Spinal Imaging in Astrocytoma 

Astrocytomas of the spinal cord are rare tumors that arise from astrocytes in the spinal cord and occur in the adult and pediatric populations.^{[1, 2, 3]} 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. (See the image below.)

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. A full neurologic examination is necessary for any patient with a possible spinal cord tumor.

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.

Intervention

The location for laminectomy is based on findings on preoperative MRI. Intraoperative ultrasonography is used to define the margins of the tumor and to locate any cysts.

Plain radiography is of limited diagnostic value in evaluating patients with a potential spinal cord tumor. On occasion, widening of the spinal canal, widening of the interpedicular distance, and scalloping of the dorsal aspects of the vertebral bodies can be appreciated on plain radiographs as a late imaging finding. Typical and atypical scoliotic curvatures can be seen in patients with a spinal cord tumor.

Plain radiographs, however, are helpful in assessing bony changes of the spine that can occur after the spinal cord tumors are treated. Examples of such changes are progressive scoliosis, kyphotic deformities, and spinal instability.

Computed tomography (CT) scanning is of limited value in the assessment of spinal cord tumors. CT scans may depict bony changes of the spine, which may occur as late secondary findings in patients with spinal cord tumors; such changes include pedicular erosion, widening of the spinal canal, and dorsal scalloping of the vertebral bodies.

CT myelography is indicated in the workup of spinal cord tumors only if MRI is contraindicated (eg, because of the presence of a pacemaker or implant). With regard to the spinal cord, CT myelography can demonstrate only the presence or absence of spinal cord expansion. The cause of the spinal cord expansion is usually not discernible during CT myelography, because such expansions secondary to a tumor, a cyst, a syrinx, and edema have similar appearances. MRI has replaced CT myelography as the study of choice in diagnosing spinal cord tumors because of its superior imaging resolution of the spinal cord itself.

MRI enables detailed assessment of spinal cord tumors with high-resolution imaging of the soft tissues.^{[4, 5]} When a spinal tumor is evaluated on MRI, it is classified into 1 of the following 3 groups:

• Extradural
• Intradural and extramedullary
• Intramedullary

Extradural masses are located in the epidural space and arise from the vertebral bodies or epidural soft tissues. Intradural extramedullary tumors arise from the leptomeninges, nerve roots, or dura, or they represent subarachnoid spread from a distant tumor. Intramedullary tumors originate in the spinal cord; thus, spinal cord astrocytomas are intramedullary tumors. (See the images below.)

The spinal cord is typically enlarged at the level of tumor. This feature helps in differentiating spinal cord tumors from non-neoplastic diseases that may mimic a spinal cord neoplasm, such as inflammatory or demyelinating processes.

T1- and T2-weighted images demonstrate the extent of tumor, the solid and cystic components of the tumor, spinal cord edema, reactive cysts, and syringeal cavities. Spinal cord tumors are typically isointense or hypointense on T1-weighted images and hyperintense on T2-weighted images. T1-weighted, gadolinium-enhanced MRI scans add information for characterizing the enhancement pattern of the tumor by distinguishing between enhancing and nonenhancing components of tumor and by distinguishing between tumoral and reactive cysts.

Astrocytomas of the spinal cord vary in size and length, with 7 vertebral-body segments being the average length. Tumoral enhancement is variable, and some astrocytomas are completely nonenhancing. The tumor margins may be well defined or indistinct. Tumoral cysts are a common finding, and reactive cysts may be observed at the tumoral poles. Drop metastases (ie, intradural extramedullary spinal metastases that arise from intracranial lesions) in the subarachnoid space are most commonly seen with high-grade astrocytomas but can occasionally occur with low-grade astrocytomas.

Gadolinium-based contrast agents have linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.

Ultrasonography is useful during surgery to determine the extent of resection. Before the dura is incised, intraoperative ultrasonography is used to define the superior and inferior margins of the mass and to locate any cysts in or adjacent to the lesion. Any cysts that are encountered should be drained.