. Radiographics. 2009;29:1767-1780.
- Oto A, Ernst RD, Shah R, et al. Right lower quadrant pain and
suspected appendicitis in pregnant women; evaluation with MR imaging –
initial experience. Radiology. 2005;234:445-451.
- Singh A, Danrad R, Hahn PF, et al. MR Imaging of the acute abdomen and pelvis: Acute appendicitis and beyond. Radiographics. 2007;27:1419-1431.
- Keeler EK, Casey FX, Engels H, et al. Accessory equipment considerations with respect to MRI compatibility. J Magn Reson Imaging. 1998;8:12-18.
- Pedrosa I, Rofsky NM. MR imaging in abdominal emergencies. Radiol Clin North Am. 2003;41:1243-1273.
- Pedrosa I, Levine D, Eyvazzadeh AD, et al. MR imaging evaluation of acute appendicitis in pregnancy. Radiology. 2006;238:891-899.
- Collins C, Maguire D, Ireland A, et al. A prospective study of
common bile duct calculi in patients undergoing cholecystectomy: Natural
history of choledocholithiasis revisited. Ann Surg. 2004;239:28-33.
- Phillips EH, Toouli J, Pitt HA, Soper NJ. Treatment of common bile duct stones discovered during cholecystectomy. J Gastrointest Surg. 2008; 12:624-628.
- Laing FC, Jeffrey RB Jr, Wing WV, Nyberg DA. Biliary dilatation: Defining the level and cause by real time US. Radiology. 1986;160:133-134.
- Stimac D, Miletić D, Radić M, et al. The role of nonenhanced
magnetic resonance imaging in the early assessment of acute
pancreatitis. Am J Gastroenterol. 2007;102:997–1004.
- Viremouneix L, Monneuse O, Gautier G, et al. Prospective evaluation of nonenhanced MR imaging in acute pancreatitis. J Magn Reson Imaging. 2007;26:331-338.
- Sharma M, Banerjee D, Garg PK. Characterization of newer subgroups
of fulminant and subfulminant pancreatitis associated with a high early
mortality rate. Am J Gastroenterol. 2007;102:2688-2695.
- Frey CF. Hemorrhagic pancreatitis. Am J Surg. 1979;137:616–623.
- Longo SA, Moore RC, Canzoneri BJ, Robichaux A. Gastrointestinal conditions during pregnancy. Clin Colon Rectal Surg. 2010;23:80-89.
- Birchard KR, Brown MA, Hyslop WB, et al. MRI of acute abdominal and pelvic pain in pregnant patients. AJR Am J Roentgenol. 2005;184:452–458.
- Oto A, Srinivasan PN, Ernst RD, et al. Revisiting MRI for appendix location during pregnancy. AJR Am J Roentgenol. 2006;186:883–887.
- Hormann M, Puig S, Prokesch SR, et al. MR imaging of the normal appendix in children. Eur Radiol. 2002;12:2313–2316.
- Ananthakrishnan AN, McGinley EL, Saeian K, Binion DG. Trends in
ambulatory and emergency room visits for inflammatory bowel diseases in
the United States: 1994-2005. Am J Gastroenterol. 2010;105:363-370.
- Loftus EV Jr, Schoenfeld P, Sandborn WJ. The epidemiology and
natural history of Crohn’s disease in population-based patient cohorts
from North America: A systematic review. Aliment Pharmacol Ther. 2002;16:51-60.
- Tolan DJ, Greenhalgh R, Zealley IA, et al. MR enterographic manifestations of small bowel Crohn disease. Radiographics. 2010;30:367-384.
- Leyendecker JR, Bloomfeld RS, DiSantis DJ, et al. MR enterography in the management of patients with Crohn disease. Radiographics. 2009;29:1827-1846.
- Broder JC, Tkacz JN, Anderson SW, et al. Ileal pouch-anal
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complications. Radiographics. 2010;30:221-233.
- Lee SS, Kim AY, Yang SK, et al. Crohn disease of the small bowel:
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- Fuchs Y, Markowitz J, Weinstein T, et al. Pediatric inflammatory
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- Pariente B, Peyrin-Biroulet L, Cohen L, et al. Gastroenterology
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