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Spinal cord tumors account for an estimated 5% to 15% of all central nervous system (CNS) tumors, with an incidence of 0.5 to 2.5 cases per 100,000. Among these, nearly 50% are primary intradural spinal cord tumors. Intradural spine tumors are divided into two main categories based on the anatomic origin of the lesion: intradural extramedullary spinal cord tumors (IESCTs), arising from within the spinal cord; and intramedullary spinal cord tumors (ISCTs), originating from the dura but located within the subarachnoid space.
IESCTs account for 80% of intraspinal tumors in adults and 65% to 70% of intraspinal tumors in children. The two most common types of IESCTs are nerve sheath tumors (NSTs) (30%) and meningiomas (25%). Because NSTs arise from perineural cells and Schwann cells, the two most common NSTs are schwannomas and neurofibromas; schwannomas account for approximately 65% of NSTs. Most NSTs are sporadic, but they are also common in the setting of inherited disorders such as neurofibromatosis type I (NF-1) and type 2 (NF-2). Sporadic NSTs usually arise in the fifth to seventh decade, whereas those in the setting of neurofibromatosis arise during childhood or early adulthood. Meningiomas originate from arachnoidal cells along the neuraxis and are also commonly associated with neurofibromatosis. However, only 10% of meningiomas arise external to the cranial fossa.
ISCTs account for 20% of intraspinal tumors in adults and 30% to 35% of intraspinal tumors in children. The two most common ISCTs are ependymomas (60%) and astrocytomas (30%). Ependymomas mainly arise in adults in approximately the third or fourth decade, and astrocytomas usually appear in children during the first decade. Given the predominant prevalence of ependymomas and astrocytomas, investigators believe that most ISCTs are of glial origin This chapter discusses the anatomic distribution, presentation, diagnosis, and management of the most common types of spinal cord tumors, including both IESCTs and ISCTs.
Intradural Extramedullary Spinal Cord Tumors
Presentation
IESCTs have a nonspecific clinical presentation that includes axial back or neck pain, as well as radicular or myelopathic signs and symptoms. Associated pain is usually most intense in the evening and morning. The specific symptoms of IESCTs mainly depend on the level involved and have no specific anatomic distribution. A study performed by Slin’ko and Al-Qashqish, however, examined 360 patients with IESCTs over an 11-year period and classified tumor location on both the axial and the longitudinal axis. The investigators found that on the longitudinal axis, most IESCTs occurred within the thoracic spine, followed by the cervical and lumbar spine, respectively. On the axial axis, the investigators determined that most lesions occurred on the dorsolateral division, followed, respectively, by the ventrolateral, dorsal, and ventral divisions.
In the case of NSTs, radicular sensory signs are the first to follow pain. Patients have pain because NSTs characteristically arise in the dorsal sensory roots. Radiculopathy with motor deficits is not common, even during involvement of functional roots of the cervical or lumbar spine. However, myelopathic motor signs manifest once the tumor achieves a critical mass, thus resulting in spinal cord compression. The myelopathy has no distinctive symptoms and may include signs such as Brown-Séquard syndrome (ipsilateral hemiplegia with ipsilateral fine touch sensory deficit and contralateral pain and temperature sensory deficit, and upper motor neuron involvement such as upward plantar reflex, hyperreflexia, and clonus). Chronicling the time progression of symptoms is important because rapidly worsening signs and symptoms indicate the presence of a fast-growing, aggressive tumor such as a malignant NST (MNST). Similarly, the presentation of spinal meningiomas is nonspecific and includes signs and symptoms such as progressive lower extremity numbness and weakness. Furthermore, many spinal meningiomas are often asymptomatic as a result of their slow growth and are discovered only incidentally during an imaging study or at autopsy.
Diagnosis
The two most common types of IESCTs are NSTs and meningiomas. The diagnosis of IESCTs is best made using magnetic resonance imaging (MRI) because plain radiography, computed tomography (CT), and CT with myelography do not provide sufficient delineation of an intradural neoplasm. However, when MRI is contraindicated, CT with myelography is the imaging modality of choice.
Of primary importance is determining whether the neoplasm is intramedullary or extramedullary. Extramedullary neoplasms have the following characteristics on MRI: displacement and compression of the spinal cord, expansion of the thecal sac, and a menisci-like interface with the cerebrospinal fluid. Intramedullary neoplasms are characterized by expansion of the spinal cord.
Most IESCTs are isointense to the spinal cord on T1-weighted imaging and hyperintense on T2-weighted images. Furthermore, IESCTs typically enhance with contrast on T1-weighted imaging ( Fig. 22-1 ). NSTs produce unique “target lesions” on MRI that correspond to the pathologic anatomy of the lesion. Despite the optimal ability of MRI to delineate the anatomic interface between the spinal cord and the neoplasm, this modality cannot provide a definitive diagnosis; the differential diagnosis also includes meningiomas, extramedullary ependymomas, mixed cell gliomas, hemangiomas, and cavernous hemangiomas. Definitive diagnosis is usually not made until pathologic examination of the surgical specimen. Patients with a positively identified IESCT should undergo further MRI of the remaining neuraxis to search for additional lesions, particularly in the setting of neurofibromatosis.
Nerve Sheath Tumors
The three most common types of NSTs are schwannomas, neurofibromas, and MNSTs. Schwannomas are the most common type of NST. Although most often classified as IESCTs, schwannomas can also be present extradurally. On imaging, schwannomas are most commonly seen encompassing the dorsal sensory root of the lumbar and cervical spine. One common but nonspecific finding on imaging is invasion of the prevertebral space and neural foramina in a “dumbbell”-shaped fashion (see Fig. 22-1 , A ). This finding is commonly accompanied by erosion of the posterior aspect of the vertebral body and widening of the spinal canal, particularly when the tumor has been present for a long time. Patients with NF-2 should be evaluated for additional lesions because these patients often have multiple schwannomas along the neuraxis.
Neurofibromas can be distinguished from schwannomas by their ability to encase nerve roots; schwannomas typically exhibit asymmetric growth resulting in nerve root displacement. When visualized on MRI, neurofibromas are often fusiform or rounded. Consistent with other IESCTs, they are isointense and hyperintense on T1- and T2-weighted MR imaging, respectively (see Fig. 22-1 , B ). Additionally, homogeneous intense enhancement can be observed with gadolinium injection (see Fig. 22-1 , B ). Patients with NF-1 may harbor numerous plexiform neurofibromas and should be evaluated for such. Furthermore, patients with NF-1 have an increased risk of malignant transformation of their neurofibromas to MNSTs. MNSTs originate most often from dedifferentiated neurofibromas in the setting of NF-1 or from sporadic neurofibromas. MNSTs are characterized by their rapid growth and should be suspected when imaging demonstrates large increases in tumor size over short periods of time.
Meningiomas
Meningiomas originate from the arachnoidal cells of the dura and thus can occur anywhere along the neuraxis. Only 10% of meningiomas occur below the cranial fossa, and they are most often located on the dorsolateral aspect of the thoracic region. Meningiomas usually manifest as solitary lesions, except in patients who also have NF-2. As with other IESCTs, meningiomas are isointense on T1-weighted imaging and hyperintense on T2-weighted imaging (see Fig. 22-1 , C ). However, the hyperintensity on T2-weighted imaging is usually milder than that seen with other IESCTs such as NSTs. Similar to other IESCTs, meningiomas enhance positively with contrast enhancement on T1-weighted imaging (see Fig. 22-1 , C ). Although uncommon, signal changes caused by spinal cord compression may also be visualized. CT imaging may demonstrate bone erosion and remodeling in addition to calcifications within the neoplasm.
Management and Prognosis
IESCTs are ideally managed by complete microsurgical excision. Selection of surgical access to IESCTs should be made after considering all the following: the region of tumor location, the axial plane location of the tumor, and the extent of spread. For example, IESCTs with predominantly ventral locations can be difficult to access and thus may not be amenable to complete tumor resection. In such a case, residual neoplasm can be managed by fractionated radiation therapy or radiosurgery.
NSTs of small size, dumbbell shape, and limited spread (i.e., occupying only the neural foramen) can be surgically managed through dorsolateral access. However, NSTs that demonstrate significant ventral growth through the neural foramen require ventrolateral access irrespective of the spinal level involved. Schwannomas are distinguished from neurofibromas in that they do not encase nerve roots but rather displace nerve roots, thus making nerve root preservation easier. Generally, if a tumor is large or extends into the extradural space, motor stimulation is employed to assess motor root involvement. In the absence of motor root involvement (i.e., dorsal root involvement or a thoracic root excluding T1 that forms part of the brachial plexus), the entire root can be sacrificed. However, if root involvement is present, the root should be preserved, and the surgeon should attempt to dissect it free from the tumor. Meningiomas commonly adhere to dura, and thus dural resection is often required to achieve complete resection. Cerebrospinal fluid leak, albeit rare, is the most common surgical complication in the management of IESCTs.
Fractionated radiation therapy or radiosurgery can also be considered acceptable as the primary intervention in the setting of recurrent tumors following previous surgical extraction, tumor presence in multiple locations, the absence of significant spinal instability, and any other surgical contraindication.
General positive prognostic factors in the setting of an IESCT include early diagnosis before the appearance of severe neurologic symptoms, complete tumor excision, young age, minor spinal cord compression, the absence of intraoperative spinal cord retraction, and optimal microsurgical technique. In addition, certain prognostic factors are specific to tumor type. Patients with sporadic NSTs who undergo complete tumor resection can remain disease free and, at the least, maintain their preoperative level of neurologic function. However, patients with NSTs in the setting of neurofibromatosis have a high incidence of both recurrent tumors and new tumors. Furthermore, neurofibromas in patients with NF-1 can undergo malignant transformation to MNSTs, which have a poor prognosis. MNSTs are often not amenable to complete resection and involve leptomeningeal spread, with an average life expectancy of less than 1 year. Analogous to patients with sporadic NSTs, patients with sporadic, slow-growing meningiomas can experience a recurrence-free life span with a neurologically stable prognosis. Younger patients more commonly have aggressive meningiomas with higher rates of recurrence.
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