Congenital malformations - Edocr

Chapter 23
Congenital Cystic
Adenomatoid Malformations
SANDRA B. CADICHON
INTRODUCTION
Congenital cystic adenomatoid malformations
(CCAM) are rare developmental abnormalities
of the lung. Early reports date from 1897, but
the term itself was not introduced until 1949. 1
The histological descriptions of CCAMs are
based on studies from Stocker et al. 2 Initially,
three varieties were recognized, types I, II, and III
and subsequently types 0 and IV have been added.
These five pathological types are based on the
site of origin of the malformation. 3 Type 0––previously
known as acinar dysplasia, but now described
as tracheal CCAM––affects the proximal
tracheo-bronchial tree and is composed of
bronchial-like structures with respiratory epithelium
surrounded by a wall containing smooth
muscle, glands, and numerous cartilage plates;
this lesion is incompatible with life. Type I or
bronchial CCAM is the most common type of
CCAM and consists of multiple large cysts or a
single dominant cyst. Type II or bronchiolar
CCAM consists of multiple small cysts that resemble
dilated terminal bronchioles. Type III or
bronchiolar/alveolar duct CCAM is a solid lesion
and microscopically shows irregular curving
channels and small airspaces. Type IV or alveolar/
distal acinar CCAM consists of peripheral cysts
with distal acinar (distal airway structures such
as the alveolar ducts and sacs) origin. 1,4–6
A revised classification of congenital cystic
adenomatous malformations was proposed in
1985, when Adzick et al proposed two categories
for CCAM based on anatomy, ultrasound
findings, and prognosis. Macrocystic CCAM,
which consists of single or multiple cysts of at
least 5 mm in diameter but often much larger;
and microcystic CCAM lesions which are more
solid and bulky with cysts less than 5 mm in diameter.
7 CCAMs consist of hamartomatous tissue
characterized by overgrowth of the terminal
bronchioles and may be cystic or solid masses.
Cystic CCAMs are more common and occupy
part or all of a hemithorax, with up to 15% of
cases having bilateral involvement. 8 While the
majority of CCAMs present in infancy, there are
a number of patients presenting later in life, or
even in adulthood. 1
EPIDEMIOLOGY
The precise incidence of CCAM is unknown.
Literature reviews report a range from 1:25,000
to 1:35,000 pregnancies 9 to as frequently as
1.2:10,000 births. 8 Approximately 2% of cases
147
Copyright © 2008 by The McGraw-Hill Companies, Inc. Click here for terms of use.