Nonembolic high-probability perfusion lung scan for pulmonary thromboembolism.

Pulmonary thromboembolism (PTE) is a disease whose diagnosis in the emergency department constitutes a challenge to the clinician. Perfusion lung scans have been important in helping in this context, mainly because of the fact that a normal perfusion lung scan rules out the presence of a clinically significant PTE. Nevertheless, false-positive results are sometimes observed, causing a diagnostic dilemma. An example is a case of bronchogenic carcinoma involving a pulmonary artery or its branches. In such patients, some characteristics of the scintigraphic imaging could guide the diagnosis toward a nonembolic origin of the perfusion defect. A case of small-cell carcinoma of the lung involving the left pulmonary artery whose clinical presentation suggested considering the possibility of PTE is reported. The so-called "stripe sign" is reviewed, and certain clues for the differential diagnosis of a massive and one-sided perfusion defect are discussed.