State-of-the-art computed tomographic and magnetic resonance imaging of the gastrointestinal system

Enhanced Release of Glucose Into the Intraluminal Space of the Intestine Associated With Metformin Treatment as Revealed by [18F]Fluorodeoxyglucose PET-MRI

OBJECTIVE

Positron emission tomography (PET)-computed tomography has revealed that metformin promotes the intestinal accumulation of [¹⁸F]fluorodeoxyglucose (FDG), a nonmetabolizable glucose derivative. It has remained unknown, however, whether this accumulation occurs in the wall or intraluminal space of the intestine. We here addressed this question with the use of [¹⁸F]FDG PET-MRI, a recently developed imaging method with increased accuracy of registration and high soft-tissue contrast.

RESEARCH DESIGN AND METHODS

Among 244 individuals with type 2 diabetes who underwent PET-MRI, we extracted 24 pairs of subjects matched for age, BMI, and HbA_1c level who were receiving treatment with metformin (metformin group) or were not (control group). We evaluated accumulation of [¹⁸F]FDG in different portions of the intestine with both a visual scale and measurement of maximum standardized uptake value (SUV_max), and such accumulation within the intestinal wall or lumen was discriminated on the basis of SUV_max.

RESULTS

SUV_max of the jejunum, ileum, and right or left hemicolon was greater in the metformin group than in the control group. [¹⁸F]FDG accumulation in the ileum and right or left hemicolon, as assessed with the visual scale, was also greater in the metformin group. SUV_max for the intraluminal space of the ileum and right or left hemicolon, but not that for the intestinal wall, was greater in the metformin group than in the control group.

CONCLUSIONS

Metformin treatment was associated with increased accumulation of [¹⁸F]FDG in the intraluminal space of the intestine, suggesting that this drug promotes the transport of glucose from the circulation into stool.

MR imaging in gastrointestinal emergencies

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.

Extracolonic tumors of the gastrointestinal tract detected incidentally at screening CT colonography

PURPOSE

The aim of this article is to report our experience with incidental detection of extracolonic tumors of the gastrointestinal tract identified prospectively at screening CT colonography.

METHODS

A total of 2014 patients (1097 females, 917 males; mean age, 56.9 years) underwent primary CT colonography evaluation at our institution over an 18-month period. Following cathartic preparation and colonic distention, supine and prone multidetector CT scans were obtained with thin-collimation low-dose technique without intravenous contrast. We reviewed our database for lesions of the extracolonic gastrointestinal tract that were detected during the prospective reading.

RESULTS

Focal extracolonic gastrointestinal tract lesions were prospectively detected in 10 (0.5 percent) of 2014 patients (8 females; 2 males; mean age, 58.5 years). All patients were asymptomatic. Tumor locations included ileum (n = 3), stomach (n = 3), jejunum (n = 2), and appendix (n = 2). Mean tumor size was 2.2 (range, 0.8-3.4) cm. Lesions in eight patients were subsequently confirmed by conventional or capsule endoscopy and/or by intravenous contrast-enhanced CT. Seven lesions were surgically excised and one was removed at endoscopy; two patients with lipomas did not undergo further evaluation or treatment. Final diagnoses were benign in all cases and included lipoma (n = 3), small-bowel hamartoma (n = 2), appendiceal mucinous cystadenoma (n = 2), gastric leiomyoma (n = 1), small-bowel lymphangioma (n = 1), and gastric fundic gland polyp (n = 1).

CONCLUSIONS

Incidental extracolonic tumors of the gastrointestinal tract detected at screening CT colonography were all asymptomatic and benign but often prompted more invasive workup. Although the incidence of these tumors was relatively low, widespread population screening with CT colonography would result in new surgical referrals for these findings.

Endoscopic ultrasound in patients with obstructive jaundice and inconclusive ultrasound and computer tomography findings

The clinical work-up of patients with presumed pancreaticobiliary obstruction is usually straightforward including laboratory investigation, abdominal ultrasound and computer tomography. Ultrasound and computer tomography may, however, yield inconclusive findings regarding underlying cause. We report a case series (n = 10) demonstrating the usefulness of endoscopic ultrasound in the work-up of patients with inconclusive ultrasound and computer tomography findings, clinically suspected of pancreaticobiliary cancer.

Incidence of visualization of the normal appendix on different MRI sequences

The purpose of this paper is to assess the incidence of visualization of the normal appendix on magnetic resonance imaging (MRI) examinations of the pelvis in a large adult population and to compare the yield of commonly used sequences. Pelvic MRI scans of 111 randomly selected patients were retrospectively reviewed by two fellowship-trained body imagers. Thirty-six cases, where the entire cecum and terminal ileum were not included in the field of view, were excluded. A normal appendix was definitively visualized in 55 of 71 patients on T1 spin echo (SE) sequences (78%). The appendix was seen on 25 of 42 (60%) half-Fourier single-shot turbo spin echo T2. Visualization rates were 42% on pre-gadolinium T1 FS GRE, 54% on post-gadolinium T1 fat-suppressed gradient echo, and 17% of short tau inversion recovery sequences. MRI is an effective modality for visualization of the normal appendix. This may have important implications in patients with abdominal or pelvic pain, as visualization of a normal appendix should exclude the possibility of acute appendicitis from the differential diagnosis.