Primary intraorbital extraocular primitive neuroectodermal (neuroepithelial) tumour.

A case is reported of primary primitive neuroectodermal (neuroepithelial) tumour occurring in the right orbit of a 52-year-old man. The intraorbital extraocular location is unique for this kind of neoplasm. The malignant tumour was differentiated into primitive neuroepithelial, ependymal, and oligodendroglial cells. The neuroglia was identified by localisation of cytoplasmic glial fibrillary acidic protein. It is suggested that this primary intraorbital, extraocular, primitive neuroectodermal tumour with neuroglial differentiation is akin to the primitive neuroectodermal tumours of the neuraxis, including the cerebellar medulloblastomas, and to some peripheral nerve tumours known as malignant neuroepitheliomas, malignant ependymomas, and neuroblastomas. The ectomesenchymal remnant of the neural crest or ectopic neuroepithelium or both may have been the origin of the present tumour. Differentiation of the neuroectodermal component of the neural crest or heterotopic neuroepithelium or both would create a primitive neuroectodermal tumour with diverse neuroglial elements.