642 - Two-dimensional head ultrasonography reference values for extra-axial fluid spaces in extremely preterm neonates

Publication Number: 2626.642

Paige M.. Nelson, University of Iowa Stead Family Children's Hospital, Iowa City, IA, United States; Allison Momany, University of Iowa Stead Family Children's Hospital, Iowa City, IA, United States; Heidi Harmon, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA, United States

Background: Prominent extra-axial space and ex-vacuo ventricular dilatation on preterm brain imaging are markers of white matter injury or dysmaturation. However, reference values of extra-axial fluid spaces by gestational age in extremely preterm (EP) neonates have not been established.

Objective: Use two-dimensional (2D) head ultrasonography (HUS) measurements to establish CSF space reference values in EP neonates at day of life (DOL) 7 and 36-weeks postmenstrual age (PMA).

Design/Methods: Subjects included 272 EP neonates (22 0/7 to 26 6/7 weeks gestational age) born from 2006 to 2019 at the University of Iowa. Exclusions included in-utero atrophy suggestive of perinatal insult, defined by enlarged extra-axial space (sinocortical width [SCW] > 3.5mm) and/or ex-vacuo ventricular dilatation (anterior horn width [AHW] > 4.0mm) at DOL 7 scan, or postnatal moderate-to-severe brain injuries. Linear measurements were obtained from clinical 2D HUS exams for extra-axial space (interhemispheric width [IHW], SCW, craniocortical width [CCW]) and the lateral ventricles (AHW and ventricular index [VI]). Exploratory reference values for extra-axial and ventricular spaces were generated by computing percentiles and applying locally estimated scatterplot smoothing (LOESS) to visualize the effect of gestational age at time of scan. Generalized additive models were utilized to examine potential sex differences in curves before plotting.

Results: Maternal and neonatal demographics, clinical characteristics, pregnancy/delivery complications, neonatal morbidities, and interventions are presented in Table 1. LOESS curves for extra-axial space at DOL 7 showed an increase in IHW with increasing gestational age, while SCW remained less than 2mm across gestational ages and CCW remained less than 1mm. AHW median showed a trend for higher values at 23-24 weeks PMA, but the 75%ile was less than 2.5mm across all gestational ages. VI showed an upward trend with increasing PMA. LOESS growth curves for 36 weeks PMA showed significant variation among EP neonates between the 5th and 95th percentiles (Figure 1). Third quartiles (75th percentiles) were ≤2.7mm for IHW, < 4.6 mm for SCW, ≤3.5 mm for CCW, < 3.1mm for AHW, and ≤11.7mm for VI, as further indicated in Table 2. There was no significant sex difference for any measures.

Conclusion(s): The exploratory reference values demonstrate patterns in extra-axial spaces in EP neonates. Future research with longitudinal data is needed to determine if linear extra-axial space measures predict developmental outcomes.

Table 1. Maternal and neonatal demographics, clinical characteristics, pregnancy/delivery complications, neonatal morbidities, and interventions
Note. Parity includes the current pregnancy.
Abbreviations: ROP, retinopathy of prematurity; PDA, patent ductus arteriosus; NEC, necrotizing enterocolitis.

Figure 1. LOESS-smoothed percentile growth curves for extra-axial (A-E) and ventricular (F-I) measurements obtained from 2D HUS scans around day of life 7, and for extra-axial (J-N) and ventricular (O-R) measurements at 36 weeks postmenstrual age (PMA), plotted against PMA at the time of scan
Shaded areas indicate percentile ranges: dark gray represents the interquartile range (25th-75th percentiles), and light gray represents the 5th-95th percentile range. Solid lines depict the smoothed percentile curves, while black points indicate individual raw measurements.

Table 2. Two-dimensional head ultrasonography measurements by gestational age at birth around day of life 7 and 36-weeks postmenstrual age
Note. Values (mm) are presented as median (IQR; Q1-Q3), where Q1 represents the 25th percentile and Q3 the 75th percentile.
Abbreviations: IHW, interhemispheric width; SCW, sinocortical width; CCW, craniocortical width; anterior horn with, AHW; ventricular index.