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|Year : 2016 | Volume
| Issue : 4 | Page : 830-831
Prenatal Blake pouch cyst with hydrocephalus
Udaya Bhaskarini Vakakmudi1, Rajeswaran Rangasami1, Varalakshmi N Gopinath2
1 Department of Radiology and Imaging Sciences, Sri Ramachandra Medical College and Research Institute, Chennai, India
2 Department of Sonography, Abirami Scans, Puducherry, India
|Date of Web Publication||5-Jul-2016|
Dr. Udaya Bhaskarini Vakakmudi
Department of Radiology and Imaging Sciences, Sri Ramachandra Medical College and Research Institute, Chennai - 600 116, Tamil Nadu
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Vakakmudi UB, Rangasami R, Gopinath VN. Prenatal Blake pouch cyst with hydrocephalus. Neurol India 2016;64:830-1
A 38-year-old female patient with 38 weeks of gestation was referred for fetal magnetic resonance imaging (MRI) for the evaluation of her fetus who showed bilateral ventriculomegaly on antenatal sonography. Her 26 -week scan done in a rural hospital was reported as showing a prominent cisterna magna. The fetal MRI performed using the half-Fourier acquisition single-shot turbo spin echo (HASTE) sequence revealed dilatation of all the ventricles. The fourth ventricle was continuous with a cystic area that extended into the cisterna magna [Figure 1]a, [Figure 1]b, [Figure 1]c. The vermis, though visualized, was mildly displaced cranially along with the cerebellum [Figure 1]a. A radiological diagnosis of Blake pouch cyst (BPC) with hydrocephalus was made, and a postnatal follow-up MRI was advised. The postnatal MRI confirmed the findings of BPC with hydrocephalus [Figure 1]d, [Figure 1]e, [Figure 1]f. Before discharge, the parents were counseled and ventricular decompression procedure was advised.
|Figure 1: Sagittal T2-weighted magnetic resonance images (a) of the fetus show a dilated IV ventricle continuous with a retrocerebellar cyst (arrow). The vermis is visualized but mildly rotated anticlockwise (arrowhead). The inferior aspect of the membrane is visualized (broken arrow). Axial sections (b and c) show inferior communication of the IV ventricle withthe retrocerebellar fluid collection (open arrow) and dilatation of all the ventricles. Sagittal (d) and axial (e and f) T2-weighted magnetic resonance images of the neonate confirming the antenatal findings|
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Embryologically, the choroid plexus divides the roof of the fourth ventricle into an anterior membranous area and a posterior membranous area. Blake's pouch appears as a protrusion of the posterior membranous area of the fourth ventricular roof. Normally, Blake's pouch communicates with the subarachnoid space through the foramen of Magendie by 8 weeks and through the foramen of Luschka by 4–5 months. When the foramen of Magendie fails to perforate, there is dilatation of the Blake's pouch till the foramen of Luschka establishes equilibrium with the subarachnoid space leading to the development of BPC. Persistent BPC represents an embryonic midline outpouching of a portion of the primitive fourth ventricle, which extends inferiorly and posteriorly from the vermis into the cisterna magna and may push the developing tentorium into an abnormal, relatively high position. One-third to one-half of the cases show its spontaneous resolution  before birth due to late fenestration of the foramen of Magendie. In the remainder of cases, fenestration of the foramen of Magendie does not occur leading to features such as cystic dilation of the fourth ventricle without cisternal communication, tetraventricular hydrocephalus, a well-developed cerebellar vermis, with mild anticlockwise rotation [Figure 2]b.
|Figure 2: Diagrammatic representation of conditions with prominent retrocerebellar space. (a) Mega cistern magna—The vermis is not rotated, the cerebellum and vermis are developed. (b) Blake pouch cyst—The vermis is mildly rotated, the cerebellum and vermis are developed. (c) Dandy–Walker variant—The vermis is moderately rotated, the cerebellum and vermis are hypoplastic. (d) Dandy–Walker malformation—The vermis is severely rotated, the cerebellum and vermis are poorly developed|
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Persistent BPC needs to be differentiated from other conditions such as (a) mega cisterna magna, (b) Dandy–Walker variant, (c) Dandy–Walker malformation, and (d) posterior fossa arachnoid cyst. In the mega cisterna magna, cerebellum and fourth ventricle are normal, and there is no anticlockwise rotation of the vermis [Figure 2]a. In the Dandy–Walker variant, there is partial vermian and cerebellar hypoplasia with a moderate anti-clockwise rotation of the vermis [Figure 2]c. In Dandy–Walker malformation, there is abnormal development of the vermis, cerebellar hemispheres, severe anti-clockwise rotation of the vermis and enlarged posterior fossa with elevation of the tentorium and torcula herophili [Figure 2]d.
The clinical significance of persistent Blake pouch cyst is that it is a benign condition that resolves spontaneously; even when it presents with hydrocephalus, the condition gesnerally carries a good prognosis. On the other hand, in Dandy–Walker malformation, the prognosis is guarded. Hence, a precise diagnosis is important for patient counseling and management. Endoscopic third ventriculostomy is the treatment of choice in BPC associated with hydrocephalus.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]