- Department of Neurosurgery, Ibn Sina Hospital, Kuwait City, Kuwait
- Neonatal Intensive Care Unit, Ibn Sina Hospital, Kuwait City, Kuwait
- Department of Neurosurgery, Ain Shams Faculty of Medicine, Cairo, Egypt
Correspondence Address:
Waleed A. Azab
Department of Neurosurgery, Ibn Sina Hospital, Kuwait City, Kuwait
DOI:10.4103/2152-7806.137533
Copyright: © 2014 Azab WA This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.How to cite this article: Azab WA, Shohoud SA, Elmansoury TM, Salaheddin W, Nasim K, Parwez A. Blake's pouch cyst. Surg Neurol Int 24-Jul-2014;5:112
How to cite this URL: Azab WA, Shohoud SA, Elmansoury TM, Salaheddin W, Nasim K, Parwez A. Blake's pouch cyst. Surg Neurol Int 24-Jul-2014;5:112. Available from: http://sni.wpengine.com/surgicalint_articles/blakes-pouch-cyst/
Abstract
Background:In 1900, Joseph Blake described a transient posterior evagination of the tela choroidea of the fourth ventricle in the normal 130-day old human embryo. He was the first to recognize and fully elucidate on the real nature of the foramen of Magendie as an aperture, which develops within a saccular expansion of the embryonic fourth ventricular cavity. The persistence of this temporary fourth ventricular outpouching into the postnatal period and its significance either as separate entity or as an entity within the Dandy–Walker continuum has over the years been one of the most controversial topics in both neurosurgical and neuroradiological literature.
Methods:A search of the medical literature was conducted for publications addressing the historical, embryological, and neuororadiological features as well as the clinical presentation and management of persistent Blake's pouch.
Results:The literature on the various features of Blake's pouch cyst has limited areas of consensus between various authors.
Conclusion:Blake's pouch cyst is a rare entity that is thought to belong to the Dandy–Walker continuum. It has a variable clinical presentation and when symptomatic can be treated with an endoscopic third ventriculostomy or shunting.
Keywords: Blake's pouch cyst, Dandy–Walker continuum, endoscopic, ventriculostomy
HISTORICAL BACKGROUND
In 1900, Joseph Blake [
Figure 2
(a) Image No. 26 from Blake's original work[
In the original description of the Dandy–Walker malformation by Dandy and Blackfan in 1914, a huge cystic dilatation of the fourth ventricle with anterior displacement of the cerebellar vermis was described and attributed to primary atresia of the foramina of the fourth ventricle.[
In contrast, Harwood-Nash and Fitz introduced the term “Dandy–Walker variant” to describe conditions with posterior evagination of the anterior membranous area (AMA), partial vermian agenesis and a normal-sized posterior fossa,[
Imprecise anatomical descriptions of mega cisterna magna and Blake's pouch cyst can be traced in the literature to parallel the overlapping and sometimes misleading terminology of the entities within the Dandy–Walker complex. In 1949, Robertson described three cases with very large cisterna magnae demonstrated by pneumoencephalograms and autopsy findings in one of them. It was speculated that the cyst had an ependymal origin based on its microscopic features, position within the posterior fossa, absence of arachnoidal abnormalities, and the relationship of the choroid plexus to the cyst wall; he nevertheless gave no name to the malformations.[
Barkovich et al. in 1989 pointed out that a clear separation of the Dandy–Walker malformation, Dandy–Walker variant, and mega cisterna magna into classical categories was not possible because of the new information obtained from magnetc resonance (MR) images. They considered these anomalies to represent a continuum of developmental anomalies of the posterior fossa and introduced the term “Dandy–Walker complex”. They classified the cystic malforamations of the posterior fossa into two basic categories; Dandy–Walker complex and arachnoid cysts.[
It was only in 1996 when Tortori-Donati et al. added persistent Blake's pouch cyst as an independent entity within the Dandy–Walker complex and proposed a classification based on embryopathogenesis. They held the opinion that anomalies of the AMA would result in either a Dandy–Walker malformation or a Dandy–Walker variant, while anomalies of the posterior membranous area (PMA) would result in a mega cisterna magna or persisting Blake's pouch. These authors stressed that a CSF collection in the posterior fossa should be termed mega cisterna magna only when there is neither hydrocephalus nor signs or symptoms secondary to compression of the nervous and ventricular structures of the posterior fossa.[
Blake's pouch cyst is currently considered one of the anomalies within the spectrum of Dandy–Walker complex by many authors.[
EMBRYOLOGY [Figure 3]
During embryogenesis, the plica choroidea divides the roof of the fourth ventricle into an AMA and a PMA. Both AMA and PMA are essentially the definitive tela choroidea that forms the roof of the posterior portion of the fourth ventricle. The embryonic roof plate, which is the primordium of the tela choroidea (or AMA and PMA), is invaginated by developing vascular structures to form the choroid plexus. The choroid plexus is not attached directly to the vermis at anytime during embryogenesis. Differentiation of the meninx primitiva around the neural tube results in the formation of the subarachnoid space of the cisterna magna.[
Figure 3
Embryonic sequence of events in the development of the roof of the fourth ventricle. The plica choroidea (choroid plexus) divides the roof of the fourth ventricle into an anterior membranous area and a posterior membranous area (a). The cerebellar vermis originates from the anterior membranous area (b), which eventually disappears. Blake's pouch appears as a protrusion of the posterior membranous area of the fourth ventricular roof (c), which later communicates with the subarachnoid space forming the foramen of Magendie (d). AMA: Anterior membranous area, C: Cerebellum, CP: Choroid plexus, IV: Fourth ventricle, PMA: Posterior membranous area. (Illustration by Waleed Azab, MD)
Blake's pouch is a transient finger-like protrusion of the PMA of the fourth ventricular roof, which extends posteriorly into the meninx primitiva caudal to the cerebellum. It is initially an ependymal-lined closed cavity, which later communicates with the subarachnoid space at a point from the 7th or 8th week up to the 4th month of gestation to form the foramen of Magendie. Persistence of the pouch with variable separation from the fourth ventricle and lack of communication with the subarachnoid space results in enlargement of the pouch to form the Blake's pouch cyst.[
In the absence of anomalies of the AMA – that is, when the vermis, cerebellar hemispheres, and fourth ventricle are normal – a defect of the PMA may produce two distinct malformations, the mega cistern magna and persisting Blake's pouch.[
It is important to note that the cerebellum, including the vermis, develops from the rhombic lip and the alar plate of the metencephalon. The rhombic lip also is the histogenic origin of the purkinje cells, external granular cell layer that becomes definitively the internal granular cell layer, the golgi cells, stellate cells, and basket cells as well as Bergmann and Fananas glial radial cells. This is germane to Dandy–Walker spectrum, because the vermis is hypoplastic or absent in that condition. This would indicate a migratory and/or proliferation arrest that would lead to genetical, epigenetical or disruption to growth factors and morphogens as etiological factors in the Dandy–Walker spectrum. The tela choroidea (or membranous area) rostrally attaches to the floccular peduncle of the flocculo-nodular lobe and does not give rise to the cerebellar lobes.
Genetic, growth, and morphogenic factors could be causative factors. The fenestration of the tela choroidea in the formation of the foramen of Luschka and foramen of Magendie is commonly accepted. Developmental apoptotic factors may be at play in such fenestrations, which take place at defined anatomical locations. Variations in the location of these foramina are rare or nonexistent. Therefore, if there is failure to obliterate a specific region of a membrane, then molecular factors may be downregulated or mutated. Alternatively, a failure of the choroid plexus to normally develop along with fenestration delays of the tela choroidea could also be taking place secondary to deviation of expression of growth factors or their receptors. Examples of such factors would include Vascular endothelial growth factor and its receptor (VEGF/VEGF-R), platelet derived growth factor and its receptor (PDGF/PDGF-R), transforming growth factor (TGF) isoforms, bone morphogenic protein, aquaporin/carbonic anhydrase (both noted in the choroids plexus) angiopoietin and its tyrosine kinase with immunoglobulin-like and EGF-like domains (TIE) receptors. Type II lissencephaly and Walker–Warburg syndrome/Fukuyumu muscle–eye–brain syndrome are associated with Dandy–Walker cyst in 50% of the cases. There is a 9q31-33 or 17 chromosomal defect in this complex. Even if there are no studies to demonstrate specifics, it is important to think in the direction of molecular etiological factors and not just be limited to evaginating mechanical origins of Blake's pouch cyst. Including the spectrum of molecular and genetical factors will be critical in future assessments as to a Blake's pouch cyst being a Dandy–Walker variant and/or continuum. The answer to these questions will come in the future not from a mechanical explanation, but a complex dysgenesis secondary to genomic/molecular errors with and without secondary mechanical consequences. The aqueductal stenosis, corpus callosal agenesis, cerebellar vermian hypoplasia, and encephaloceles of Dandy–Walker syndrome go beyond any mechanical origin to a singular effect of a delay in fenestration of the tela choroidea foraminal openings and is rather a more global central nervous system (CNS) developmental error.
RADIOLOGICAL FINDINGS [Figures 4 and 5]
The differential diagnosis of Blake's pouch cyst includes all other posterior fossa cysts in the Dandy–Walker complex [
Figure 4
Diagrammatic representation of the cerebellar vermis in various entities within the Dandy–Walker complex. (a) Mega cisterna magna. Normal cerebellum and fourth ventricle. (b) Blake's pouch cyst. The vermis is relatively well-developed and nonrotated along with a cystic dilation of the fourth ventricle (c) Dandy-Walker malformation. Rotated small vermis with abnormal foliation and enlarged posterior fossa with elevation of the tentorium and torcula herophili. (d) Dandy-Walker variant. Partial vermian and cerebellar hypoplasia with a prominent retrocerebellar space. (Illustration by Waleed Azab, MD)
Figure 5
(a) Sagittal T2 - weighted MRI image in a case with Blake's pouch cyst. Note the infracerebellar position of the cyst with compressed nonrotated relatively intact cerebellar vermis. The continuation of the fourth ventricular choroid plexus into the Blake's pouch cyst (white arrowhead) and the thin membrane demarcating the cyst from subarachnoid space (black arrowhead) are evident. (b, c) Images from one case reported by Cornips et al.2011[
Prenatal ultrasound usually reveals a large cisterna magna in many cases of Blake's pouch cyst,[
Typically, the radiological features of a Blake's pouch cysts [BPC] are (1) tetraventricular hydrocephalus, (2) infra- or retrocerebellar localization of the cyst, (3) a relatively well-developed, nonrotated cerebellar vermis, (4) a cystic dilation of the fourth ventricle without cisternal communication, and (5) some degree of compression on the medial cerebellar hemispheres. Ideally, one may see the fourth ventricular choroid plexus continuing in the roof of the cyst on sagittal MR images.[
Other imaging features include a large posterior fossa and anterior displacement of the brainstem against the clivus.[
Blake's pouch cysts usually communicate with the fourth ventricle.[
CLINICAL PRESENTATION AND TREATMENT
Clinically, Blake's pouch cysts may present with impaired neurological development, progressive hydrocephalus in young age, become symptomatic in adulthood or remain asymptomatic.[
The number of case series of Blake's pouch cyst and therefore data on its clinical spectrum and treatment options remains very limited. Gilles and Rockett in 1971 treated cysts thought to be originating from remnants of Blake's pouch with cyst wall excision and ventriculoureteral shunt insertion.[
Table 1
Clinical presentations, treatment and outcome of the series by Cornips et al., 2010[
CONCLUSION
Blake's pouch cyst is a rare entity that is thought to belong to the Dandy–Walker continuum. It has a variable clinical presentation and when symptomatic can be treated with an endoscopic third ventriculostomy or shunting.
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