The pleural tail sign.

The pleural tail sign is widely thought to indicate malignancy. However, of 18 patients with the tail sign, 9 had benign disease. Bronchioloalveolar carcinoma was the most common malignant tumor, but adenocarcinoma, squamous-cell carcinoma, and metastatic adenocarcinoma of the colon were also found. The location of nodules and the radiographic characteristics of the pleural tails did not help differentiate benign from malignant lesions. However, nodules 2 cm or larger were malignant while those 1 cm or smaller were benign. Histologically, pleural tails reflected thickened, fibrotic connective tissue septae with indrawing of the visceral pleura. Their occurrence with neoplasm reflects desmoplastic reaction or scar carcinoma.