Prevention of obesity-linked renal disease: age-dependent effects of dietary food restriction

BACKGROUND: Hyperphagic obese Zucker rats develop glomerular injury and die of renal disease, an outcome prevented by food restriction at an early age. We examined the effects of food restriction imposed at different ages on systemic, renal hemodynamic, and hormonal changes to gain insight into the mechanisms of obesity-linked glomerular injury. METHODS: At 6 weeks of age obese Zucker rats were either fed ad libitum or were restricted in food intake at various ages (6, 12, 26, or 50 weeks) to that consumed by lean Zucker rats (14 g/day). Every four weeks 24-hour urine collections, blood pressure, and venous blood samples were obtained until the end of study (60 weeks). RESULTS: Food restriction at 6 or 12 weeks of age prevented glomerular injury and hypertrophy and delayed the development of hypertension, hypercholesterolemia, and hyperinsulinemia. Food restriction at 26 weeks of age reduced proteinuria, while restriction at 50 weeks prevented further increases in proteinuria without altering pre-existing hypercholesterolemia, hypertension, or hyperinsulinemia. Hypertriglyceridemia and glomerular hyperfiltration in the obese animals were reversed at any age by food restriction. Plasma leptin levels were elevated in all obese groups. CONCLUSIONS: (1) Early food restriction provided the greatest metabolic and renal benefits; (2) glomerular injury correlated with hyperphagia-induced hyperfiltration and hypertriglyceridemia and both were prevented by food restriction; (3) hypercholesterolemia was due to an increase in LDL and/or VLDL cholesterol; and (4) leptin does not directly contribute to glomerular injury in the obese Zucker rat.     

Positron emission tomography imaging in nonmalignant thoracic disorders

The role of the fluorodeoxyglucose (FDG) technique positron emission tomography (PET) is well established in the management of patients with lung cancer. Increasingly, it is becoming evident that FDG-PET can be effectively employed to diagnose a variety of benign pulmonary disorders. Knowledge of such applications further expands the domain of this powerful modality and further improves the ability to differentiate benign from malignant diseases of the chest. We describe pertinent technical factors that substantially contribute to optimal imaging of the thoracic structures. Particularly, the complementary role of attenuation correction (AC) to that of non-AC images is emphasized. We further outline the need for and the state of the art for co-registration of PET and anatomic images for diagnostic and therapeutic purposes. We then review patterns of physiologic uptake of FDG in thoracic structures, including the lung, the heart, the aorta and large arteries, esophagus, thymus, trachea, thoracic muscles, bone marrow, and joints and alterations following radiation therapy to the thorax. A great deal of information is provided with regard to differentiating benign from malignant nodules and in particular, we emphasize the role of dual time point imaging and partial volume correction for accurate assessment of such lesions. Following a brief review of the diagnostic issues related to the assessment of mediastinal adenopathies, the role of FDG-PET imaging in environment-induced lung diseases, including pneumoconiosis, smoking, and asthma are described. A large body of information is provided about the role of this technology in the management of patients with suspected infection and inflammation of the lungs such as acquired immunodeficiency syndrome, fever of unknown origin, sarcoidosis, chronic granulomatous disease and monitoring the disease process and response to therapy. Finally, the value of FDG-PET in differentiating benign from malignant diseases of the pleura including asbestosis-related disorders is described at the conclusion of this comprehensive review.     

Incidental detection of colon cancer by FDG positron emission tomography in patients examined for pulmonary nodules

PURPOSE: Fluorodeoxyglucose (FDG) positron emission tomographic (PET) imaging has been used extensively to diagnose cancer with high rates of sensitivity and specificity. One of its applications is to distinguish benign from malignant pulmonary nodules. It is common to observe colonic uptake on whole-body FDG-PET images. Because patients with lung cancer also tend to be in the age group with the highest incidence of colon cancer, the authors tried to assess the efficacy of FDG-PET for detecting occult colon cancer in patients referred for the evaluation of lung nodules. METHODS: The records of 500 consecutive patients referred for the evaluation of pulmonary nodules were reviewed retrospectively. Among the patients, 197 had no previous clinical or radiographic evidence of abnormalities in the gastrointestinal tract, and none had been found to have any cancer before undergoing an FDG-PET study. All colon lesions were verified either by histologic analysis or by clinical course. RESULTS: Among the 197 patients analyzed, 59 had diffuse colonic uptake in various segments of the colon. Seventeen of the patients had focal colonic uptake, five of which were proved to be colon cancer. CONCLUSIONS: The routine use of FDG PET to characterize lung lesions significantly increases the probability of detecting unexpected extrathoracic disease. In these patients, the incidental finding of colon cancer had an important effect on their treatment and may prove to be very cost-effective.     

Detection of small bowel involvement by mantle cell lymphoma on F-18 FDG positron emission tomography

F-18 fluorodeoxyglucose positron emission tomography (FDG PET) is highly sensitive and specific for the detection of nodal and extranodal disease in patients with malignant lymphoma. However, no previous reports have shown lymphomatous involvement of the small bowel that was recognized on the basis of FDG-PET imaging findings. The authors present two cases of clinically unsuspected small bowel involvement by mantle cell lymphoma that were initially detected on FDG PET.     

Use of a corrected standardized uptake value based on the lesion size on CT permits accurate characterization of lung nodules on FDG-PET

The purpose of this study was to determine the actual standardized uptake value (SUV) by using the lesion size from computer tomography (CT) scan to correct for resolution and partial volume effects in positron emission tomography (PET) imaging. This retrospective study included 47 patients with lung lesions seen on CT scan whose diagnoses were confirmed by biopsy or by follow up CT scan when the PET result was considered negative for malignancy. Each lesion's FDG uptake was quantified by the SUV using two methods: by measuring the maximum voxel SUV (maxSUV) and by using the lesion's size on CT to calculate the actual SUV (corSUV). Among small lesions (2.0 cm or smaller on CT scan), ten were benign and 17 were malignant. The average maxSUV was 1.43+/-0.77 and 3.02+/-1.74 for benign and malignant lesions respectively. When using an SUV of 2.0 as the cutoff to differentiate benignity and malignancy, the sensitivity, specificity, and accuracy were 65%, 70%, and 67% respectively. When an SUV of 2.5 was used for cutoff, the sensitivity, specificity, and accuracy were 47%, 80%, and 59% respectively. The average corSUV was 1.65+/-1.09 and 5.28+/-2.71 for benign and malignant lesions respectively. Whether an SUV of either 2.0 or 2.5 was used for cutoff, the sensitivity, specificity, and accuracy remained 94%, 70%, and 85% respectively. The only malignant lesion that was falsely considered benign with both methods was a bronchioalveolar carcinoma which did not reveal any elevated uptake of fluorine-18 fluorodeoxyglucose (FDG). Of the large lesions (more than 2.0 cm and less than 6.0 cm), one was benign and 19 were malignant and the corSUV technique did not significantly change the accuracy. It is concluded that measuring the SUV by using the CT size to correct for resolution and partial volume effects offers potential value in differentiating malignant from benign lesions in this population. This approach appears to improve the accuracy of FDG-PET for optimal characterization of small lung nodules.