Chapter 25 Intradural Extramedullary and Intramedullary Spinal Cord Tumors
• Surgery is the initial and primary treatment of choice in most spinal tumors.
• Intradural extramedullary spinal tumors, mostly benign peripheral nerve sheath tumors and meningiomas, carry an excellent prognosis. Surgery allows most of the time complete resection and neurological improvement or recovery.
• The main objective should be preserving the patient’s functional condition and making an accurate diagnosis. Postoperative results depend on the preoperative neurological status, the tumor grade, tumor location, and the surgical team’s experience.
• Many intramedullary spinal tumors, such as ependymomas, astrocytomas, and some of nonglial origin, have a favorable prognosis because they may be completely resected based on the favorable surgical plane between the tumor and spinal cord.
Intradural Extramedullary Tumors
Incidence and Types
Spinal intradural extramedullary tumors (SIEMTs) are primarily peripheral nerve sheath tumors (PNSTs) and meningiomas in similar numbers.1 In the largest reported study on SIEMTs, nerve sheath tumors and meningiomas accounted for almost 70% of all lesions.1 Other SIEMTs and lesions include arachnoid cysts, hamartomas, and ependymomas, with an incidence between 5.5-7.5% each.1 The differential diagnosis for SIEMTs and lesions is broad and includes angioblastoma, cavernoma, chordomas, dermoid, epidermoid, exophytic astrocytoma, germinoma, hemangiopericytoma, lipoma, lymphoma, malignant teratoma, medulloblastoma, melanocytoma, melanoma, metastasis, myxoma, neuroblastoma, and sarcoma.1,2
In about 50% of cases, SIEMTs are located at the thoracic level.1 Lesions with an extradural extension are seen at the cervical level in more than half of patients.1 Benign nerve sheath tumors are the most common SIEMT and are associated with extradural extension with an approximate incidence of 77%.1 Meningiomas, hamartomas, and sarcomas are other SIEMTs with extradural extension.1
Peripheral Nerve Sheath Tumors
Most schwannomas are purely intradural but 15% have an extradural component, being either solely extradural or both intra- and extradural. These tumors originate from the dorsal sensory nerve root.3 Typically, these lesions are well encapsulated and rarely include a cystic portion. In contrast, neurofibromas are not well encapsulated and rarely occur alone. Multiple plexiform neurofibromas are usually seen with neurofibromatosis type 1 (NF1), a genetic disorder associated with mutations of chromosome 17.4–6 Diffuse plexiform neurofibromas are detected clinically and radiologically, respectively, in 26.3% and 50% of the patients with NF1.6 They appear in early childhood and have a variable growth pattern. Lesions may grow rapidly until adolescence and then become quiescent.6 The presence of a tumor is not an indication for surgery. Resection is indicated in NF1 patients if the tumor is growing or is causing progressive neurological deficits. In 2% to 5% of the cases, malignant changes may be observed with rapid expansion of the tumor mass.6 Surgery can be challenging in malignant tumors when the tumor is attached and infiltrates surrounding soft tissue. Neurofibromatosis type 2 (NF2) is another genetic condition associated with chromosome 22 anomalies.6 The clinical picture of NF2 may include SIEMTs such as schwannomas, neurofibromas, and meningiomas in 30% of patients.6 Pathologically, nerve sheath tumors are subdivided according to the WHO (World Health Organization) classification into schwannomas (WHO grade I), neurofibromas (WHO grade I), and malignant peripheral nerve sheath tumors (WHO grade III/IV).
Meningiomas
Spinal meningiomas commonly occur in middle-aged patients with a predilection for women.7 Most of the sporadic meningiomas are solely intradural. Of those remaining, one third are intra- and extradural and two thirds are primarily extradural.8 These lesions have a strong tendency to develop at the thoracic level with a frequency reported in the literature between 55% and 83%.7,9–11
Clinical Picture
Most patients present with a long history of progressive symptoms and neurological deterioration because SIEMTs are slow-growing tumors. It is uncommon for a patient to abruptly deteriorate due to spontaneous tumor hemorrhage with spinal compression. SIEMTs appear with signs and symptoms indicative of upper and lower motor neuron involvement, related to the severity of the nerve root insult and spinal cord compression. In half of the cases, the first symptom reported by patients with SIEMTs is pain.1 The tenderness and pain are characteristically increased at night or in the supine position and are relieved after returning to an upright position. Pain is often described along a radicular dermatome but can also reach varying distribution. It is usually described as a dull, aching sensation, and less frequently as burning. Radicular involvement results in lower motor neuron dysfunction, with weakness, sensory disturbances, hyporeflexia, atrophy, and fasciculation at the affected level. Myelopathic symptoms are correlated with the severity, level, and site of spinal cord compression. Nerve sheath tumors typically compress the lateral aspect of the spinal cord and are therefore more likely to be associated with the development of a Brown-Sequard syndrome. Upper motor neuron deficits manifest by gait ataxia and spasticity of the affected extremities. Hyperreflexia as well as other pyramidal signs such as the Hoffman and Babinski signs may be detected upon clinical examination. Patients present with pain, gait ataxia, motor weakness, and sensory deficits in 70% to 77% of the cases, and dysesthesias and sphincter disturbances are found in about 40%.1
Preoperative Imaging
Magnetic resonance imaging (MRI) is currently the gold standard method for imaging. MRI provides accurate diagnoses and delineates the soft tissue components.12,13 Gadolinium administration highlights enhancing portions of the tumor. MR myelography is a special study that is particularly useful for showing small schwannomas.13
On MRI, schwannomas and meningiomas often appear as isointense to the spinal cord on T1-weighted images (WI). On T2-WI, schwannomas are most often hyperintense, as opposed to meningiomas that appear isointense.13 After gadolinium administration both lesions enhance intensely and homogeneously.13 A cystic component and hemorrhagic foci may be noted in schwannomas or neurofibromas, respectively, in 40% and 10% of the cases.13 Less frequently than with cranial lesions, there is often a characteristic dural tail associated with spinal meningiomas.3
The computed tomography (CT) scan enables detection of calcifications as well as of spinal canal and neural foramen enlargement in cases of extradural extension.13 CT angiography (CTA) and MRI angiography (MRA) provide relevant information for cervical dumbbell-shaped neurofibromas that develop in close proximity to the vertebral artery (VA).14 Conventional angiography has a few indications for some of these tumors. It is helpful for providing relevant information about the anterior spinal artery at the cervical level14 and the Adamkiewicz artery at the thoracolumbar junction. CT myelography is invasive and thus not as useful as MRI. It is no longer recommended as the primary imaging modality.13
Surgery
The surgical approach should be adjusted according to the presumed diagnosis and tumor location. The surgical strategy of a PNST is different from that with a meningioma. First, PNSTs most often develop on the anterolateral aspect of the spinal cord, mainly at the cervical level, inducing a posteromedial displacement of the neuraxis. Second, few of them are solely intradural/extramedullary lesions; numerous are dumbbell-shaped lesions extending into the vertebral foramen. Third, at the cervical spine level, their vascular supply from the vertebral artery (VA) requires special considerations.14
Peripheral Nerve Sheath Tumors
Several surgical techniques have been described for PNST resection. These lesions are accessed using a posterolateral approach, as described for meningiomas. The posterolateral approach through a laminectomy is adequate for the resection of the intradural component. In the case of cervical PNST extending through the vertebral foramen and in close proximity to the VA, the posterior approach has several drawbacks.14 First, a significant portion of the facet must be resected to reach the foraminal component of the tumor. This may potentially cause postoperative instability requiring fusion.15 Second, the VA providing the tumor blood supply is reached at the end of the surgical procedure, precluding any devascularization of the tumor supply before the final surgical step.14 Moreover, without proximal control of the VA, the risk of VA damage is higher.14 Finally, it often results in leaving tumor remnant that remains vascularized, and thus has a potential to grow in the future. For some anterior lesions, the anterolateral approach may be useful in select patients. It allows for complete devascularization of the tumor at the beginning of the procedure, cutting down on blood loss. Then, tumor resection can most often be completed in a single surgical step.14 The intradural component of the lesion may be accessed through the enlarged vertebral foramen that may be drilled out slightly. This tailored opening rarely destabilizes the spine and subsequent fusion is not uniformly required. The primary reason for a fusion is a history of previous laminectomy, which completely removes the facets. The anterolateral approach requires VA control, which requires experience. However, this approach is safe and associated with low morbidity rate in experienced hands;15,16 the incidence of permanent deficits drops to less than 3%.15,16 The main risk is a postoperative Horner syndrome.
The Anterolateral Approach with Vertebral Artery Control for Cervical Dumbbell-Shaped Tumors (Fig. 25.1)
Preoperatively, the VA position has to be anticipated by an MRA or CTA: anatomical variations must be ruled out, as well as VA displacement induced by the tumor.17,18 The tumor often grows at the posterior VA aspect therefore pressing on the artery anteriorly or anteromedially. The patient is placed in the supine position, with head lying on a small cushion, slightly extended with a tape passing under the chin and turned to the contralateral side at 30 degrees.15,16 Fluoroscopy is used to check the correct level. Electrophysiological monitoring (consisting of motor and somatosensory evoked potentials [MEP, SSEP] and electromyography [EMG]) is maintained throughout the surgical procedure. The skin incision follows the medial border of the sternomastoid muscle. After division of the platysma, the dissection is pursued medially to the medial border of the sternomastoid muscle and laterally to the internal jugular vein. The carotid-jugular sheath is left undissected and is retracted medially. Dissection of the sympathetic chain is an important step in avoiding the main complication of this approach, which is Horner syndrome. The sympathetic chain must be differentiated from the longus colli muscle (LCM) and retracted laterally using stitches applied on the LCM aponeurosis that has been divided medially to the chain. At the C6-C7 level, the thoracic duct on the left side or the accessory thoracic duct on the right side must be preserved to avoid a leak.19,20 After its exposure, the LCM must be resected. In order to prevent VA injury, the LCM must be resected down to the transverse processes above and below the level of tumor. It is safe because, in the absence of anatomical variations, the VA is protected inside the bone of the transverse foramen.15–18 Afterward, the muscle is resected along the lateral border of the cervical vertebrae. From an anatomical point of view, it must be pointed out that, between C6 and the foramen magnum, a venous plexus enclosed inside a periosteal sheath surrounds the VA. The periosteal sheath is continuous with the periosteum of each transverse process. It means the periosteal sheath should be left intact inside the transverse foramen. It can be achieved only by performing a subperiosteal dissection of the anterior branch of the transverse process with a smooth spatula before resecting the bone with a Kerrison rongeur.15,16 In case of tearing of the periosteal sheath, troublesome venous bleeds may arise but can easily be controlled by direct bipolar cauterization of the sheath itself or packing with resorbable cellulose.15,16 At this point, the VA is controlled from above and below the tumor. The vertebral foramen, already enlarged by the tumor, may be made slightly larger by drilling. The tumor feeders will be cauterized during the separation between the anterior aspect of the nerve root and the VA posterior border, facilitating further tumor resection.15,16 In the case of a schwannoma, the tumoral nerve root fascicle may be separated from the normal nerve roots. The nerve root may be sacrificed if there is already a neurological deficit by nerve root involvement.14 Intraoperative stimulation may provide additional relevant information for this decision.14 Pursuing a lateromedial tumor resection will allow entrance into the intradural compartment. The dura mater opening through which the tumor has passed may be enlarged as much as necessary to provide the appropriate intradural exposure. The use of an ultrasonic aspirator (the Cavitron ultrasonic aspirator, CUSA) is helpful for debulking the lesion.14 The tumor should then be cautiously separated from the spinal cord using a microsurgical technique.
Meningiomas (Fig. 25.2)
In the case of meningiomas, the tumor origin can be found anywhere along the surface of the dura. A general rule is that the neuraxis is displaced to the side opposite to the tumor origin. Therefore, posterior meningiomas put pressure on the spinal cord anteriorly and for this reason are better approached directly with a laminectomy. Posterolateral and lateral meningiomas displace the neuraxis anteromedially and medially, respectively. A posterolateral approach is advocated, by laminectomy possibly extended on the tumor side to the medial aspect of the facets. With anterolateral meningiomas, the posterior displacement of the neuraxis requires a more location-specific approach because surgical access is limited. In this situation, we still advocate a posterior approach, extended laterally on the side of the tumor, but the lateral surgical corridor must be enlarged by dividing dentate ligaments. With that maneuver, most lesions can be adequately resected. Rare reports have advocated the use of an anterior approach for anterior meningiomas.21 This anterior approach is considered safe and has several theoretical advantages: a large bony window of access, extradural cauterization of the anterior blood supply, direct visualization of the entire tumor ventralto the spinal cord, and tumor resection without spinal cord manipulation; but it is nevertheless associated with drawbacks, such as the need for fusion and a more challenging access route.21 It is nevertheless associated with drawbacks such as the need for fusion and a more challenging access route. The depth and narrowness of the working channel present a significant technical challenge. In addition, dural closure is also very difficult, resulting in a higher probability of CSF leakage.21
The Posterior Approach
The patient is placed in the prone position under continuous electrophysiological monitoring, especially for cervical lesions. At this level, we use a Mayfield head holder and are careful to position the head in a neutral position to avoid tumor-induced spinal cord compression. Fluoroscopy is used to accurately target the pathological levels. Usually, only two vertebrae must be exposed. The laminectomy may be extended laterally to facets on the side of the tumor. The dura mater is usually incised longitudinally over the tumor. The dural edges are retracted laterally with several 4-0 silk sutures. Lateral lesions may require section of the dentate ligaments to provide exposure. Sutures from dentate ligament to opposite dura keeps the surgical space open and offers good control of anterior dura as a result of gentle rotation of the spinal cord. Great care must be taken to avoid any traction or compression on the spinal cord itself. Cottonoids are placed at each end of the tumor to avoid intradural soiling. Most of the time, the arachnoid can be separated and the resection completed in the extra-arachnoidal plane. The tumor surface is cauterized and incised with a knife or microscissors. Samples are sent to the pathologist for immediate analysis. In lateral meningiomas, the tumor debulking is performed with either microinstruments or an ultrasonic aspirator, starting along the dural base if possible. Bleeding of feeding vessels is gently controlled with bipolar cauterization. In this way, the tumor is progressively devascularized and becomes mobile. The pressure at the tumor–spinal cord interface and at the dural insertion base is then released. Shrinkage of the tumor by electrocautery may also help to keep the plane open. Only vessels supplying the tumor should be sacrificed. Progressively, the dural base may be divided, resulting in tumor devascularization. Nevertheless, we advise keeping a small dural attachment until the tumor is completely released from the spinal cord. Otherwise, the lesion may become too mobile, thereby increasing difficulties and risks in completing the dissection of the spinal cord–tumor interface. At the completion of surgery, the dural base should be either cauterized or resected. The choice is guided by the location of the pathological dura and the possibilities of performing a watertight reconstruction. Resection and reconstruction with a patch graft is advised for posterior and posterolateral lesions. Contrarily, we advise only coagulating anterior or anterolateral dura mater portions. Cauterization instead of resection of the dura mater is not associated with a higher risk of recurrence.9,11,22 Finally, the intradural compartment is copiously washed with a normothermic saline solution. The dura mater is closed with a 5-0 nonabsorbable running watertight suture to prevent CSF leakage. The aponeurosis is also closed with a watertight running suture to avoid a CSF leak. Drains may be inserted at the level of the muscular layer.
Postoperative Outcome
Short-term outcome after the resection of SIEMTs is usually excellent, with the neurological condition generally improving significantly.2 Resolution of preoperative deficits has been noted in about 80% of the cases.7,8 The patient’s neurological condition remains stable in 14% of patients and few deteriorate.7 Several factors influence the outcome such as the preoperative neurological status, the duration of preoperative symptoms, and the type of surgical resection.7 The histological characteristics of the tumor may influence the long-term outcome: the psammomatous type is associated with a less favorable neurological outcome than the nonpsammomatous type. Psammomatous tumors consist essentially of acellular concretions, rendering blood vessels and spinal roots extremely adherent.8 Location of the tumor below C4 and posteriorly or laterally in the intradural compartment is, however, a favorable factor.8 Complete tumor resection is possible in 96% to 97% of the cases7,22 and is associated with a recurrence rate of 6% after 15 years of follow-up. Subtotal resection of a tumor resulted in recurrence in 17% of the cases.22 Serious complications may develop in case of perioperative vascular or medullar injuries but are unusual. Physical therapy hastens neurological recovery. Most patients can resume a normal or nearly normal neurological condition. A gratifying quick recovery may be observed within the first 6 weeks after surgery, but progressive recovery may be expected by 1 year after surgery. We see patients at 6 months, 1 year, and 2 years with performance of an MRI and then every 5 years in the absence of recurrence.
Radiation Therapy
When dealing with a malignant PNST, current consensus advocates postoperative radiation therapy (RT), started as soon as possible after surgery even if resection margins are tumor free.23,24 The role of radiotherapy in the management of spinal meningiomas is controversial. The slow indolent growth of these lesions and the risk associated with irradiating the vicinity of the spinal cord are confounding issues.7 Several indications for adjuvant radiation therapy have been proposed: early recurrence after total or subtotal resection, partial resection, and high-risk surgical treatment.7 If possible, we prefer repeat surgery over radiation for recurrence.
Intramedullary Spinal Cord Tumors
Surgery on spinal cord intramedullary tumors (SCIMTs) has been refined over the past few decades. The pioneering work of Elsberg25 and subsequently of many others such as Cooper,26 Epstein and Epstein,27 Guidetti and associates,28 McCormick and colleagues,29 Malis,30 Stein and McCormick,31,32 and many others33,34 have greatly contributed to advancing the microsurgical technique and success in removing spinal cord lesions. Several tools have added safety features to the microsurgical resection of these lesions. The advent of MRI has definitively improved diagnosis accuracy. The introduction of ultrasonic aspiration (CUSA) and intraoperative electrophysiological monitoring has modified the surgical approach and improved safety and outcome significantly.
Incidence and Types
With an incidence in adulthood of 2% to 4% of all central nervous system tumors, SCIMTs are considered rare.30,32,35–37 Three main groups of SCIMTs can be distinguished: tumors of glial origin, tumors of nonglial origin, and other mass lesions.
Tumors of Glial Origin
These tumors primarily consist of ependymomas and astrocytomas.13,38 Other glial tumors such as oligodendriogliomas are rare.39
Ependymomas
Spinal cord ependymomas are the most frequent SCIMTs in adult patients. They may reach considerable size prior to diagnosis. The majority of spinal cord ependymomas in adults have a good prognosis because usually they can be completely removed and are primarily grade II by the WHO classification. In the literature, the rate of complete removal varies from 69% to 97%.40–42 The vast majority of patients, 48% to 75%, are stabilized after the radical surgical resection, thereby highlighting the need for timely surgery in case of neurological deterioration.41–45 The overall rate of neurological improvement for this patient population varies between 10% and 40%.41–45 A rate of postoperative deterioration has been reported in the literature between 9% and 15%.41–45 Subtotal resection has been reportedly associated with a lack of clinical improvement,43 and incomplete resection is the most important factor correlating with tumor recurrence.41,46,47 The 5- and 10-year survival rates are respectively quoted between 83% to 96% and 80% to 91%.40,42,43,45,48,49
Astrocytomas
Spinal cord astrocytomas represent more than 80% of the SCIMTs in children,43 and in adults astrocytomas are the second most common type of tumor.43 Only 10% to 17% of astrocytomas in childhood are anaplastic lesions or glioblastomas, whereas in adults, the percentage is higher, 25% to 30%.28,34,43,50–53 In large studies, the proportion of pilocytic astrocytomas varies greatly from more than 30% to 60%.42,43 By their nature, grade II to IV tumors are infiltrating. Therefore, in contrast to ependymomas, radical resection of astrocytomas is not always possible. Surgery consists of removing as much tumor as possible. In some instances, one can only perform biopsy or decompression with duraplasty. In the literature, the rate of complete and subtotal removal varies between 11% to 31% and 21% to 62%, respectively.42,43,54 The pathological diagnosis of pilocytic astrocytoma and surgical experience are factors associated with higher rates of complete resection.42,43 Low spinal level (conus), malignancy, and adult onset are considered important factors associated with a higher tumor recurrence rate.43 The degree of resection, and spinal canal decompression via tumor debulking, have not been found to be directly related to progression-free survival or overall survival in many studies.26,32,43,50,52,55,56 In low-grade astrocytomas, the 5- and 10-year survival rates range from about 77% to 82%.43,56 These rates drop, respectively, to 27% and 14% for malignant astrocytomas.43,56
Gangliogliomas
Gangliogliomas are very uncommon lesions mainly reported as case reports and a few studies.57,58 These lesions are mainly encountered in children and young adults.57 In a large series of 56 patients, complete or subtotal resection has been achieved in 82%, and 18% of the patients had a 5-year survival rate of 88% and a progression-free survival rate of 67%.57
Factors Determining Outcome
The major determinant of long-term patient survival is based on the histological characteristics of the tumor. The 5-year progression-free survival (PFS) rate drops from 78% for low-grade gliomas to 30% for high-grade gliomas.50 A longitudinal database (Surveillance, Epidemiology, and End Results [SEER] database) encompassing 26% of the U.S. population was published in 2010 and included 1814 patients with spinal cord gliomas.59 In this study, age, histology, and grade were defined as significant predictors of outcome.59
Tumors of Nonglial Origin
Other lesions such as metastases, epidermoids, dermoid cysts, lipomas, intramedullary schwannomas, PNETs, and teratomas may also be encountered.13,43,55 In addition to these rare lesions, we have also encountered lymphomas and neuroglial cysts.
Hemangioblastomas
Hemangioblastomas are highly vascular lesions that represent almost 2% to 15% of SCIMTs in some studies.42,43,60–63 These lesions consist of two main components: (1) large vacuolated stromal cells that have been identified as the neoplastic cell of origin and (2) a rich capillary network.64 Hemangioblastomas are often observed as encapsulated lesions abutting the pia, especially at the posterior or posterolateral aspect of the spinal cord close to the dorsal root entry zone. They may also be encountered anteriorly or in intramedullary sites.43,60,
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