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Figure 22 Mycobacterium tuberculosis infection manifesting as hypermetabolic nodule on [18F] fluorodeoxyglucose (FDG) positron emission tomographic scan. (A) Posteroanterior radiograph shows poorly marginated nodule in right upper lobe. (B) Coronal positron emission tomographic image with [18F] fluorodeoxyglucose shows marked FDG uptake within nodule (arrow) when compared to mediastinum. Findings are suggestive of malignancy. Transthoracic needle aspiration biopsy was negative for malignancy; culture was positive for M. tuberculosis. Radiograph following antituber-culous therapy showed complete resolution of tuberculoma. M, mediastinum; L, liver.

cies from benign nodules so that appropriate treatment can be initiated. The detection of specific patterns of calcification and stability in size for 2 years or more have historically been the only reliable findings useful for determining nodule benignity. More recently, the ability to distinguish benign and malignant SPNs has improved with assessment of nodule perfusion and metabolism using contrast-enhanced CT and FDG PET imaging, respectively. Together with transthoracic needle aspiration biopsy, these new imaging modalities have dramatically improved preoperative identification of benign nodules and reduced the number surgically resected. Many nodules still, however, remain indeterminate in etiology after extensive radiological evaluation. Thus, research efforts continue toward development of entirely new or at least improved imaging and analytical techniques for evaluation of these nodules.

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