F-18 fluorodeoxyglucose positron emission tomography in the diagnosis of inflammatory bowel disease

Focal incidental colorectal fluorodeoxyglucose uptake: Should it be spotlighted?

Fluorine-18 fluorodeoxyglucose (F-18 FDG) positron emission tomography/computed tomography (PET/CT) has emerged as a cornerstone in cancer evaluation imaging, with a well-established history spanning several years. This imaging modality, encompassing the examination of the body from the base of the skull to the upper thighs, comprehensively covers the chest and abdominopelvic regions in a singular scan, allowing for a holistic assessment of nearly the entire body, including areas of marginal interest. The inherent advantage of this expansive scan range lies in its potential to unveil unexpected incidental abnormal hypermetabolic areas. The identification of incidental focal FDG uptake within colorectal regions during PET/CT scans is not an uncommon occurrence, albeit fraught with challenges associated with non-specific FDG uptake. The presence of benign colorectal lesions or physiological uptake poses a particular obstacle, as these may manifest with FDG uptake levels that mimic malignancy. Consequently, physicians are confronted with a diagnostic dilemma when encountering abnormal FDG uptake in unexpected colorectal areas. Existing studies have presented divergent results concerning these uptakes. Standardized uptake value and its derivatives have served as pivotal metrics in quantifying FDG uptake in PET images. In this article, we aim to succinctly explore the distinctive characteristics of FDG, delve into imaging findings, and elucidate the clinical significance of incidental focal colorectal uptake. This discussion aims to contribute valuable insights into the nuanced interpretation of such findings, fostering a comprehensive understanding.

Unexpected focal fluorodeoxyglucose uptake in main organs; pass through or pass by?

Since the inception of fluorine-18 fluorodeoxyglucose (F-18 FDG), positron emission tomography/computed tomography (PET/CT) utilizing F-18 FDG has become widely accepted as a valuable imaging modality in the field of oncology, with global prevalence in clinical practice. Given that a single Torso PET/CT scan encompasses the anatomical region from the skull base to the upper thigh, the detection of incidental abnormal focal hypermetabolism in areas of limited clinical interest is both feasible and not uncommon. Numerous investigations have been undertaken to delineate the distinctive features of these findings, yet the outcomes have proven inconclusive. The incongruent results of these studies present a challenge for physicians, leaving them uncertain about the appropriate course of action. This article provides a succinct overview of the characteristics of fluorodeoxyglucose, followed by a comprehensive discussion of the imaging findings and clinical significance associated with incidental focal abnormal F-18 FDG activity in several representative organs. In conclusion, while the prevalence of unrecognized malignancy varies across organs, malignancies account for a substantial proportion, ranging from approximately one-third to over half, of incidental focal uptake. In light of these rates, physicians are urged to exercise vigilance in not disregarding unexpected uptake, facilitating more assured clinical decisions, and advocating for further active evaluation.

FDG PET/CT in Crohn's disease: correlation of quantitative FDG PET/CT parameters with clinical and endoscopic surrogate markers of disease activity

PURPOSE

The aim of this study was to determine the feasibility and potential clinical utility of assessment of Crohn's disease (CD) activity by (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT employing a new quantitative approach.

METHODS

A total of 22 subjects (mean age 37) with CD who had undergone FDG PET/CT followed by ileocolonoscopy within 1 week were included in this analysis. The CD endoscopy index of severity (CDEIS) for various bowel segments was calculated. The CD activity index (CDAI) was evaluated, and fecal calprotectin was measured. On PET, regions with increased FDG uptake in large bowel were segmented with an adaptive contrast-oriented thresholding algorithm, and metabolically active volume (MAV), uncorrected mean standardized uptake value (SUV(mean)), partial volume-corrected SUV(mean) (PVC-SUV(mean)), SUV(max), uncorrected total lesion glycolysis (TLG = MAV × SUV(mean)), and PVC total lesion glycolysis (PVC-TLG = MAV × PVC-SUV(mean)) were measured. Global CD activity score (GCDAS) was calculated as the sum of PVC-TLG over all clinically significant FDG-avid regions in each subject. Correlations between regional PET quantification measures (SUVs, TLGs) and CDEIS were calculated. Correlations between the global PET quantification measure (GCDAS, global SUVs) with CDAI, fecal calprotectin, CDEIS, and CRP level were also calculated.

RESULTS

SUV(max), PVC-SUV(mean), and PVC-TLG significantly correlated with segment CDEIS subscores (r = 0.50, r = 0.69, and r = 0.31, respectively; p < 0.05). GCDAS significantly correlated with CDAI and fecal calprotectin (r = 0.64 and r = 0.51, respectively; p < 0.05).

CONCLUSION

By employing this new quantitative approach, we were able to calculate indices of regional and global CD activity, which correlated well with both clinical and pathological disease activity surrogate markers. This approach may be of clinical importance in measuring both global disease activity and treatment response in patients with CD.

The Clinical Meaning of Benign Colon Uptake in (18)F-FDG PET: Comparison with Colonoscopic Findings

Background/Aims

Benign colon ¹⁸F-fluorodeoxyglucose (FDG) uptake is frequently observed in asymptomatic individuals. Aims of this study were to investigate the benign colon uptake by whole body FDG-positron emission tomography (PET) in asymptomatic adults and to correlate those results with colonoscopic and histologic findings.

Methods

Among 3,540 subjects who had undergone FDG-PET, 43 subjects who were diagnosed to have benign colon uptake in FDG-PET and underwent colonoscopy were retrospectively reviewed. Subjects were classified as diffuse or focal groups based on their FDG uptake patterns. PET results were analyzed together with colonoscopic and histologic findings.

Results

Forty-three subjects showed benign colon uptake in FDG-PET; 28 of them were shown as the diffuse group, while other 15 subjects were classified as the focal group. Five subjects among those showed diffuse uptake were diagnosed as adenoma. Seven among 15 subjects who showed focal uptake were diagnosed as adenocarcinoma (n=2), adenoma (n=3), or non-neoplastic polyp (n=2). Positive predictive values were 25% in the diffuse group and 47% in the focal group.

Conclusions

We recommend that patients showing benign FDG uptake in the colon should be further evaluated by colonoscopy, especially for patients with focal FDG uptake.

Differentiation of incidental intestinal activities at PET/CT examinations with a new sign: peristaltic segment sign

PURPOSE

The aim of this study was to present the effect of the peristaltic segment sign for the differential diagnosis between malignant, physiological and gastrointestinal focal fluorodeoxyglucose (FDG) uptakes as an alternative method to maximum standardized uptake value (SUVmax).

MATERIALS AND METHODS

Gastrointestinal tract (GIT) sections of 823 FDG positron emission tomography/computed tomography (FDG-PET/CT) performed in our center were reviewed retrospectively. Images of these cases that have been reported for positive intestinal focal FDG uptake areas were included. Through the sectional images, any accompanying short segment expanded with air just after or before the uptake area was marked as "positive peristaltism sign". The cases were confirmed with endoscopy plus biopsy (n:42), endoscopy (n:5), laparotomy (n:1), transabdominal biopsy (n:1), enteroclysis (n:1), CT-colonoscopy (n:5), rectal contrast enhanced CT (n:4). Distinguishing features of the sign were analyzed statistically compared to the conventional method for differentiation of malignity.

RESULTS

Localized FDG uptake was reported in 59 of 823 cases. A SUVmax greater than 2.5 with intestinal wall thickening allowed the diagnosis of malignity with sensitivity 33%, specificity 65%, positive predictive value 69% and negative predictive value 46%. The peristaltic segment sign, considered as a benign finding, increased the statistical values to 68%, 80%, 82% and 65%, respectively.

CONCLUSION

In case of gastrointestinal increased focal FDG uptake, the new parameter of peristaltic segment sign may differentiate the physiologic uptakes from the malignant ones more accurately than the conventional SUVmax.

A rare case of Tolosa-Hunt syndrome imaged with FDG PET/CT and MRI

We report on the imaging findings of Tolosa-Hunt syndrome in a 59-year-old patient. Clinical findings included periorbital pain, ptosis, disordered eye movements, and blurred vision. Treatment with intravenous administration of steroid resolved all symptoms. Currently, magnetic resonance imaging plays a key role in the diagnosis of Tolosa-Hunter syndrome for locating the inflammatory tissue and follow-up. This case of Tolosa-Hunter syndrome with representative (FDG PET/CT) images may imply that FDG PET/CT is a useful tool in detecting and monitoring of this disease.

Noninvasive assessment of pediatric inflammatory bowel disease with ¹⁸F-fluorodeoxyglucose-positron emission tomography and computed tomography

OBJECTIVES

¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) is a less invasive diagnostic tool and promising in detecting gastrointestinal lesions of pediatric inflammatory bowel disease (IBD) patients. Co-registration of low-dose computed tomography (CT) could lead to improvements in the assessment of disease. Therefore, this retrospective study evaluates the value of PET±CT in pediatric IBD patients.

PATIENTS AND METHODS

We analyzed ¹⁸F-FDG-PET scans without (n=24) or with combined (n=21) low-dose CT in children (18 females, 27 males, age: 3.7-16.7 years, median 13.2 years) who presented with the diagnosis of IBD (n=45). Results of PET±CT scans and conventional diagnostic procedures (endoscopy, histology, and ultrasound) were compared by a segment-based analysis.

RESULTS

Overall, 253 segments of the gastrointestinal tract (GIT) were explored by endoscopy/histology and ¹⁸F-FDG-PET±CT. Twenty-five additional small bowel segments were assessed by abdominal ultrasound and further 152 GIT segments not reached during endoscopy were evaluated by PET±CT. PET±CT revealed a segment-based sensitivity, specificity, positive predictive value, negative predictive value, and an accuracy for the detection of GIT lesions of 82, 97, 96, 88, and 91%, respectively. The patient-based sensitivity and specificity was 97 and 100%, respectively. Interestingly, the co-registration of CT did not improve the diagnostic informative value.

CONCLUSION

FDG-PET±CT is especially suitable for the assessment of IBD in children. The radiation exposure of 3-7 mSv is justified by the accuracy of this approach. FDG-PET seems to be a reliable tool for detecting inflamed gut segments in IBD with high sensitivity and specificity. The co-registration of CT had no additional benefit.

Incidental finding of focal FDG uptake in the bowel during PET/CT: CT features and correlation with histopathologic results

OBJECTIVE

The purpose of this study was to identify and characterize the clinically significant lesions associated with incidental detection of focal uptake of (18)F-FDG in the bowel at PET/CT.

MATERIALS AND METHODS

Among 2,250 consecutively registered patients with various nongastrointestinal malignant diseases who underwent FDG PET/CT as part of their care, patients with the incidental finding of focal bowel uptake of FDG were included in the study. All patients underwent an endoscopic or surgical procedure for characterization of the lesions. The location, intensity of uptake, and appearance of the lesions on PET/CT images were recorded and compared with the endoscopic and surgical pathologic results.

RESULTS

Twenty-one of 25 foci of intense uptake in the bowel were associated with endoscopic or surgical abnormalities (positive predictive value, 84%). Seven lesions were malignant (two primary, five secondary); 13 were premalignant (nine tubovillous adenoma, four tubular adenoma); and one lesion was benign (hyperplastic polyp). Eleven lesions detected with endoscopy were not FDG avid, and all 11 were smaller than 1 cm in diameter. There was no statistically significant difference in the maximum standardized uptake values of the benign and malignant lesions.

CONCLUSION

The incidental finding of focal FDG uptake in the bowel justifies further investigation of these foci and should not be dismissed as physiologic uptake. Premalignant lesions, such as adenoma, are often found, and early treatment may prevent the development of carcinoma.

PET-CT enteroclysis: a new technique for evaluation of inflammatory diseases of the intestine

PURPOSE

While CT/MR enteroclysis provides excellent anatomical details, it fails to provide information on metabolic activity of the inflammatory lesions of the intestine. We conceptualized a fusion of metabolic imaging techniques such as PET and an anatomical imaging modality such as CT enteroclysis to derive information both on morphological details and functional activity of lesions at the same time.

PATIENTS AND METHODS

In a prospective study, we included 17 adult patients with newly diagnosed inflammatory diseases of the intestine. Low dose whole body PET-CT scan was obtained first, which began at approximately 60 min after injection of 10 mCi of (18)fluoro-deoxyglucose (FDG). Subsequently, PET-CT enteroclysis of the abdomen was performed after infusion of 2 l of 0.5% methylcellulose through a naso-jejunal catheter.

RESULTS

Fourteen patients had abnormal and three had normal PET-CT enteroclysis studies. Twenty-three segments of small intestine and 27 segments of large intestine showed increased FDG uptake. The detection rate of PET-CT enteroclysis was significantly higher (total =50 segments, 23 segments of small intestine and 27 segments of large intestine) as compared with barium studies (16 segments of small intestine) and colonoscopy (17 segments of large intestine) combined together (total =33 segments). In addition PET-CT enteroclysis showed extra-luminal FDG uptake (lymph nodes in two, sacroilitis in two, and mesenteric fat proliferation in five).

CONCLUSIONS

As a single investigation, PET-CT enteroclysis detects a significantly higher number of lesions both in the small and large intestine in comparison to that detected by conventional barium and colonoscopy combined together. This technique is non-invasive, feasible and very promising.

Bowel hot spots at PET-CT

Positron emission tomography (PET) with 2-[fluorine-18]fluoro-2-deoxy-d-glucose (FDG) has been shown to be sensitive in the detection of many bowel malignancies, but its specificity is lower because of various physiologic and pathologic patterns of bowel FDG uptake. PET-computed tomography (CT) can be useful in localizing and characterizing foci of increased FDG uptake within the bowel. As the use of PET-CT in the staging and monitoring of oncologic disease continues to expand, familiarity with these patterns of bowel FDG uptake is essential and can help determine the need for and the relative urgency of further testing. Although a variety of imaging protocols are used for PET-CT, the use of negative oral contrast agent allows improved bowel distention while eliminating potential artifacts caused by high-density oral contrast agents. In addition, correlation with the CT portion of the combined PET-CT examination can sometimes help identify the cause of focal or segmental bowel uptake. The radiologist should be aware of potential pitfalls in the evaluation of FDG-avid foci within the abdomen, including bowel motility and low-attenuation lesions mimicking bowel. Nevertheless, even though the precise role of combined PET-CT for bowel assessment has yet to be determined, the application of sound basic principles of image interpretation will help ensure the accurate interpretation of bowel findings seen with this combined modality.

Lymphomatous involvement of gastrointestinal tract: evaluation by positron emission tomography with (18)F-fluorodeoxyglucose

AIM

To demonstrate the (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) findings in patients with non-Hodgkinos lymphoma (NHL) involving the gastrointestinal (GI) tract and the clinical utility of modality despite of the known normal uptake of FDG in the GI tract.

METHODS

Thirty-three patients with biopsy-proven gastrointestinal NHL who had undergone FDG-PET scan were included. All the patients were injected with 10-15 mCi FDG and scanned approximately 60 min later with a CTI/Siemens HR (+) PET scanner. PET scans were reviewed and the maximum standard uptake value (SUV(max)) of the lesions was measured before and after the treatment, if data were available and compared with histologic diagnoses.

RESULTS

Twenty-five patients had a high-grade lymphoma and eight had a low-grade lymphoma. The stomach was the most common site of the involvement (20 patients). In high-grade lymphoma, PET showed focal nodular or diffuse hypermetabolic activity. The average SUV(max)+/-SD was 11.58+/-5.83. After the therapy, the patients whose biopsies showed no evidence of lymphoma had a lower uptake without focal lesions. The SUV(max)+/-SD decreased from 11.58+/-5.83 to 2.21+/-0.78. In patients whose post-treatment biopsies showed lymphoma, the SUV(max)+/-SD was 9.42+/-6.27. Low-grade follicular lymphomas of the colon and stomach showed diffuse hypermetabolic activity in the bowel wall (SUV(max) 8.2 and 10.3, respectively). The SUV(max) was 2.02-3.8 (mean 3.02) in the stomach lesions of patients with MALT lymphoma. ONCLUSION: (18)F-FDG PET contributes to the diagnosis of high-grade gastrointestinal non-Hodgkin's lymphoma, even when there is the normal background FDG activity. Furthermore, the SUV plays a role in evaluating treatment response. Low-grade NHL demonstrates FDG uptake but at a lesser intensity than seen in high-grade NHL.

An abnormal accumulation of fluorine-18-FDG PET in cytomegalovirus enteritis—A case report

The source of a fever of unknown origin (FUO) and watery diarrhea in a 63-yr-old female with a history of disturbance of consciousness due to moyamoya disease was examined. Fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET), colonoscopy, blood analysis, and determination of cytomegalovirus (CMV) antigenemia were performed. FDG was found to be accumulated in the wall of a dilated colon, and extended from the transverse to sigmoid colon. Colonoscopy revealed edematous, inflammatory, and punched out lesions in accordance with the areas of abnormal FDG uptake. A biopsy specimen showed the antibody of CMV in the colonic mucosa, and CMV antigenemia was detected by an immunohistochemical assay using a monoclonal antibody for CMV pp65 antigen. From these findings, we strongly suspected CMV enteritis.

Evolving role of positron emission tomography in the management of patients with inflammatory and other benign disorders

Fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) has evolved from a research imaging modality assessing brain function in physiologic and pathologic states to a pure clinical necessity. It has been successfully used for diagnosing, staging, and monitoring a variety of malignancies. FDG-PET imaging also is evolving into a powerful imaging modality that can be effectively used for the diagnosis and monitoring of a certain nononcological diseases. PET has been shown to be very useful in the diagnosis of osteomyelitis, painful prostheses, sarcoidosis, fever of unknown etiology, and acquired immunodeficiency syndrome. Based on recent observations, several other disorders, such as environment-induced lung diseases, atherosclerosis, vasculitis, back pain, transplantation, and blood clot, can be successfully assessed with this technique. With the development and the introduction of several new PET radiotracers, it is expected that PET will secure a major role in the management of patients with inflammatory and other benign disorders.