This article includes discussion of ependymal cysts, glio-ependymal (glioependymal) cysts, neuroepithelial cysts, solitary ependymal cysts, multiple ependymal cysts as part of a congenital malformation syndrome, and ependymal cysts due to a genetic ciliopathy. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Ependymal cysts within or adjacent to the brain and spinal cord most probably arise during the embryo-fetal period and may be silent for a long period to become symptomatic through their space-occupying properties at any age, including the fetal period and adulthood. This entity presents as cyst of ependymal epithelial origin, probably arising by budding and separating from the embryonic central canal and presenting as a space occupying process, at any time during life. They have to be differentiated from neoplastic cysts, arachnoid cysts, neurocysticercosis, and enterogenous cysts. A subgroup arises as part of multisystem disorders, such as orofaciodigital syndromes and Aicardi syndrome. The outcome of treatment of solitary cysts has vastly benefited from the application of endoscopic neurosurgery. The improvement in neurosurgical techniques underlines the need for refined differential diagnosis, separating this group from malignant cystic tumors such as cystic gliomas by making use of neuroradiological and histopathological characteristics. A separate group of ependymal cysts is formed by congenital disorders with multiple ependymal cysts. In this article, the author, whose special interest is in developmental and genetic disorders, reviews the present knowledge of ependymal cysts.
• Ependymal cysts arise from focal collections of ependymal cells, inside or outside the brain and spinal cord.
• Ependymal cysts may become space occupying and may require neurosurgical intervention.
• Ependymal cysts can arise as part of congenital malformation syndromes such as Aicardi syndrome or orofaciodigital syndromes.
Historical note and terminology
Different types of nonmalignant space-occupying cysts are associated with the central nervous system. The first case reports of ependymal cysts date from the thirties cited by Friede and Yasargil (Friede and Yasargil 1977). Gradual improvement in pathological techniques, using electronmicroscopy of the cyst wall, and antibody staining helped to refine the diagnostic criteria. Because of the rarity of the diagnosis, most of the literature has accrued from case reports, mentioned in this article. Clinical interest in ependymal cysts centers on 2 different entities:
(1) Ependymal cysts may present as solitary space-occupying cysts with clear fluid, originating inside the central nervous system or its surrounding membranes. In the transverse axis they may arise anywhere between the central canal or cerebral ventricles and the leptomeningeal spaces surrounding the brain and spinal cord. Growth in volume may prompt symptoms at any age. Proper radiological and neuropathological diagnosis of this essentially benign process is required to exclude other space-occupying lesions such as cystic gliomas and arachnoid cysts. Treatment results have improved through better differential diagnosis and refined neurosurgical interventions in the last decades.
(2) Multiple ependymal cysts may arise as part of a congenital disorder, some of which may carry a genetic risk for recurrence.
The group of true intracranial epithelial cysts includes ependymal (also known as glioependymal cysts) and enterogenous cysts. Ependymal cysts develop as ectopic ependyma, with the inner layer recognizable as ependyma. They contain an outer layer of neuroglial tissue (astrocytes). However, ependymal cells themselves may also be positive for astroglial immunostaining. A layer of connective tissue on the outside may be present due to vascularization. These cysts may arise in any place within or surrounding the central nervous system. They may be the only structural abnormality, or they may form part of a compound cerebral and extracerebral malformation syndrome.
Ependymal cysts may be space occupying, either by displacement of adjacent structures or by obstructing CSF circulation. Clinical signs are due to these effects or to associated malformations (callosal dysgenesis, neuronal heterotopia, cortical dysplasia) or associated malformation syndromes (orofaciodigital syndromes, especially types I and II, and Aicardi syndrome).
Antibody staining on ependymal cyst specimens allows their differentiation (Coca et al 1993; Nagano et al 2010; Park et al 2012). Ependymal cysts are immunoreactive for glial fibrillary acidic protein (GFAP) and S-100, both glial markers expressed by normal ependymal epithelium. Cytokeratin staining is positive in ependymal as well as in cysts that develop from non-neural epithelia, such as colloid cysts and enteric cysts, but the latter display negative results for glial markers (Lach et al 1993). Inoue and colleagues studied a variety of epithelial cysts and found S-100 positive and GFAP negative in 2 neurenteric cysts and a case of colloid cyst (Inoue et al 1988). Therefore, S-100 may be less specific for ependymal cysts than GFAP.
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