Enlarged posterior fossa on prenatal imaging: differential diagnosis, associated anomalies and postnatal outcome
Anja Wüest1, Daniel Surbek1, Roland Wiest2
1Department of Obstetrics and Gynecology, Inselspital, University of Bern, Bern, Switzerland.
Insights
Enlarged posterior fossa (PF) in fetuses can indicate various conditions, with Dandy-Walker malformation being common. Many cases, like isolated megacisterna magna, have normal outcomes, but careful diagnosis is crucial for accurate prognosis.
Area of Science:
- Prenatal Diagnosis
- Fetal Medicine
- Neuroimaging
Background:
- Enlarged posterior fossa (PF) in fetuses presents diagnostic challenges.
- Understanding the prevalence and associated anomalies is crucial for accurate prenatal counseling.
- Evaluating postnatal outcomes is essential for assessing the impact of PF anomalies.
Purpose of the Study:
- To determine the prevalence of individual conditions and associated anomalies in fetuses with enlarged PF.
- To assess the diagnostic accuracy of ultrasound in identifying these fetal anomalies.
- To evaluate the postnatal outcomes of infants diagnosed with PF anomalies prenatally.
Main Methods:
- Retrospective analysis of fetuses with enlarged PF diagnosed via prenatal sonography (2001-2015).
- Inclusion of fetal MRI and volume ultrasound examinations for detailed assessment.
- Classification of PF anomalies included Dandy-Walker malformation (DWM), megacisterna magna (MCM), Blake's pouch cyst, vermian hypoplasia, vermian agenesis, arachnoid cyst (AC), and cerebellar hypoplasia (CH).
Main Results:
- Among 69 fetuses, MCM (n=29) and DWM (n=28) were most common.
- Associated malformations occurred in 37/69 cases; 13/41 karyotyped fetuses were aneuploid.
- Normal development was observed in 6/11 confirmed DWM cases and 12/12 isolated MCM cases; 8 false-positive diagnoses were noted.
Conclusions:
- Specific diagnoses for enlarged PF are necessary for optimal prenatal counseling.
- The term "Dandy-Walker variant" should be discontinued.
- Isolated MCM and Blake's pouch cyst may resolve or represent normal variants, but can also signify more severe anomalies.
Introduction:
The primary aim of this study was to ascertain the prevalence of the individual conditions and of associated anomalies in fetuses with the prenatal diagnosis of enlarged posterior fossa (PF) and to explore the diagnostic accuracy of ultrasound in these anomalies. The secondary aim was to evaluate the postnatal outcome of children affected by PF anomalies.
Material And Methods:
All fetuses with enlarged PF detected by prenatal sonography at a referral center from 2001 to 2015 were analyzed retrospectively. Some were also studied by fetal magnetic resonance imaging (MRI) or volume ultrasound examinations. Fetal sonographic and MRI were compared using following classification: Dandy-Walker malformation (DWM); megacisterna magna (MCM); Blake's pouch cyst; isolated vermian hypoplasia; vermian agenesis; PF arachnoid cyst (AC); and cerebellar hypoplasia (CH).
Results:
The ultrasound diagnoses of the 69 fetuses were as follows: MCM (n = 29; of these isolated n = 15), DWM (n = 28, isolated n = 4), vermian hypoplasia (n = 5, isolated n = 4), Blake's pouch cyst (n = 4, isolated n = 1), CH (n = 2; none isolated) and AC in the PF (n = 1, isolated). Thirteen of the 41 karyotyped fetuses were aneuploid, including seven with DWM. Associated malformations were found in 37/69 cases. There were 39 live births, including 11 with confirmed DWM, six of whom show a normal development. Twelve infants with isolated MCM show normal development. There were eight false-positive prenatal diagnoses (or resolution until birth) of "enlarged PF": three with Blake's pouch cyst, two with MCM and one with vermian hypoplasia.
Conclusions:
An enlarged PF requires specific diagnoses for the best possible counseling. The term "Dandy-Walker variant" should not be used anymore. Isolated MCM and Blake's pouch cyst can either resolve or be normal variants, but may also indicate the presence of a more severe anomaly or associated malformations.
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