Evaluation of Pulmonary Hypoplasia in Various Congenital Anomalies with a Comparison of Two Conventional Methods of Assessment: Radial Alveolar Count (RAC) and Lung Weight: Body Weight Ratio (LBW)
Deepu Mathew CHERIAN1, C. N. Sai SHALINI2, Chitra ANDREWS3, Uma MAHESWARI4, Prathiba D2
1Department of Pathology, Indian Institute of Medical Science and Research, Warudi, MAHARASHTRA, INDIA
2Department of Pathology, Sri Ramachandra Institute of Higher Education and Research, TAMIL NADU, INDIA
3Department of Obstetrics and Gynecology, Sri Ramachandra Institute of Higher Education and Research, TAMIL NADU, INDIA
4Department of Neonatology and SCOPE, Sri Ramachandra Institute of Higher Education and Research, TAMIL NADU, INDIA
Keywords: Congenital anomalies, Pulmonary hypoplasia, Lung weight, Body weight ratio, Radial alveolar count
Pulmonary hypoplasia is common in the perinatal period and causes death in newborn infants. It is commonly associated with a
number of malformation syndromes. Various parameters are used to estimate pulmonary hypoplasia at fetal autopsy including Lung Weight
Body Weight ratio (LW:BW), Radial Alveolar Count (RAC) and DNA estimation.
Material and Method: This study was carried out as a retrospective analysis of 108 lung specimens of fetuses with congenital anomalies for a
period of five years. All terminated fetuses with anomalies were received with 10% formalin. An inverted Y-shaped incision was made on the
fetus to remove the lungs. Lung weight and body weight were measured and the ratio was calculated. Morphometric estimation of RAC was done
microscopically by counting the number of alveoli using the Q capture software. RAC was calculated based on gestational age.
Results: Among the restrictive lung diseases, pulmonary hypoplasia by the LW:BW ratio was prevalent in 43% while the same by RAC was 19%.
Similarly, pulmonary hypoplasia by the LW:BW ratio was prevalent in 35% while the same by RAC was 26% among cases with non restrictive
lung diseases. Oligohydramnios showed the highest prevalence of pulmonary hypoplasia (23.7%), followed by renal anomalies (16.9%) and CNS
Conclusion: Pulmonary hypoplasia is a common occurrence in many congenital anomalies, premature rupture of membranes, and hydrops
fetalis. Identifying the anomaly during the intrauterine period will help to anticipate and accordingly manage the baby in the postpartum period.
Early diagnosis of correctable condition like oligohydramnios will also help in the early intervention and prevention of pulmonary hypoplasia.
Pulmonary hypoplasia can be defined as arrested or
incomplete development of the lungs. A number of growth
factors are necessary for appropriate lung development,
including appropriate space, normal respiratory motion,
and adequate fluid, which normally distends the developing
lung. Pulmonary hypoplasia can result when any one
or a combination of these factors is absent or impaired
(1). Pulmonary hypoplasia is common in the perinatal
period and is a significant cause of death in newborn
infants. Pulmonary hypoplasia in newborns is commonly
associated with a number of malformation syndromes that
commonly include diaphragmatic hernia and renal agenesis
or dysgenesis. Other associations include skeletal muscle disorders, exomphalos, skeletal dysplasia, hydrops fetalis,
trisomy 18, and prolonged rupture of the membranes.
For this study, the underlying abnormalities that may
result in pulmonary hypoplasia can be categorized as
either restrictive or non-restrictive types. Restrictive types
include space-occupying lesions in the thorax, such as
misplaced abdominal organs in congenital diaphragmatic
hernia (CDH), pleural effusion, skeletal deformity, or
cardiac anomaly restricting the intra-thoracic space.
Non-restrictive types include oligohydramnios, urinary
outflow obstruction, prolonged premature rupture of the
membranes, or chromosomal anomalies (Trisomy 21).
Congenital acinar dysplasia is an extremely rare primary
maldevelopment of the lungs that results in pulmonary hypoplasia wherein there are multiple cystic outpouchings
in each lobule lined by bronchial type epithelium, without
any alveoli (2). The pulmonary hypoplasia associated with
trisomy 21 is due to reduced numbers of alveoli and a
smaller alveolar surface area. Therefore, hypoplastic lungs
have a decreased number of airway generations, with fewer
and smaller peripheral airspaces than normal.
Lungs which are hypoplastic as a result of oligohydramnios
are also structurally and biochemically immature for
gestational age (3). In contrast, lungs that are hypoplastic
from all other causes usually have a structure that is
appropriate for gestational age. The maturation arrest,
which occurs with pulmonary hypoplasia due to
oligohydramnios, may be specifically related to failure to
retain fetal lung liquid. However, studies have shown no
difference in the structure and maturity of hypoplastic
lungs secondary to renal agenesis or dysplasia, compared
with those associated with other types of malformations
like chromosomal abnormalities and intrauterine growth
Various parameters are used to estimate pulmonary
hypoplasia at fetal autopsy including the Lung Weight:Body
Weight ratio (LW:BW), radial alveolar count, and DNA
estimation (1,3,4). Identification of pulmonary hypoplasia
is important for postnatal management. As pulmonary
hypoplasia can produce a spectrum of respiratory
complications, anticipating pulmonary hypoplasia will
help in deciding the mode of treatment.
This study was carried out to estimate lung weight with
reference to body weight (LW:BW ratio) and radial alveolar
count (RAC) in the lungs of fetuses having congenital
anomalies, and to compare the data in the restrictive and
|Study Setting and Subjects
This study was carried out as a retrospective analysis of
the lung specimens of fetuses with congenital anomalies
received in the Department of Pathology of our tertiary
care hospital for a period of five years between 2012 and
2016. A total of 742 fetal specimens of which 227 cases had
associated congenital anomalies were received for autopsy
during the study period. Among these autopsies, medical
records containing complete clinical information were
present in 108 anomaly cases and these cases were selected
for the study. Approval was obtained from the Institutional
Ethics Committee prior to commencing the study. All procedures performed in the current study were approved
by the IRB and/or national research ethics committee (IEC
NO: CSP-MED/15/OCT/ 25/59) in accordance with the
1964 Helsinki declaration and its later amendments.
Data Collection Tools
All terminated fetuses with anomalies were received in a
plastic container with 10% formalin (9 times the volume of
fetus). The umbilical cord was cut. An inverted Y-shaped
incision was made on the fetus to open the thoracic and
abdominal cavity. The heart and the lungs were taken out
en-bloc. The lungs were separated by cutting at the hilum
and were weighed separately.
The LW: BW Ratio
The fetus was tap dried and weighed using a CAS computing
scale baby weighing scale with a minimum count of 100.000
g to record the body weight. The lungs were weighed
separately using a Shimadzu BL-220H high precision
electronic balance with a minimum count of 0.001 g, and
the CAS SW-LR weighing scale with a minimum count of
1.000 g. The ratio of Lung weight to Body weight (LW:BW)
was calculated. A LW:BW ratio < 0.018 is considered as
A block of tissue was taken from each lobe at right angles
to the direction of the main bronchus and at a distance of
approximately one-third from the root of the lung to the
periphery. The lung tissues were processed in the Leica ASP
300 automatic tissue processor. After tissue processing, the
tissue was mounted in paraffin wax. Sections measuring 4-5
microns were made using a microtome and these sections
were stained with Hematoxylin and Eosin. Morphometric
estimation of radial alveolar count was done by the method
proposed by Emery and Mithal (7). Under the microscope,
a perpendicular line from the center of terminal bronchiole
was dropped on to the nearest and definite connective
tissue septum using the Q Capture software. The number
of alveoli cut by this line was then counted. Ten such counts
were done from each case and the average was taken as the
Radial Alveolar Count (RAC). For calculating RAC, the
cases were divided into 4 categories based on gestational
age (Table I) (1).
Data were entered and analyzed using a Microsoft Excel
spreadsheet. The prevalence of pulmonary hypoplasia was
calculated in percentages.
This study was carried out among 108 specimens received
for autopsy at the Department of Pathology. Out of the 108
specimens, 42 fetuses were of the restrictive type and 66
fetuses of the non-restrictive type. Of the restrictive type,
26 cases had a cardiac anomaly, nine cases had a skeletal
anomaly, and seven cases had pulmonary anomalies. Of
the non-restrictive type, seven cases had abdominal wall
defects, six cases had chromosomal anomalies, 16 cases
had central nervous system anomalies, 21 cases were of
anhydramnios/oligohydramnios, 10 cases were of renal
anomalies, 4 cases had hydrops fetalis, 1 case had the
amniotic band syndrome, and 1 cases had a storage disorder
(beta glucosidase deficiency) (Table II
The prevalence of pulmonary hypoplasia is given in
Table III. Among the restrictive lung diseases, pulmonary hypoplasia by the LW:BW ratio was prevalent in 43% while
the same by RAC was 19%. Similarly, pulmonary hypoplasia
by the LW: BW ratio was prevalent in 35% while the same
by RAC was 26% among cases with non-restrictive lung
The system-wide prevalence of pulmonary hypoplasia based
on the :BW ratio is given in Table IV. Oligohydramnios
showed the highest prevalence of pulmonary hypoplasia
(23.7%), followed by renal anomalies (16.9%) and CNS
Click Here to Zoom
|Table IV: System-wise prevalence of pulmonary hypoplasia based on the LW:BW ratio.
The system-wide prevalence of pulmonary hypoplasia
based on RAC is given in Table V. The highest prevalence
was observed with oligohydramnios and cardiac anomalies
(24%), followed by other anomalies like CNS and
chromosomal anomalies (12%).
Pulmonary hypoplasia, as defined by Boyden, is a
maldevelopment of lungs in which normal pulmonary
tissue is present but is underdeveloped. Pulmonary
hypoplasia is noted in more than 10% of neonatal autopsies
and occurs in association with another malformation (or
malformations) in more than 85% of the cases (8). The
most frequently occurring anomalies are diaphragmatic
defects and renal malformations, but a wide variety of
anomalies have been described. The common feature of
most of these anomalies is that they directly compromise
the thoracic space available for lung growth. In utero
accumulation of fluid within the thorax as pleural effusion
or chylothorax has also been implicated in the production
of pulmonary hypoplasia. Pulmonary hypoplasia may
also occur in the absence of other anomalies or in cases of
preterm premature rupture of amniotic membranes. As
with infants with hypoplasia secondary to other anomalies,
these infants present with respiratory distress, are difficult
to ventilate, and frequently have episodes of pneumothorax
and interstitial pulmonary emphysema.
The abdominal wall is an integral component that
determines the thoracic cavity dimensions. Defects in the
ventral abdominal wall alter respiratory mechanics and
can impair diaphragm function. Congenital abdominal
wall defects also are associated with abnormalities in lung
growth and development that lead to pulmonary hypoplasia,
pulmonary hypertension, and alterations in thoracic
cage formation (9). The findings of our study showed
the evidence of arrest in alveolar development in cases
of abdominal wall defect with normal lung parenchymal developmental maturation. This was in concordance with
the study conducted by J. Craig Argyle (10).
The mean LW:BW value was 0.036 ± 0.01 and the RAC
count was 2.54±0.5. This was in concordance with the
study by Askenazi and Perlman (6). Reale and Esterly (11)
showed a mean LW:BW ratio of 0.013 and RAC of 4.6.
All the cases of renal anomalies showed a LW:BW ratio
<0.018. This was in concordance with the study conducted
by Monique (12), Askenazi and Perlman (6), and Husain
and Hessel (1).
Pulmonary hypoplasia was evidenced in 66.7% of the cases
with anhydramnios and premature rupture of membranes,
similar to studies done by Wigglesworth (13). Out of the
four cases of hydrops fetalis, pulmonary hypoplasia was
present in 100%, similar to studies by Askenazi (13) and
Hussain (1). This establishes the strong association between
lung hypoplasia and hydrops fetalis. None of the 4 cases
were associated with pleural effusion which suggests that
the reduction in the thoracic cavity is not the primary cause
of lung hypoplasia.
Pleural effusion in the intrauterine period is a predictor of
pulmonary hypoplasia. If the fluid collection occurs before
the 24th to the 26th of gestation, it produces irreversible
damage whereas when it occurs in the alveolar stage, it
may not produce irreversible damage (14,15). Pleural
effusions occurring in the mid-trimester can be detected
by antenatal scans and definitive in utero therapy can
be considered when no other major fetal abnormality is
detected. Decompression of the thorax either by repeated
transfusions or placing a pleural amniotic shunt can be tried
in such cases in the fetus (16,17). Our study demonstrated 100% pulmonary hypoplasia among fetuses with pleural
effusion, similar to the study conducted by Castillo (18).
Development of the lung is intrinsically related to that of
the heart. An association between pulmonary hypoplasia
and congenital heart diseases has previously been suggested
based on postnatal studies. Autopsy studies have shown
that the affected infants have an abnormally small number
of alveoli (19,20). The impaired alveolarization in patients
with right outflow obstruction may be an important
cause of the low lung volumes measured in children and
adults operated for the tetralogy of Fallot (21-25). About
13% of congenital heart disease cases showed pulmonary
hypoplasia in a study conducted by Isabelle (26) but this
value was 30.8% in our study.
The LW:BW ratio detected a greater number of anomaly
cases compared to RAC. Identification of pulmonary
hypoplasia by both the methods was almost similar in
case of cardiac anomalies. LW:BW showed 8 cases with
pulmonary hypoplasia while RAC showed 6 cases with
pulmonary hypoplasia. The LW:BW ratio detected 5 cases
of pulmonary hypoplasia in lung anomalies and skeletal
anomalies, while RAC detected only 1 case of pulmonary
hypoplasia in lung anomalies and skeletal anomalies.
It is well established that renal anomalies produce
pulmonary hypoplasia. The LW:BW ratio could detect
10 cases of pulmonary hypoplasia in renal anomalies. On
the other hand, RAC detected only one case of pulmonary
hypoplasia among renal anomaly cases. Detection of
pulmonary hypoplasia cases was more common by
LW:BW in preterm premature rupture of the membranes
(PPROM)/Oligohydramnios and CNS anomalies, with 14
and 9 cases respectively detected, while RAC detected 6 and
3 cases, respectively.
In conclusion, our study demonstrated that PPROM/
Anhydramnios was the most common cause of pulmonary
hypoplasia. Renal anomalies and Hydrops fetalis are
strongly associated with pulmonary hypoplasia. Abdominal
wall defect and cardiac anomalies are less frequent causes
of pulmonary hypoplasia. We conclude that pulmonary
hypoplasia is a common occurrence in many congenital
anomalies, premature rupture of membranes, and hydrops
fetalis. Identifying the anomaly during the intrauterine
period will help to anticipate and accordingly manage
the baby in the postpartum period. Early diagnosis of
correctable defects like oligohydramnios will also helps
in the early intervention and prevention of pulmonary
hypoplasia. This study also highlights the significance of
performing fetal autopsy, especially in case of congenital
CONFLICT of INTEREST
The authors declare that they have no potential conflicts of
interest to disclose.
Concept: PD, CNSS, Design: PD, CNSS, Data collection
or processing: CNSS, DMC, CA, UM, Analysis or
Interpretation: CNSS, DMC, Literature search: CNSS,
DMC, Writing: CNSS, DMC, Approval: PD, CNSS, DMC,
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