ABSTRACT
The central nervous system, i.e. the brain and the spinal cord, is composed of two types of tissues, both involved in disease processes. The first consists of the highly specialized nerve cells and the neuroglial cells, all of which are neuroepithelial in origin. The second comprises the meninges, the blood vessels and their supporting connective tissue, all derived from mesoderm, and the microglia. Meningiomas are solid, lobulated tumours, well demarcated from the brain tissue into which they project, forming a depression. The tumours of the eyelid, conjunctiva, and orbital tissues do not differ significantly in morphology and behaviour from those occurring elsewhere. Spontaneous, non-familial tumours are usually unilateral and present at a later age. The tumour is composed of small, round cells with scanty cytoplasm and a high mitotic rate. Tumour cells may spread through the subarachnoid space, sometimes without an associated deposit of solid tumour in the brain or spinal cord.
