# Spinal Cord Tumors: Intramedullary and Intradural Extramedullary ## Overview Spinal cord tumors account for 2 to 4 percent of all central nervous system neoplasms. They are classified by anatomic compartment into three categories. Intramedullary tumors arise within the spinal cord parenchyma itself and represent approximately 20 to 30 percent of spinal tumors. Intradural extramedullary tumors grow within the dural sac but outside the spinal cord, accounting for approximately 40 percent. Extradural tumors lie outside the dura and comprise 30 to 40 percent, most commonly representing metastatic disease. Intradural extramedullary tumors are more common in adults, while intramedullary tumors span all age groups. The majority of spinal cord tumors are benign and surgically curable if diagnosed before irreversible neurological damage occurs. | Compartment | Frequency | Most Common Tumors | Key Features | |-------------|-----------|-------------------|--------------| | Intramedullary | 20-30% | Ependymoma (adults), Astrocytoma (children), Hemangioblastoma | Within cord parenchyma; widened cord on MRI | | Intradural extramedullary | ~40% | Schwannoma, Meningioma, Myxopapillary ependymoma | Within dural sac, outside cord; displaces cord | | Extradural | 30-40% | Metastases, Lymphoma, Primary bone tumors | Outside dura; most common compartment for malignancy | ## Intramedullary Tumors ### Ependymoma Ependymoma is the most common intramedullary tumor in adults, representing 60 percent of adult intramedullary neoplasms. These tumors are well-circumscribed and centrally located, arising from ependymal cells lining the central canal. The myxopapillary subtype occurs specifically at the conus medullaris and filum terminale. On MRI, ependymomas appear as well-defined, homogeneously enhancing masses that are T2 hyperintense. The "cap sign," a hemosiderin rim at the tumor poles visible as dark signal on T2, is characteristic and results from prior subclinical hemorrhage. Associated syringomyelia is present in 50 to 80 percent of cases. The critical surgical feature of ependymomas is the presence of a cleavage plane between the tumor and surrounding cord tissue, which allows gross total resection in the majority of cases. Five-year survival exceeds 90 percent with gross total resection. Adjuvant radiation is reserved for subtotal resection or recurrence. Most are WHO Grade II, with rare anaplastic Grade III variants. ### Astrocytoma Astrocytoma is the most common intramedullary tumor in children, accounting for 60 percent of pediatric intramedullary tumors and 30 percent of adult cases. Unlike ependymomas, astrocytomas demonstrate an infiltrative growth pattern without a clear cleavage plane, which fundamentally alters the surgical strategy. Most are low-grade, either WHO Grade I pilocytic or Grade II diffuse astrocytomas, though high-grade variants are rare but aggressive. MRI shows an ill-defined, eccentric mass with heterogeneous enhancement that may span multiple spinal segments. Syrinx is associated in 25 to 50 percent of cases. Gross total resection is often not possible without unacceptable neurological morbidity due to the infiltrative nature. Subtotal resection with monitoring is the standard approach for diffuse astrocytomas. Pilocytic astrocytomas (Grade I) may have a better-defined interface and are more amenable to complete resection. Adjuvant radiation is indicated for high-grade or progressive tumors. Prognosis follows the grade hierarchy: pilocytic carries the best outcome, followed by diffuse, then anaplastic, and finally glioblastoma with the worst prognosis. ### Hemangioblastoma Hemangioblastomas represent 3 to 8 percent of intramedullary tumors. They are highly vascular, well-circumscribed tumors typically located on the dorsal surface of the cord. An association with von Hippel-Lindau disease exists in 25 to 33 percent of cases, particularly when multiple tumors are present. VHL syndrome also features retinal angiomas, renal cell carcinoma, and pheochromocytoma. MRI demonstrates an intensely enhancing nodule with associated cyst or syrinx and prominent flow voids reflecting the tumor's vascularity. The key surgical principle is that the tumor is contained entirely within the enhancing nodule; the cyst wall is reactive and not neoplastic. Gross total resection is curative. Preoperative spinal angiography identifies feeding arteries for surgical planning. Embolization is rarely performed for spinal cord lesions due to the risk of cord ischemia. ### Other Intramedullary Tumors Less common intramedullary lesions include lipomas, dermoids, and epidermoids, which are developmental in origin. Cavernous malformations are not true neoplasms but may present similarly. Intramedullary metastases are rare, with lung and breast carcinoma being the most common primary sites. ## Intradural Extramedullary Tumors ### Schwannoma Schwannoma is the most common intradural extramedullary tumor. These tumors arise from Schwann cells of the dorsal nerve root and are well-encapsulated, typically displacing rather than invading the spinal cord. Most are solitary; multiple schwannomas suggest NF2 or schwannomatosis. On MRI, schwannomas appear as well-circumscribed masses that are T1 isointense to hypointense, T2 hyperintense, and enhance homogeneously. A "dumbbell" configuration occurs when the tumor extends through the neural foramen with both intradural and extradural components. Gross total resection is curative and may require sacrifice of the involved nerve root, which is usually sensory; motor root sacrifice is avoided when possible. Recurrence after complete resection is less than 5 percent. ### Meningioma Meningioma is the second most common intradural extramedullary tumor. These tumors arise from arachnoid cap cells and demonstrate a strong female predominance with a 4:1 ratio, peaking in the fifth to seventh decades. Eighty percent occur in the thoracic spine. They are typically ventral or ventrolateral to the cord. MRI shows a well-defined mass isointense on T1 with homogeneous enhancement, a broad dural base, and the characteristic "dural tail" sign. Treatment is gross total resection with cauterization or excision of the dural base, aiming for Simpson Grade I or II resection. Recurrence is low at 5 to 10 percent but higher for atypical or malignant subtypes. An en plaque growth pattern can make complete resection difficult. ### Myxopapillary Ependymoma Myxopapillary ependymoma arises from the filum terminale and conus region, making it the most common tumor of the filum terminale. It is well-encapsulated, and gross total resection is achievable in most cases. MRI reveals a well-defined, enhancing mass in the conus or filum region that may contain mucoid material. Prognosis is excellent with complete resection; recurrence is associated with subtotal removal. ### Neurofibroma Neurofibromas are less common than schwannomas in the spine and are associated with NF1, particularly when multiple or plexiform in morphology. Unlike schwannomas, neurofibromas grow within and around nerve fascicles, meaning they cannot be separated from the nerve and en bloc excision requires nerve sacrifice. In NF1, there is a 5 to 10 percent lifetime risk of malignant transformation to malignant peripheral nerve sheath tumor. ## Surgical Technique ### Intramedullary Tumors The patient is positioned prone with Mayfield fixation for cervical lesions or on a Wilson frame or Jackson table for thoracolumbar tumors. Exposure involves laminectomy or laminoplasty spanning one level above and below the tumor. Laminoplasty is preferred in children and for multilevel exposure to reduce the risk of post-laminectomy kyphotic deformity. After midline durotomy with tack-up sutures to retract the dura, myelotomy is performed through the dorsal median sulcus. The midline is identified by the bilateral dorsal root entry zones and the dorsal median vein. Microsurgical technique with bipolar cautery at the lowest settings is essential. Tumor resection proceeds with internal debulking using the CUSA or laser followed by circumferential dissection. For ependymomas, the surgeon develops the plane between tumor and cord, progressively rolling the tumor out of its cavity. For astrocytomas, no clear plane exists; resection continues until abnormal tissue transitions to normal cord, and the surgeon stops when uncertain of the boundary. Associated syrinx typically decompresses spontaneously with tumor removal and does not require shunting. Closure involves watertight dural repair with fibrin glue and replacement of the laminoplasty flap. ### Intradural Extramedullary Tumors Laminectomy or laminoplasty provides exposure. After midline durotomy, the tumor is identified and the spinal cord gently displaced. For schwannomas, the nerve root is stimulated to assess function; if non-functional or purely sensory, the root is sacrificed and the tumor excised en bloc. For meningiomas, the dural attachment is devascularized, the plane between tumor and cord or nerve roots is developed, the tumor is excised, and the dural base is cauterized or resected. Dumbbell tumors may require an additional posterolateral or anterior approach for the extradural component. ### Intraoperative Neurophysiological Monitoring Monitoring is essential for all spinal cord tumor surgery. Motor evoked potentials monitor corticospinal tract integrity. Somatosensory evoked potentials monitor dorsal column function. D-wave recording is the most reliable indicator of long-term motor outcome for intramedullary tumors; preservation of greater than 50 percent of D-wave amplitude predicts preserved motor function. Loss of the D-wave should prompt cessation of resection regardless of MEP status. Free-run and triggered EMG provide nerve root monitoring. ## Postoperative Management Neurological examination is performed immediately after surgery. MRI within 24 to 48 hours assesses the extent of resection. Early mobilization with physical and occupational therapy is initiated. The wound is monitored for CSF leak. Long-term surveillance MRI is obtained every 6 to 12 months initially and then annually. ## Adjuvant Therapy Radiation therapy is indicated for subtotal resection, recurrence, or high-grade tumors. Conventional fractionated radiation is used for intramedullary tumors, while stereotactic radiosurgery may have a role for small, well-circumscribed recurrences. Chemotherapy has a limited role; temozolomide may be considered for high-grade astrocytomas with limited evidence. Observation alone is appropriate after gross total resection of benign tumors including ependymoma, schwannoma, and meningioma. Sagittal T2-weighted and post-contrast T1-weighted MRI of the cervical spinal cord showing an intramedullary ependymoma spanning C3-C5, demonstrating a well-circumscribed homogeneously enhancing mass expanding the cord with characteristic hemosiderin cap sign (dark rim) at the superior and inferior poles and associated rostral syringomyelia Axial post-contrast T1-weighted MRI of the thoracic spine demonstrating an intradural extramedullary meningioma ventral to the spinal cord at the T6 level, showing a homogeneously enhancing well-circumscribed mass with a broad dural base and dural tail sign, displacing the spinal cord posteriorly and laterally Intraoperative photograph through the operating microscope during posterior midline myelotomy for resection of a cervical intramedullary ependymoma, showing the dorsal surface of the spinal cord with the myelotomy performed along the dorsal median sulcus, exposing the well-circumscribed tumor beneath with visible cleavage plane between tumor and surrounding cord tissue Sagittal post-contrast MRI of the lumbar spine showing a well-enhancing myxopapillary ependymoma arising from the filum terminale at the conus medullaris level, with the mass surrounded by cauda equina nerve roots within the thecal sac ## Clinical Pearls The cap sign, a hemosiderin rim on T2 MRI, is highly suggestive of ependymoma and helps distinguish it from astrocytoma preoperatively. This distinction is surgically critical because ependymomas have a cleavage plane allowing gross total resection, while astrocytomas typically do not. D-wave monitoring is the single most important intraoperative neurophysiology parameter for intramedullary tumor surgery; a decline greater than 50 percent should prompt immediate cessation of resection. For intramedullary tumors broadly, subtotal resection with preserved neurological function is always preferable to gross total resection with devastating deficit; staged resection may be considered when tumor remains. All patients with spinal hemangioblastoma should be screened for VHL syndrome with retinal examination, abdominal imaging, and genetic testing. Laminoplasty is preferred over laminectomy in children and for multilevel exposure to minimize the risk of post-laminectomy kyphotic deformity. Dumbbell schwannomas require careful preoperative planning with CT and MRI to assess the extent of foraminal and extraforaminal components, as they may necessitate a combined surgical approach. ## References 1. Sandalcioglu IE et al. Spinal cord ependymomas: surgical outcome and complications. World Neurosurg. 2016;92:494-501. 2. Manzano G et al. Current and future treatment strategies for intramedullary ependymomas. Expert Rev Neurother. 2017;17(8):799-806. 3. Jinnai T, Koyama T. Clinical characteristics of spinal nerve sheath tumors: analysis of 149 cases. Neurosurgery. 2005;56(3):510-515. 4. Kothbauer KF, Deletis V. Intraoperative neurophysiology of the conus medullaris and cauda equina. Childs Nerv Syst. 2010;26(2):247-253. 5. Klekamp J. Treatment of intramedullary tumors: analysis of surgical morbidity and long-term results. J Neurosurg Spine. 2013;19(1):12-26.