Evaluation of Relative Frequency of Pulmonary Hypoplasia and Various Anomalies Associated with Pulmonary Hypoplasia in Fetal Autopsy Study
Aparna SAJJAN, Surekha U ARAKERI, Subhashchandra MUDANUR
Department of Pathology, B.L.D.E. (Deemed to be University), Shri B.M.Patil Medical College Hospital and Research Centre, KARNATAKA, INDIA
Keywords: Fetal autopsy, Lung weight to body weight (LW:BW) ratio, Pulmonary hypoplasia (PH), Radial alveolar count (RAC)
Pulmonary hypoplasia (PH) is one of the commonest causes of neonatal morbidity and mortality. The suggested diagnostic criteria
for PH are the Lung Weight:Body Weight (LW:BW) ratio ≤ 0.012 and/or Radial Alveolar Count (RAC) ≤ 4.1. The present study was done to
determine the relative frequency of PH in fetal autopsy study by the LW:BW ratio and RAC along with evaluation of the defects/anomalies
associated with PH.
Material and Method: A prospective observational study was done on fetal autopsy specimens in the Department of Pathology. Examination
and grossing were done as per the standard format of fetal autopsy study. Evaluation of PH was done using the LW:BW ratio and RAC. Diagnostic
criteria for PH were taken as LW:BW ratio <0.012 and/ or RAC < 4.1. Chi-square test, Student T test and Kruskal Wallis test were used in
Results: A diagnosis of PH was made in 45 cases. Concordance between the LW:BW ratio and RAC was observed in 33 cases amounting to 73.33%.
The mean LW:BW ratio was the lowest in oligohydramnios. The mean RAC was the lowest in congenital cystic adenomatoid malformation.
Conclusion: A diagnosis of PH was rendered in a greater number of cases when evaluation was done by considering both the LW:BW ratio and
RAC. Hence, evaluation by both the LW:BW ratio and RAC provides a reliable index of lung growth and should be an essential part of fetal
Pulmonary hypoplasia (PH) is one of the commonest causes
of neonatal morbidity and mortality 1
. The incidence of
PH is 9 to 11 per 10000 in the general population and its
reported prevalence in perinatal autopsies is 7.8% to 26%
PH is defined as unilateral or bilateral defective or
incomplete development of lung parenchyma, airway, and
vessels or incomplete development of the lung which is not
appropriate for gestational age 1-3. Pathologically, lung
hypoplasia is defined as a decrease in the Lung Weight to
Body Weight (LW:BW) ratio and reduced Radial Alveolar
Count (RAC) based on findings of autopsy examination
3. The LW:BW ratio is the consistent and better method
of diagnosing PH 2. The lower limit for LW:BW ratio for
fetuses older than or equal to 28 weeks is 0.012. The lower
limit of LW:BW ratio in fetuses <28 weeks of gestation
is 0.015 3. PH is also diagnosed by RAC. RAC can be
a reliable criterion for PH 4. RAC is measured by the
number of alveoli that are traversed by a perpendicular line drawn from the center of a respiratory bronchiole to the
nearest connective tissue septum 4.
PH may be primary or secondary. Primary PH is rare as
compared to secondary PH. The exact etiology is not
known in primary PH. However, deficiency of Vitamin
A and viral infection during pregnancy are considered
as possible etiological conditions. Genetic or iatrogenic
factors are also mentioned as possible causes for primary
PH 5. Secondary PH can occur due to abnormalities in
the thoracic cavity, heart, kidneys, abnormal fetal breathing
movements, and decrease in the volume of amniotic
fluid 1,2. In the majority of cases, PH is the result of
the reduction in thoracic volume, followed by reduced
production of amniotic fluid due to renal anomalies 1.
Fetal autopsy study may help to evaluate the relative
frequency of PH by evaluating the LW:BW ratio and RAC.
Evaluation of PH may provide an explanation for loss of
pregnancy. Hence this study was undertaken to evaluate
the frequency of PH by the LW:BW ratio and RAC and also
to determine the various conditions/anomalies associated
A prospective observational study was done on fetal
autopsy specimens sent to the histopathology section
of the Department of Pathology of our institute from 01
December 2019 to 31 July 2021.
Method of Collection of Data
Fetal autopsy specimens of intrauterine death (IUD), still
births, and neonatal deaths sent to histopathology section
of the Department of Pathology were processed according
to the standard protocol. Detailed obstetric history
and ultrasonography (USG) findings were collected.
Anthropometric data of fetus and external examination
were recorded. Internal examination was done by making
an I-shaped incision and en-mass dissection was done.
Internal examination of all organs was done. Details of
measurements, weight, gross and microscopic examination
findings of various organs were noted.
Gross examination of the lung was done as per the study
done by Husain and Hessel 6. Lungs were separated
from the heart, thymus, and mediastinum. Trachea was
cut above its bifurcation. Weight of both the lungs was
recorded in fresh state. Lungs were fixed in 10% buffered
formalin. After fixation, the lungs were serially sectioned
in the sagittal plane and the middle slice was submitted for
routine processing of the tissue. Gross examination of other
organs was done as per the standard protocol and tissue
bits were given from each organ and processing was done.
Sections of 3-6 μ thickness were taken and Hematoxylin
and Eosin-staining was done. RAC of both right and left
lung was recorded by evaluating the number of alveoli cut
by a line that was dropped at a right angle to the bronchial
epithelium from the center of terminal respiratory
bronchioles to the nearest connective tissue septum. RAC
was evaluated by counting the number of alveoli in 10
high power fields in two sections taken from lung. The
average was taken as RAC 4,7. Bronchioles partly lined
by epithelium were also selected 8. Diagnostic criteria for
PH was taken as LW:BW ratio less than 0.012 and/or RAC
less than 4.1.
All the fetal autopsy specimens of IUD, stillborn and
neonatal deaths that were sent to the Department of
Pathology were included. Macerated foetuses with
extensive autolytic changes in the lungs were excluded
from the study.
With anticipated prevalence of PH 7.8-26% in the study
done by Pena et al. 3 the sample size is 62.
The data collected was entered into Microsoft Excel and then
analyzed using the 20th version of the Statistical Package
for Social Sciences (SPSS) for Windows. Categorical
variables were presented as numbers and continuous data
was presented as Mean±standard deviation and charts.
The association between qualitative data was determined
by applying the Chi-square test. The continuous data was
compared by Student’s T-test and Kruskal-Wallis test
whenever required. A p value < 0.05 was taken as significant.
Total number of fetal autopsies included was 62. Detailed
history and Ultrasonography findings were collected for
all cases from the records available. Evaluation of PH was
done in all cases by the LW:BW ratio and RAC. Evaluation
of conditions and anomalies associated with PH was also
The majority of the fetal autopsy cases had a gestational age
of 16 to 20 weeks followed by 21 to 25 weeks amounting
to 27.42% vs 24.20% of the cases. The male to female ratio
was 1:1, having 30 cases each of male and female. Gender
ambiguity was noted in two cases.
IUD was the commonest associated condition followed by
oligohydramnios, neural tube defect and renal pathology.
other associated anomalies were congenital cystic adenomatoid
malformation (CCAM), congenital diaphragmatic
hernia (CDH), premature rupture of membranes (PROM),
ascites, hydrops fetalis, gastroschisis and arthrogryposis
multiplex congenita (AMC) (Figure 1-4).
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|Figure 1: Gross photograph of fetal autopsy specimen showing
neural tube defect- anencephaly with bilateral cleft lip and
protrusion of eyes.
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|Figure 2: Gross photograph of autopsy specimen showing CCAM
of lungs. Imprints of rib cage seen on lungs.
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|Figure 3: Gross photograph of CDH with intestinal loops in chest
Categorization of PH was done based on the LW:BW ratio
into four groups. In 18 cases amounting to 29.03%, the
LW:BW ratio was less than and/or equal to 0.009. These
cases were diagnosed as PH. In 19 cases (30.65%), the
LW:BW ratio was in the range of 0.010 to 0.012. These
cases were categorized as cases having a probability of PH.
In 18 cases (29.03%), the LW:BW ratio was in the range of
0.013 to 0.017, where the possibility of PH was considered.
In 7 cases (11.29%), the LW:BW ratio was more than and/
or equal to 0.018, and in these cases PH was unlikely as per
the LW:BW ratio.
The mean LW:BW ratio was highest at the GA range of 10
to 15 weeks and lowest at the GA range of 26 to 30 weeks.
The mean RAC was highest at the GA range of 31 to 35
weeks, followed by 36 to 40 weeks, and was lowest at GA
range of 10 to 15 weeks.
In 18 cases in which the LW:BW ratio was less than 0.009
and RAC was less than 4.1, the diagnosis was PH. In 19 cases the LW:BW ratio was between the range of 0.010 to
0.012. Out of these 19 cases, in 15 cases RAC was less than
4.1 and thus 15 cases were diagnosed as PH. However, in 4
cases RAC was higher than 4.1, and hence these cases were
not categorized as PH based on RAC. In 18 cases where the
LW:BW ratio was between the range of 0.013 to 0.017, in 11
cases RAC was below 4.1. Out of these 11 cases, 2 cases were
of IUD cases of GA of 14 weeks. According to the review of literature the lungs are in pseudoglandular stage at less than
15 weeks of GA where developing airways resemble glands
and there is no definitive lining of bronchioles 8. RAC in
this age group is not conclusive. Hence, out of 11 cases only
9 cases were considered as PH. In 7 cases, the LW:BW ratio
was more than 0.018 and the RAC was less than 4.1. Out of
the remaining 7 cases, the GA was less than 15 weeks with
lungs in the pseudo glandular stage in 4 cases. Therefore,
these 4 cases were not considered as PH. Out of the 7 cases,
PH was considered as per RAC in 3 cases. Thus, in 45
cases PH was considered based on the LW:BW ratio and
RAC. Out of the 45 cases of PH, concordance between the LW:BW ratio and RAC was noted in 33 cases amounting to
73.33% of the cases. In these cases, RAC was less than 4.1
and the LW:BW ratio was also less than 0.012. Discordance
between the LW:BW ratio and RAC was noted in 12 cases
amounting to 26.66%. In these cases, RAC was less than 4.1
and the LW:BW ratio was more than 0.012. Out of these 12
cases, 4 cases were of NTD, 2 cases were of CCAM, 1 case
was of gastroschisis, and 5 cases were of IUD (Table I).
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|Table I: Distribution of fetal autopsy cases showing concordance/discordance between LW:BW ratio and RAC.
The mean LW:BW ratio was lowest in oligohydramnios
as compared to other associated conditions/anomalies.
The mean LW:BW ratio and RAC was also lower in IUD
and renal pathology as compared to other anomalies and
the difference was statistically significant with a p value of
less than 0.0001 and 0.028 respectively. RAC was lowest in CCAM as compared to other associated conditions/
anomalies but only 2 cases of CCAM were noted in the
present study. In neural tube defect, RAC was slightly
higher than CCAM but lower than other associated
conditions/anomalies, and the difference was statistically
significant with p value of 0.0001 (Table II).
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|Table II: Association of mean gestational age, LW:BW ratio and RAC with associated conditions/anomalies.
Out of the 62 cases, meconium aspiration was noted in 23
cases amounting to 37.1%. The maximum number of cases
of meconium aspiration was noted in the cases having a
GA range of 31 to 35 and 36 to 40 weeks, amounting to
100% and 75% respectively. Meconium aspiration was
not observed in the lung specimen of fetal autopsy cases
having a gestational age less than 15 weeks. The frequency
of meconium aspiration increased as the GA advanced.
PH is congenital anomaly, caused by the arrest of normal
development of the lungs during intrauterine growth.
The arrest of normal development is due to insults in the
thoracic cavity and extrathoracic cavities 1-3,5,9
Askenazi and Perlman 4 mentioned that a LW:BW ratio
of 0.012 and/or RAC of less than 4.1 are diagnostic criteria
for PH. They also recommended that when the LW:BW
ratio is less than 0.009, PH is very likely and RAC is not
mandatory. When the LW:BW ratio is between 0.010-
0.012, PH is probable and RAC should be indicated for
confirmation. When the LW:BW ratio is between 0.013-
0.017, PH is possible and RAC is must. When LW:BW
ratio is more than 0.018, PH is unlikely and RAC is not
indicated. In the existing study, PH evaluation was done by
the LW:BW ratio and RAC as mentioned in the study done
by Askenazi and Perlman 4.
In study done by Cherian et al. 10, PH was noted in more
than 10% of neonatal autopsies and they also mentioned
that more than 85% of cases PH occur in association with
other conditions/malformations. In the present study,
out of 62 cases of fetal autopsy PH was noted in 45 cases
amounting to 72.58% of cases.
In studies done by Aghabiklooei et al. 1, Wigglesworth
and Desai 11, Husain and Hessel 6 and Cherian et
al. 10, PH was noted in 11.3%, 14.5%, 26%, and 43%
respectively. In the present study, PH was noted in 72.58%.
Out of 45 cases of PH, concordance between the LW:BW
ratio and RAC was noted in 33 cases amounting to 73.33%
of the cases. In these cases, RAC was less than 4.1 and
the LW:BW ratio was also less than 0.012. Discordance
between the LW:BW ratio and RAC was noted in 12 cases
amounting to 26.66%. In these cases, RAC was less than
4.1 and the LW:BW ratio was more than 0.012. Further analysis of these cases was done to conclude the diagnosis
of PH. Out of these 12 cases, 4 cases were of NTD, 2 cases
were of CCAM, 1 case was of gastroschisis, and 5 cases were
Askenazi and Perlman 4 observed a discrepancy between
the LW:BW ratio and RAC in cases of PH with neural tube
defects. They mentioned that this discrepancy could be
due to a low body weight due to the absence of the brain
leading to a higher LW:BW ratio and a delay in alveolar
development due to absence of pituitary gland leading to
a low RAC. They observed that neural tube defects had a
mean GA of 38 weeks, mean LW:BW ratio of 0.016, and
mean RAC of 3.1. A similar explanation holds true in our
study. Six cases of neural tube defects had a mean GA of
28.1 weeks, a mean LW:BW ratio of 0.016, and a mean RAC
of 2.3, which might be the reason for the discordance in the
findings between the LW:BW ratio and RAC (Figure 5).
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|Figure 5: Photograph of microscopy of lung section in a case of
anencephaly with mean RAC of 1.6. (H&E stain, 100x).
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|Figure 6: Photograph of microscopy of lung section with mean
RAC of 1.7 in another case of congenital cystic adenomatoid
malformation. (H&E stain, 100x)
Chikkannaiah et al. 12, in their study with 2 case reports
of CCAM in the lungs mentioned that enlargement of the
affected lungs and multiple cysts of varying sizes are noted
in CCAM. Dos Reis et al. 13 mentioned in their autopsy
findings that the affected lungs in CCAM weighed 75.9 gm
in their study on CCAM with GA of 25 weeks and showed
varying sized cysts with RAC less than 3. In the present
study, 2 cases of CCAM of lungs were seen with mean
gestational age of 23 weeks. Both cases showed enlarged
lungs with one case showing imprint of the rib cage on the
lung surface. In these 2 cases, the LW:BW ratio was more
than 0.012 as the lung weight was increased as mentioned
in studies done by Chikkannaiah et al. 12 and Dos Reis
et al. 13. This might be the reason for the discordance
between the LW:BW ratio and RAC findings of these cases
in present study (Figure 6).
Nimrod et al. 14 found that there is greater impact on
fetal growth when PROM occurred before 26 weeks of GA in their study on effect of PROM on oligohydramnios and
fetal development. PROM leading to oligohydramnios
syndrome consists of the tetrad of PH, skeletal deformities,
Potter’s facies, and intrauterine growth retardation.
Rotschild et al. 15 observed PH in 16% of fetuses that
experienced oligohydramnios following rupture of
membranes before 29 weeks of GA. Husain and Hessel 6
observed that 4 cases with oligohydramnios had PH with
mean LW:BW ratio of 0.011 and mean RAC of 2.7 in their
study. In the present study, 6 cases of oligohydramnios and
one case of PROM amounting to 11.29% were considered
as PH with all cases having GA of less than 29 weeks. These
cases had a mean GA of 22.85 weeks, mean LW:BW ratio of
0.006, and mean RAC of 2.65, which correlated with these
In the current study, 6.45% of the cases of renal pathology
cases had a mean GA of 21.2 weeks, mean LW:BW ratio
of 0.010, and mean RAC of 2.43. Our study findings
correlate with the studies by Askenazi and Perlman 4 and
Husain and Hessel 6; in their studies, they observed renal
pathology cases at a mean GA of 36 weeks and 31 weeks
with a mean LW:BW of 0.010 and 0.012 and mean RAC of
3.2 and 2.6, respectively.
In the present study 3.22% cases of hydrops fetalis had a
mean GA of 30 weeks, mean LW:BW ratio of 0.007, and
mean RAC of 3.1. Our study findings correlate with the
studies by Askenazi and Perlman 4 and Husain and Hessel
6; in their studies they observed that hydrops fetalis cases
had a mean GA of 34 weeks and 24 weeks, mean LW:BW of
0.013 and 0.011, and mean RAC of 4.4 and 2.2, respectively.
In the present study associated anomalies such as neural tube
defect, oligohydramnios, renal pathology, lung pathology,
hydrops fetalis, diaphragmatic hernia, musculoskeletal
deformity, premature rupture of membranes, and
gastroschisis were noted in 24 cases amounting to 53.34%.
In PH, 40% cases were of IUD, 13.34% cases were of NTD,
13.34% were cases of oligohydramnios, 8.90% cases were
of renal pathology, 4.44% cases each were of CCAM and
hydrops fetalis, and 2.22% cases each were of PROM,
gastroschisis, CDH and AMC.
Aghabiklooei et al. 1 in their study found 11.3% of primary
causes of PH. Husain and Hessel 6 found 22% cases of
primary PH where one third of the cases were not associated
with any congenital malformations. In the current study,
18 cases of PH had no congenital malformation or other
In a study by Ward and Caughey 16, it was observed that
the risk of meconium aspiration syndrome increases as the gestational age increases. In their study, they mentioned
that meconium aspiration syndrome was observed in 1.3%
at 38 weeks of GA and 4.8% at 42 weeks of GA. They also
mentioned that the risk of meconium aspiration syndrome
increased by 30% with each week of GA. Fischer et al. 17
also stated that the risk of meconium aspiration syndrome
and meconium-stained amniotic fluid increases with
advancing gestational age. The rate of meconium aspiration
syndrome in their study was 0.11% at 37-38 weeks of GA,
0.20% at 39-41 weeks of GA, and 0.49% at 42-43 weeks of
GA. Our study findings also correlate with the observations
by these authors. In the present study, meconium aspiration
was noted in 37.1% of the cases. The maximum number of
cases of meconium aspiration was noted in the cases having
a GA range of 31 to 35 and 36 to 40 weeks amounting to
100% and 75 % respectively.
In the current study, PH was incidentally discovered in
some clinically unsuspected cases, which may be cause of
mortality. The diagnosis of PH was rendered in a greater
number of cases when evaluation was done by considering
both the LW:BW ratio and RAC. Thus, evaluation by both
the LW:BW ratio and RAC provides a reliable index of
lung growth and should be an essential part of fetal autopsy
Conflict of Interest
Concept: AS, SUA, Design: AS, SUA, Data collection or processing:
AS, SUA, Analysis or Interpretation: AS, SUA, Literature search: AS,
SUA, Writing: AS, SUA, Approval: AS, SUA, SM.
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