Objective: To describe a new radiological sign, the enhancing rim sign, that indicates that a solitary pulmonary nodule is benign rather than malignant. Patients and Methods: Sixteen adult patients underwent computed tomographic (CT) evaluation with intrave. nous contrast enhancement of an indeterminate solitary pulmonary nodule between May 25, 2000, and March 21, 2002, at the Mayo Clinic in Scottsdale, Ariz. In each patient, we identified a rim of enhancing soft tissue at the periphery of a solitary pulmonary nodule; this rim surrounds a homogeneous, lower-density central portion of the nodule. Surgical or biopsy specimens from 6 patients and clinical data from 10 patients were evaluated to determine whether the nodules with the enhancing rims were benign or malignant. Results: Pulmonary nodules in 6 patients were diagnosed as benign after histological evaluations of tissue obtained by surgical resection (3 patients), bronchoscopic biopsy (1 patient), and CT-guided needle biopsy (3 patients) (1 patient had a needle biopsy and wedge resection). In another 10 patients, pulmonary nodules were diagnosed as benign during clinical follow-up (range, 2-24 months; median, 11 months): in 1 patient, the nodule disappeared; in 1 patient, the nodule's size was stable; in 3 patients, the nodule's size decreased; and in 5 patients, no further radiological studies were performed, but no symptoms or signs of pulmonary disease were present during follow-up. Coccidioides immitis spherules were identified in 2 surgical specimens and in 1 CT-guided biopsy specimen. Serologic results for C immitis were positive for 3 patients: 1 at the time of lobectomy and 2 during clinical follow-up. Conclusion: Th enhancing rim sign, seen on chest CT with intravenous contrast enhancement of a solitary pulmonary nodule, has been useful to distinguish some benign pulmonary nodules from malignant pulmonary nodules.
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