The parasternal defect.

The parasternal defect, or Morgagni hernia, may not be as rare as previous authors have stated. Brown (1952) gives its incidence as 3 % of diaphragmatic defects, and Harrington (1951) in a review of 334 cases of diaphragmatic hernia found it in 14 only. In the mass radiography units at Portsmouth and Southampton 30 cases have been picked up and a further three cases have been found in patients who were admitted to the Surgical Unit -for other conditions. Since this defect causes symptoms in a small proportion of patients the majority do not come to medical scrutiny and investigation. The increasing use of mass radiography and our awareness of what this shadow probably is may lead to an increased recognition of Morgagni hernia. There is no doubt that many cases have been mis-labelled in the past, and they have often been designated as pleuro-pericardial cysts when indeed they were herniae of the foramen of Morgagni. Most of the herniae through the diaphragm can be explained satisfactorily on an embryological basis, and in the majority of cases a certain error in embryological development will lead to the adult defect which would be expected both in situation and shape; the size depends upon the severity of the developmental error. We do not feel, however, that the herniae which occur anteriorly through the foramen of Morgagni have been satisfactorily correlated with regard to the anatomical findings at operation and the original embryological incoordination which probably caused them.