The CT angiogram sign.

The CT angiogram sign has been described as a finding in the lobar form of bronchoalveolar cell carcinoma (1). Bronchoalveolar cell carcinoma represents a subgroup of adenocarcinoma and accounts for approximately 5% of all bronchogenic carcinomas in most series, although a recent increase in its prevalence to as high as 20.3% has been reported (2). Histopathologically, bronchoalveolar cell carcinoma can be separated into two basic morphologic types—mucinous and Clara cell or type II pneumocyte—and two spread pattern types—tumors with aerogenous spread and those without aerogenous spread. The mucinous tumors account for approximately 20%–30% of all bronchoalveolar cell carcinomas (3,4) and are characterized by tall, mucus-filled columnar cells. The mucinous tumors tend to spread aerogenously, infiltrating along the preexisting normal framework of the lung (ie, lepidic growth). Abundant secretion of mucin positive for periodic acid–Schiff reagent that fills the alveoli and small airways is more characteristic of the mucinous tumors; however, minimal amounts of this mucin can be seen in the nonmucinous tumors. Four clinical manifestations have been reported: (a) a single nodule, (b) multiple nodules, (c) a single consolidation, and (d) multiple lobar consolidations. Single and multiple lobar consolidations are more common in the mucinous tumors. Bronchoalveolar cell carcinoma in a patient with alveolar consolidation remains difficult to diagnose clinically and radiologically. Bronchorrhea, with up to liters of mucus discharged per day in some cases, was once considered a standard clinical finding; however, it is seen in a minority of patients. Bronchorrhea was found in 5% of the patients with bronchoalveolar cell carcinoma examined by Miller et al in 1978 (5). Some patients present for radiologic evaluation of a nonresolving alveolar consolidation that was initially diagnosed as pneumonia. Without underlying causes of hemorrhage, edema, or infection, persistent alveolar consolidation is suggestive of bronchoalveolar cell carcinoma. An incidental asymptomatic mass is another common manifestation. The CT angiogram sign was initially described as a specific sign of lobar bronchoalveolar cell carcinoma; specificity can be as high as 92.3% (1). Recently, the results of several retrospective studies have challenged the specificity of the CT angiogram sign; the CT angiogram sign was reported to be seen in both benign and malignant entities, including bronchoalveolar cell carcinoma, pneumonia, pulmonary edema, obstructive pneumonitis due to central lung tumors, lymphoma, and metastasis from gastrointestinal carcinomas (6–14). In cases of obstructive pneumonitis and primary pulmonary lymphoma, investigators have suggested that it is the relative difference between the attenuation of the pulmonary vessels