(Radiology. 1999;210:323-324.)
© RSNA, 1999
The CT Angiogram Sign
Roberto L. Maldonado, MD1
1 Department of Radiology, St Elizabeth Health Center, 1044 Belmont Ave, Youngstown, OH 44501.
Index terms: Bronchi, CT, 671.12112, 671.12116 • Bronchi, neoplasms, 671.3216 • Computed tomography (CT), angiography, 671.12116 • Lung, infection, 60.20
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APPEARANCE
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The computed tomographic (CT) angiogram sign is a finding that may be seen on CT scans of the chest after intravenous contrast material administration. It consists of enhancing branching pulmonary vessels in a homogeneous low-attenuating consolidation of lung parenchyma relative to the chest wall musculature (1) (Figure).
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Figure 1a. (a) Chest radiograph obtained in a patient with bronchoalveolar cell carcinoma shows an area of consolidation in the right lower lobe. (b) Corresponding CT scan of the chest with intravenous administration of contrast material demonstrates the CT angiogram sign—that is, a low- attenuating consolidation of the lung parenchyma with enhancing pulmonary vessels (arrow) in relation to the chest wall musculature.
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Figure 1b. (a) Chest radiograph obtained in a patient with bronchoalveolar cell carcinoma shows an area of consolidation in the right lower lobe. (b) Corresponding CT scan of the chest with intravenous administration of contrast material demonstrates the CT angiogram sign—that is, a low- attenuating consolidation of the lung parenchyma with enhancing pulmonary vessels (arrow) in relation to the chest wall musculature.
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EXPLANATION
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The low-attenuating component of the CT angiogram sign represents consolidation of the lung parenchyma, which can be caused by production of mucin within the air spaces. The CT angiogram sign is seen on contrast material–enhanced scans and results from the normally enhancing pulmonary vessels within the low-attenuating consolidated lung parenchyma relative to the chest wall musculature.
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DISCUSSION
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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 and that of the consolidated lung parenchyma rather than an absolute low attenuation value of the consolidated lung that is responsible for the CT angiogram sign. Vincent et al (6) reported a case of the CT angiogram sign on the images obtained in a patient with primary pulmonary lymphoma; the absolute attenuation of the consolidated lung was similar to that of the muscle. Murayama et al (7) also found the attenuation values of the lung parenchyma to be similar to those of muscle in several cases of obstructive pneumonitis and pneumonia in which the CT angiogram sign was seen. They stress the importance of technical factors such as bolus injection of intravenously administered contrast material and postulate that the absence of the CT angiogram sign in many cases of pneumonia may be due to inadequate contrast material enhancement of the pulmonary vessels (7).
The reported low specificity of the CT angiogram sign for the detection of bronchoalveolar cell carcinoma in subsequent series may be attributable in part to a lack of adherence to the precise criteria used to define this sign. The criteria used by Im et al (1) to define the CT angiogram sign were pulmonary vessels extending 3 cm or more along a single channel and diffuse homogeneous low attenuation of the consolidated lung parenchyma compared with the attenuation of the chest wall musculature. A mean attenuation value of 27.6 HU was found in cases of bronchoalveolar cell carcinoma in contrast to the mean attenuation value of 73.5 HU on the images obtained in patients who did not have bronchoalveolar cell carcinoma; the mean attenuation value of muscle on the images obtained in these patients was 74 HU (1).
Although the CT angiogram sign is not specific for bronchoalveolar cell carcinoma, it still may be considered a useful sign in imaging. The sign is seen with a limited number of entities, all of which involve the enhancement of unaffected pulmonary vessels coursing through low-attenuating consolidated lung parenchyma. Correlation of the imaging findings with the clinical findings may help to further narrow the differential diagnosis to a specific entity.
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Footnotes
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Address reprint requests to the author, 1200 E. Pecan, Altus, OK 73522.
A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor and provide the name of the sign to avoid duplicate preparation of the same sign.
Received March 25, 1998;
revision requested April 29, 1998; revision received July 30, 1998;
accepted August 4, 1998.
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References
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Im JG, Han MC, Yu EJ, et al. Lobar bronchioloalveolar cell carcinoma: angiogram sign on CT scans. Radiology 1990; 176:749-753.[Abstract/Free Full Text]
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Colby TV, Koss MN, Travis WD. Atlas of tumor pathology, no 3. Washington, DC: Armed Forces Institute of Pathology, 1995.
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Miller WT, Husted J, Freiman D, et al. Bronchioloalveolar cell carcinoma: two clinical entities with one pathologic diagnosis. AJR 1978; 130:905-912.[Abstract]
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Vincent JM, Ng YY, Norton AJ, Armstrong P. CT "angiogram sign" in primary pulmonary lymphoma. J Comput Assist Tomogr 1992; 16:829-831.[Medline]
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Murayama S, Onitsuka H, Murakami J, Torii Y, Masuda K, Nishihara K. CT angiogram sign in obstructive pneumonitis and pneumonia. J Comput Assist Tomogr 1993; 17:609-612.[Medline]
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Gondouin A, Manzoni P, Ranfaing E, et al. Exogenous lipid pneumonia: a reprospective multicentre of 44 cases in France. Eur Respir J 1996; 9:1463-1469.[Abstract]
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