Journal of Neuro-Oncology 47: 253–270, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. Hemangioblastomas and other uncommon intramedullary tumors Daniel J. Miller and Ian E. McCutcheon Department of Neurosurgery, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA Key words: ganglioglioma, hemangioblastoma, intramedullary tumor, metastasis, subependymoma Summary Astrocytoma and ependymoma make up 90% of intramedullary tumors between them. However, a host of less com- mon tumors form the remaining 10%: these include hemangioblastomas, subependymomas, gangliogliomas and other neuronal variants, metastases from extraneural cancers, and a host of other lesions that typically occur intracra- nially but which present on rare occasions in the intramedullary location. Most neurosurgeons will encounter the unusual tumors of the spinal cord described in this review only a few times during their professional careers, but it is nevertheless important to recognize the distinct radiological and intraoperative features of those for which signif- icant series of patients have been accumulated. Metastases and germinomas aside, the other neoplasms described here are relatively benign in their clinical and histological behavior, and can be meaningfully resected by careful microsurgical technique. Introduction From the initial days of diagnosis and exploration based solely upon neurological examination and plain radiographs, through the era of myelography [1], then computed tomography (CT) [2], our understanding of uncommon spinal cord tumors has only slowly pro- gressed. Technical advances such as magnetic reso- nance imaging (MRI) [3–6], electron microscopy [7,8], and histochemical techniques [9,10], have contributed greatly to the present understanding of these lesions. MRI should now increase the incidence of discovery of previously ‘rare’ entities and their hidden subtleties [11,12]. Advances in immunohistochemistry [13–15] and molecular genetic analysis [16,17] will further characterize these entities. Still, given their actual rarity, information about uncommon intramedullary tumors can only be compiled slowly, case by case and decade by decade. The objective of this paper is to sum- marize what is known about each of these less common intramedullary tumors. Histology In order to simplify comprehension of which type of intramedullary spinal cord tumors can occur, one needs only to bear in mind which cell type occur within the central nervous system (CNS). A general simi- larity exists between the brain and spinal cord with regards to cellular types and therefore tumor types, although the prevalence of each type varies between these two anatomic locations. Indeed, it is likely that the biology of any tumor growing from constituents of the spinal cord will differ from that of histolog- ically similar tumor growing in the brain. The cel- lular constituents of the CNS are neuroectodermal or mesenchymal. The neuroectodermal elements are either neurons or glia (astrocytes, oligodendroglia, and ependymocytes). The mesenchymal elements are meninges, blood vessels, adipose tissue, and microglia. Microglia are macrophages/monocytes and are part of the reticuloendothelial system. This delineation of the cellular constituents leads directly to a better com- prehension of the tumor types as they are derived from these cell lineages and named according to their histological similarity to the architecture of nor- mal tissues during development (Table 1) [18]. In order to better appreciate the above delineation of intramedullary tumor types as they relate to histolog- ical cellular elements, as well as their overall inci- dence, two large series of intramedullary tumors may be cited: (1) 301 cases from the Mayo clinic over a 45-year period [19], (2) 159 cases from the University