Astrocytoma Spinal Imaging

Astrocytomas of the spinal cord are rare tumors that arise from astrocytes in the spinal cord and occur in both adult and pediatric populations. ^{[1, 2, 3, 4]} 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.

Patients usually present with symptoms at or below the level of the spinal cord tumor. The most common signs and symptoms of spinal cord tumor 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.

The examination modality of choice for diagnosing and evaluating spinal cord astrocytoma is 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.

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 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. However, plain radiographs are helpful in assessing bony changes of the spine that can occur after spinal cord tumors are treated. Such changes include progressive scoliosis, kyphotic deformities, and spinal instability.

Computed tomography (CT) scanning is of limited value in assessment of spinal cord tumors. CT scans may depict bony changes in the spine, which may occur as late secondary findings in patients with spinal cord tumors. 

Ultrasonography is useful during surgery to determine the extent of resection. Before the dura is incised, intraoperative ultrasonography is used to define 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.

The location for laminectomy (surgery to relieve pressure on the spinal cord or nerves) is based on preoperative MRI findings. Intraoperative ultrasonography is used to define tumor margins and to locate any cysts.

Yang and colleagues investigated the prognostic factors of spinal cord astrocytoma (SCA) and sought to establish a nomogram prognostic model for management of patients with SCA. They found that nomograms demonstrated good calibration, discrimination, and clinical utility in predicting prognosis for patients with SCA. These investigators concluded that their findings might benefit clinical decision-making and patient management for SCA and that, before further use, more extensive external validation is required for established web-based online calculators. ^[5]

(See the image below.)

 

CT scans are of limited help in assessing spinal cord tumors. They may show bony changes in the spine that can occur as late secondary findings, including pedicular erosion, widening of the spinal canal, and dorsal scalloping of vertebral bodies. ^[6]

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 an implant). With regard to the spinal cord, CT myelography can demonstrate only the presence or absence of spinal cord expansion. The cause of spinal cord expansion usually is not discernible during CT myelography, because such expansion occurs secondary to a tumor, a cyst, a syrinx, or edema with similar appearance. 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.

Magnetic resonance imaging (MRI) enables detailed assessment of spinal cord tumors with high-resolution imaging of soft tissues. ^{[7, 8, 9]} When a spinal tumor is evaluated on MRI, it is classified into 1 of 3 groups:

• Extradural

• Intradural and extramedullary

• Intramedullary

Extradural masses are located in the epidural space and arise from vertebral bodies or from epidural soft tissues. Intradural extramedullary tumors arise from 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.

In a retrospective review, She and associates sought to determine MRI features of pilocytic astrocytoma (PA) in the spinal cord to help neuroradiologists preoperatively differentiate PA from other intramedullary tumors. They found that eccentric growth pattern, well-defined margins, an intermixed cystic and solid appearance, focal nodular enhancement of solid components, and syringomyelia are relatively frequent features of spinal PA, as are relatively high apparent diffusion coefficient values with normal-appearing spinal cord parenchyma. They concluded that PA should be considered in the differential diagnosis of intramedullary tumors that occur in the cervical and thoracic regions. ^[10]

Pilocytic astrocytoma is a low-grade central nervous system tumor most commonly seen in children. Dissemination from a primary intracranial tumor along the neuroaxis has been described at both presentation and disease progression. However, development of an intradural extramedullary pilocytic astrocytoma independent of a primary intraparenchymal tumor in an adult patient with no history of pilocytic astrocytoma has rarely been reported. The literature includes a report of an elderly patient presenting with a primary spinal multifocal intradural extramedullary pilocytic astrocytoma. Case authors reveal that no conventional primary tumor was identified in this patient, suggesting that these tumors may arise from heterotopic gliomas. ^[11]

(See the images below.)

The spinal cord is typically enlarged at the level of the 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 show tumor extent, 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 between tumoral and reactive cysts.

Astrocytomas of the spinal cord vary in size and length, with average length of 7 vertebral body segments. Tumoral enhancement is variable, and some astrocytomas are completely nonenhancing. Tumor margins may be well defined or indistinct. Tumoral cysts are a common finding, and reactive cysts may be observed at 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 occasionally occur with low-grade astrocytomas.

Caruso and coworkers reported that pregnancy may be associated with progression of aggressively recurring cervical intramedullary anaplastic astrocytoma. This case report discusses associated imaging approaches and points out the importance of close neurologic monitoring and counseling regarding risk of progression in pregnant patients with spinal glioma. ^[12]

Gadolinium-based contrast agents have been linked to development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). This disease has occurred in patients with moderate to end-stage renal disease after they were given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography (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.

Neurofibromatosis type 1 (NF1), one of the most common genetic neurocutaneous disorders, is well known to be associated with peripheral or central nervous system malignancies. The most common malignant tumors are malignant peripheral nerve sheath tumors (MPNSTs), which are the most common cause of death in patients with NF1. Central nervous system malignancies rarely occur. So far, the occurrence of spinal cord malignancies is exceedingly rare. One case report describes a 69-year-old male with NF1 following tumor resection twice for cutaneous MPNSTs who developed a rare case of intramedullary diffuse astrocytoma in the conus medullaris, which initially presented with traumatic spinal cord injury associated with compression fracture from a fall. Contrast-enhanced MRI and biopsy of the spinal cord were required to establish the final diagnosis. ^[13]