Introduction
Background
Astrocytomas of the spinal cord are rare tumors that arise from astrocytes in the spinal cord and occur in the adult and pediatric populations. Most spinal cord astrocytomas are benign, low-grade tumors that are readily diagnosed with magnetic resonance imaging (MRI). These tumors characteristically cause the spinal cord to appear expanded, often with cysts and a variable enhancement pattern.
In the past, few treatment options were available for these astrocytomas. However with the advent of modern surgical techniques, intraoperative microscopy, intraoperative ultrasonography, ultrasonic aspiration, and electrophysiologic monitoring, most intramedullary spinal cord tumors can be surgically removed, with acceptable morbidity and mortality rates.
(Also see the eMedicine articles Astrocytoma [Oncology], Astrocytoma, Brain [Radiology], and Low-Grade Astrocytoma [Neurology].)
Pathophysiology
The 4 types of macroglial cells found in the central nervous system (CNS) are astrocytes, Schwann cells, oligodendrocytes, and ependymal cells; these cells serve a variety of supportive functions. Astrocytomas arise from astrocytes, which provide structural and metabolic support to the CNS.
On microscopy, spinal cord astrocytomas are similar in appearance to cerebral astrocytomas. In general, astrocytomas are divided into 2 groups: diffuse fibrillary astrocytomas and specialized (or circumscribed) astrocytomas.
Diffuse fibrillary astrocytomas of the CNS include low-grade astrocytomas, anaplastic astrocytomas (high grade), and glioblastomas (high grade). Most spinal cord astrocytomas are diffuse fibrillary astrocytomas. Approximately 80% of spinal cord astrocytomas are low grade in histology. Specialized (circumscribed) astrocytomas of the CNS include pilocytic astrocytomas, subependymal astrocytomas, subependymal giant-cell astrocytomas, pleomorphic xanthoastrocytomas, and desmoplastic cerebral astrocytomas of infancy.
The specialized astrocytomas distinguish themselves from the diffuse, low-grade astrocytomas in that they show astrocytic differentiation and do not widely infiltrate the adjacent CNS parenchyma. As such, the specialized astrocytomas are easier to surgically remove than diffuse fibrillary astrocytomas. Consequently, more complete surgical resections — and therefore better long-term prognoses — are obtained with specialized astrocytomas than with diffuse, low-grade lesions.
The cause of astrocytomas — or, for that matter, all glial tumors — is unknown. However, the literature does describe chromosomal abnormalities and overexpression of oncogenes as possible causes of spinal cord astrocytomas. Nonetheless, to the authors' knowledge, the available data or research findings do not explain the exact cause of these tumors.
Frequency
United States
Spinal cord tumors are rare, with an incidence of 1.1 cases per 100,000 people, and represent 4-10% of all CNS tumors. Approximately 30% of pediatric and adult intramedullary spinal cord tumors are astrocytomas. Together, astrocytomas and ependymomas account for approximately two thirds of all intramedullary spinal cord tumors, with astrocytomas the most common in the pediatric population and ependymomas the most common in adults.
The most common tumors that involve the spine are metastatic disease to bone. Lung, breast, prostate, and other cancers can spread hematogenously to the vertebral bodies or to the epidural soft tissues. Metastatic disease accounts for about 55% of all tumors that involve the spine.
(Also see the eMedicine articles Ependymoma [Neurology], Ependymoma [Oncology], and Ependymoma, Spine [Radiology].)
Mortality/Morbidity
Mortality
Most spinal cord gliomas are benign, low-grade neoplasms, and it has been well documented that radical surgery can decrease the neurologic symptoms and increase survival time.1,2,3 If a patient with a low-grade astrocytoma of the spinal cord undergoes a gross total resection, the likelihood of progression-free survival at 5 years is greater than 50%.1
PrognosisHigh-grade astrocytomas of the spinal cord are associated with a poor prognosis. On occasion, a low-grade astrocytoma of the spinal cord can progress to a malignant astrocytoma. This transformation and progression can take months to years.
MorbidityMany potential complications are associated with surgical resection of a spinal cord astrocytoma. The risk of a postoperative motor deficit in a patient without preoperative weakness is approximately 5%. If a patient has motor weakness before surgery, the risk of a motor deficit is increased postoperatively.2 Injury to the posterior columns of the spinal cord can cause loss of proprioception. This is an obvious surgical risk, given the posterior surgical approach that is taken to remove spinal cord tumors. Injury to the posterior columns is more common in adults than in children. (See also Intervention.)
Sex
Reports suggest a slight male predominance with spinal cord astrocytomas. The male-to-female ratio ranges from 1:1 to 1.5:1.
Age
The incidence of spinal cord astrocytomas peaks between the third and fifth decades of life, but these tumors may occur in individuals of any age.
- Intramedullary astrocytomas occur in adult and pediatric patients, with some differences between the age groups.
- The most common pediatric spinal cord tumor is an astrocytoma. Approximately 30% of all pediatric spinal cord astrocytomas have anaplastic features. Juvenile pilocytic astrocytomas are more common in pediatric patients than in adults. (Also see the eMedicine articles Astrocytoma [Pediatrics] and Juvenile Pilocytic Astrocytoma [Radiology].)
- In adults, ependymomas are the most common spinal cord tumor, with astrocytomas being the second most common. Approximately 25% of adult spinal cord astrocytomas have anaplastic features. Pilocytic astrocytomas are less common in adults than in pediatric patients.
Anatomy
Spinal cord tumors are intradural intramedullary lesions that arise from the glial cells in the spinal cord. Spinal cord astrocytomas can occur at any level, with the thoracic cord being the most common site and the cervical cord being the second most common location. Holocord tumors are sometimes seen in children but are rarely present in adults. Spinal cord astrocytomas occasionally have an exophytic component that projects into the subarachnoid space.
About 40% of astrocytomas are associated with tumoral cysts. An associated spinal cord syrinx is often a secondary finding.
Presentation
Patients usually present with symptoms at or below the level of the spinal cord tumor. The most common signs and symptoms of spinal cord tumors include back pain, numbness and paresthesias, unilateral or bilateral weakness, ataxia, bowel or bladder dysfunction, mild spasticity, and gait difficulties. Back pain may be localized or radicular and typically increases at night — likely because of increased venous congestion in the spinal compartment in the recumbent position, which increases distention of the dural tube.
A full neurologic examination is necessary for any patient with a possible spinal cord tumor. The spinal axis should be palpated for any areas of tenderness, as approximately 70% of patients have spinal pain. All motor groups should be examined to evaluate for any focal weakness. Patients may have a sensory level or a deficit of a particular sensory modality. Intramedullary spinal cord astrocytomas may cause increased reflexes, clonus, mild spasticity, and a positive Babinski sign (ie, plantar reflex, in which the great toe extends in response to a stimulus). The examination must also include watching the patient walk and carefully evaluating his or her gait. A rectal examination should be performed to assess for sphincter control.
Preferred Examination
The examination modality of choice for diagnosing and evaluating spinal cord astrocytomas is a contrast-enhanced MRI of the spine with a closed magnet. The extent of the tumor mass, the enhancement pattern of the tumor, and the presence of associated tumoral cysts and syringeal cavities are well delineated on MRI.
Differential Diagnoses
Astrocytoma
Ependymoma, Spine
Hemangioblastoma, Spine
Meningioma, Spine
Spinal Cord Tumors: Management of Intradural
Intramedullary Neoplasms
Other Problems to Be Considered
Intramedullary germ cell tumors
Intramedullary fibromas
Intramedullary meningiomas
Other rare tumors
Non-neoplastic processes
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Further Reading
Keywords
spinal cord tumor, intramedullary spinal cord tumor, diffuse fibrillary astrocytoma
