A boy had been born to a 28-year-old mother who had chronic hepatitis B virus (HBV) infection, gestational diabetes, and late prenatal care beginning at 19 weeks of gestation. At 29 weeks of gestation, an enlarged cisterna magna of 1.1 cm had been discovered on fetal ultrasonography. Repeated measurement at 36 weeks had shown a dilation of 1.2 cm. The child was large for gestational age, and thus the mother had undergone elective cesarean delivery.
After delivery, the neonate’s Apgar score was 8 at 1 minute and 9 at 5 minutes of life. His birth weight was 4850 g, birth length was 53 cm, and birth frontal occipital circumference was 35.5 cm. The patient was admitted to the nursery, was monitored closely for hypoglycemia, and was administered the HBV vaccine and immunoglobulin. Postnatal ultrasonography confirmed a diagnosis of mega cisterna magna (MCM).
In the nursery, he developed tachypnea and temperature fluctuations that self-resolved, and he did not have any hypoglycemic events. Additional physical examination findings included caput succedaneum and bilateral hydroceles. He was discharged home after a 4-day hospital stay. At 2-week and 2-month follow-up visits, the boy was developing normally and was meeting developmental milestones.
Discussion. A posterior fossa malformation (PFM) occurs in 1 in 5000 live births. Cerebellar vermis malformations are a subset of PFMs that are sometimes described on a spectrum known as the Dandy-Walker continuum. This continuum includes various anomalies such as Dandy-Walker malformation, Dandy-Walker variant, inferior vermis hypoplasia, and mega cisterna magna.
Cisterna magna, also known as posterior cerebellomedullary cistern, is a dilation of the subarachnoid space located in the region posterior to the medulla and caudal to the cerebellum. If this dilation is greater than 10 mm measured from the posterior side of the cerebellar vermis to the inner aspect of the occipital bone, with the concomitant presence of a normal vermis and fourth ventricle, it is then categorized as enlarged or mega cisterna magna.
Most cases of MCM are found prenatally but may not be discovered until after birth. MCM appears to have a male predominance, with 3.75 reported cases among males for every 1 reported case among females. MCM can be an isolated condition; however, as many as 62% of cases are associated with other chromosomal, central nervous system (CNS), or extra-CNS anomalies. In a meta-analysis that included 144 fetuses with MCM, 12.6% had additional CNS anomalies such as ventriculomegaly (the most common), cerebellar hypoplasia, and arachnoid cysts. Extra-CNS anomalies were found in 16.6% of the fetuses. The most common extra-CNS anomalies were renal defects such as horseshoe kidney.
Although children born to mothers with diabetes have higher rates of CNS anomalies such as caudal regression syndrome, anencephaly, holoprosencephaly, and spina bifida, no evidence in the literature shows an increased prevalence of MCM in infants born to mothers with pregestational or gestational diabetes. In our patient, prenatal care had been initiated at 19 weeks, and it is unknown whether the mother had hyperglycemia in the first 8 weeks of pregnancy, during the crucial period of organogenesis. Nonetheless, this case suggests gestational diabetes as having a potential association with MCM.
Developmental or cognitive delay occurs in as many as 8% of patients with MCM; however, the full impact of this condition on language and behavioral development is still unknown. A study of 123 fetuses with isolated MCM or MCM in conjunction with other CNS anomalies (ie, nonisolated MCM) followed the cases of these patients for the first 2 years of life to assess for developmental deficits. The study found slight impairments in gross motor skills and adapting abilities in the isolated MCM group compared with the control group. The group of patients with nonisolated MCM scored significantly lower than the control group and the isolated MCM group in gross motor skills, fine motor skills, adapting ability, language, and social behavior categories of the Gesell Developmental Schedules. However, in general, children with isolated MCM (such as our patient) have a favorable neurodevelopmental prognosis, with normal development occurring in more than 90% of cases.
Recently, prenatal imaging techniques have improved, leading to more frequent and earlier diagnosis of MCM. These developments have made parental counseling increasingly important after diagnosis and crucial in patient follow-up after birth. However, due to the paucity of literature on MCM and other PFMs, understanding of the clinical implications and prognosis of these abnormalities remains very limited. This lack of information makes it more difficult for clinicians and families to make decisions about the care of these patients. One set of data indicates that nearly 80% of parents prefer to abort fetuses identified with PFAs in some parts of the world. This may be unwarranted, given that cases of isolated MCM have a favorable developmental prognosis.
Dharmarpandi JM, Martini A, Naqvi M. Mega cisterna magna. Consultant. 2018;58(6):e189.
Bolduc ME, Du Plessis AJ, Sullivan N, Khwaja OS, Zhang X, Barnes K, Robertson RL, Limperopoulos C. Spectrum of neurodevelopmental disabilities in children with cerebellar malformations. Dev Med Child Neurol. 2011 May;53(5):409-16.
Advances in perinatal care and neuroimaging techniques have increased the detection of cerebellar malformations (CBMs) in the fetus and young infant. As a result, this has necessitated a greater understanding of the neurodevelopmental consequences of CBMs on child development. The aim of this study was to delineate the impact of CBMs on long-term neurodevelopmental outcomes.
We conducted a cross-sectional study and systematically identified children with CBMs born between December 2000 and December 2006. We then performed follow-up magnetic resonance imaging studies, neurologic examination, and standardized neurodevelopmental outcome testing (Mullen Scales of Early Learning, Vineland Adaptive Behavior Scale, Child Behavior Checklist, Modified Checklist for Autism in Toddlers, and the Pediatric Quality of Life Inventory).
Our sample comprised 49 children (29 males, 20 females; mean age, 28.4 mo, SD 16.4) with a CBM. Infants with evidence of acquired fetal or neonatal brain injury, intracranial birth trauma, inherited metabolic disease, or major pre- or postnatal cerebral ischemia were excluded. Our findings highlight that children with CBMs experience a high prevalence of neurologic, developmental, and functional disabilities including motor, cognitive, language, and social-behavioral deficits, as well as poor quality of life. The associated supratentorial anomalies, chromosomal findings, and malformations affecting the cerebellar vermis were significant independent predictors of neurodevelopmental disabilities in young children with CBMs. The associated supratentorial anomalies and chromosomal findings were also predictive of global developmental delay (p=0.01), cognitive impairment (p=0.03), gross and fine motor delay (p=0.02 and p=0.01 respectively), and positive screening for autism spectrum disorder (p=0.01). Additionally, malformations affecting the cerebellar vermis were significant independent predictors of expressive language (p=0.04) and gross motor delays (p=0.02).
Developmental surveillance and early intervention programs should be an integral part of the long-term follow-up of survivors of CBM.
From the paper:
Despite these advances, the long‐term neurodevelopmental consequences of cerebellar malformations in children remain poorly defined. However, their consideration requires stressful and often critical decisions from both clinicians and families. This is particularly important in view of the fact that studies are now showing that up to 80% of parents choose to terminate their pregnancy after a prenatal diagnosis of a cerebellar malformation, even in the absence of rigorous outcomes data.
Sources for the latter statement:
Ecker JL, Shipp TD, Bromley B, Benacerraf B. The sonographic diagnosis of Dandy-Walker and Dandy-Walker variant: associated findings and outcomes. Prenat Diagn. 2000 Apr;20(4):328-32.
Outcomes of pregnancies with sonographically diagnosed Dandy-Walker (DW) or Dandy-Walker variant (DWV) syndromes vary widely. We examined our own experience with these diagnoses in an effort to identify those sonographic features that best predicted neonatal outcome. We identified 50 fetuses with DW and 49 with DWV diagnosed sonographically. Eighty-six per cent of fetuses with DW and 85% of fetuses with DWV had other sonographically identifiable anomalies, the most common being ventriculomegaly (DW: 32%; DWV: 27%) and cardiac defects (DW:38%; DWV: 41%). Forty-six per cent and 36% of available karyotypes in cases of DW and DWV, respectively, were abnormal. 50 out of 99 women in our series elected pregnancy termination. Only three pregnancies with DW resulted in a living infant, and only one of these had a normal paediatric examination at six-week follow-up. Thirteen out of 49 infants with DWV survived the neonatal period and 7 of 13 were reported initially as normal infants, including six with an isolated finding of DWV. We conclude that overall, the prognosis for these posterior fossa defects is grim but not uniformly fatal. The presence of other anomalies is associated with the worst prognosis. Isolated Dandy-Walker variant has the highest chance of leading to a normal neonate.
Forzano F, Mansour S, Ierullo A, Homfray T, Thilaganathan B. Posterior fossa malformation in fetuses: a report of 56 further cases and a review of the literature. Prenat Diagn. 2007 Jun;27(6):495-501.
The purposes of this study were to determine the outcome of fetuses diagnosed as having a posterior fossa abnormality (PFA) and to find out if there are associated features helpful in determining the prognosis.
This is a retrospective study of all posterior fossa abnormalities detected prenatally in our Units within the last 10 years. Fifty six patients were selected. Outcome data was collected from the Clinical Genetics Department records and the attending obstetrician or pediatrician.
An enlarged cisterna magna (ECM, diameter greater than 10 mm at 18-23 gw) was detected in 22 fetuses, which was isolated in 14 cases. All the patients followed-up (n = 11) with isolated ECM were normal at birth (100%). Non-isolated ECM was present in 8 cases. Further information was available in 7, 5 (71%) of whom had a poor outcome. A Dandy Walker complex abnormality (DWC) was detected in 34 patients. The majority of them had a poor prognosis, 54% if isolated and 84% if non-isolated.
Isolated ECM detected on prenatal scans has a favourable outcome, while DWC is associated with a very high chance of a poor prognosis.