BackgroundThe diagnostic value of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) as the first imaging approach in the evaluation of rising carcinoembryonic antigen (CEA) is not clear. The objective of this study was to investigate the value of 18F-FDG PET/CT in patients with colorectal cancer (CRC) and suspected recurrence based on rising CEA.MethodsA total of 73 patients with CRC were referred to PET/CT after radical surgery. Generally, all patients were scheduled to follow a CT-based post-surgical follow-up regimen. In the case of rising CEA, 18F-FDG PET/CT was performed in most patients with contrast-enhanced CT. The PET/CT images were independently reviewed by two readers. The presence or absence of recurrence was based on histology and/or standardized clinical follow-up.ResultsAmong 35 patients who had confirmed recurrence of CRC, PET/CT demonstrated recurrence with a sensitivity of 85.7 %, a specificity of 94.7 %, a positive predictive value of 93.8 %, and a negative predictive value of 87.8 %. The SUVmax ranged from 1.3 to 19.9. The mean time since the last postoperative imaging and PET/CT was 8 months (median 4 months). CEA values at referral ranged from 1.5 to 164.0 μg/L (median 5.6 μg/L). The diagnostic properties of PET/CT were analyzed in subgroups of patients with a single rising CEA sample (30 patients, 41 %), 31 patients (43 %) with two or more consecutive increases, and 12 patients (16 %) with persistently elevated values.Conclusions18F-FDG PET/contrast-enhanced CT has high diagnostic accuracy in the diagnosis of recurrent CRC, even in patients in a conventional CT-based follow-up program.

Background and study aims Further diagnostics of incidental colorectal lesions on 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is questionable. Therefore, we aimed to evaluate the clinical importance of incidentally detected colorectal lesions on FDG-PET/CT. Patients and methods In the North Denmark Region, a retrospective study was performed among 19,987 patients who had an FDG-PET/CT from January 2006 to December 2015. Among these patients, we identified patients with a colonoscopy within 12 months from the PET/CT scan and a description of incidental colorectal PET-avid lesions on the PET/CT. PET findings were compared with colonoscopy-detected lesions and eventually histopathology. Results Incidental PET-avid lesions were observed in 549 patients. Colonoscopy revealed lesions in 457 (83 %), among whom 338 patients had a final histopathological diagnosis. Malignant and premalignant lesions were found in 297 patients (54 % among patients with a PET-avid lesion). The lesions were cancer in 76 patients and adenoma in 221 patients of whom 30 had high-grade and 191 low-grade adenomas. The findings changed patient management in 166 cases (30 % of all patients with a PET-avid lesion). A colonoscopy-based surveillance program was initiated for 80 % of patients with high-grade adenoma. No patients with PET-avid lesions but normal colonoscopy developed colorectal cancer during 3 years of observation (median observation time 7 years). Conclusions Incidental colorectal FDG uptake was infrequently observed, but when present, it was associated with a high rate of malignant or premalignant lesions. Our results indicate that patients with incidental colorectal FDG uptake should be referred to diagnostic work-up including colonoscopy.

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Incidental focal uptake of 18F-fluorodeoxyglucose (FDG) in the thyroid on positron emission tomography (PET/CT) is rare but often associated with malignancy. The epidemiology of thyroid incidentalomas has only to some extent been described in countries with iodine deficiency. Here we report data from Denmark, a country with known iodine deficiency and wide access to PET/CT. All FDG PET/CT comprising the head and neck region, during 2014, were retrospectively reviewed, and patients with focal FDG uptake in the thyroid gland were identified. A total of 2451 patients had an FDG PET/CT of which 59 (2.4%) patients presented with FDG-avid focal lesions in the thyroid gland. Among the 59 patients with FDG-avid lesions, 33 patients (56%) received work up with ultrasound, thyroid technetium scintigraphy, fine needle aspiration, and/or histology of which 20 patients had a conclusive pathology report. Ten patients with FDG-avid lesions were identified with thyroid malignancy. The risk of thyroid malignancy was 16.9% among patient with incidental FDG-avid thyroid lesions. Our findings indicated a similar frequency of FDG thyroid incidentalomas and malignancy rates in an iodine deficient population compared to summary data from prior studies, studies mostly performed in geographical areas of normal or excess iodine supplementation.

Late CE-CT, compared with late LD-CT, did not significantly improve the sensitivity of dual-phase Tc-99m MIBI parathyroid SPECT/CT in a population of patients with primary hyperparathyroidism. These findings were consistent regardless of the size, location, or histology of the adenomas.