Chapter 62. Malformations of The Lower Respiratory Tract - Review of Medical Embryology Book

AGENESIS: resulting in a total absence of the bronchial tree, alveolar tissue, and vascular system. It is unusual to find bilateral agenesis with the trachea ending in a blind end. In unilateral agenesis, there is no lung bud on the affected side
APLASIA is generally unilateral. There is a stump of the lung bud present
HYPOPLASIA is characterized by insufficient development. It may be partial, involving only a restricted segment, or total, involving an entire lung

BRONCHIAL VARIATIONS: where the abnormality involves only the division of the bronchopulmonary tree. These anomalies are frequent
ABNORMALITIES OF BRONCHIAL DIVISION resulting in supernumerary bronchi and lungs
ABNORMALITIES OF SYMMETRY leading to situs inversus and mirror-image lungs

THESE ABNORMALITIES of bronchopulmonary tissue most often may show clear predominance of bronchial structures with cysts and yet retain a normal appearance even though the alveoli are not expanded
THE SEQUESTRATIONS are most often intralobar (sometimes extralobar)

Their bronchi are not part of the tracheobronchial tree
Their vascularization is systemic, coming directly off the aorta or one of its collateral branches. There is no blood supply by way of the pulmonary artery

SUCH CYSTIC STRUCTURES, regardless of origin, result in those parts of a lung being poorly ventilated or not ventilated at all. As a result they cannot oxygenate blood

Tracheoesophageal fistulas are caused by incomplete separation of the esophagus and trachea at the time of cleavage of the tracheoesophageal groove, during week 4 of development. Fistulas almost always accompany esophageal atresia
There are 5 anatomic types, according to Ladd

Types 1, simple atresia without fistula, and 2, atresia with fistula, are extremely rare
Types 3 and 4 are by far the most frequent and occur in 95% of all cases. They are tracheoesophageal and bronchoesophageal fistula on the lower portion of the esophagus, below the atresia
Type 5 is rare and consists of a double fistula, surrounding the atresia

Tracheal stenosis or atresia: narrowing (stenosis) and closure (atresia) of trachea are rare malformations and associated with one of the varieties of tracheoesophageal fistulas. Probably due to unequal partitioning of foregut into trachea and esophagus
Laryngeal web: rare malformation due to incomplete recanalization of larynx in week10. A membranous web forms at vocal cord level and partly obstructs passage
Tracheal diverticulum: rare deformity consisting of a blind bronchuslike projection from trachea. May end in normal-appearing lung tissue to form a tracheal lobe
V Azygos lobe: abnormal fissures and lobes are common and usually insignificant. This one is due to azygos vein not moving medially and forming a fissure in the developing lung in the area of the main upper right lobe
Congenital bronchial cysts: the terminal bronchioles rarely may form abnormal saccular enlargements which may give rise to cysts