21 Intradural Extramedullary Tumors Abstract Intradural extramedullary tumors of the thoracic spine are predominantly meningiomas, schwannomas, and neurofibromas. Other lesions, like lymphoma or metastases, can occur but are far less likely. While most of these lesions are benign and rarely progress to malignant forms, surgical resection is indicated for tumors that cause spinal cord compression or become symptomatic. Even for ventrally situated tumors, a posterior or posterolateral approach can result in adequate decompression in most cases. Instrumented fusion in association with tumor resection should be considered for lesions that require laminectomies at three or more levels, junctional levels, or when bilateral facetectomies are required. All patients should have neurophysiologic monitoring during the procedure to prevent catastrophic spinal cord injury by reversible causes. Gross total resection is curative in most cases; however, adjuvant radiation has shown benefit for recurrent tumors. Keywords: intradural extramedullary, spinal cord, tumor, schwannoma, meningioma, neurofibroma Clinical Pearls • Surgical resection is the gold standard for the treatment of symptomatic intradural extramedullary (IDEM) thoracic tumors or those with radiographic evidence of spinal cord compression. • Radiosurgery has shown benefit as a primary treatment modality or as adjuvant treatment for recurrent tumors; however, this is an area of current research. • Most thoracic IDEM tumors can be resected safely from a posterolateral approach, precluding high-risk lateral and anterior approaches. • Instrumented fusion should be considered for tumors that require three or more laminectomies for dural exposure, or for those at transitional levels. • Intraoperative neurophysiologic monitoring (somatosensory evoked potentials and motor evoked potentials) should be used on all surgeries to prevent spinal cord injury from reversible causes, including spinal cord rotation maneuvers and low mean arterial pressures leading to spinal cord hypoperfusion. Intradural extramedullary (IDEM) tumors occur in the thoracic spine in 26 to 29% of cases1,2 and can cause significant morbidity by spinal cord compression or involvement of thoracic nerve roots. While these tumors can present in individuals of all ages, in the pediatric population they are most often associated with leptomeningeal metastases from intracranial tumors.3 In the adult population, there are broadly three tumor subtypes which predominate, which are meningiomas, schwannomas, and neurofibromas (the latter two are often grouped together as nerve sheath tumors). Presenting symptoms include localized thoracic back pain, radicular pain, dermatomal paresthesias, and myelopathy. Optimal management is based on a number of factors, including age at presentation, symptomatology, radiographic degree of spinal cord compression, rate of growth, and location within the thecal sac. The focus of this chapter will be on these three tumor types; however, a subset of rarer tumors can also be seen in the thoracic IDEM compartment, including metastases, paragangliomas, epidermoid, hemangiomas, and lymphoma.4,5 Meningiomas of the spinal canal account for 25 to 45% of all IDEM spinal tumors.6 While histologically similar to those seen intracranially, spinal meningiomas account for only 2% of all central nervous system meningiomas.7 These tumors have a nearly 4:1 predilection for the female sex in adults, for reasons that remain to be elucidated, and are most commonly diagnosed in the fifth and sixth decades of life. Histopathologically, the vast majority are World Health Organization grade I, and rarely progress to higher grades. In this regard, invasion of the spinal cord is typically not seen; however, long-standing tumors can be scarred to the spinal cord making a distinct plane difficult to distinguish. These tumors are over three times as likely to form in the thoracic spine compared with the cervical spine and are exceedingly rare in the lumbar spine.7 There is a strong association of these tumors forming in the context of neurofibromatosis type 2 (NF2). This inherited cancer predisposition syndrome is caused by mutation in the NF2 gene on chromosome 22. A diagnosis of multiple intradural meningiomas should prompt investigation into this genetic syndrome, which are characterized by café au lait spots and the development of intracranial schwannomas (most commonly vestibular schwannomas). IDEM nerve sheath tumors can be divided into two primary subtypes, schwannomas and neurofibromas. These tumors are usually indistinguishable on imaging and require histopathology to obtain a definitive diagnosis. Schwannomas are the most common IDEM tumors of the spine in general; however, these are less commonly seen in the thoracic spine compared with meningiomas. These tumors are benign and arise from the Schwann cells of nerve roots. Pathologic evaluation of schwannomas demonstrates spindled (Antoni A) areas and microcystic (Antoni B) areas comprised of macrophages and collagen, and tumors express S100 protein on immunohistochemistry.8 Neurofibromas not only arise from Schwann cells, but also incorporate nonneoplastic nerve components, including axons, perinerual cells, and fibroblasts.8 As with IDEM meningiomas, multiple IDEM schwannomas should raise the suspicious of NF2. Moreover, in a similar regard, both schwannomas and neurofibromas have the ability to transform into malignant peripheral nerve sheath tumors which are aggressive tumors that carry poor prognosis and most commonly observed in patients with a history of NF1.9 Gadolinium contrast-enhanced magnetic resonance imaging is the primary imaging modality used for diagnosis of thoracic IDEM tumors. Meningiomas homogenously contrast enhance and are well circumscribed. A broad-based dural attachment and/or a dural tail indicating the initial growth point of the tumor are commonly seen ( Schwannomas can demonstrate solid and cystic regions that heterogeneously contrast enhance due to internal hemorrhage or intracystic fluid signal intensity. These tumors are also more likely to present with intradural and extradural components (
21.1 Introduction
21.2 Tumor Subtypes
21.2.1 Meningioma
21.2.2 Nerve Sheath Tumors
21.3 Imaging Characteristics
Fig. 21.1 and 
Fig. 21.2). T1- and T2-weighted hypointensities can indicate calcifications as seen with their intracranial counterparts. Computed tomography (CT) imaging should be considered for patients that will require instrumented fusion following resection to assess for bony anatomy and quality. CT imaging may also more clearly demonstrate calcifications in the region of the tumor or dural margin (most commonly with meningiomas) and posterior vertebral body scalloping due to long-standing mass effect (most commonly with schwannomas). Unlike intracranial meningiomas, hyperostosis of surround bony structures is typically not seen when confined to the intradural compartment.
Fig. 21.3 and 
Fig. 21.4), sometimes forming a characteristic dumbbell shape, as the tumor expands on the medial and lateral side of the foramen that it exits. CT imaging may demonstrate bony remodeling from these slow-growing tumors, including expanded foramen, thinned pedicles, and/or posterior vertebral bodies scalloping.
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