Accurate grading of 3 synchronous liposarcomas assessed by PET-CT in a single patient.

Positron emission tomography (PET) with 2-fluoro-deoxyglucose (FDG) has become an established imaging modality that can accurately and noninvasively differentiate malignant neoplasms from benign masses. It is increasingly being used to grade malignant neoplasms as well and has almost replaced other studies like gallium 67-citrate scans for metabolic imaging. We describe an interesting case of 3 synchronous liposarcomas with different radio-opacifications on computed tomography (CT). The more aggressive lesion with more opacity on CT showed intense FDG activity and was found to be a high-grade liposarcoma on pathology. The well-differentiated lesion with more fat content appearing less radio-opaque on CT showed almost no FDG activity and an intermediate grade lesion with intermediate radio-opacity on CT showed mildly increased FDG activity. Dual modality imaging with integrated PET/CT systems have strengthened the confidence of classifying these lesions even before knowing the pathology as depicted in this case.

Superior vena cava and right atrial thrombus detected on lung perfusion scintigraphy.

Ventilation and perfusion scanning is still used as the first modality for evaluating pulmonary embolism in pregnant and renal failure patients and those who are allergic to radiographic contrast. Hot spots in the right atrial area on perfusion scan are the result of the presence of thrombi. These thrombi are of 2 varieties. One type is a free-floating thrombus, which needs emergency thrombectomy, and another type is thrombus formation in the atria, predisposed by the presence of catheters. We report a study showing essentially normal perfusion but intense tracer uptake in the superior vena cava and right atrium. Noncontrast computed tomography confirmed the thrombus.

FDG uptake in brown adipose tissue mimicking an adrenal metastasis: source of false-positive interpretation.

Brown adipose tissue (BAT) uptake of F-18 fluorodeoxyglucose (FDG) poses a significant challenge to positron emission tomography interpretation. BAT is not only localized to the supraclavicular areas, but is also seen in the neck, mediastinum, axillae, costovertebral junctions, and retrocrural and periadrenal regions. We illustrate a case of typical supraclavicular BAT uptake in association with a discrete right adrenal region focus. On repeat study after diazepam administration, both the supraclavicular and periadrenal uptake were abolished. BAT uptake is an important cause of false-positives; when typical supraclavicular BAT uptake is seen, abnormalities in other areas of BAT distribution should be viewed with caution.

F-18 FDG PET imaging in gastrointestinal stromal tumor.

Gastrointestinal stromal tumor (GIST) is the most frequent mesenchymal malignancy of the gastrointestinal tract. Liver and peritoneum are the most frequent metastatic sites. Surgery is the mainstay of treatment in patients with localized disease. Imatinib mesylate (Gleevec; Novartis Pharmaceuticals, East Hanover, NJ), an inhibitor of tyrosine kinase activity of KIT receptor, has been shown to be an effective treatment in metastatic or unresectable disease. Follow-up of patients treated with Gleevec is controversial. The authors present a case of GIST that showed near-total response with Gleevec on fluorodeoxyglucose positron emission tomography. They suggest positron emission tomography as a useful imaging modality for the monitoring of therapy response in GIST tumors treated with Gleevec.

Obstructed ectopic kidney mimicking Chilaiditi syndrome on F-18 FDG imaging.

Fluorine-18 fluorodeoxyglucose positron emission tomography was obtained in a patient with a duodenal mass. Conventional imaging revealed multiple dilated intestinal loops. Initial impression of positron emission tomographic images was interposition of a loop of bowel between the liver and diaphragm (Chilaiditi syndrome) in an unusual location, with absent right kidney activity. Computed tomography and magnetic resonance imaging of the abdomen showed an obstructed ectopic kidney in this position with a markedly dilated collecting system. There is absence of fluorodeoxyglucose in the markedly dilated renal collecting system resulting from acute obstruction, giving the false appearance of gas-filled bowel loops with an unusual location of the interposition.