Horseshoe lung: differential diagnosis.

A detailed radiologic and anatomic study of one horseshoe lung syndrome has already been published from this centre. A further case of horseshoe lung, which was also diagnosed prospectively by radiology, is described. Alongside, this is a set of a group of three conditions: we describe a right accessory lung with a peculiar feeding arterial branch originating from the left basal pulmonary artery. The bronchogram and oesophagogram of this case were normal. The other is a case of bridging bronchus where the left lower lobe bronchus originates from the right main stem bronchus. This was discovered at post mortem bronchogram performed on a 19 weeks foetus. Finally, in the dog, we found that the pulmonary angiogram and bronchogram display close similarity to human horseshoe lung though the dog has two separate lungs. The common denominator of all above cases is the presence of a pulmonary arterial branch or bronchus crossing the midline from the ipsi to the contralateral side. Therefore, it may be concluded "in contradiction to the common belief" that pulmonary angiography or bronchography alone is not sufficient for the diagnosis of horseshoe lung. When only one of these investigations is available, computerized tomography is necessary to show the isthmic lung tissue before the diagnosis of horseshoe lung is confirmed.