Yiyan Liu

Physiology and pathophysiology of incidental findings detected on FDG-PET scintigraphy.

A routine feature of positron emission tomography/computed tomography (PET/CT) imaging is whole-body acquisition that results in many unexpected findings identified outside of the primary region of abnormality. Furthermore, (18)F-fluorodeoxyglucose (FDG) is a marker of glycolysis and does not specifically accumulate in malignancy. Understanding the physiology and pathophysiology of normal FDG distribution and common incidental findings is therefore essential to the physician interpreting whole-body FDG-PET/CT studies. Whereas many incidental findings are benign and of limited clinical significance, others represent uncommon manifestations of the primary malignancy, second malignancies, or various clinically significant pathologic processes. Patients with a single malignancy are at greater risk of developing synchronous or metachronous second malignancies, possibly related to exposure to shared carcinogenic agents or presence of prooncogenic mutations. The decision of how to pursue an intervention on the basis of an incidental finding is generally left to clinical judgment.

Adenomyomatosis of the Gallbladder: Another Cause for a “Hot” Gallbladder on 18F-FDG PET

WEB This is a Web exclusive article. tudies of small numbers of patients have shown that 18F-FDG PET is useful in differentiating benign from malignant lesions within the gallbladder [1, 2]. However, a limitation of FDG PET is that inflammatory conditions with increased glucose metabolism cannot be distinguished from neoplasms because those conditions also show increased uptake of the agent. We present a patient with increased activity within the fundus of the gallbladder on an FDG PET scan obtained for staging of colon carcinoma. Pathologic examination of the gallbladder showed focal adenomyomatosis with no evidence of malignancy. Adenomyomatosis of the gallbladder and the resulting chronic inflammation can lead to false-positive FDG PET findings.

18F-FDG PET Evaluation of Sinonasal Papilloma

OBJECTIVE It has been suggested that (18)F-FDG uptake determined by PET can differentiate squamous cell carcinoma from benign sinonasal papilloma. We wish to present our experience with sinonasal papillomas and PET/CT to determine if the degree of FDG uptake is indicative of benign or malignant disease. CONCLUSION Benign sinonasal papilloma may be associated with intense FDG uptake on PET/CT. FDG PET/CT does not appear to reliably differentiate benign from malignant sinonasal papilloma.

'Shine through' on dual tracer parathyroid scintigraphy: a potential pitfall in interpretation.

Dual tracer scintigraphy has become the procedure of choice for preoperative localization of parathyroid adenomas. The typical protocol used by most laboratories is to initially perform a Tc-99m sestamibi (MIBI) study with early and delayed (2–3 hours) washout phase images. This is followed by a thyroid-specific Tc-99m pertechnetate study. A potential pitfall exists if the delayed phase of the initial MIBI study shows an intense, abnormal focus of retention. This focus may interfere with interpretation of the subsequent pertechnetate study because of a “shine through” effect. To differentiate a parathyroid adenoma from a thyroid adenoma, it may be necessary to repeat the thyroid-specific pertechnetate scan on a separate day after the dual tracer study.