62. Malformations of The Lower Respiratory Tract

  1. Bronchial anomalies as a result of failure of the lung bud to develop
    1. 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
    2. APLASIA is generally unilateral. There is a stump of the lung bud present
    3. HYPOPLASIA is characterized by insufficient development. It may be partial, involving only a restricted segment, or total, involving an entire lung
  2. Bronchial anomalies due to malposition
    1. BRONCHIAL VARIATIONS: where the abnormality involves only the division of the bronchopulmonary tree. These anomalies are frequent
    2. ABNORMALITIES OF BRONCHIAL DIVISION resulting in supernumerary bronchi and lungs
    3. ABNORMALITIES OF SYMMETRY leading to situs inversus and mirror-image lungs
  3. Anomalies due to bronchial detachment or sequestration
    1. 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
    2. THE SEQUESTRATIONS are most often intralobar (sometimes extralobar)
      1. Their bronchi are not part of the tracheobronchial tree
      2. 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
    3. 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
  4. Failure of cleavage of the tracheal groove
      1. 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
      2. There are 5 anatomic types, according to Ladd
        1. Types 1, simple atresia without fistula, and 2, atresia with fistula, are extremely rare
        2. 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
        3. Type 5 is rare and consists of a double fistula, surrounding the atresia
  5. 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
  6. Laryngeal web: rare malformation due to incomplete recanalization of larynx in week10. A membranous web forms at vocal cord level and partly obstructs passage
  7. Tracheal diverticulum: rare deformity consisting of a blind bronchuslike projection from trachea. May end in normal-appearing lung tissue to form a tracheal lobe
  8. 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
  9. Congenital bronchial cysts: the terminal bronchioles rarely may form abnormal saccular enlargements which may give rise to cysts
malformations of  the lower respiratory tract: image #1