From our study of eight pineoblastomas and five pineocytomas and a review of the literature, we have described two clinicopathologic syndromes that characterize these neoplasms. Pineoblastomas highly resemble the medulloblastoma-neuroblastoma group of tumors and occur mostly in young people. The tempo of progression of the disease is fast, the length of illness is short. These are infiltrating neoplasms that commonly spread via the cerebrospinal fluid. They are radiosensitive. Histologically they are also similar to the medulloblastoma-neuroblastoma group and are characterized by the scarcity of cytoplasmic processes and by the Homer Wright rosette. They contain giant cells. Pineocytomas are tumors of adults. The tempo of progression of the disease is slow, and the length of illness is long. They expand by compressing the surrounding tissues. Histologically they are characterized by the abundance of cytoplasmic processes and by the pineocytomatous rosette. They contain giant cells. Areas composed of neoplastic gangliocytes and astrocytes in various combinations are common variants in some of these neoplasms.

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This communication deals solely with a group of cases, hitherto rather obscure, in which damage to the cervical part of the spinal cord occurs without radiographic evidence of vertebral injury or displacement. Two alternative explanations of such injury have been postulated. The first is that the spinal cord pressure is due to acute massive prolapse of an intervertebral disc : but our limited experience of this lesion suggests that as a rule this is recognisable on radiographic examination by narrowing of the intervertebral space. The second explanation is that paraplegia is due to hyperfiexion dislocation which undergoes spontaneous reduction ; but it is doubtful whether this occurs at all, because forward flexion or dislocation of the cervical spine which is sufficient to damage the cord would necessarily be associated with locking of the articular facets, or crush fracture of a vertebra, or both. Neither of these lesions undergoes spontaneous reduction, and moreover both are demonstrable by radiographic examination. \Ve suggest that the usual mechanism of these injuries, in which radiographic examination reveals no significant displacement, is forced hyperextension.

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