Horse-shoe lung-rediscovered via volume rendered images
A 1-month-old male child initially presented with complaints of irritability and continuous crying. The child subsequently developed fever and chest infection. A chest radiograph done for the same revealed dextrocardia, and further evaluation by 2D echocardiography was done to look for congenital heart disease. The 2D echo findings showed dextroposed heart with lack of normal four pulmonary veins draining into the left atrium. A suspicion of scimitar syndrome was raised and further evaluation by CT scan was advised to assess the arterial supply and venous drainage of the right lung. CT imaging was preferred over MR angiography as there was a need to exclude lung sequestration besides delineating the pulmonary venous drainage.\nCT pulmonary angiography was performed on a 64 detector GE Lightspeed VCT scanner using non-ionic contrast media and bolus-tracking method. Contrast was injected through an intraven intervenues (IV) line placed in the right hand as lower limb venous access was small and would limit the flow rate. The study was performed under short acting general anesthesia wherein 1.5 cc/kg of contrast was injected through a dual head pressure injector with a flow rate of 0.4 cc/s. Images were acquired on 64-detector CT scanner without ECG gating, using a slice thickness of 0.7 mm and collimation 0.6 mm, followed by overlapping reconstruction. The acquired CT images were post-processed with focus on establishing the arterial supply to both lungs, the size and location of the main pulmonary artery (MPA), the right and left pulmonary arteries (RPA and LPA), and the venous drainage of both lungs. Volume-rendered (VR) reconstructions were done for depicting the pathology in 3D to aid understanding of the anomaly.\nA scout topogram of the chest taken for planning of CT imaging showed the heart shadow in the right hemithorax []. Evaluation of CT images showed that the right lung was small in size with compensatory emphysema of the left lung []. There was associated dextroposition of the heart with atrio-ventircular and ventriculo-arterial concordance.\nAll components of the pulmonary venolobar syndrome, also known as hypogentic lung or scimitar syndrome, were identified. These findings included systemic supply to the right lung base by two large collaterals arising from the upper abdominal aorta, one of which was a branch of the coeliac trunk []. These collaterals were seen supplying the basal segments of the right lower lobe. No collateral supply from the thoracic aorta was identified. There was no systemic collateral supply to the left lung. The right lung showed venous drainage to the suprahepatic inferior vena cava (IVC) through multiple small channels (at least three) []. In addition to these findings, there was also seen an anomalous tissue of lung extending in the retrocardiac region across the midline []. On standard axial images, both on mediastinal and lung windows, this lung tissue looked no different from the hyperinflated left lung tissue. However, on VR imaging with tracing of the main and branch pulmonary arteries and evaluation of the bronchi, peculiar findings of horseshoe lung were apparent [Figures and ]. These included a branch of the right pulmonary artery (RPA) extending across the midline to the left side. An associated bronchial supply also extending to the left was seen on VR imaging. These findings were reassessed on axial images and diagnosis of horseshoe lung was made in association with pulmonary venolobar syndrome. This highlights the importance of VR imaging in the evaluation of congenital anomalies. In this case, it helped in depicting the findings of a rare association of horseshoe lung with pulmonary venolobar or scimitar syndrome.