Horseshoe lung: demonstration by electron-beam CT.

Abstract

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.

Horseshoe lung associated with scimitar syndrome

“…Both horseshoe lung and scimitar syndrome are rare congenital anomalies; however, the association of the horseshoe lung with scimitar syndrome is common, with the incidence as high as 80%–85% 5–8. In horseshoe lung, posterobasal segments of lungs fuse by a narrow isthmus behind pericardial reflection between heart and aorta 9 10.…”

“…Pleural line around the horseshoe lung can readily be seen on CT scan 2. In horseshoe lung, arterial and bronchial supply of the isthmic portion is invariably from the hypoplastic lungs 1 2 6 8–10 13. Historically, conventional angiography and bronchography were used to show this.…”

Clinics in diagnostic imaging (173)

“…(9) This fissure corresponds to a pleural line separating the displaced right lung and the adjoining left lung, and is a consistent finding of horseshoe lung on CT. (12) The fused posterobasal segments of the right and left lungs may show imaging features of air trapping, suggesting possible stenosis of anomalous bronchus of the isthmus. (13) The functional importance of excluding a stenosed anomalous bronchus lies in the fact that impaired bronchial clearance results in recurrent pneumonia in the horseshoe lung segment, necessitating pneumonectomy or lobectomy. In the absence of other malformations, the prognosis of scimitar syndrome with horseshoe lung primarily depends on the pulmonary arterial pressure.…”

Horse-shoe lung-rediscovered via volume rendered images

“…with free breathing in a 2-year-old child. [8] With the advent of MDCT scanners, excellent VR images can be generated to optimally depict the vascular distribution and eliminate the need for invasive imaging techniques such as angiography and bronchography. We evaluated the infant on 64-MDCT which could show the hypoplastic right lung; however, the scimitar vein was absent, instead there were multiple small veins draining into the IVC.…”