Diagnostic ultrasound ( PDFDrive )

1178 PART IV Obstetric and Fetal Sonography
obstructive hydrocephalus). Alternatively, the site of blockage
may be outside the ventricular system, or there may be failure
of absorption (extraventricular obstructive hydrocephalus or
communicating hydrocephalus). Second and less oten, VM
results from excess CSF secretion with choroid plexus papillomas.
hird, VM can follow cerebral destruction and brain shrinkage
as a result of abnormal brain development or diverse insults
(hydrocephalus ex vacuo). Fourth, it may be a feature of generalized
cerebral malformation. Apart from the efects of the basic
underlying disorder, the degree of brain injury with HC varies
with age of onset and magnitude and duration of the dilation,
all of which afect periventricular axons, myelin, and microvasculature,
resulting in cerebrovascular injury, gliosis, and inlammation
and compensation by neuroplasticity. 66,82
Examples of Conditions Associated With
Ventriculomegaly
Obstructive hydrocephalus
Aqueduct stenosis (idiopathic, infections, bleeding,
X-linked, obstructing masses)
Spina biida with Chiari II malformation
Large choroid plexus cyst
Excess cerebrospinal luid (CSF) production
Choroid plexus papillomas
Destructive processes (encephaloclasis)
Vascular insult
Infection
Ischemia
Schizencephaly
Hydranencephaly
Cerebral malformations
Aneuploidy (trisomies 21, 18, 13)
Agenesis of corpus callosum
Vermian dysgenesis and Dandy-Walker malformation
Holoprosencephaly
Neuronal migration abnormalities (lissencephaly,
schizencephaly)
Microcephaly
Ultrasound Evaluation of Ventriculomegaly
he detection of VM is generally straightforward, but the
determination of its etiology can be diicult. Several approaches
to measuring ventricular size have been described: atrial width,
choroid separation, ventricle-to-hemisphere ratio, combined
anterior horn width, and visual anatomic appearance. Of these,
the universally accepted method is the transverse measurement
of the atrium of the occipital horn (see Figs. 34.3, 34.9A, and
34.11A). Methodological scanning can oten determine speciic
causes. 39 he size of the head is not helpful in detecting VM,
and frequently the BPD remains normal even with severe
ventricular enlargement. Nomograms of other parts of the
ventricles are available but not in common use. 83
In the irst trimester the choroid plexus should ill the
prominent-appearing lateral ventricle, except for the conspicuous
luid containing anterior frontal horn of the lateral ventricle,
which should not be mistaken for abnormality (see Fig. 34.1B).
VM manifests as a small-appearing choroid plexus with excess
surrounding luid. 8
Qualitative appearances suggesting ventricular enlargement
include convexity (outward bulge) to the lateral wall of the lateral
ventricle and asymmetrical position of the let and right choroids,
which fall with gravity when unsupported by ventricular walls
because the choroids are denser than CSF (“droopy” or “dangling”
choroids) (Fig. 34.11B, Video 34.5). With massive ventricular
enlargement, the interhemispheric structures, particularly the
septum pellucidum, undulate with maternal pulse and movements
and can become disrupted (fenestrate), allowing the let and
right lateral ventricles to communicate. he upper choroid can
fall across the midline through this hole and into the lower
ventricle (Fig. 34.11C).
Once ventricular enlargement is suspected, attention turns to
etiology and a detailed search for associated cerebral and somatic
abnormalities that may suggest speciic causes or syndromes.
Both let and right ventricles should be measured, and both
hemispheres evaluated. 5,39,67,68 Associated brain abnormalities
may be subtle and not readily appreciated on standard axial
scanning. Coronal and sagittal views both transabdominally
and transvaginally and use of 3-D multiplanar scans can be
especially helpful to detect abnormalities of the cerebellar vermis
and corpus callosum. 5,79 MRI adds additional information in 5%
to 50% of cases, especially with respect to parenchymal injury,
migrational disorders, ischemia, hemorrhage, and brainstem
abnormalities. 17,71,76,84-86
Fetuses with suspected VM should be evaluated by a knowledgeable
team with experience in the investigation, counseling,
management, and follow-up of prenatally discovered abnormalities.
Additional testing can be ofered including karyotype and
molecular analysis, testing for infection (especially CMV, Toxoplasma,
and rubella), platelet antibodies, and follow-up examinations
to follow ventricle growth and to detect additional
late-appearing indings that may relate to prognosis (porencephaly,
malformation of cortical development, hemorrhage). Postpartum
evaluation is important to evaluate for additional prenatally
unsuspected abnormalities and to plan treatments. 39,66,68,71,82
Prognosis relates to the degree of VM, progression of VM,
and especially the presence of associated abnormalities. In
cases of VM associated with chromosomal or other CNS and
somatic abnormalities, the prognosis and recurrence risk relate to
underlying conditions. 71,87 When VM is truly isolated, neurodevelopmental
outcome relates to the degree of enlargement. Normal
functional outcome is reported in about 85% to 96% of mild
(10-12 mm), 76% of moderate (12-15 mm), and 28% of severe
(>15 mm) cases. Outcome is better if VM is stable or decreases,
and worse with enlarging ventricles. Unilateral cases behave
similarly. 71,78,88,89
Counseling of parents remains diicult, and long-term outcome
remains guarded. Laskin and colleagues 88 reported that initially
85% of children had a favorable outcome, but this decreased to
79% by 20 months. Remember also that 2% to 3% or more of
entirely normal-appearing fetuses and children can also have
developmental disability, and it is not clear how this rate compares
with those with IVM. 71,76