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volume 56 number 2 | NOVEMBER 2018
THE SOUTH AFRICAN RADIOGRAPHER
26 www.sorsa.org.za
OPEN ACCESS online only
peer reviewed ORIGINAL ARTICLE
Normal value of cephalic index and craniotypes: a pilot sonographic
cephalometric survey of pregnant women of Yoruba ethnic origin in
Lagos, southwest Nigeria
CU Eze1 BSc (Nig), MHPM (Uniben), MSc (Nig), PhD (Nig) | DC Ene2 BSc (Nig), Pg. Cert Med. Us (Nig) | LC Abonyi1 BSc (Nig),
MSc (Unilag), PhD (Guyana) | DO Omiyi1 DIR (Nig), Pg. Cert (Sheffield), BSc (Edinburgh), MSc (Unizik)
1University of Lagos
2Hospital Support Diagnostic Center, Ketu, Lagos
Abstract
Background: Sonographic cephalometry is used to identify ethnic differences. Biparietal diameter (BPD) and occipito-frontal
diameter (OFD) may be used to compute cephalic index (CI).
Methods: A sonographer measured the BPD and OFD in 200 pregnant women of Yoruba ethnic origin. The formula BPD/OFD
x 100 was used to compute the CI. Mean CI was used to determine craniotypes. Coefficient of correlation, line graph, and the
Bland-Altman plot, were used to determine the relationship between CI, BPD and OFD.
Results: Mean CI was 77.24 ± 3.88 mm. There was a statistically significant difference (p < 0.05) in mean CI between fetuses of
Yoruba, Igbo and Indian ethnic origin. Correlation was significant between CI and BPD (r = 0.163; p = 0.02) and between CI and
OFD (r = -0.02; p = 0. 000); 68.0% of fetuses had mesocephaly. The formula CI = 0.0371(BPD) + 74.656 and CI = 0.0035 (OFD)
+ 77.559 may be used to calculate CI on the basis of respective sonographically measured BPD and OFD.
Conclusion: While the skull appeared to have grown to its full length and breadth in the first trimester of pregnancy, a typical
fetus of Yoruba ethnic origin in Lagos metropolis most likely would have a long and flat skull at birth. Even as ethnic differences
appear to be a major factor in the development of cranial development in the population studied, a simple regression equation
can be used to compute cephalic index and to correct atypical craniotypes among fetuses without craniofacial anomalies.
Keywords Fetus, simple regression, Bland-Altman plot, craniometry
INTRODUCTION
Morphological features in different ethnic
groups are usually not randomly distrib-
uted. Instead, they appear in geographical
clusters.[1] Cephalometry may literally be
defined as the study and measurement of
the head. Anthropologists were among the
earliest to use cephalometric values to de-
scribe and generalise facial appearances
to specific populations. It is believed that
cephalometry is arguably the most useful
technique in the investigation of cranio-
facial morphology because of its validity
and practicality.[2] Craniometry is useful
in the diagnosis of craniosynostosis (also
known as synostosis) which is early fusion
of two or more bones of the calvarium that
results in an abnormal head shape.[3] Al-
though sporadic cases have been reported,
syndromic craniosynostosis is inherited
and is often associated with genetic disor-
ders such as Apert, Baller-Gerold, Pfeiffer
and Muenke syndromes.[4] Lemon-shaped
head is associated with spina bifida in
31.6% of fetuses; strawberry-shape is as-
sociated with aneuploidy in 18.4% of
fetuses.[5] Trisomy-13, on the other hand,
is associated with facial defects and uro-
genital malformations while trisomy-21 is
characterised by facial dysmorphism.[6-7]
Standardised cephalometric values are
useful when comparing patients with
the normal population and also useful in
pediatrics, forensic medicine, and plastic
as well as orodental surgery.[1-2] In fact,
knowledge of the normal cephalic index
(CI) range is important in determining
atypical fetal head shapes.[8] CI has been
described as the relationship between
the long and short axes of the foetal cal-
varium used to distinguish a normal fetal
head shape from an abnormal one. It is
the ratio of the maximum width (i.e. BPD)
of the head multiplied by 100 divided
by its maximum length (i.e. OFD) and a
quantitative and objective method of de-
termining skull shape.[9-11] To neurosur-
geons, knowledge of the normal range of
CI is useful in a pre-operative work-up as
well as in a post-operative assessment of
correction of skull deformities.[8,12] Crani-
ometry is also useful in studies pertaining
to primate phylogeny.[1]
There are significant variations in cranial
shape and size in different ethnic groups.
Chinese heads, for instance, have been
reported to be more round than their
Caucasian counterparts.[13-15] Among the
Idoma and Igede ethnic nationalities in
northcentral Nigeria, mesocephaly was
reported as the predominant head shape;
dolichocephaly was reported as predomi-
nant craniotype in a population of Yoruba
people of southwest Nigeria.[16-17] Since
geographic, ethnic and dietary differences
exist amongst different population groups,
information about morphometric charac-
teristics becomes important for purposes
of comparison. Due to ethnic differences,
age and population-specific data on cra-
nial morphometry are not only useful in
clinical practice as indicators of growth
and development, but are also important
in determining changes in size and shape
or abnormalities of the crania.[18] With the
existence of ethnic differences in cranial
size well known, it is little wonder that
postnatal cephalometric normal values of
cephalic length, cephalic breath and ce-
phalic index (CI) have been reported for
different ethnic groups.[17,19-20]
Early diagnosis of congenital fetal anoma-
lies helps a physician to choose between
27
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the non-aggressive obstetric management
and termination of pregnancy.[21] In spite
of the role of postnatal craniometry in dif-
ferentiating craniotypes, it is imperative
to note that cranial anomalies are mostly
congenital with cranial vault shape re-
ported to be more dependent on genetic
factors than on cerebral development.[8]
Imaging modalities such as computed
tomography (CT), magnetic resonance
imaging (MRI), and ultrasonography may
be used for prenatal metric evaluation of
craniofacial form.[1] Sonography does not
involve ionising radiation, it is less expen-
sive than CT or MRI, and is commonly
available in developing countries like Ni-
geria. It therefore is preferred in the intra-
uterine evaluation of the fetus.
In sonographic cephalometry, stand-
ardised measurement of fetal biparietal
diameter (BPD), head circumference
(HC), as well as occipito-frontal diameter
(OFD), may be used to estimate fetal age
as well to diagnose congenital anomalies.
Studies have demonstrated the effective
use of sonographic CI in the diagnosis of
closure of sutures in the third trimester
of pregnancy, strawberry-shaped cranial
vault and narrow flattened front-occip-
ital region in trisomy 18 while sonogra-
phy has equally been used to determine
normal CI values in early cyesis using the
transvaginal approach in various ethnic
populations.[8,22-25] Data on CI obtained
from fetal sonographic craniometry is
sparse in Nigeria that has many distinct
ethnic groups. To the best of our knowl-
edge, there is no data on sonographic
fetal craniometry in any population of
Yoruba people who make up one of the
largest ethnic groups in Nigeria. The pur-
pose of this study was to perform fetal
craniometry in a Nigerian population
of fetuses of Yoruba ethnic extraction in
Lagos, southwest Nigeria using ultra-
sonography technique in order to provide
baseline cephalometric data, cephalic in-
dices and craniotypes for clinical use and
future reference.
METHODS
A prospective longitudinal study was
carried out at a private hospital in Lagos
metropolis between November 2016 and
August 2017. Ethics approval was obtained
from the Human Research Ethics Commit-
tee at the hospital located in Ketu, Lagos.
Informed written consent was obtained
from women before they were recruited.
In line with the standards for reporting di-
agnostic accuracy studies (STARD), poten-
tially eligible participants were identified.
They were pregnant women who were re-
ferred to the ultrasound centre at the hos-
pital for routine antenatal examination.
From potentially eligible participants, a
convenience sample of 200 healthy Nige-
rian women of Yoruba ethnic origin with
singleton pregnancy was selected. Partici-
pants were recruited on first-to-come first-
to-be recruited basis. Only Yoruba women
who were married to Yoruba men were
included in the study to ensure that fetus-
es were of Yoruba ethnic origin. Women
who were sure of the date of onset of their
last menstrual period (LMP) who agreed
to undergo first trimester ultrasound ex-
amination for pregnancy dating as well as
2nd and 3rd trimester follow-up examina-
tions were recruited. Sonographic meas-
urement of crown-rump length (CRL)
was done within 7-13 weeks of cyesis.
In line with recommendations,[26] each
participant was included in the present
study only when the difference between
fetal age calculated from LMP and ultra-
sound estimation was ≤7 days. Socio-de-
mographic and anthropometric data were
collected. Trans-abdominal ultrasonogra-
phy was performed using Mindray DC-N3
ultrasound machine with a 3.5MHz
convex probe. All sonographic measure-
ments were performed by one sonogra-
pher who has >8 years of experience in
obstetric sonography. Each participant
was examined while lying supine. In line
with recommended protocols for perform-
ing obstetric sonography,[27] the probe was
placed perpendicular to the central axis
of the fetal head on a plane that traversed
the thalami and cavum septum pellucid-
ium and care was taken to ensure that
Table 1. Mean Cephalic Index for the population, 2nd trimester and 3rd trimester
MEAN ± STANDARD DEVIATION
p VALUE
POPULATION
n = 200
2nd TRIMESTER
n = 200
3rd TRIMESTER
n = 200
Cephalic index 77.24 ± 3.88 76.77 ± 3.25 77.58 ± 4.26 0.147§
Range 69.33 - 114.87 69.33 - 84.62 71.80 - 114.87
§ Independent samples t-test for 2nd and 3rd trimester only
Table 2. Comparison of mean CI in the present study with Igbo population in Nigeria
MEAN ± STANDARD DEVIATION
p VALUE MEAN
DIFFERENCE
PRESENT STUDY UGWU et al.
(2007)
Cephalic index 76.77 ± 3.25 85.92 ± 4.88 0.000‡-8.677445
Range 69.33 - 84.62 71.80 - 114.87
‡ One sample t-test
Figure 1. Sonogram of fetal head showing BPD and OFD measurement
volume 56 number 2 | NOVEMBER 2018
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cerebellar structures were avoided. Both
BPD and occipito-frontal diameter (OFD)
were measured at the level of the thalami
and septum pellucidium. For BPD (width
of the skull) measurement, the cursor was
placed at the outer edge of the proximal
and then taken to the inner edge of the
distal calvarial wall. For OFD (the longi-
tudinal diameter of the calvarium) meas-
urement, the cursor was placed at the
proximal outer and drawn to the distal
outer calvarial wall (Figure 1). As was pre-
viously done in several similar studies[13,19]
the cephalic index (CI) was thereafter
computed using the formula: CI = BPD/
OFD x 100. Craniotyping was thereafter
performed using Mishra et al’s method[19]
as follows:
Ultra-dolichocephalic:
cephalic index = 55.0 - 59.9
Hyper-dolichocephalic:
cephalic index = 60.0 - 64.9
Dolichocephalic:
cephalic index = 65.0 - 74.9
Mesocephalic:
cephalic index = 75.0 - 79.9
Brachycephalic:
cephalic index = 80.0 - 84.9
Hyper-brachycephalic:
cephalic index = 85.0 - 89.9
Ultra-brachycephalic:
cephalic index = 90.0 - 94.9
Mean CI ± standard deviation (SD) was
computed for the population and for 2nd
and 3rd trimester. Paired t-test was used to
compare mean CI in the present study with
previously published means in different
populations. Pearson’s product moment
correlation analysis and line graphs were
used to determine correlation between CI,
BPD and OFD. Bland-Altman plot was
used to determine 95% confidence inter-
val of CI (mean CI ± 2 SD) in the popu-
lation. Thereafter, the proportion for each
head shape (craniotype) was computed.
Simple logistic regression analysis was
used to produce equations (nomograms)
that could be used to compute CI in the
population. Data were analysed using
SPSS software version 17 (SPSS Inc., Chi-
cago, Illinois, USA). Results were tested
for statistical significance at p≤0.05.
RESULTS
The mean age of the population was 33.4
± 2 years. The mean CI in the population
was 77.24 ± 3.88 mm; mean CI for the
2nd and 3rd trimester was 76.77 ± 3.25 mm
and 77.58 ± 4.26 mm, respectively. Mean
CI for 2nd and 3rd trimesters was not statisti-
cally different from each other (p=0.147;
Table 1). Mean CI in the population was
statistically different (p=0.000) from mean
CI previously reported in an Igbo popula-
tion (Table 2). There was a statistically sig-
nificant difference (p<0.05) in the mean
CI obtained in the present study com-
pared with means reported in different
Indian populations (Tables 3 and 4). Most
fetuses (68.0%) had mesocephalic head
shape whereas the head was hyper brach-
ycephalic in 3.0% of fetuses (Table 5).
There was significant correlation between
CI and BPD (r=0.163; p=0.02) (Table
6) and between CI and OFD (r=-0.02;
Table 3. Comparison of mean CI in the present study with an Indian population
CEPHALIC
INDEX
MEAN ± STANDARD DEVIATION
p VALUE‡MEAN
DIFFERENCE
PRESENT
STUDY
RAJLAKSHMI
et al.
16 - 20 76.4 ± 3.2 79.2 ± 3.6 0.0001 -2.793000
21 - 25 76.9 ± 3.6 80.6 ± 3.7 0.0001 -3.743375
26 - 30 76.9 ± 2.4 82.6 ± 6.5 0.0001 -5.719432
31 - 35 77.2 ± 2.4 82.5 ± 1.7 0.0001 -5.284127
36 - 40 78.4 ± 6.4 88.7 ± 2.3 0.0001 -6.09926
‡ One sample t-test
Table 4. Comparison of mean CI in the present study with Manipuri Indian population
CEPHALIC
INDEX
MEAN ± STANDARD DEVIATION
p VALUE‡MEAN
DIFFERENCE
PRESENT
STUDY LOKESH et al.
16 - 20 76.41 ± 3.16 80.36 0.0001 –3.953000
21 - 25 76.86 ± 3.59 77.00 0.802 –0.143375
26 - 30 76.89 ± 2.44 80.59 0.0001 –4.52447
31 - 35 77.22 ± 2.39 79.77 0.0001 –2.554127
36 - 40 78.42 ± 6.40 80.41 0.054 –1.988171
‡ One sample t-test
Table 5. Classification of fetal head shapes in the population studied
TYPE OF HEAD SHAPE N (%)
Dolichocephaly 10 (5.0)
Mesocephaly 136 (68.0) *
Brachycephaly 48 (24.0)
Hyperbrachycephaly 6 (3.0)
Total (100.0)
*Mesocephaly was the commonest head shape in the population
Table 6. Correlation of CI with BPD and OFD
CI BPD OFD
Cephalic Index (CI)
Pearson Correlation 1 .163* -.020
Sig. (2-tailed) .021 .782
N 200 200 200
Biparietal Diameter
(BPD)
Pearson Correlation .163* 1 .983**
Sig. (2-tailed) .021 .000
N 200 200 200
Occipito-frontal
Diameter (OFD)
Pearson Correlation -.020 .983** 1
Sig. (2-tailed) .782 .000
N 200 200 200
* Correlation is significant at the 0.05 level (2-tailed).
** Correlation is significant at the 0.01 level (2-tailed).
29
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Figure 2. Line graph showing goodness-of-fit HCI/BPD plot. Figure 3. Line graph showing goodness-of-fit HCI/OFD plot.
Figure 4. Bland-Altman plots of horizontal cephalic index and biparietal diameter.
Figure 5. Bland-Altman plots of horizontal cephalic index and OFD.
p=0. 000) (Table 6). Figures 2 and 3 are
line graphs depicting significant correla-
tion between CI and BPD as well as be-
tween CI and OFD. Figures 4 and 5 are
Bland-Altman graphs showing CI ± 2
standard deviations (SD) for CI against
BPD and for CI against OFD, respectively.
Simple regression equation for calculat-
ing CI on the basis of BPD and OFD are
CI = 0.0371 (BPD) + 74.656 and CI =
0.0035 (OFD) + 77.559, respectively.
DISCUSSION
It is well known that ethnic characteris-
tics of a population are expressed in phe-
notype skeletal morphology. The view
of Williams et al[28] is that their best and
most obvious expression is in the skull.
They also opine that cranial morphom-
etry (CI in particular) establishes the most
significant characteristic for defining the
ethnic difference. It is an established fact
that a comparison of CI between parents,
offspring and their siblings has the poten-
tial to give a reliable clue towards genetic
transmission of inherited characteristics.
Craniometry is also important for facial
reconstruction in cases of disputed iden-
tity. Cephalometry is a simple and accu-
rate method for investigating craniofacial
skeletal morphology hence its continued
popularity in the assessment of such char-
acteristics.[30] This study appears to be the
first to undertake prenatal sonographic
measurement of CI. It provides data that
could be useful regarding cephalic indi-
ces and craniotypes in a population of fe-
tuses of Yoruba origin in Lagos, southwest
Nigeria.
There was a statistically significant differ-
ence (p<0.05) in mean CI (77.24 ± 3.88
mm; range = 69.33 - 114.87 mm) in the
present study. In accordance with the clas-
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sification of Mishra et al,[19] mesocephaly
was the dominant craniotype in the pop-
ulation studied. This craniotype suggests
that a fetus from the Yoruba ethnic nation-
ality, in Lagos Nigeria, with no craniofa-
cial anomaly will almost certainly have a
long and flat head at birth. We noted a
significant difference when the mean CI
in our study was compared with the mean
CI that was reported by Ugwu et al[8] in
an Igbo population in southeast Nigeria.
There was also statistically significant dif-
ference between mean CI observed in the
present study compared to mean CI report-
ed in different Indian populations.[31-32]
These differences support the view that
ethnicity/genetic makeup plays a role in
the development of craniotypes.[18]
With respect to fetuses in the 16-20 weeks
gestational age range, we observed a sta-
tistically significant difference in mean CI
(76.4 ± 3.2 mm) compared to 79.2 ± 3.6
mm reported by Rajlakshmi et al[31] in Ma-
nipuri, Indian fetuses between the ages of
16 and 20 weeks. While we cannot rule
out that the sonographic technique and
the quality of ultrasound machines used
could have contributed to differences in
CI, we are inclined to believe that our
study appears to reaffirm the opinion that
ethnic differences exist in CI. We observed
a marginal increase in CI mostly within the
2nd trimester which strongly suggests that
fetal head/brain development was proba-
bly more rapid within the first trimester of
pregnancy. Although we did not compute
the rate of cranial growth, our observa-
tion somewhat agrees with Rajlakshmi et
al’s[31] earlier submission to the effect that
CI increased with advance in fetal age.
A mixed pattern of craniotypes was ob-
served in the present study; mesocephaly
was the commonest fetal head shape in
the population. This suggests that most
fetuses of Yoruba extraction in the popu-
lation studied would most likely have
medium sized heads. It also points to the
fact that other factors, other than genetic
makeup, play appreciable roles in cranial
development. The proportion of fetuses
with mesocephaly in our study (68.5%)
is more than 33.6% reported in an India
population.[32] In the same Indian popula-
tion, 54% of fetuses had brachycephaly
whereas 48% of fetuses had brachycepha-
ly in the present study. This suggests that a
typical Indian fetus in the Manipuri region
would most likely be born with a relatively
broader and shorter skull than its Yoruba
counterpart in Lagos metropolis. The
5% of fetuses with dolichocephaly and
3% with hyper brachycephaly observed
in the population studied suggest that it
would not be totally unusual for a typical
Yoruba couple in Lagos metropolis to have
a baby with a relatively long skull or an
extremely short skull in spite of their ge-
netic makeup. More Indian fetuses in the
Manipuri region[32] had dolichocephaly
and hyper brachycephaly (4% and 8.4%,
respectively). This appears to reaffirm
that fetuses in the Manipuri region would
mostly have shorter and broader skull at
birth than their Yoruba counterparts in
Lagos metropolis. While we concede
that errors in measurement could have
contributed to differences in craniotypes
reported, we are inclined to suggest that
ethnic/dietary differences most certainly
played dominant roles in cranial develop-
ment in those populations. It is therefore,
not implausible to submit that fetuses of
Yoruba origin are likely to be born with
flatter/longer skull than their Indian coun-
terparts from the Manipuri region.
Within the 2nd and 3rd trimester of cyesis,
we observed that fetal skull was generally
mesocephalic; no significant difference in
mean CI was observed between 2nd and
3rd trimesters. This suggests that the fetal
skull was more or less fully developed in
the 1st and probably early 2nd trimester
in the population studied. This supports
Tuli et al[33] who earlier reported no sig-
nificant change in CI between the 2nd and
3rd trimester of gestation with fetal heads
generally mesocephalic in the 2nd and 3rd
trimester of cyesis. This study thus reiter-
ates the importance of performing 1st and
early 2nd trimester sonographic evaluation
in a patient with high risk for congenital
anomaly. Our study, however, does not
support Bharati et al’s opinion[34] which
states that the head is usually flat and long
(dolichocephalic) in tropical regions but
generally round (mesocephalic/brachyc-
ephalic) in temperate regions.
We observed a significant correlation
between BPD and CI, and between OFD
and CI in the population studied. While
this might not be totally unexpected as
pregnancy advanced, we believe that it
underscores the need for sonographic
measurement of OFD and subsequent
computation of CI in obstetric evalua-
tion of women at high risk of congenital
anomalies. It also highlights the superior-
ity of sonographic cephalometry in the
evaluation of atypical craniotypes in-
stead of visual inspection and measure-
ment of BPD that is usually done by a few
sonographers in Lagos metropolis. In the
present study, simple regression analysis
showed that atypical craniotypes can be
corrected using an equation while Bland-
Altman graphs showed that within 2-SD
of the mean, CI could be used to catego-
rise fetal head shape thereby reaffirming
that computation of CI should be consid-
ered when the fetus presents with atypical
craniotype.
Mesocephaly had earlier been reported by
Obaje et al[16] as the dominant head shape
among the Idoma and Igede ethnic nation-
alities in northcentral Nigeria. Oladipo et
al[17] also reported dolichocephaly as the
dominant craniotype in a cohort of Yoruba
people in the southwest of the country.
Neither studies[16,17] carried out prenatal
cephalometric studies which made their
results unsuitable for comparison with
ours. Another limitation of our study was
the small sample size in terms of the pop-
ulation of people of Yoruba ethnic origin
in Nigeria. Although it can be argued that
data obtained in the present study were
reliable since only one sonographer per-
formed sonographic measurements, we
think that without further validation, ref-
erence values of CI, craniotypes and the
nomogram developed in the present study
might be valid only among fetuses in the
population studied.
CONCLUSION
While the skull may appear to have grown
to its full length and breadth in the first
trimester of pregnancy, a typical fetus of
Yoruba ethnic origin in Lagos metropolis
would most likely have a long and flat
skull at birth. Even as ethnic differences
appear to be a major factor in cranial de-
velopment in the population studied, a
simple regression equation can be used
to compute cephalic index and to correct
atypical craniotypes among fetuses with-
out craniofacial anomalies.
CONFLICT OF INTEREST
We have none to declare.
CONTRIBUTIONS OF AUTHORS
CUE (University of Lagos) was the main
researcher; DCE (Hospital Support Diag-
nostic Center, Ketu, Lagos) was respon-
sible for data collection; LCA (University
of Lagos) assisted with data analysis and
interpretation of the results. DOO (Uni-
versity of Lagos) drafted the manuscript.
31
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