A theory of the origin of intralobar sequestration of lung.

In addition to the lung tissue formed from the ventral pharyngeal diverticulum which represents the normal lung bud, pulmonary tissue may be formed from any part of the primitive foregut, and at birth is usually found lying in the left lower region of the pleural cavity; to this condition the name of lower accessory lung or extralobar sequestration is given. Such tissue should be distinguished from the additional bud which may arise from the normally developed bronchial tree, and is commonly found as an accessory lobe attached to the right side of the trachea or right main bronchus. These accessory formations may or may not survive during development; they may or may not reveal their origin after birth by connexions with the portion of foregut, trachea, or bronchus from which they are derived; and they may receive their blood supply from the normal pulmonary trunk, from an aberrant systemic supply, or from both sources. Some are consistently associated with other congenital intrathoracic defects, others never. It is not intended to engage in the controversy that has continued for many years on the origin of the many and various congenital abnormalities that have been reported. Too many problems would require simultaneous discussion and obscure the simple purpose of this paper, which is, by using the condition defined as intralobar sequestration of lung with an aberrant arterial supply as the thesis, to inquire into the origin of the aberrant supply, the effect of this systemic supply on the structure of the lung, and to suggest an alternative explanation for the combined abnormality based on that originally described by Pryce (1946). Further information from such a discussion would seem sufficient reason for continuing to take a conjectural approach to an important clinical condition, and, although the origin of the condition is of itself unimportant to the patient, some addition may be made to the limited information on the origin and effect of systemic arterial vessels to the lung. Bruwer, Clagett, and McDonald (1950) pointed out that anomalous arteries to the lower lobes of lungs make the lobe which they supply an interesting laboratory for the study of the effects of raised pressure. Although these authors accepted the sequestration theory of Pryce (1946) they anticipated the present hypothesis in stating: