Introduction
Spinal cord astrocytomas are quite uncommon and account for only 3% to 4% of all central nervous system (CNS) astrocytomas. Furthermore, although intracranial glioblastomas are the most common primary brain parenchymal neoplasm, spinal cord glioblastomas are exceedingly rare.
The characteristic asymmetric location of small spinal cord astrocytomas is due to the location of their peripherally located astrocytic cells of origin, as well as their affinity to grow along the spinal cord white matter tracts. Both on gross inspection and imaging evaluation, astrocytomas tend to be poorly defined with infiltration beyond the visible margins ( Figs. 34.1 and 34.2 ).
At the time of diagnosis many of these lesions are often quite extensive, on average covering five vertebral segments. These infiltrating astrocytomas therefore appear as expansile, T1 isointense/hypointense and T2 hyperintense lesions often spanning multiple levels ( Fig. 34.3 ). An association with NF-1 exists.
Evolution: Overview
Intramedullary spinal cord astrocytomas arise from spinal cord astrocytes that form part of the support structure of the CNS. Astrocytomas are characterized into four grades, including pilocytic astrocytoma (World Health Organization [WHO] grade I), diffuse, low-grade or fibrillary astrocytoma (WHO grade II), anaplastic astrocytoma (WHO grade III), and glioblastoma (grade IV). Spinal cord pilocytic astrocytomas generally displace the adjacent spinal cord tissue rather than infiltrate the cord ( Fig. 34.4 ). In contrast to the localized nature of spinal pilocytic astrocytomas, grade II-IV lesions are expansile, red-gray, glossy tumors spanning multiple spinal segments and characterized by their infiltrative nature and poorly defined planes. Grades II-IV are therefore referred to as infiltrative astrocytomas ( Fig. 34.5 ). Rare astrocytomas involving nearly the entire spinal cord are referred to as holocord tumors ( Fig. 34.6 ).
Distinct demographic characteristics are associated with the various subtypes; spinal cord pilocytic astrocytomas are more common in children, whereas fibrillary spinal cord astrocytomas are more common in adults. In other words, adults tend to present with higher-grade lesions, and malignant degeneration occurs in approximately 25% of adult astrocytomas. Approximately 85% to 90% of astrocytomas are low grade (fibrillary or pilocytic), 10% to 15% are high grade (predominantly anaplastic), and 0.2% to 1.5% are glioblastoma multiforme.
The initial step in management of an intramedullary spinal cord tumor is tissue diagnosis and resection of the safest maximum portion of the lesion. After a spinal cord astrocytoma has been diagnosed, the most important predictive factor is histologic grade (see Figs. 34.5 and 34.6 ). Although pilocytic astrocytomas lend themselves to complete or near complete resection, infiltrative astrocytomas are difficult and most often impossible to completely resect due to their lack of clearly delineated tissue planes. Because the tumor cells infiltrate normal spinal cord tissue, the development of a safe surgical dissection plane for total resection is usually precluded. Therefore surgery is generally limited to resection of obvious tumor while minimizing postoperative neurologic impairment ( Fig. 34.7 ). Furthermore, high-grade astrocytomas have a poor prognosis despite the degree of tumor resection, and surgical management is not infrequently limited to biopsy.
After a grade II-IV astrocytoma has been diagnosed, treatment generally consists of radiation therapy with the possible addition of chemotherapy. The characteristics and treatment of different grades of spinal cord astrocytoma are summarized in Table 34.1 .
| WHO Grade | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Percentage of all SCA | 27%–51% | 23%–29% | 14%–18% | 6%–12% |
| Imaging characteristics | Enhancing mural nodule, rim enhancement | Expansile, T2 hyperintensity | Expansile, T2 hyperintensity, and contrast enhancement | Expansile, T2 hyperintensity, and contrast enhancement |
| Treatment considerations | Surgical resection in well-selected patients | Biopsy with expansile duraplasty, XRT, resection can be considered if clear planes identified | Biopsy for tissue diagnosis, XRT, gross total resection often difficult, high risk of neurologic deficit with resection | Biopsy for tissue diagnosis, XRT, gross total resection often difficult, high risk of neurologic deficit with resection |
| Incidence of good resection planes at surgery | 29%–38% | <57% | <25% | <25% |
| Perioperative neurologic morbidity and mortality rate | 13%–33% | 40%–73% | >67% | >67% |
| 5-year survival rate | 67%–91% | 50%–63% | <23% | <11% |
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