Congenital malformations - Edocr

Chapter 21
Pulmonary Agenesis
SANDRA B. CADICHON
INTRODUCTION
Pulmonary agenesis was first described in 1874 in
a report by E. Klebs on a patient with a “missing
lung.” 1 This is a rare abnormality that results from
failure of development of the primitive lung
buds. 2,3 Three types are recognized: (1) bilateral
complete agenesis of the lungs, which is incompatible
with life; (2) unilateral lung agenesis, which
can occur in isolation, but is often associated with
additional congenital anomalies of the cardiovascular,
vertebral, facial, urogenital, or gastrointestinal
systems; and (3) lobar agenesis. 4 The range of
maldevelopment in a patient with unilateral lung
agenesis includes: (a) complete absence of bronchi,
(b) rudimentary bronchus present but no alveolar
tissue, or (c) poorly developed main bronchus
with poorly organized parenchyma. Unilateral
lung agenesis is more common than bilateral agenesis
and the prognosis for unilateral agenesis is
dependent on the complexity of the associated
anomalies. Agenesis of the right or left lung is reported
to occur with similar frequencies although,
patients with left lung agenesis are likely to have
a much better prognosis. 5
EPIDEMIOLOGY/ETIOLOGY
Agenesis of a lung occurs in approximately
1 per 100,000 births. 6 While the true etiology of
pulmonary agenesis is unknown, animal studies
suggest a possible association with maternal
gestational vitamin A deficiency. 5 Chromosomal
abnormalities such as duplications and trisomies
of chromosome 2 and reciprocal translocation
t (2; 21) have also been reported, and suggest a
possible genetic etiology in some cases of pulmonary
agenesis. 5 Familial pulmonary agenesis,
though rare, has been described. 5,7,8 Consanguinity
was documented in two of these families
which supports a possible autosomal recessive
inheritance pattern for unilateral pulmonary
agenesis in some cases. 7,9
EMBRYOLOGY/PATHOLOGY
Lung development is divided into five stages: (1)
Embryonic (0–7 weeks gestation); (2) Pseudoglandular
(7–17 weeks gestation); (3) Canalicular
(17–27 weeks gestation); (4) Saccular (28–36 weeks
gestation); and (5) Alveolar (36 weeks gestation-
2 years of age). During the embryonic stage, the
lung develops as an out-pouching of the ventral
wall of the primitive foregut endoderm; dichotomous
branching occurs to form the proximal
structures of the tracheo-bronchial tree and the
pulmonary arteries are derived from the sixth aortic
arches concurrent with the developing airways.
Disruptions during the embryonic stages of development
result in pulmonary agenesis.
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