Widened subarachnoid space in pre-discharge cranial ultrasound: evidence of cerebral atrophy in immature infants?

Cerebral biometry at birth and at 4 and 8 months of age. A prospective study using US

BACKGROUND

Although longitudinal reference intervals for ventricular size are crucial for the diagnosis of dilated ventricles, such data are sparse.

OBJECTIVE

To establish references for ventricular measurements at birth, and at 4 and 8 months follow-up, and to examine the inter-observer variation of the measurements.

MATERIALS AND METHODS

This prospective, longitudinal study included 120 term newborns (boys 65, girls 55), mean age 1.5 days on initial scans, with re-examination at 4 months and 8 months of age. One examiner performed all the examinations, measuring: ventricular index, frontal horn width, third ventricle width, frontal subarachnoid space depth, optic nerve sheath diameter and resistive index.

RESULTS

One hundred eight (90%) and 90 (75%) of the infants, respectively, attended for follow-up at 4 and 8 months of age. All measures increased with age, except for the depth of the subarachnoid spaces that showed an initial rise, followed by a mild drop at 8 months, and for the resistive index that remained stable at 0.6. The increase was particularly significant for frontal horn width with an increase from 2.2 mm at birth to 6.5 mm at 4 months in boys, and 2.1-5.8 mm in girls. The agreement between two observers was fair to moderate for most of the measurements.

CONCLUSION

The increase in the width of the frontal horns between birth and 4 months of age, as well as the wide normal range found among all three age groups are noteworthy and should inform future diagnostics.

A limited range of measures of 2-D ultrasound correlate with 3-D MRI cerebral volumes in the premature infant at term

Two-dimensional (2-D) cranial ultrasound (US) is the principal method for the detection of cerebral injury in the newborn. The aim of this study was to compare 2-D sonographic methods with more advanced 3-D magnetic resonance imaging (MRI) for assessing brain structure. From July 1998 to November 2000, we conducted a prospective methodological study comparing 2-D cranial sonographic measurements with volumes of cerebrospinal fluid (CSF), white matter, grey matter and total volume of brain obtained using 3-D MRI. The study group comprised 63 infants (33 boys), mean gestational age 28 weeks (range 23 to 33 weeks), with imaging studies within 15 days of term equivalent. The highest correlations were between the occipital horn length and total brain volume (R2 = 0.30), the subarachnoid space and both CSF volume (R2 = 0.46) and relative intracranial space occupied by brain tissue (R2 = 0.48). Only 8 (30%) of the 2-D cranial US measures demonstrated good reproducibility. 2-D sonographic measures are limited in reflecting variations in overall cerebral structure, although certain measures, such as subarachnoid space and occipital lobe measures, may be useful in better defining cerebral parenchymal and CSF volumes.

Ventriculomegaly, delayed myelination, white matter hypoplasia, and "periventricular" leukomalacia: how are they related?

Preterm infants, including some who have sustained intracranial hemorrhage, appear to be at increased risk of lateral ventricular enlargement. Although some occurrences might be due to an impairment of cerebrospinal fluid flow or absorption, many instances of ventriculomegaly without accompanying macrocephaly reflect diffuse white matter damage resulting in diminished (i.e., hypoplastic) white matter or an inadequate density of axons. Perinatally acquired widespread white matter damage is sometimes associated with the focal white matter necrosis. We hypothesize that in some infants both ventriculomegaly and delayed myelination are consequences of disturbances to myelinogenesis that result from an impairment of cells destined to become oligodendroglia or of disturbances to rapidly growing axons. The vulnerability of developing white matter in preterm newborns might, in part, reflect the diminished availability of growth/ survival factors, or a vulnerability to toxins or physiologic perturbations. Awareness that some ventriculomegaly reflects widely distributed white matter damage should prevent overtreatment of what might appear to be hydrocephalus, but is not due to impaired cerebrospinal fluid dynamics. Increased understanding of the phenomena leading to ventriculomegaly related to paucity of white matter should lead to successful efforts to prevent white matter damage in preterm newborns.

Temporary Enlargement of the Subarachnoid Space in Very Premature Infants

The authors used a high-frequency, 10-MHz ultrasound transducer to improve near field de- tails on cranial ultrasound scans to detect enlargement of the subarachnoid space without ventriculomegaly on the first day of life in 14 of 17 premature infants on mechanical ventilation for respiratory distress syndrome secondary to lung immaturity and in 1 of 9 premature infants with mild or no respiratory problems. Factors correlated with this finding were a birth weight of less than 1250 g (P ≤ 0.05), gestational age of 28 weeks or less (P ≤ 0.02), presence of respiratory distress (P ≤ 0.01), and necessity of mechanical ventilation (P ≤ 0.001). Enlargement of the subarachnoid space regressed completely during the neonatal period. Enlargement of the subarachnoid space in very premature infants is indicative of brain immaturity.