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First developing from a pair of longitudinal mesenchymal condensations in utero, the right and left sternal bars meet along the midline and fuse to form a single cartilaginous rod. Fusion commences at the manubrium and proceeds caudad [1]. Incomplete fusion of lower sternebrae results in well-known bony defects variously named sternal foramen, cleft or fissure [2].

Although clefts and foramina are commonly found in the corpus sterni, description of manubrial fissure or foramen had been sparse [3-5] before the study by Yekeler et al., who reported a manubrial cleft in the sterna of six of 1,000 adults [2]. In all of the six patients the cleft was confined to the superior portion of the bone, associated with a sclerotic band just inferior to it in five of them. To our knowledge, a complete manubrial cleft is extremely rare, with only two cases having been reported in the non-English literature [3, 4]. In one of the two cases, reported in 1979, Botsch et al. used conventional tomography to diagnose complete fissure of the manubrium [4], which showed slightly jagged and sclerotic medial margins of the right and left hemimanubria and an inverted-Y shape, almost identical to that in our patient, formed by the interhemimanubrial and hemimanubriosternal joints (Fig. 1b and c in the case presentation).

It is difficult to postulate the developmental origin of a manubrial fissure. However, we suppose that there might be two possible mechanisms: first, on rare occasions, the cephalo-most part of the sternal bar might have been left unfused in utero. Second, there might have been some muscular dynamics facilitating horizontal segmentation of the manubrium at a later stage, similar to diversified movements of the forelimbs facilitating longitudinal segmentation of the sternum [6].

Now that thin-section CT scanning of the bony thorax is becoming routine in clinical practice, we believe that more cases of this condition will be found in the future.