Fast MR imaging and the detection of small-bowel obstruction

The role of magnetic resonance imaging in acute abdominal pain in paediatric age group

Background

The purpose of this study is to evaluate the utility of magnetic resonance imaging in the assessment of acute atraumatic abdominal pain as the first line cross sectional modality in children, so as to prevent excessive radiation exposure from computed tomography scan and to review the magnetic resonance imaging features of common acute abdominal and pelvic conditions.

Results

30 patients (0–18 years) underwent rapid unenhanced magnetic resonance imaging. The results of our study indicated that for the diagnosis of causes for acute abdominal pain, magnetic resonance imaging had sensitivity of 92% (95% confidence interval 73.8–97.6%) and a specificity of 80% (95% confidence interval 28.4–99.5%). The positive predictive value was 95.8% (95% confidence interval 79.9–99.3%) and negative predictive value was 67% (95% confidence interval 33.1–89.0%) which had a highly significant statistical association (p < 0.001).

Conclusion

Unenhanced magnetic resonance imaging is an excellent option for the initial, detailed evaluation of acute abdominal emergencies in pediatric patients because it can diagnose the whole range of presenting abnormalities which include the causes of abdominal pain warranting surgical and nonsurgical management.

Imaging Modalities for Evaluation of Intestinal Obstruction

It is essential for the colon and rectal surgeon to understand the evaluation and management of patients with both small and large bowel obstructions. Computed tomography is usually the most appropriate and accurate diagnostic imaging modality for most suspected bowel obstructions. Additional commonly used imaging modalities include plain radiographs and contrast imaging/fluoroscopy, while less commonly utilized imaging modalities include ultrasonography and magnetic resonance imaging. Regardless of the imaging modality used, interpretation of imaging should involve a systematic, methodological approach to ensure diagnostic accuracy.

Diagnostic value of hepatic artery perfusion fraction combined with TGF-β in patients with hepatocellular carcinoma

Diagnostic value of hepatic artery perfusion fraction (HAF) combined with transforming growth factor-β (TGF-β) in the diagnosis of primary liver carcinoma (PLC) was evaluated. The clinical data of 128 PLC patients undergoing radical hepatectomy in Affiliated Hospital of Jining Medical University were regarded as the study group. Seventy-four healthy volunteers examined in Affiliated Hospital of Jining Medical University were collected as the control group. Double-antibody sandwich enzyme-linked immunosorbent assay was used to detect the expression level of serum TGF-β. The upper abdomen of the subjects was scanned by a 64-slice spiral CT, and the perfusion parameters were analyzed and calculated. According to the HAF and the expression level of TGF-β in the two groups, single and combined detection of TGF-β and HAF parameters were detected, respectively, by ROC curve. The expression of TGF-β in serum of the study group was higher than that of the control group (P<0.05). The expression level of serum TGF-β was closely related to total bilirubin, ascites, TNM stage, prothrombin time and tumor diameter. Blood flow (BF), blood volume (BV), permeability surface (PS), HAF and other perfusion parameters in the study group were higher than those in the control group (P<0.05). The specificity and sensitivity of TGF-β expression level in diagnosing PLC were 73 and 93%, respectively; the specificity and sensitivity of HAF parameter in diagnosing PLC were 73 and 100%, respectively; the specificity and sensitivity of HAF parameter combined with TGF-β expression level were 84 and 100%, respectively. TGF-β is highly expressed in serum of PLC patients; HAF parameter combined with TGF-β expression level can improve the specificity and has an important value in the diagnosis of PLC, which is worthy of clinical promotion.

Ingestible Contrast Agents for Gastrointestinal Imaging

Gastrointestinal (GI) ailments cover a wide variety of diseases involving the esophagus, stomach, small intestine, large intestine, and rectum. They bring about many inconveniences in daily life in chronic diseases and can even be life threatening in acute cases. Rapid and safe detection approaches are essential for early diagnosis and timely management. Contrast agents for GI imaging can enhance contrast to distinguish abnormal lesions from normal structures. Computed tomography and magnetic resonance imaging are two important diagnostic tools for the evaluation of GI conditions. This review mainly involves several common GI diseases, including inflammatory diseases, intestinal tumors, diarrhea, constipation, and gastroesophageal reflux diseases. Selected contrast agents, such as barium sulfate, iodine-based agents, gadolinium-based agents, and others, are summarized. Going forward, continued endeavors are being made to develop more emerging contrast agents for other imaging modalities.

Emergency Medicine Evaluation and Management of Small Bowel Obstruction: Evidence-Based Recommendations

BACKGROUND

Small bowel obstruction (SBO) is a commonly diagnosed disease in the emergency department (ED). Recent literature has evaluated the ED investigation and management of SBO.

OBJECTIVE

This review evaluates the ED investigation and management of adult SBO based on the current literature.

DISCUSSION

SBO is most commonly due to occlusion of the small intestine, resulting in fluid and gas accumulation. This may progress to mucosal ischemia, necrosis, and perforation. A variety of etiologies are present, but in adults, adhesions are the most common cause. Several classification systems are present. However, the most important distinction is complete vs. partial and complicated vs. simple obstruction, as complete complicated SBO more commonly requires surgical intervention. History and physical examination can vary, but the most reliable findings include prior abdominal surgery, history of constipation, abdominal distension, and abnormal bowel sounds. Signs of strangulation include fever, hypotension, diffuse abdominal pain, peritonitis, and several others. Diagnosis typically requires imaging, and though plain radiographs are often ordered, they cannot exclude the diagnosis. Computed tomography and ultrasound are reliable diagnostic methods. Management includes intravenous fluid resuscitation, analgesia, and determining need for operative vs. nonoperative therapy. Nasogastric tube is useful for patients with significant distension and vomiting by removing contents proximal to the site of obstruction. Surgery is needed for strangulation and those that fail nonoperative therapy. Surgical service evaluation and admission are recommended.

CONCLUSION

SBO is a common reason for admission from the ED. Knowledge of recent literature can optimize diagnosis and management.

[Minimally invasive treatment of rare forms of mechanical intestinal obstruction]

AIM

To develop medical algorithms for reduction of morbidity and mortality in rare forms of mechanical intestinal obstruction.

MATERIAL AND METHODS

17 patients with mechanical intestinal obstruction have been operated in Sklifosovsky Research Institute for Emergency Care for the period 2010 - 2016. There were 13 women and 4 men aged 56 (44,5-74,5) years on the average. Phytobezoar was detected in 7 patients (41.2%), tumor in 7 patients (41.2%) and gallstone ileus in 3 patients (17.6%).

RESULTS

There were no complications in group 1. In group 2 postoperative complications occurred in 3 patients: gastrocnemius vein thrombosis followed by successful medication (Clavien-Dindo type II), abdominal abscess drained under ultrasonic control (Clavien-Dindo type IIIa) and 1 (8.3%) death (Clavien-Dindo type V). Postoperative mortality in group 2 was 8.3%.

CONCLUSION

Despite small sample size and no statistically reliable results the advantages of minimally invasive access are obvious. However, further trials are required to ensure the reliability of the results.

Early MRI findings of small bowel obstruction: an experimental study in rats

PURPOSE

This study was undertaken to identify the early magnetic resonance imaging (MRI) findings of small bowel obstruction (SBO) and to analyse their evolution over time comparing them with histological findings.

MATERIALS AND METHODS

SBO was surgically induced in 10 rats divided into two groups monitored at predetermined time points until the 8th hour: group 1, macroscopically observed and group 2, investigated with 7-Tesla micro-MRI (7 T μ-MR). At the end of observation, the bowel was excised for histological analysis.

RESULTS

7 T μ-MRI T2-w sequences acquired 15 min after SBO, showed early evidence of bowel wall hyperintensity and a small amount of peritoneal free fluid. At 1 h, a hyperintensity of the loop proximal to the obstruction was found and, after 4 h, free fluid between the loops, bowel wall thickening and increased wall hyperintensity were also found. After 6 h hypotonic reflex ileus (only gas-filled dilated loops) was detected, which became paralytic ileus (dilation with air-fluid levels) after 8 h. The MRI findings were all confirmed at histological examination.

CONCLUSIONS

This study allows definition of the early MRI features of SBO (peritoneal free fluid and hyperintensity of the injured bowel) and their chronological evolution, also confirmed by histological examination. Our data suggest a potential role of MR imaging in the early diagnostic assessment and management of patients with SBO. The chance to achieve an early detection of bowel injury and to correlate the histological pattern with imaging findings could contribute to a finer and earlier diagnosis and a more effective treatment.

Adult small bowel obstruction

BACKGROUND

Small bowel obstruction (SBO) is a clinical condition that is often initially diagnosed and managed in the emergency department (ED). The high rates of potential complications that are associated with an SBO make it essential for the emergency physician (EP) to make a timely and accurate diagnosis.

OBJECTIVES

The primary objective was to perform a systematic review and meta-analysis of the history, physical examination, and imaging modalities associated with the diagnosis of SBO. The secondary objectives were to identify the prevalence of SBO in prospective ED-based studies of adult abdominal pain and to apply Pauker and Kassirer's threshold approach to clinical decision-making to the diagnosis and management of SBO.

METHODS

MEDLINE, EMBASE, major emergency medicine (EM) textbooks, and the bibliographies of selected articles were scanned for studies that assessed one or more components of the history, physical examination, or diagnostic imaging modalities used for the diagnosis of SBO. The selected articles underwent a quality assessment by two of the authors using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool. Data used to compile sensitivities and specificities were obtained from these studies and a meta-analysis was performed on those that examined the same historical component, physical examination technique, or diagnostic test. Separate information on the prevalence and management of SBO was used in conjunction with the meta-analysis findings of computed tomography (CT) to determine the test and treatment threshold.

RESULTS

The prevalence of SBO in the ED was determined to be approximately 2% of all patients who present with abdominal pain. Having a previous history of abdominal surgery, constipation, abnormal bowel sounds, and/or abdominal distention on examination were the best history and physical examination predictors of SBO. X-ray was determined to be the least useful imaging modality for the diagnosis of SBO, with a pooled positive likelihood ratio (+LR) of 1.64 (95% confidence interval [CI] = 1.07 to 2.52). On the other hand, CT and magnetic resonance imaging (MRI) were both quite accurate in diagnosing SBO with +LRs of 3.6 (5- to 10-mm slices, 95% CI = 2.3 to 5.4) and 6.77 (95% CI = 2.13 to 21.55), respectively. Although limited to only a select number of studies, the use of ultrasound (US) was determined to be superior to all other imaging modalities, with a +LR of 14.1 (95% CI = 3.57 to 55.66) and a negative likelihood ratio (-LR) of 0.13 (95% CI = 0.08 to 0.20) for formal scans and a +LR of 9.55 (95% CI = 2.16 to 42.21) and a -LR of 0.04 (95% CI = 0.01 to 0.13) for beside scans. Using the CT results of the meta-analysis for the 5- to 10-mm slice subgroup as well as information on intravenous (IV) contrast reactions and nasogastric (NG) intubation management, the pretest probability threshold for further testing was determined to be 1.5%, and the pretest probability threshold for beginning treatment was determined to be 20.7%.

CONCLUSIONS

The potentially useful aspects of the history and physical examination were limited to a history of abdominal surgery, constipation, and the clinical examination findings of abnormal bowel sounds and abdominal distention. CT, MRI, and US are all adequate imaging modalities to make the diagnosis of SBO. Bedside US, which can be performed by EPs, had very good diagnostic accuracy and has the potential to play a larger role in the ED diagnosis of SBO. More ED-focused research into this area will be necessary to bring about this change.

Evaluation and management of small-bowel obstruction: an Eastern Association for the Surgery of Trauma practice management guideline

BACKGROUND

Small-bowel obstruction (SBO) represents as many as 16% of surgical admissions and more than 300,000 operations annually in the United States. The optimal strategies for the diagnosis and management of SBO continue to evolve secondary to advances in imaging techniques, critical care, and surgical techniques. This updated systematic literature review was developed by the Eastern Association for the Surgery of Trauma to provide up-to-date evidence-based recommendations for SBO.

METHODS

A search of the National Library of Medicine MEDLINE database was performed using PubMed interface for articles published from 2007 to 2011.

RESULTS

The search identified 53 new articles that were then combined with the 131 studies previously reviewed by the 2007 guidelines. The updated guidelines were then presented at the 2012 annual EAST meeting.

CONCLUSION

Level I evidence now exists to recommend the use of computed tomographic scan, especially multidetector computed tomography with multiplanar reconstructions, in the evaluation of patients with SBO because it can provide incremental clinically relevant information over plains films that may lead to changes in management. Patients with evidence of generalized peritonitis, other evidence of clinical deterioration, such as fever, leukocytosis, tachycardia, metabolic acidosis, and continuous pain, or patients with evidence of ischemia on imaging should undergo timely exploration. The remainder of patients can safely undergo initial nonoperative management for both partial and complete SBO. Water-soluble contrast studies should be considered in patients who do not clinically resolve after 48 to 72 hours for both diagnostic and potential therapeutic purposes. Laparoscopic treatment of SBO has been demonstrated to be a viable alternative to laparotomy in selected cases.

Nontraumatic abdominal pain in pregnancy: imaging considerations for a multiorgan system problem

Nontraumatic abdominal pain in the pregnant patient can present a clinician with a variety of diagnostic possibilities. The overlap between signs and symptoms expected in normal pregnancy and these many pathologic possibilities does little to help focus the clinician's diagnostic efforts. Fear of ionizing radiation's effects on the fetus has driven efforts to refine medical imaging algorithms in such a way as to attempt to eliminate its use at all cost. In today's world, we are nearly there. In this review the differential diagnosis of nontraumatic abdominal pain in the pregnant patient will be explored. Of note is the recurring theme that much of what can be done today with regard to diagnostic imaging, both in general and with regard to this specific subset of patients, centers on the use of the non-ionizing modalities of ultrasound and magnetic resonance imaging.

Low b-value diffusion-weighted imaging for diagnosing strangulated small bowel obstruction: a feasibility study

PURPOSE

To assess the feasibility of low b-value diffusion-weighted imaging (DWI) for diagnosing strangulated small bowel obstruction (SBO).

MATERIALS AND METHODS

Five volunteers and 14 patients with SBO underwent DWI at b-values of 0 and 50 s/mm(2). Apparent diffusion coefficients (ADCs) and signal preservation ratios (SPRs) were measured in the distal jejunum in the volunteers before and after butylscopolamine administration, and in the (strangulated) closed loop, near the obstructive site, and far from the obstructive site in the patients. Low b-value diffusion-weighted images in the patients were quantitatively evaluated for diagnosing strangulation.

RESULTS

In the volunteers, mean ADC (10(-3) mm(2)/s) and SPR (%) before butylscopolamine administration (18.3 ± 5.9 and 41.4 ± 11.5) were significantly different (P < 0.05) from those after butylscopolamine administration (6.4 ± 3.6 and 73.7 ± 12.9). In the patients, mean ADCs and SPRs among the strangulated closed loop (3.8 ± 2.2 and 83.3 ± 9.3), near the obstructive site (12.1 ± 6.9 and 57.3 ± 18.5), and far from the obstructive site (26.8 ± 10.7 and 29.9 ± 16.4) were significantly different (P < 0.05). Areas under the receiver operating characteristic curve for the diagnosis of strangulation varied between 0.937 and 1.000.

CONCLUSION

Low b-value DWI is a feasible technique to distinguish the strangulated closed loop from nonstrangulated loops in SBO, and show promise for diagnosing strangulated SBO.

Malignant tumours of the small intestine: a review of histopathology, multidetector CT and MRI aspects

Small bowel neoplasms, including adenocarcinoma, carcinoid tumour, lymphoma and gastrointestinal stromal tumours, represent a small percentage of gastrointestinal cancers, yet are among those with the poorest prognosis compared with other gastrointestinal malignancies. Unclear clinical scenarios and difficult radiological diagnosis often delay treatment with negative effects on patient survival. Recently, multidetector CT (MDCT) and MRI have been introduced as feasible and accurate diagnostic techniques for the identification and staging of small bowel neoplasms. These techniques are gradually replacing conventional barium radiography as the tool of choice. However, the inherent technical and physiological challenges of small bowel imaging require a familiarity with patient preparation and scan protocols. Adequate knowledge of the histopathology and natural evolution of small bowel neoplasms is also important for differential diagnosis. The aim of this article is to review MDCT and MRI protocols for the evaluation of small bowel tumours and to provide a concise yet comprehensive guide to the most relevant imaging features relative to histopathology.

Magnetic resonance imaging for the evaluation of acute abdominal pain in pregnancy

The investigation of acute abdominal pain in pregnancy is challenging. The use of ultrasound may be limited due to the patient's change in body habitus and computed tomography is not desirable due to fetal irradiation. Magnetic resonance imaging (MRI) has thus become increasingly popular in the evaluation of such patients, due to its lack of ionizing radiation, multiplanar capability and high contrast resolution. This review will detail the MRI technique required to image the pregnant abdomen and describe the MRI features of common causes of acute abdominal pain in pregnancy.

MR enterography with polyethylene glycol as oral contrast medium in the follow-up of patients with Crohn disease: comparison with CT enterography

BACKGROUND

To compare magnetic resonance enterography (MRE) and computed tomography enterography (CTE) in detecting inflammatory bowel disease activity (IBD) in patients with Crohn's disease (CD).

METHODS

A total of 29 patients (M 20; F 9; mean age 43.8 ± 15.9) with known CD underwent MRE. MRE was performed at 1.5 T using phased-array sense body coil, after oral administration of 1.5-2 L of PEG solution as oral contrast agent. MRE protocol included T1-weighted, sSShT2, sBTFE and gadolinium-enhanced THRIVE sequences acquired on coronal and axial planes. CTE was performed using a 16 multidetector-row computed-tomography before and after intravenous administration of 120 mL of iodinated contrast. MRE images and CTE scans were reviewed by a radiologist for bowel thickness and enhancement, mesenteric lymph nodes, vascular engorgement, fibrofatty proliferation, fistulas and abscesses. The disease activity was also defined by CDAI > 150.

RESULTS

MRE has demonstrated a good sensitivity in detection of CD activity, particularly in depiction of mural thickening, mural enhancement, and vascular engorgement. The level of agreement between the two technique was excellent in evaluating wall thickening with mucosal hyperenhancement (κ = 1), comb (κ = 0.90) and halo signs (κ = 0.86). In detecting fibrofatty proliferation and mesenteric lymph nodes, CTE was superior to MRE (accuracy: P < 0.05), while MRE was superior in visualization of fistulas.

CONCLUSION

MRE is an accurate method in monitoring the activity of CD as compared to CTE and may be considered an alternative to CTE in assessing degree of CD and evaluating therapeutic effectiveness.

MR enterography in the evaluation of small bowel dilation

Magnetic reasonance (MR) enterography enables high contrast resolution depiction of the location and cause of bowel obstruction through a combination of predictable luminal distension and multiplanar imaging capabilities. Furthermore, because the patient is not exposed to ionizing radiation, sequential "dynamic" MR imaging can be performed repeatedly over time further facilitating depiction of the site and/or the cause of obstruction. With increasing availability of MR imaging and standardization of the oral contrast medium regimens, it is likely that this technique will assume an ever-increasing role in the evaluation of small bowel dilation in the coming years. We illustrate the utility of MR enterography in the evaluation of small bowel dilation, whether it be mechanical, functional (e.g., ileus), or related to infiltrative mural disease.

Updating magnetic resonance imaging of small bowel: Imaging protocols and clinical indications

High soft tissue contrast resolution, acquisition of multi-planar images and the possibility to obtain functional information make magnetic resonance an interesting imaging technique to evaluate the small bowel disease. The absence of ionizing radiation is an important feature of magnetic resonance imaging (MRI) examinations because inflammatory diseases such as Crohn’s disease (CD) are studied most frequently, which are prevalent among children and young adults. MRI, using modern equipment and a rigorous technical approach, can offer detailed morphologic information and functional data on the small bowel. This article discusses the MRI protocols for small bowel and the MR imaging findings of small bowel diseases, such as CD and small bowel neoplasms.

Adult celiac disease: MRI findings

The purpose of our report is to describe a spectrum of findings of celiac disease at MR enterography. MR enterography is a non-invasive, feasible, and reproducible imaging technique for the evaluation of small bowel. Findings on MR enterography, similar to those of conventional barium studies, may suggest a diagnosis of celiac disease.

MR imaging of the small bowel

Cross-sectional imaging techniques such as CT and MR imaging have advantages over traditional barium fluoroscopic techniques in their ability to visualize superimposed bowel loops better and to improve visualization of extraluminal findings and complications. This article discusses MR imaging of the small bowel with enterography and enteroclysis techniques. It reviews the advantages, limitations, technique, and indications and reviews the results that have been obtained in evaluating different disease processes.

MR imaging of acute right lower quadrant pain in pregnant and nonpregnant patients

The use of magnetic resonance (MR) imaging in the evaluation of acute abdominal pain is increasing, particularly in those circumstances where computed tomography (CT) is not desirable (eg, pregnancy, allergy to iodinated contrast material). Although ultrasonography (US) is considered the imaging study of choice for evaluation of abdominal pain in pregnant patients, MR imaging is a valuable adjunct to US in evaluation of pregnant patients with acute right lower quadrant (RLQ) pain who have inconclusive US results. MR imaging is also frequently used in patients with renal failure, in whom the use of iodinated contrast material is contraindicated, as well as in cases where CT results are inconclusive. In patients with acute RLQ pain, the breadth of abnormalities visible at MR imaging is very broad, with pathologic conditions potentially originating from multiple organ systems, but most commonly from the gastrointestinal and genitourinary systems. MR imaging is an excellent imaging modality for evaluation of RLQ pain and should be strongly considered in those patients in whom use of iodinated contrast media or radiation is not desirable.

Magnetic resonance imaging of abdominal pain during pregnancy

The objective of this review is to demonstrate magnetic resonance imaging as an important adjunct to ultrasound and computed tomography in the evaluation of the pregnant patient with abdominal pain. With the advent of ultrafast T2-weighted pulse sequences, fetal and bowel motion cause minimal artifact on the images. An accurate diagnosis can often be made in a few minutes based on these high-contrast images performed in 2 or 3 planes. T1-weighted gradient echo images with and without fat saturation are useful for identifying blood and fat, especially in the case of adnexal masses. Gadolinium-diethylenetriamine pentaacetic acid is rarely used to diagnose inflammatory or obstructive disease and is reserved for those patients with suspected malignancies.

ACR Appropriateness Criteria® on Suspected Small-Bowel Obstruction

With no one generally accepted approach to evaluate patients with suspected small-bowel obstruction (SBO), standard CT has emerged as the preeminent imaging modality and should be considered in the initial evaluation of patients with suspected high-grade SBO. Playing less significant roles in the diagnosis of acute SBO are barium enemas and the small-bowel examination.

MR Imaging Evaluation of Acute Abdominal Pain During Pregnancy

MR imaging enables diagnosis of a variety of maternal diseases presenting as acute abdominal pain in pregnant patients. MR imaging is a valuable complement to ultrasound in the determination of the exact etiology of acute abdominal pain, and it is important for the radiologist to recognize the MR imaging appearance of common causes of acute abdominal pain during pregnancy. This article reviews the MR imaging technique and findings of various abnormalities causing acute abdominal pain in pregnant patients.

Magnetic resonance imaging in the oncology patient: evaluation of the extrahepatic abdomen

In the oncology patient MR imaging provides excellent depiction of all forms of extrahepatic tumor. Rapid breath-hold imaging techniques are combined with intravenous and intraluminal contrast material to demonstrate tumors of the solid visceral organs, the gastrointestinal tract, peritoneum, mesentery, omentum, bile ducts, lymph nodes, and osseous structures. The unmatched soft tissue contrast of MR imaging allows one to depict subtle tumors involving all of these extrahepatic sites. MR imaging has become an integral and essential element in the management of oncology patients.

Imaging of acute small-bowel obstruction

OBJECTIVE

The objective of this pictorial essay is to review the different imaging techniques used for diagnosing small-bowel obstruction.

CONCLUSION

Small-bowel obstruction is a common presentation, for which safe and effective management depends on a rapid and accurate diagnosis. Conventional radiographs remain the first line of imaging. CT is used increasingly more because it provides essential diagnostic information not apparent from radiographs. MRI may play a role in the future as technology improves and it becomes more readily available.

Small bowel

MR imaging, using modern equipment and a rigorous technical approach, can offer detailed morphologic information and functional data on the small bowel. The optimal study technique is debatable, although the oral administration of contrast material as a first-line approach is less expensive, faster, easier to perform, and better tolerated by patients. MR enteroclysis might be reserved for selected cases as a second-line study. The major clinical indication is the evaluation of patients who have suspected or known Crohn's disease. The absence of ionizing radiation, considering the young age of most of the patients and the frequency of the examinations, is an important advantage over other techniques (radiograph and CT enteroclysis).

MRI for small bowel diseases

The role of radiologic studies has been well established in the diagnosis and management of patients with small bowel diseases. While small bowel follow-through examination or enteroclysis is widely accepted as the primary imaging method for small bowel investigation, additional cross-sectional imaging studies are often required for an accurate diagnosis and the precise evaluation of the extraluminal disease. Since fast magnetic resonance imaging (MRI) sequences have become available, there is increasing interest in the use of MRI for small bowel evaluation, attributed to its inherent advantages such as the lack of radiation exposure, excellent soft tissue contrast, and direct multiplanar capabilities. In this article, we review the current techniques, clinical applications, and limitations of MRI for the evaluation of patients with small bowel diseases.

MR imaging in abdominal emergencies

The use of MR imaging in the emergency setting is evolving. Clear indications include situations in need of contrast media when iodinated contrast cannot be administered or to facilitate assessments in pregnant patients and children when exposure to ionizing radiation is considered unacceptable. The availability of rapid, motion-immune sequences now makes MR imaging a feasible study in less cooperative patients extending the range of patients for whom a diagnostic study can be achieved. Capitalizing on the unique benefits of MR imaging there is optimism that MR imaging can eliminate test redundancy and impact patient care in a cost-effective manner. Further investigations are needed to identify the diagnostic algorithms for which this favorable use holds true.

Distinguishing benign from malignant bowel obstruction in patients with malignancy: findings at MR imaging

PURPOSE

To retrospectively evaluate the features of benign versus malignant bowel obstruction on unenhanced and gadolinium-enhanced spoiled gradient-echo magnetic resonance (MR) images in patients with malignancy.

MATERIALS AND METHODS

Forty-eight patients with malignancy and bowel obstruction underwent abdominal and pelvic MR imaging. Two blinded radiologists independently evaluated each study for dilated bowel, transition point, level of obstruction, obstructing mass, mural thickening and enhancement, and peritoneal disease. Benign obstruction was recorded if no mass was present and if mural thickening (when present) was segmental or diffuse. Malignant bowel obstruction was recorded if there was a mass, a disseminated abdominal tumor, or focal mural thickening. MR images were compared with surgical findings, follow-up imaging studies, and clinical outcome. chi2 test and Fisher exact test were used to assess the relationship between the MR features and benign versus malignant obstruction.

RESULTS

Bowel obstruction had a benign cause in 19 patients and a malignant cause in 29 patients. Observer 1 correctly characterized benign bowel obstruction in 17 of 19 patients and malignant bowel obstruction in 27 of 29 patients. The sensitivity of observer 1 for characterizing malignant obstruction was 93%, specificity was 89%, and accuracy was 92%. Observer 2 correctly characterized benign bowel obstruction in 18 of 19 patients and malignant bowel obstruction in 26 of 29 patients. The sensitivity of observer 2 for characterizing malignant obstruction was 90%, specificity was 95%, and accuracy was 92%. Malignant bowel obstruction was present in 24 of 25 patients with an obstructing mass (P <.001). All 16 patients with focal mural thickening had malignant obstruction. Benign obstruction was present in four of five patients with diffuse mural thickening. Segmental mural thickening occurred in four patients with serosal metastases and in 11 patients with benign bowel obstruction. More extensive peritoneal thickening and enhancement correlated with malignant obstruction.

CONCLUSION

In patients with malignancy who have symptoms indicative of bowel obstruction, gadolinium-enhanced MR imaging can help distinguish benign from malignant causes of bowel obstruction.

[Small bowel obstruction by a congenital band in 16 adults]

During embryogenesis, abnormal adhesion of the peritoneal folds induces a congenital band which can cause small bowel obstruction.

PATIENTS AND METHODS

From 1987 to 2001, 16 adult patients underwent surgery for small bowel obstruction due to a congenital band. There were 8 men and 8 women with a mean age of 59 years (range 23-90). None presented previous abdominal surgery.

RESULTS

Six patients presented acute abdominal pain the month before hospitalization. Among the 16 patients, 9 were operated at admission, and 7 after initial surveillance. Suspected diagnosis before operation was small bowel obstruction in 8 cases (with a diagnosis of congenital band in 3); perforated duodenal ulcer (n = 2); appendicitis (n = 2); mesenteric infarction (n = 1); diverticultis (n = 1); cholecystitis (n = 1); and strangulated hernia (n = 1). During operation performed through laparotomy or laparoscopy, a congenital band was noted in 100% of the cases, associated with intestinal necrosis in 5. One patient died postoperatively.

CONCLUSION

Because small bowel obstruction by congenital band is a rare condition, it represents a frequent problem of diagnosis. In this situation, the possibility of intestinal necrosis expose the patient to a possible fatal outcome.

MR enteroclysis

MR enteroclysis provides adequate image quality and sufficient distention of the entire small bowel. The functional information provided by MR enteroclysis equals that provided by conventional enteroclysis, which implies the ability reliably to depict even low-grade SBO. The inherent advantages of enteroclysis over conventional enteroclysis are the potential to detect extraluminal pathologic conditions and the ability to provide detailed information about the wall of the small bowel and the entire abdomen. Unlike conventional enteroclysis, MR enteroclysis does not have problems with overlapping bowel loops. MR enteroclysis has the potential to be an excellent diagnostic method for examinations of small bowel disease because of the functional information, the soft tissue contrast, and multiplanar imaging capabilities.

Oral contrast agents for magnetic resonance imaging of the bowel

The development of fast imaging sequences, which provide the ability to acquire motion-free T1- and T2-weighted images of static fluids, has greatly increased the interest in magnetic resonance imaging of the small bowel. Luminal distension is a necessary prerequisite for small bowel imaging methods because collapsed bowel loops can hide even large lesions and may mimic wall thickening. Poor distension of normal bowel loops in basal conditions has led researchers to study different oral contrast media to optimally distend the bowel lumen. Several MR oral contrast agents with various signal properties are available. According to these signal properties, agents are classified as positive ("bright" lumen), negative ("dark" lumen), or biphasic ("bright" lumen on T1 and "dark" on T2, or conversely "dark" lumen on T2 and "bright" on T1). Positive contrast agents cause a reduction in T1 relaxation time; consequently, these agents act on T1-weighted images by increasing the signal intensity of the bowel lumen. Negative contrast agents are based on superparamagnetic particles and act by inducing local field inhomogeneities, which results in shortening of both T1 and T2 relaxation times. Using superparamagnetic contrast agents, T2-weighted effects are predominant. Biphasic contrast agents are substances that have different signal intensities on different sequences, depending on the concentration at which they are administered. The choice of a single agent presents advantages and disadvantages; thus, the radiologist should choose the appropriate contrast medium according to the clinical setting, MR experience, availability of the agent, and patient tolerance.

Small bowel magnetic resonance imaging for inflammatory bowel disease

The presented concept of hydro-magnetic resonance imaging (MRI) using a 2.5% mannitol solution as an orally applicable intraluminal contrast agent is a meaningful, reproducible, and reliable imaging method for the depiction of the small bowel. Especially in patients with Crohn's disease, hydro-MRI is the imaging method of first choice because hydro-MRI offers the advantage of a superior depiction of the inflamed bowel wall and the extramural complications of this disease without radiation exposure. In addition, hydro-MRI allows for a reliable assessment of the inflammatory activity, especially for the differentiation between an active and an inactive (scarred) stenosis. In particular, the mural enhancement, the length as well as the wall thickness of inflamed bowel segments, are considered to be significant MR parameters for the determination of the activity of Crohn's disease. Hydro-MRI of the colon is suitable for the depiction of pathologic changes in ulcerative colitis, but in contrast to Crohn's disease, the assessment of disease activity by hydro-MRI is unreliable in ulcerative colitis, probably because of the low spatial resolution (mucositis in ulcerative colitis vs. transmural inflammation in Crohn's disease). Hydro-MRI does not allow a reliable classification of inflammatory bowel diseases, but in ambiguous cases, hydro-MRI may provide helpful information for the differentiation of Crohn's disease and ulcerative colitis. There are no data of larger patient groups published regarding MR findings in inflammatory bowel diseases besides Crohn's disease and ulcerative colitis, but hydro-MRI is a promising imaging tool for these entities, which should be assessed in additional studies.

MR colonography: development of optimized method with ex vivo and in vivo systems

An ex vivo magnetic resonance (MR) colonographic system with a bovine colon with polyps of predetermined dimensions was developed for evaluation and optimization of different combinations of imaging sequences and intraluminal contrast agents. Findings were then applied during in vivo testing in human subjects. The results show that optimized contrast and lesion conspicuity and minimized motion artifacts can be obtained with true fast imaging with steady-state precession combined with water as an intraluminal contrast agent.

Intestinal obstruction role of CT

CT has significantly advanced the evaluation of small and large bowel obstruction, especially in the acute situation where high-grade or possibly strangulating obstruction is being encountered. Any physician involved in evaluating patients with bowel distention and abdominal pain where obstruction becomes a distinct diagnostic possibility should be aware of the attributes and limitations of this modality to provide the best patient care. New technological advances will hopefully limit radiation exposure and provide even more definitive information in the diagnosis of bowel obstruction.

Preoperative evaluation by magnetic resonance imaging in patients with bowel obstruction

BACKGROUND

Bowel obstruction is a problematic condition because the main clinical issue is to determine whether emergency laparotomy or observation with a long tube is required. The recent development of imaging diagnostic modalities such as magnetic resonance imaging (MRI) is thought to be promising to support therapeutic decisions in patients with bowel obstruction.

METHODS

Twenty-seven patients with bowel obstruction who underwent laparotomy were evaluated by plain x-ray film, computed tomography (CT) scan, and MRI preoperatively with regard to the presence or absence of bowel obstruction, and the site and cause of bowel obstruction. Diagnostic accuracies were compared among these radiological modalities.

RESULTS

The presence of bowel obstruction was detected in 22 (81.5%) of 27 patients by plain abdominal x-ray film, in 24 (92.3%) of 26 patients by CT scan, and in 25 (92.6%) of 27 patients by MRI. The sites of obstruction were consistent with surgical findings in 25 (92.6%) of 27 patients by MRI, and in 15 (57.7%) of 26 patients by CT scan. The causes of bowel obstruction were accurately diagnosed by MRI in 25 (92.6%) of 27 patients, and in 23 (88.5%) of 26 patients by CT scan.

CONCLUSIONS

MRI could identify the presence and the site and cause of bowel obstruction in most of the cases. MRI is assumed to be superior to CT scan in the preoperative diagnosis of bowel obstruction.

Small bowel MRI: comparison of a polyethylene glycol preparation and water as oral contrast media

PURPOSE

To compare water and a polyethylene glycol (PEG) preparation as potential oral contrast media for magnetic resonance imaging (MRI) of the small bowel.

MATERIALS AND METHODS

Twenty-two healthy volunteers underwent separate MRI examinations after drinking up to two liters of water or PEG preparation. Small bowel images were obtained every 10 minutes for at least two hours using breath-hold single shot half-Fourier imaging, including both thick section projection and thin section images. Examinations were evaluated by two radiologists in consensus, blinded to the volunteer and contrast details, for arrival at the terminal ileum, transit time, and demonstration of small bowel segments.

RESULTS

The PEG preparation was significantly better than water at reaching the terminal ileum (PEG 21/22 volunteers [95.45%], water 14/22 volunteers [63.6%], P = 0.04). There was no significant difference in the mean transit time (water 51 +/- 48 minutes, PEG 37.7 +/- 22 minutes) or in the demonstration of the stomach, duodenum, and jejunum, but the PEG preparation was significantly better at demonstrating the ileum (P = 0.005) and terminal ileum (P = 0.002).

CONCLUSION

A PEG preparation is significantly better than water as an oral contrast medium for demonstrating the distal small bowel during breath-hold T2-weighted MRI.

Crohn disease with endoscopic correlation: single-shot fast spin-echo and gadolinium-enhanced fat-suppressed spoiled gradient-echo MR imaging

PURPOSE

To compare T2-weighted breath-hold single-shot fast spin-echo (SE) and gadolinium-enhanced spoiled gradient-echo (GRE) MR imaging with contrast material administered orally and rectally for evaluating patients with Crohn disease.

MATERIALS AND METHODS

Twenty-eight patients with Crohn disease received 2% barium sulfate and water enema. The abdomen and pelvis were imaged with transverse and coronal single-shot fast SE and gadolinium-enhanced spoiled GRE MR imaging. Two radiologists reviewed the two types of images for bowel disease. The extent, severity, and conspicuity of the disease were determined. Proof of bowel disease at MR imaging was compared with that at endoscopy, barium study, and surgery. Statistical analysis was performed with the McNemar test.

RESULTS

Twenty-five of 28 patients had proven abnormal bowel segments. The per-patient sensitivity of gadolinium-enhanced spoiled GRE MR imaging for the two radiologists was 100% and 96% versus 60% and 60% (P <.05) with single-shot fast SE MR imaging. Gadolinium-enhanced spoiled GRE MR images depicted more segments (54 and 52 of 61 segments; sensitivity, 89% and 85%, respectively) of the diseased bowel than did single-shot fast SE MR images (31 and 32 of 61 segments; sensitivity, 51% and 52%, respectively; P <.001). Severity of Crohn disease was correctly depicted at gadolinium-enhanced spoiled GRE imaging in 93% of patients versus in 43% of patients at single-shot fast SE imaging.

CONCLUSION

In patients with Crohn disease, gadolinium-enhanced fat-suppressed spoiled GRE MR imaging better depicted the extent and severity of intestinal disease compared with single-shot fast SE imaging.

Acute intestinal obstruction: diagnosis and management

In acute intestinal obstruction, the clinician must distinguish between acute small bowel obstruction (ASBO) and acute colonic obstruction (ACO). In cases of ASBO, management depends on whether the patient has had previous abdominal surgery. Most cases of ACO require surgery, although mechanical causes must be distinguished from pseudo-obstruction for different management techniques.

Technologic advances in abdominal MR imaging

Magnetic resonance (MR) imaging is finding an ever-growing role in the evaluation of a wide range of conditions in the abdomen. No longer confined to problem solving regarding abnormalities in solid organs, such as the liver and kidneys, MR imaging is increasingly being applied to the evaluation of the pancreatic and biliary ductal systems and even the bowel. Recent technical advances in hardware and software have allowed the acquisition of MR images that are largely free of artifact secondary to bowel peristalsis or respiratory motion; images providing excellent anatomic detail can now be obtained routinely. Faster sequences have reduced image acquisition time, thereby improving patient acceptance and allowing more efficient utilization of machine time. New three-dimensional sequences allow rapid image acquisition, reducing section misregistration and motion artifact while improving multiplanar reformations. The potential of MR imaging to provide functional and anatomic information is intriguing, and new techniques, including diffusion and perfusion imaging, are being evaluated. This review considers the advances in imaging hardware and pulse sequence design that underlie the increasing role of MR imaging in evaluation of the abdomen and discusses evolving clinical applications.