Abstract
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Purpose: Pituitary adenomas (PAs) are common primary intracranial tumours. Of late, 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/computed tomography (CT) has been repeatedly reported as a complementary tool for the diagnosis and evaluation of PAs, particularly in cases where magnetic resonance imaging (MRI) results are equivocal. However, the appearance of PAs on 18F-FDG PET/CT remains controversial. Hybrid PET/MRI scanners have became available over the past few years. The purpose of this study was to compare the usefulness of 18F-FDG PET/ MRI with that of 18F-FDG PET/ CT for the detection of PAs.
Methods: With Institutional Review Board approval and written informed consent, 53 and 39 patients who underwent 18F-FDG PET/CT and 18F-FDG PET/MRI, respectively, and were pathologically diagnosed with PA after surgery were recruited for this study. In total, 24 and 29 patients with primary and recurrent tumours, respectively, underwent 18F-FDG PET/CT. Of the 39 patients who underwent 18F-FDG PET/MRI, 18 had primary tumours and 21 had recurrent tumours. Fifteen of these patients underwent both 18F-FDG PET/CT and 18F-FDG PET/MRI. All patients showed undiagnosable suspicious lesions or negative findings on conventional contrast-enhanced 3T MRI performed before recruitment. Trans-sphenoidal adenomectomy was performed within 2 weeks of imaging, and histopathological analysis of the surgical specimens confirmed a diagnosis of PA. Imaging characteristics and 18F-FDG uptake levels for all lesions were correlated with the surgical findings and pathological results. Chi-square and McNemar statistics were calculated for frequencies of factors. Results: Conventional contrast-enhanced MRI revealed suspicious findings for 38 (71%) of the 53 patients who underwent 18F-FDG PET/CT, which alone provided a definitive diagnosis for 32 (60%) patients. Among the 39 patients who underwent 18F-FDG PET/MRI, 16 (41%) had suspicious lesions on conventional contrast-enhanced MRI and 33 (84%) were definitively diagnosed by PET/MRI. Thus, the detection rate for PA was significantly higher with PET/MRI than with PET/CT (P = 0.01). PET/MRI provided a definitive diagnosis for 12 (80%) of the 15 patients who underwent both imaging procedures, while PET/CT showed obvious lesions in only seven of the 15 (46%) patients.
Conclusions: Our findings suggest that 18F-FDG PET/MRI is more effective and confidential than 18F-FDG PET/CT for the detection of PAs. Figure legend: Figure 1. 18F-FDG PET/MR and 18F-FDG PET/CT images for a 49-year-old woman with elevated ACTH levels 6 years after the removal of an ACTH-secreting pituitary adenoma.The contrast-enhanced T1-weighted MR images showed only postoperative changes (A, B, C). The fused PET/CT images (D, E, F) were undiagnosable without clear relationships among the post-surgery structures. The fused PET/MR images (G, H, I) showed the specific position of the 18F-FDG-avid lesion (arrow) within the mild-18F-FDG-uptake pituitary tissue (triangle).Follow-up surgery confirmed a recurrent functional pituitary adenoma (5 × 3 × 3 mm3) on the left side, with positive ACTH and growth hormone staining.