Cystic Adenomatoid Malformation

Updated: Dec 08, 2015
  • Author: Anne E Stone, MD; Chief Editor: Michael R Bye, MD  more...
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Overview

Background

Congenital cystic adenomatoid malformation (CCAM) is a rare abnormality of lung development. CCAM is a type of congenital thoracic malformation and refers to a group of malformations of the airways. There are different types of lesions (types 0-4), some associated with cystic areas and adenomatous overgrowth of the terminal bronchioles. [1, 2]

The routine use of prenatal ultrasonography has led to frequent prenatal diagnosis and has provided great insight into the natural history of CCAM. Improvements in surgical techniques (ie, both prenatal and postnatal) as well as greatly enhanced imaging modalities have altered the surgical approach to this lesion.

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Pathophysiology

The pathophysiologic effects of CCAM may be divided into prenatal and postnatal effects. Large lesions may be associated with the development of hydrops fetalis in as many as 40% cases and is a poor prognostic sign. Hydrops is thought to arise from compression of the inferior vena cava, which compromises venous return and leads to a decrease in cardiac output and the development of effusions. Fetal demise may result; premature delivery is attempted in order to salvage the fetus. [3] The other main prenatal event is compromised pulmonary growth. Resultant pulmonary hypoplasia may lead to the postnatal development of respiratory distress.

Polyhydramnios has also been associated with CCAM. This develops as a result of elevated intrathoracic pressure that leads to esophageal compression and the inability to swallow. [4]

CCAM may remain undiagnosed until it is discovered as an incidental finding later in life; however, its usual postnatal presentation is respiratory distress in the newborn period. This may be due to pulmonary hypoplasia, mediastinal shift, spontaneous pneumothorax, and pleural effusions secondary to hydrops. Recurrent chest infections may be a feature later in life. [5] A risk of malignant transformation in later years is noted. [6]

Prenatal regression and complete prenatal resolution have also been described. [6, 7, 8]

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Epidemiology

Frequency

United States

No data are available regarding the frequency of this lesion; however, it is a rare condition.

International

A review of 48 cases from 5 centers in Canada led to an estimated incidence of 1:25,000 to 1:35,000 of patients who were prenatally diagnosed. [7] The use of prenatal ultrasonography has led to an increase in prenatal diagnosis.

Mortality/Morbidity

Most series report a mortality rate of 25-30% of all children who present in the newborn period with CCAM; however, these figures do not include asymptomatic children who present later in life. Furthermore, the use of elective abortion may lead to an underestimation of perinatal mortality by preferentially terminating fetuses with a higher risk of mortality. The reported mortality rate of prenatally diagnosed CCAMs ranges from 9-49%. Reviews of children who are asymptomatic in the neonatal period with antenatally diagnosed lesions suggest that 3-10% will develop symptoms in the first year of life. [9, 10] A more recent study suggested that 18 of 21 patients developed symptoms at a median age of 2 years. [11]

Risk factors for a poor outcome include hydrops fetalis. [3, 7] Other indicators of poor prognosis include the type of lesion; microcystic CCAM is associated with much poorer outcomes. [7, 12]

The overall size of the lesion has also been reported as being an important predictor of survival; [13, 14] however, this index may be compromised by the fact that CCAM may decrease in size or even resolve over time in utero. [7] The major morbidity is related to pulmonary compromise. A large lesion may be associated with pulmonary hypoplasia. [10] This can cause respiratory distress at birth.

Some authorities have suggested that the presence of bilateral lesions is associated with a worse outcome. More controversially, left-sided lesions may be associated with a greater mortality rate than right-sided lesions.

One study suggested that polyhydramnios is also associated with a poorer outcome.

The potential for malignant transformation is recognized in all cases of CCAM. [6, 15, 16] Whether or not complete resection of the affected area completely removes this risk is not known.

Other complications that have been described include the development of spontaneous pneumothorax, hemopneumothorax, and associated hemoptysis. [7]

Age

CCAM is a congenital condition. Cases are typically identified prenatally by routine ultrasonography screening. [7] Most postnatally identified cases present in the newborn period. CCAM may present in the older child and adult as an incidental finding or secondary to repeated infection. [17, 5, 18]

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