Annals of African Medicine

ORIGINAL ARTICLE
Year
: 2015  |  Volume : 14  |  Issue : 3  |  Page : 132--136

Relationship between ultrasound estimated fetal gestational age and cerebellar appearance in healthy pregnant Nigerian women


Ademola A Adeyekun, Michael O Orji 
 Department of Radiology, University of Benin Teaching Hospital, PMB 1111, Benin City, Nigeria

Correspondence Address:
Ademola A Adeyekun
Department of Radiology, University of Benin Teaching Hospital, PMB 1111, Benin City
Nigeria

Abstract

Background: Fetal biometry by ultrasound provides reliable and important information about fetal growth and wellbeing. Evaluation of the fetal posterior fossa is useful in the assessment of neural tube-defects. Studies on normal ultrasound fetal cerebellar appearance and diameter across gestational age (GA) are scanty in the Nigerian medical literature. This study was carried out to study normal fetal cerebellar appearance and diameter at various GAs among healthy pregnant Nigerian Africans. Materials and Methods: This was a prospective study of 450 healthy singleton pregnant women between 13 and 42 weeks gestation. A curvilinear probe with a 3.5 MHz transducer of a SonoAce X6 (Medison Inc., Korea 2010) scanner was used to assess fetal transcerebellar diameter (TCD) and appearance. GA was also determined using fetal biometric parameters such as the biparietal diameter, femur length, and abdominal circumference. Fetal cerebellar appearance was correlated against GA. Results: The cerebellar appearance was graded into: Grade I: 164 fetuses (36.4%), Grade II; 102 fetuses (22.7%) and Grade III: 184 fetuses (40.9%). Mean GA and TCD was 21 weeks and 21.2 mm for Grade I; 28 weeks and 32.6 mm for Grade II; and 35 weeks and 47.1 mm for Grade III. There was significance difference among the cerebellar grades at the GA groups and transverse cerebellar diameter (P < 0.000). Conclusion: There is a gradual and steady change in ultrasonographic appearance of the fetal cerebellar and diameter appearance with advancing gestation. The changes ranged from anechoic, DQpair of eye glassDQ appearance at second trimester to relatively echogenic, DQdumb-bellDQ appearance at early third trimester, and solid, DQfan-shapeDQ in late third trimester.



How to cite this article:
Adeyekun AA, Orji MO. Relationship between ultrasound estimated fetal gestational age and cerebellar appearance in healthy pregnant Nigerian women.Ann Afr Med 2015;14:132-136


How to cite this URL:
Adeyekun AA, Orji MO. Relationship between ultrasound estimated fetal gestational age and cerebellar appearance in healthy pregnant Nigerian women. Ann Afr Med [serial online] 2015 [cited 2020 Nov 27 ];14:132-136
Available from: https://www.annalsafrmed.org/text.asp?2015/14/3/132/149908


Full Text

 Introduction



The cerebellum is a suprasegmental portion of the brain located within the posterior cranial fossa that receives input from virtually the entire nervous system, playing a key role in movement coordination. [1] It develops in the 5 th week of gestation as a protuberance covering the 4 th ventricle. Early in the fetal period, the union of the two halves results in the vermis which develops folia, and becomes largely obscured by the cerebellar hemispheres. [2],[3]

The fetal cerebellum can be visualized sonographically as early as 10-11 postmenstrual weeks. It grows rapidly in the second trimester following a linear relationship with gestational age (GA), such that during this period, measurement of the fetal cerebellum in millimeters approximates the GA in weeks. [2],[4]

Previous studies have evaluated the fetal cerebellar appearances, including its dimensions. Chang et al. [5] described three-dimensional ultrasonography as a promising tool in the evaluation of the fetal cerebellum, particularly its dimension and growth and showed its superiority over the two-dimensional methods. Hashimoto et al. [6] evaluated the changes in ultrasonographic appearance of the fetal cerebellum with advancing gestation. The authors classified the cerebellum into 3 grades: Grade I (a) -each cerebellar hemisphere is round, (b) the vermis is not well-developed and the cerebellum appears as "a pair of eye-glasses" at ultrasound, (c) the hemispheres are relatively anechoic and appears as two fluid-containing cysts.

Grade II: (a) The vermis is more prominent and appears as an echogenic rectangular tissue connecting the two hemispheres, giving the "dumb-bell" appearance (b) Each hemisphere is oval, and the central portion is more echogenic than other background structures.

Grade III (a) the cerebellum appears triangular or "fan-shaped" (b) tissues in the central portion of the hemispheres show similar echogenicity to the margins and vermis, thus, the cerebellar appears more like a solid tissue than a cyst.

Malik et al. [7] similarly graded the cerebellar appearance from Grades I to III, and stated that the grading reflects the progressive histological development and Purkinje cell differentiation in the cerebellum.

There are publications on sonographic fetal cerebellar diameter and appearance during gestation among Caucasians. However, such data are scanty among Nigerian Africans. This is the justification for this study.

 Materials and Methods



Four hundred and fifty normal pregnant women were prospectively studied by ultrasound from September 2011 to March 2012. Approval of the hospital's Ethics and Research Committee was obtained. The subjects were those referred from the antenatal clinic and were within 13-42 weeks gestation. Only those who were certain of their last menstrual period and had normal singleton pregnancy were included. Those with maternal conditions such as diabetes, sickle cell hemoglobinopathy, and pregnancy-induced hypertension were excluded. The sonograms were obtained with a SonoAce X6 scanner (Medison Company Limited, 1003 DAECHI-dung, Gangnam, Seoul, Korea 2010), using curvilinear probe with 3.5 MHz transducer.

The fetal cerebellum was located by first using the horizontal plane of the fetal head to identify the cavum septum pellucidum, and the thalami as landmarks similar to the plane for the biparietal diameter (BPD). The transducer was then slightly rotated caudally, to bring the characteristic "butterfly" appearance of the cerebellum into view, according to Meyer et al.[4] The transverse cerebellar diameter (TCD) was measured, in an outer-to-outer-fashion [Figure 1]. The BPD, abdominal circumference (AC), femur length (FL) were also measured to calculate fetal GA. The parenchyma of the fetal cerebellum was then evaluated and its appearance classified into Grades I, II, and III, according to Meyer et al., [4] as described under introduction.{Figure 1}

Data analysis was done using Statistical Package for the Social Sciences (SPSS) Version 16.0 (SPSS Incorporated, Chicago IL, USA). The TCD values and fetal biometric indices were tested for significance with analysis of variance (ANOVA) while Pearson's correlation coefficient and Kruskal-Wallis nonparametric ANOVA was used for cerebellar appearance and TCD. At less than 95% confidence levels, P ≤ 0.05 were considered significant.

 Results



Four hundred and fifty healthy pregnant women with singleton intrauterine fetuses and GA range from 13 to 42 weeks, who met the inclusion criteria, were assessed. The age range of the subjects was 15-45 years (mean: 30.8 ± 4.4 years), and the parity ranged from 0 to 7. One hundred and seventy-five subjects (38.9%) were nulliparas. The GA group 33-37 weeks was the modal group scanned (111 women or 24.2%); followed by 23-27 weeks (81 women or 18.0%) and 14-22 weeks (78 women or 17.3%).

The TCD of the fetuses studied ranged from 11.9 mm to 59.3 mm (mean 34.2 ± 14.1 mm. With advancing menstrual age, there was corresponding increase in the mean TCD of the fetuses [Table 1]. There was significant correlation between TCD and menstrual age (r = 0.984; P < 0.000) as well as between BPD, FL, AC, and menstrual age (r = 0.974, 0.969 and 0.963, respectively). The cerebellar appearances for the 450 fetuses were sonographically graded (using shape and echotexture) as follows: 164 (36.4%) were assigned Grade I, 102 (22.7%) classified Grade II, while 184 (40.9%) were graded as III. The mean GA and TCD were 21 weeks and 21.2 mm for Grade I; 28 weeks and 32.6 mm for Grade II, while 35 weeks and 47.1 mm was recorded for Grade III. The gradings are depicted in [Figure 2],[Figure 3] and [Figure 4]. There were significant differences among the three cerebellar grades in terms of GA and TCD using Kruskal-Wallis nonparametric ANOVA; P < 0.000 [Figure 5]. The frequency of each cerebellar grade with respect to GA showed a gradual and continuous shift from Grade I through II to III [Figure 6].{Figure 2}{Figure 3}{Figure 4}{Figure 5}{Figure 6}{Table 1}

 Discussion



Ultrasound in obstetric practice remains an invaluable tool not only for fetal biometry but also in assessment of normal fetal anatomy and exclusion of congenital anomalies including those involving the posterior fossa. Magnetic resonance imaging is an adjunct for evaluating the posterior fossa. However, its use in most developing countries is limited by cost and availability. Assessment of the fetal posterior fossa has found its greatest application in the evaluation of neural tube-defects. In a previous ultrasound study, Nicolaides et al. [8] demonstrated the anterior curvature of the cerebellum and obliteration of the cisterna magma due to Arnold-Chiari malformation in 60% of fetuses with spinal bifida. The prenatal diagnosis of Dandy-Walker malformation also relies on detection of a posterior fossa cyst, a defect in the inferior cerebellar vermis and hydrocephalus. [9]

In this study, the earliest GA at which the fetal cerebellum was demonstrated was 13 weeks. Reece et al. [10] demonstrated fetal cerebellum, using ultrasonography as early as 10-11 weeks gestation. This is probably due to use of different types of ultrasound equipment in these studies.

Sherer et al. [11] correlated cerebellar circumference and area with GA and described its usefulness in cases of unilateral cerebellar agenesis and hypoplasia. Thus, measurement of cerebellar dimensions, including the TCD may be helpful in detecting cerebellar malformations in utero, if nomograms of TCD are available for a selected population.

Previous studies have found a close correlation between cerebellar dimensions and GA using fetal growth parameters such as BPD, head circumference, FL, and estimated fetal weight; [12],[13],[14] this relationship has been found to be nondependent on fetal gender. [15]

The mean TCD in this study was 34.2 ± 14.1 mm (range: 11.9 mm to 59.3 mm). There was significant correlation between TCD and GA (r = 0.0984; P < 0.000). TCD also correlated better than the three other biometric parameters of FL, BPD and AC which gave r = 0.974, 0.969 and 0.963, respectively, in the assessment of GA. This finding is in agreement with previous studies on the same subject among Caucasians. [10],[16],[17]

The present study found gradual and steady changes in the sonographic appearance of the fetal cerebellum. These changes include shape, echogenicity, and dimensions. The echotexture of the cerebellum changed from "hypoechoic or cystic" - Grade I, to "iso- or slightly echogenic" with an echogenic rim - Grade II and homogenously "hyperechoic" or "solid" - Grade III, near term.

The shape of the cerebellum changed from "pair of eye-glasses" appearance - Grade I early, in the study to "dumb-bell" - Grade II, and finally to "fan" or "butterfly" shape, with advancing gestation [Figure 2],[Figure 3] and [Figure 4]. These changes, especially in echotexture, have been proposed to be reflective of the histological development of the cerebellum during pregnancy. [6],[18]

The frequency of cerebellar grading relative to GA in this study was 164 fetuses or 36.4% corresponding to GA between 13 and 23 weeks for Grade I; 102 fetuses or 22.7% between 24 and 30 weeks for Grade II; and 184 fetuses or 22.7% between 31 and 42 weeks for Grade III. Hashimoto et al., [6] made a similar observation in a Japanese study. The median GA and TCD were 21 weeks and 21.1 mm, respectively, for Grade I, 28 weeks and 32.6 mm for Grade II, while the values were 35 weeks and 47.1 mm for Grade III; [Figure 4]. Similar results were obtained by Malik et al. [7] in their study among Indian women, where median GA and TCD values of 20 weeks and 21 mm for Grade I; 31 weeks and 36 mm for Grade II; and 36 weeks and 42 mm for Grade III were obtained. Overlap in grading between 23 and 32 weeks was noted. This study found significant difference among the three cerebellar grades in terms of GA and TCD using Kruskal-Wallis nonparametric ANOVA, P < 0.000. It has been hypothesized that these changes may be due to progressive cerebellar histologic development and Purkinje fiber differentiation, [18],[19] possibly related to progressive decrease in the cerebellar water content with advancing gestation. [20]

 Conclusion



There is a gradual and steady change in the ultrasonographic appearance of the fetal cerebellum with increasing GA. Such changes include those of shape and echogenicity; from hypoechoic, "pair of eye-glasses, to echogenic," "fan" or "butterfly" shape.

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