Findings: Chest radiograph shows large cystic structure within RML. Chest CT shows multiple cysts predominantly within the RML with associated air-fluid levels. In addition, there is compression of the RLL and mediastinal shift.

Diagnosis: Congenital adenomatoid malformation.

Discussion: Congenital adenomatoid malformation consists of disorganized pulmonary tissue with or without discrete cysts. The etiology is unknown, but is thought to represent a hamartoma.

Type I: Consists of one or more large cysts with multiple smaller cysts.
Type II: Consists of numerous small cysts (1mm-1cm).
Type III: Consists of a solid mass of tissue without gross cyst formation.

Congenital adenomatoid malformation generally presents as a cystic space-occupying lesion causing displacement of normal lung tissue and occasionally mediastinal shift. The cysts may contain air or fluid or both, and can be confused with congenital diaphragmatic hernia. Clinically, the majority of patients present with increasing respiratory distress as a neonate or, less commonly, with persistent respiratory infections in infants beyond the immediate neonatal period.

References:
Fraser R. Synopsis of Diseases of the Chest, 2nd edition. WB Saunders Inc.,
Philadelphia, PA, 1994:263-265.

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