ABSTRACT
INTRODUCTION Developmental cysts and other tumour-like conditions of the central nervous system (CNS) include epidermoid, dermoid, colloid, neurenteric and other benign cysts, as well as nasal glial heterotopia, inflammatory tumours and histiocytic disorders, the malignant lymphomas and other haemopoietic neoplasms covered separately in Chapter 40. Rathke cleft cysts, which are topographically and pathogenically closely associated with craniopharyngiomas, are covered separately in Pituitary and Suprasellar Tumours (Chapter 41). The epithelial cysts can be roughly divided into those of ectodermal (epidermoid, dermoid), neuroectodermal (ependymal, choroid plexus) and endodermal (Rathke cleft, colloid, neurenteric) origin. Secondary changes, such as epithelial atrophy, ulceration, squamous metaplasia and cyst rupture with haemorrhage, inflammation and granuloma formation are common and may hinder precise classification. Immunohistochemistry is helpful for further characterization, although some limited samples can only be descriptively diagnosed as ‘benign epithelial cyst’. In others, both the diagnosis and patient management rely heavily on a careful radiologic workup to rule out connections between intracranial and extracranial contents.
