Spinal Imaging in Astrocytoma
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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, 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 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.
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.
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.
(See the image below.)
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. [5]
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. [6, 7, 8] 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.
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Horbinski C, Hamilton RL, Nikiforov Y, Pollack IF. Association of molecular alterations, including BRAF, with biology and outcome in pilocytic astrocytomas. Acta Neuropathol. 2010 Jan 1. epub ahead of print. [Medline].
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Pinter NK, Pfiffner TJ, Mechtler LL. Neuroimaging of spine tumors. Handb Clin Neurol. 2016. 136:689-706. [Medline].
Naito K, Yamagata T, Arima H, Abe J, Tsuyuguchi N, Ohata K, et al. Qualitative analysis of spinal intramedullary lesions using PET/CT. J Neurosurg Spine. 2015 Jul 31. 1-7. [Medline].
Bloomer CW, Ackerman A, Bhatia RG. Imaging for spine tumors and new applications. Top Magn Reson Imaging. 2006 Apr. 17(2):69-87. [Medline].
Ducreux D, Lepeintre JF, Fillard P, et al. MR diffusion tensor imaging and fiber tracking in 5 spinal cord astrocytomas. AJNR Am J Neuroradiol. 2006 Jan. 27(1):214-6. [Medline]. [Full Text].
Thoriya PJ, Watal P, Bahri NU, Rathod K. Primary spinal primitive neuroectodermal tumor on MR imaging. Indian J Radiol Imaging. 2015 Oct-Dec. 25 (4):459-63. [Medline].
Michael E Tobias, MD Fellow in Pediatric Neurosurgery, LeBonheur Children’s Medical Center and St Jude’s Children’s Research Hospital, University of Tennessee
Disclosure: Nothing to disclose.
V Michelle Silvera, MD
Disclosure: Nothing to disclose.
George I Jallo, MD Professor of Neurosurgery, Pediatrics, and Oncology, Director, Clinical Pediatric Neurosurgery, Department of Neurosurgery, Johns Hopkins University School of Medicine
George I Jallo, MD is a member of the following medical societies: American Association of Neurological Surgeons, American Medical Association, American Society of Pediatric Neurosurgeons
Disclosure: Nothing to disclose.
Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.
C Douglas Phillips, MD, FACR Director of Head and Neck Imaging, Division of Neuroradiology, New York-Presbyterian Hospital; Professor of Radiology, Weill Cornell Medical College
C Douglas Phillips, MD, FACR is a member of the following medical societies: American College of Radiology, American Medical Association, American Society of Head and Neck Radiology, American Society of Neuroradiology, Association of University Radiologists, Radiological Society of North America
Disclosure: Nothing to disclose.
L Gill Naul, MD Professor and Head, Department of Radiology, Texas A&M University College of Medicine; Chair, Department of Radiology, Baylor Scott and White Healthcare, Central Division
L Gill Naul, MD is a member of the following medical societies: American College of Radiology, American Medical Association, American Roentgen Ray Society, Radiological Society of North America
Disclosure: Nothing to disclose.
Mahesh R Patel, MD Chief of MRI, Department of Diagnostic Imaging, Santa Clara Valley Medical Center
Mahesh R Patel, MD is a member of the following medical societies: American Roentgen Ray Society, American Society of Neuroradiology, Radiological Society of North America
Disclosure: Nothing to disclose.
Spinal Imaging in Astrocytoma
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