MR Imaging in Gastrointestinal Emergencies

Abstract

Accurate and rapid diagnostic imaging is essential for the appropriate management of acute gastrointestinal conditions. Computed tomography (CT) is the modality most often used in this setting because of its widespread availability and the relative speed, ease, and uniformity with which evaluations can be performed. CT allows the diagnosis of a wide spectrum of acute gastrointestinal diseases with the adjustment of only a few variables in the acquisition protocol. For example, the contrast material volume, injection rate, and delay before image acquisition can be manipulated to enhance vascular or organ-specific contrast for myriad gastrointestinal diagnoses. Magnetic resonance (MR) imaging has similarly robust potential, although its integration into the acute care setting requires greater technical and logistical effort. Improved MR imaging sequences, advances in coil technology, streamlined imaging protocols, and increased technical and professional familiarity with the modality make it an increasingly attractive option when there is concern about patient radiation exposure or allergy to iodinated contrast material. A variety of acute abdominal conditions, including pancreatic and biliary tract trauma, choledocholithiasis, gallbladder disease, acute pancreatitis, and appendicitis can be rapidly and accurately demonstrated with MR imaging. MR imaging also can play a vital role in the follow-up assessment of treatment response and in the diagnosis of indeterminate findings at CT or ultrasonography. Nevertheless, incompatibility of patient monitoring devices with the MR magnet, lack of MR imaging system availability, and the acuity of illness may limit the use of the modality.

Magnetic resonance imaging for acute pancreatitis

“…As with the development of high-field-strength magnetic resonance imaging (MRI), it has been established that several techniques such as abdominal rapid gradient-echo breath-hold, magnetic resonance cholangiopancreatography (MRCP) and three-dimensional dynamic contrastenhanced sequences are performed to depict satisfactorily the normal pancreas and pancreatic disorders [14,15] . Advantages for using MRI in patients with acute pancreatitis are as follows: (1) it is a diagnostic imaging method without radiation hazard; (2) it is particularly useful in patients who cannot receive iodinated contrast material owing to allergic reactions or other contraindications; (3) MRCP has the unique capability of providing noninvasive images of pancreatic parenchyma and pancreatic duct integrity, and it has the advantage of demonstrating possible communication of a pancreatic pseudocyst with pancreatic ducts [8,15] ; (4) MRI has a potential advantage over CT in detecting bile duct lithiasis and pancreatic hemorrhage of pseudocysts or pseudoaneurysm, which can help plan surgery; (5) nonenhanced MRI seems to be more accurate and reliable for the early assessment of severity and prognosis of acute pancreatitis than is contrast-enhanced CT [12,16,17] ; and (6) non-enhanced MRI is superior to CT for depiction and confirmation of mild forms of acute pancreatitis [18] .…”

Emergency abdominal MRI: current uses and trends

“…This is particularly true in select patient populations such as children and pregnant patients. [6][7][8] Ultrasound is a fast, inexpensive and readily available 8 alternative to CT and does not use ionizing radiation. The major disadvantage of ultrasound is its inability to penetrate bowel gas, which often precludes full assessment for pathology.…”

“…Choledocholithiasis can be suggested on CT or ultrasound when dilatation of the common bile duct (.8 mm) is detected, but neither modality is sensitive or specific for detection of biliary stones. 6,7 MR cholangiopancreatography has demonstrated high sensitivity (93-99%) and specificity (95-99%) for the detection of abnormalities of the biliary tree. Filling defects in the biliary tree, as seen on heavily T 2 weighted imaging, can represent calculi, sludge, air, malignancy or blood clot.…”

“…Filling defects in the biliary tree, as seen on heavily T 2 weighted imaging, can represent calculi, sludge, air, malignancy or blood clot. 6,18 One finding of particular importance, which may be seen on heavily T 2 weighted images, is extrinsic compression of the common hepatic duct secondary to impacted calculi within the gallbladder neck or cystic duct, an entity known as Mirizzi syndrome (Figure 4). 6,7,19 Detection of this finding as a cause of intrahepatic ductal dilatation is important, as it can mimic cholangiocarcinoma.…”

“…6,18 One finding of particular importance, which may be seen on heavily T 2 weighted images, is extrinsic compression of the common hepatic duct secondary to impacted calculi within the gallbladder neck or cystic duct, an entity known as Mirizzi syndrome (Figure 4). 6,7,19 Detection of this finding as a cause of intrahepatic ductal dilatation is important, as it can mimic cholangiocarcinoma. 19 As with cholelithiasis, evaluation for acute cholecystitis in the ED also begins with an abdominal ultrasound.…”