Cystic Adenomatoid Malformation

The first case of cystic adenomatoid malformation described was published by Ch’in and Tang in 1947. In 1975, Garret conducted the first antenatal diagnostic report of a cystic adenomatoid malformation using echography. Today, almost 90% of these malformations are diagnosed before birth, and correspond to small lesions that are almost always asymptomatic, at least during the neonatal period.

These malformations are cystic lesions that are circumscribed to a segment or lung lobe in more than 95% of the cases, and any lobe may be compromised. Bilateral lesions are rare (<3%) and have a poor prognosis. Histology reveals a proliferation of terminal bronchioles, which form communicated cysts covered in respiratory epithelium with different degrees of differentiation, as well as a reduction in the number of alveoli. There is no cartilage and there is an increase of the elastic fibers. The exact cause of cystic adenomatoid malformation is unknown, and there are arguments to sustain that its different types can originate in different stages of the lung development process. Bronchiolar types (type 1, 2, and 3) may develop during the pseudo-glandular phase, while those of the acinar-alveolar type (type 4) may be the consequence of a late injury in the saccular stage. It has been proven that in cystic adenomatoid malformations there is an increase in the proliferation and a reduction of apoptosis. All these details give strength to the hypothesis of a localized interruption during lung maturation.

At first, Stocker classified them in three types based on postnatal histology. Afterward, he added types 0 and 4, which correspond to infrequent forms of cystic adenomatoid malformation. Type 0, or acinar dysplasia, refers to a tracheobronchial defect characterized by hard and small lungs connected to a tracheobronchial path, whereas type 4 corresponds to an alveolar defect located in the periphery of the lung. Only types 1 and 3 are adenomatoid, and types 1, 2, and 4 are cystic. Stocker himself has proposed to change the name of cystic adenomatoid malformation to congenital lung airway malformation, which has become popular, although it has not been universally adopted (Table 54.1, Fig. 54.2).

Table 54.1

Classification of congenital lung malformations in the lung airway

	Incidence	Size of cysts	Histology	Notes
0	Infrequent		Complete failure of development after pseudo-glandular phase	Congenital acinar dysplasia (lethal)
1	Frequent 50%	>2 cm, may be multiple	Dilated alveolar structure, with scarce to minimum adenomatoid component. Ciliated pseudostratified columnar epithelium, with interposition of mucosal cells
2	Frequent 40%–45%	Multiple cysts, small, “sponge”	Dilation of structures with bronchial appearance, with interposition of the alveolar parenchyma. Occasional presence of striated muscle.	Associated with genitourinary and gastrointestinal malformations
3	Infrequent 5%	Solid (cysts <3 mm)	Bronchiolar structures separated by small air spaces covered by the cuboidal epithelium, similar to late fetal lung
4	Very infrequent	Large cysts	Peripheral cysts with alveolar or bronchial epithelium on elastic mesenchymal tissue	Related to type pleuropulmonary blastoma

The clinical presentation forms of cystic adenomatoid malformation are variable. During the antenatal period, large cystic lung lesions may cause mediastinal deviation, poor venous return, hydrops, and fetal mortality during the third trimester. During the first months of life, respiratory distress, caused by compression or pneumothorax because of the rupture of a cyst, can be an early indication of surgery in about 20% of the cases. Older children tend to be asymptomatic, and the infection of the anomalous tissue will cause recurrent pneumonias. The median for the development of the symptoms caused by infections is 10 months. The treatment is surgery, which consists of resecting the affected lobe or segment (Fig. 54.3).

Lung Sequestration

Lung sequestration is defined by the presence of lung tissue inside or outside the visceral pleural (intra- or extralobar sequestration), with no connection to the normal tracheobronchial path, and characterized by an anomalous blood delivery in the systemic veins. Venous drainage of intralobar sequestration runs toward the pulmonary veins, while the extralobar sequestration runs to the azygous vein. It has been estimated that lung sequestration is a consequence of an anomalous accessory lung bud, which was created in the primitive intestine that descends toward the caudal along with the esophagus. Extralobar sequestration may be related to other esophageal and bronchial malformations, as well as diaphragmatic defects. Most lung sequestration cases do not present symptoms during the neonatal period, and they present as an incidental image in a routine chest X-ray. They are usually located in the inferior lobes: 70% are in the left inferior lobe; 10% are under the diaphragm; and in 20% of the cases arterial irrigation comes from the infradiaphragmatic aorta. In infants, the most frequent presentation form of lung sequestration is the presence of recurrent pneumonia, which may cause localized bronchiectasis, and a particular complication is congestive heart failure, which is not present in cystic adenomatoid malformation, and is caused by the presence of aberrant circulation, and in some cases, by a significant shunt.

Lung sequestration may be diagnosed through echography and Doppler, but computerized axial tomography with contrast agent is the examination of choice, for planning and studying the surgical treatment of these lesions. This treatment consists of resection of the pathological tissue with anomalous vasculature control (Fig. 54.4). There is a superposition between cystic adenomatoid malformation and lung sequestration in several surgical series of lesions that do not exactly fulfill some of the previous categories and that are classified as mixed:

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  Anatomical extralobar sequestration, but with cystic adenomatoid malformation histology

  
  
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  Extralobar sequestration and cystic adenomatoid malformation in the same patient

  
  
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  Cystic adenomatoid malformation in one lobe, but with systemic irrigation

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