VARIATIONS IN THE SIZE AND TIME OF CLOSURE OF THE ANTERIOR FONTANEL FROM BIRTH TO 24 MONTHS OF AGE IN NIGERIAN CHILDREN IN PORT HARCOURT

Abstract

The size of the anterior fontanel (AF) and the occipito-frontal circumference (OFC) are
useful indices of the rate of brain growth and ossification of the calvarium. They may also reflect
changes in intracranial pressure seen in different disease conditions and so form essential parts of
the neuro-developmental assessment of newborns and infants. However, there is a dearth of data
on AF size from cosmopolitan settings in Nigeria, particularly for infants between 12 and 24
months of age. The wide variation in the size of the AF underscores the need to establish local
reference standards for a given population. This study was done to address the gap in knowledge
on AF size in the South-South Geo-political Zone.
This was a cross-sectional observational and analytical study of 2895 consecutively
recruited children (313 neonates and 2582 infants) from two tertiary health institutions in Port
Harcourt. The AF size (determined by the modified method of Faix) and the OFC (determined by
the Student’s method), were measured in apparently healthy Nigerian children aged 48 hours to 7
days and at 6 weeks, 10 weeks, 14 weeks, 6 months, 9 months, 12 months, 18 months and 24
months of age.
The mean ± SD AF size for the newborns was 4.5 ± 1.7 cm while at 24 months the mean
AF size was 0.2 ± 0.7 cm. The mean ± SD OFC in the newborns was 35.8 ± 2.7 cm while at 24
months the mean ± SD OFC was 48.0 ± 2.3 cm. There was a statistically significant negative
correlation (r = -0.648, p = 0.000) between AF size and OFC with increasing post-natal age,
represented by the formula y = 14 – 0.265x, where y = AF size, and x = OFC.
Of the 2895 subjects, 667 (23.04%) had a closed AF. The number (%) with a closed AF was
9 (2.9%) among the 313 newborns and 288 (88.9%) of the 324 infants at 24 months of age. In
between these two 7/325 (2.2%), 76/321 (23.7%) and 273/321 (85.1%) had a closed AF at 6, 12
and 18 months of age respectively. The proportion of females (57.7%) with a closed AF was
significantly higher than that of males (45.6%), (p< 0.0001). Among the newborns, there was a
statistically significant difference between the ethnic groups in the mean AF size (p < 0.05). The
largest AF size was observed among the Ogoni (6.4 ± 1.5 cm) while the Hausa/Fulani had the
least (3.0 ± 3.5 cm). However at 24 months, the Bini/Esan had the largest AF size (2.2 ± 1.8 cm)
followed by the Hausa/Fulani (1.4 ± 0.0 cm).
It is concluded that there is a strong negative correlation between the AF size and OFC.
This relationship, mathematically represented by the formula AF size = 14 – 0.265 x OFC can be
utilized to derive the expected AF sizes of infants from the OFC especially in a busy clinic setting
instead of physical measurement which is cumbersome and time consuming. This can assist in the
early identification of infants whose AF sizes deviate significantly from expected values for age
and who may benefit from further evaluation.

VARIATIONS IN THE SIZE AND TIME OF CLOSURE OF THE ANTERIOR FONTANEL FROM BIRTH TO 24 MONTHS OF AGE IN NIGERIAN CHILDREN IN PORT HARCOURT