Horseshoe lung: demonstration by electron-beam CT.

Horseshoe lung is a rare pulmonary anomaly characterized by fusion of the posterobasal portions of the right and left lungs behind the pericardial reflection, anterior to the aorta. The majority of reported cases occur in conjunction with scimitar syndrome, including hypoplasia of the right lung, anomalous right pulmonary venous return and systemic arterial supply to the lung. Horseshoe lung is usually diagnosed on pulmonary arteriography when the right inferior pulmonary artery crosses the midline and extends to the left lung base. Bronchography is also diagnostic when the branch of horseshoe portion arises from the right bronchus and passes within the lung parenchyma to midline of the lung tissue. The only described CT finding of horseshoe lung is the contiguity of the right and left lungs behind the heart. Most cases are infants under 12 months of age and CT images are severely hampered by respiration motion artefacts. Such artefacts are minimized by using electron-beam computed tomography, allowing a more detailed CT appearance of horseshoe lung in this case.