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CPAM type 4

Tuesday 16 November 2004

CPAM, type 4, the peripheral acinar cyst type, appears to be a hamartomatous malformation of the distal acinus. This variant is seen equally in boys and girls, with an age range of newborn to 4 years and accounts for 10% to 15%of cases.

Until recently, most of these cases were included in the type 1 category.

Clinically, the type 4 lesions may present with mild respiratory distress, sudden respiratory distress from tension PT, pneumonia, or on occasion, as an incidental finding with no symptoms.

Radiographically, the lesion displays large air-filled cysts with mediastinal shift and, occasionally, is associated with a PT.

The lesion involves a single lobe in about 80% of cases and rarely may be bilateral.

Grossly, large thin-walled cysts are present at the “periphery” of the lobe and appear to be lined by a smooth membrane.

Microscopically, the cysts are lined by flattened epithelial cells (type I and II alveolar lining cells) over most of wall, with occasional low cuboidal epithelium seen.

The wall of the cyst is composed of loose mesenchymal tissue with prominent arteries and arterioles.

Loose mesenchyme must not be confused with similar features seen in the cystic type of PPB.

Dense connective tissue may be present in some cases in older patients.

See also

- congenital pulmonary airway malformations

  • CPAM type 0
  • CPAM type 1
  • CPAM type 2
  • CPAM type 3
  • CPAM type 4
  • CPAM type 5


- Hill DA, Dehner LP. A cautionary note about congenital cystic adenomatoid malformation (CCAM) type 4. Am J Surg Pathol. 2004 Apr;28(4):554-5; PMID: 15087677