Korean J Radiol.  2013 Dec;14(6):951-959. 10.3348/kjr.2013.14.6.951.

Is There Any Additional Benefit of Contrast-Enhanced CT as Part of Routine PET/CT Protocols for the Differentiation of Suspicious Incidental Gastrointestinal 2-Deoxy-18F-FDG Uptake?

• Brendle CB
• Aschoff P
• Kratt T
• Schraml C
• Reimold M
• Claussen C
• Pfannenberg CA

• KMID: 1711463
• DOI: http://doi.org/10.3348/kjr.2013.14.6.951

Abstract

OBJECTIVE
Suspicious incidental gastrointestinal FDG uptake during positron-emission tomography/computed tomography (PET/CT) examinations can be caused by different diseases, including malignancies. However, differentiation with PET alone is difficult. The aim of this study was to investigate the potential of PET alone, contrast-enhanced CT (ceCT), and low-dose CT (ldCT) in routine PET/CT protocols for differentiation of incidental gastrointestinal lesions.
MATERIALS AND METHODS
Sixty patients with incidental gastrointestinal lesions who underwent a routine PET/CT protocol with ldCT and ceCT were retrospectively analysed. The PET lesions were evaluated regarding their FDG uptake patterns and the standard uptake value. The anatomical correlates in both CT protocols were compared in regard to the correct lesion classification with the reference standard endoscopy.
RESULTS
Sixty-two lesions were found in 60 patients (17 malignant, 10 premalignant, 5 benign, 13 inflammatory, 17 physiological). The differentiation of the FDG uptake patterns did not enable reliable lesion classification. The positive predictive value for pathology was 0.81 for ceCT in PET/CT and 0.70 for ldCT. Malignancies were detected in 100% of the patients by ceCT vs. 29.4% by ldCT. The false negative rate of ceCT for all pathologies was 31.1%, vs. 68.9% for ldCT. False positive results (17/62) could not be excluded sufficiently by either CT protocol.
CONCLUSION
PET/ceCT protocols provide additional benefit especially in detecting gastrointestinal malignancies as a cause of suspicious incidental gastrointestinal FDG uptake. However, since follow-up endoscopy cannot be forgone due to the considerable false negative rate even with ceCT, the addition of ceCT to a routine PET/ldCT protocol cannot be recommended for this purpose.

Keyword

PET/CT; PET; CT; Incidental FDG uptake; Gastrointestinal lesions

MeSH Terms

Adult
Aged
Aged, 80 and over
Contrast Media/diagnostic use/pharmacokinetics
Female
Fluorodeoxyglucose F18/*diagnostic use/pharmacokinetics
Follow-Up Studies
Gastrointestinal Diseases/*diagnosis/metabolism
Gastrointestinal Tract/*metabolism/radiography/radionuclide imaging
Humans
Male
Middle Aged
Positron-Emission Tomography/*methods
Reproducibility of Results
Retrospective Studies
Tomography, X-Ray Computed/*methods
Contrast Media
Fluorodeoxyglucose F18

Figure

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  Fig. 1 Flow diagram shows selection process and final diagnosis of 60 patients with suspicious incidental gastrointestinal FDG uptake. ldCT = low-dose CT, ceCT = contrast-enhanced CT, GIT = gastrointestinal tract

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  Fig. 2 Distribution lesion number in subgroups of endoscopic lesions differs in different parts of gastrointestinal tract.

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  Fig. 3 Seventy two-year-old male patient with bronchial carcinoma in left lower lobe presented with suspicious incidental gastrointestinal FDG uptake in sigmoid colon. MIP of PET shows primary tumour in lung (black arrow) and suspicious incidental gastrointestinal FDG uptake in sigmoid (white arrow) (A). Axial PET (B) and axial PET/CT fusion (C) show focal FDG uptake in sigmoid. No correlate was found in non-enhanced low-dose CT (D), whereas contrast-enhanced CT showed corresponding intraluminal mass (1.3 cm) (white arrow) (E). Endoscopy revealed adenomatous mass with carcinoma in situ in histological examination (F).

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