19: Resection of Intradural Intramedullary or Extramedullary Spinal Tumors

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Procedure 19 Resection of Intradural Intramedullary or Extramedullary Spinal Tumors

John Christos Styliaras, Ashwini Sharan, John Birknes, John K. Ratliff, James S. Harrop

image

Indications

image Spinal cord compression can manifest as

• Weakness (in either upper or lower extremities, or both)
• Loss of bowel and bladder function
• Sensory loss (to light touch or pinprick)
• Incoordination of hands or gait

image Symptomatic neuronal compression, manifesting as radiculopathy

image Progressive growth of lesion on serial imaging

image Persistent pain or radiculopathy

image Spinal deformity resulting from remodeling of osseous elements

Indications Pitfalls

• Presence of concurrent neural axis lesions

Examination/Imaging

image Physical examination

• Spinal cord compression—myelopathy
• Radicular signs or symptoms
• Dermatologic findings in neurocutaneous disorders (e.g., neurofibromatosis)

image Plain films/computed tomography (CT) scan

• Typically nondiagnostic
• Bone erosion or remodeling of osseous elements (scalloping) resulting from prolonged presence of the lesion may be seen, but not often.
• May use CT scan to diagnose bony versus soft tissue cord compression

image Magnetic resonance imaging (MRI) with gadolinium

• Study of choice, because it provides more information about the lesion itself
• Differentiates type of intradural lesion
♦ Extramedullary—extrinsic to the spinal cord

• Meningioma—dural based. On T1- and T2-weighted images, it appears as a homogenous hypointense lesion compared with the cord, while on contrast-enhanced MRI, it enhances homogenously. In addition, many times it is calcified.
• Nerve sheath tumor (schwannoma and neurofibroma): The tumor is a dumbbell-shaped lesion that has a separate plane, is extrinsic to the spinal cord, and follows the nerve through the neural foramina (Figure 19-1, A). Coronal Images (Figure 19-1, B) illustrate the path of nerve sheath tumor exiting the foramen around the pedicle. On T1-weighted images, it is isointense to the cord, while on T2 images, it appears heterogenous and hyperintense. On contrast-enhanced MRI, it often appears with an irregular margin and ring-shaped enhancement.
♦ Intramedullary—located within spinal cord parenchyma (Figure 19-2)

• Expansion of the spinal cord
• Associated with intraparenchymal cyst or syrinx
• Primary glial neoplasms (e.g., ependymoma) predominate. On T1-weighted images, they appear isointense to the cord, while on T2-weighted images, they are hyperintense. On contrast-enhanced MRI, these lesions present with a well-defined margin and homogenous enhancement.

image image

FIGURE 19-1, A-B

image

FIGURE 19-2

Treatment Options

• Maximal tumor resection: Favorable outcomes postoperatively on intramedullary tumors are based on the histopathology of the tumor, total resection, and neurologic status preoperatively. In extramedullary tumors, postoperative neurologic recovery is very favorable in the vast majority of cases.

• Serial observation with imaging and clinical assessment is an option for intradural spinal cord tumor management in neurologically intact patients.

• Radiation therapy is a secondary treatment option or an adjuvant therapy in malignant or rapidly recurrent intramedullary spinal tumors (although optimum management in such cases remains controversial).

Surgical Anatomy

image Spinal column defines boundaries of the spinal canal. These boundaries are

• Anterior—vertebral body
• Lateral—pedicles
• Posterior—laminae and spinous processes

image Levels of the spinal column are

• Cervical—7 vertebrae
• Thoracic—12 vertebrae
• Lumbar—5 vertebrae

image Spinal meninges or coverings of the spinal cord

• Dura mater
♦ Thick fibrous layer
♦ Separated from osseous region by a space containing epidural veins, adipose, and fibrous tissue
• Arachnoid
♦ Delicate layer in between the dura and pia mater, containing the subarachnoid space
♦ The subarachnoid space is filled with cerebrospinal fluid and extends down to S2
• Pia mater
♦ Thin layer on the surface of the spinal cord
♦ Contacts the spinal cord and is adherent to blood vessels entering the spinal cord

image Spinal cord

• Approximately 45 cm in length
• Thirty-one pairs of spinal nerves arise from the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
• Conus medullaris: terminal end of the spinal cord (ends at level L1-2)
• Filum terminalis: fibrous band that continues distally and attaches to the dorsum of the first coccygeal vertebrae
• Spinal cord: highly organized, somatotopically arranged tissue composed of two functionally and anatomically distinct regions
♦ Gray matter—central portion; consists of neuronal cell bodies and supporting structures

• Axial plane—central bridge of gray matter connecting each side such that, in an axial section, it resembles the letter H
• Ventral portion—anterior horn motor cells
♦ White matter

• Encircles gray matter
• Composed of both myelinated and unmyelinated axonal tracts
♦ Central canal—in the middle of the H

• Embryologic remnant from neurulation of the neural plate
• Continuation of the fourth ventricle from the medulla
• Spans the entire length of the spinal cord and terminates as a fusiform terminal ventricle in the conus medullaris
• Lined with cuboidal ependymal cells

Positioning

image General anesthesia with neurophysiologic monitoring

image Prone position with spinal axis in the midline

• Ensure eyes are not subject to external compression
• Ensure endotracheal tube is free and not obstructed
• Pad extremity peripheral nerves over bony protuberances (i.e., ulnar and peroneal)

image Occiput to T4 lesions (Figure 19-3)

• Application of a Mayfield headholder
• Neck remains in neutral position, and no external compression on the orbit or endotracheal tube
• Shoulder taped to facilitate imaging

image T4 to sacrum lesions (Figure 19-4)

• Andrews frame or laminectomy rolls
• Abdomen free of pressure, which provides for a decrease in the epidural venous pressure
image

FIGURE 19-3

image

FIGURE 19-4

Positioning Pearls

• With surgical positioning, minimizing compression upon the abdomen reduces intraabdominal pressure and thus epidural venous pressure. This reduces intraoperative blood loss.

• Localization of thoracic lesions may be difficult. Either preoperative localizer or entire spine radiograph may aid in localizing incision and tumor.

Positioning Pitfalls

• If shoulders are taped, ensure that the brachial plexus is not stretched. Intraoperative free-running electromyography or intraoperative upper extremity somatosensory evoked potentials may help limit plexus palsies.

Portals/Exposures

image Localize midline region and plan extent of laminectomy or bony removal.

image Make a midline incision down to the paraspinal fascia.

image Avascular subperiosteal dissection is continued bilaterally, centered over spinous process and laminae.

image The retractor system should be low profile and away from the surgical site.

image Use a high-speed drill to resect posterior elements.

image Drill through the laminae bilaterally at the facet–laminae junction.

image Resect the rostral and caudal interspinous ligaments.

image Resect the laminae en bloc and carefully dissect free all dural adhesions (Figure 19-5).

image Confirm that the extent of dural exposure is adequate through

• Palpation of the lesion
• Radiographic confirmation
• Intraoperative ultrasound

image Confirm that hemostasis is excellent, particularly at dural margins.

image

FIGURE 19-5

Portals/Exposures Pearls

• A short-acting muscle relaxant will provide easier dissection but also enable the use of neurophysiologic monitoring.

• An intraoperative localizing radiograph aids in minimizing osseous removal.

• Laminectomy should provide exposure of dural region necessary to define neoplasm margins, and a slightly greater incision provides for manipulation of the lesion.

• A hemostatic agent applied along the epidural and bony edges will be useful to tamponade any venous bleeding.

Portals/Exposures Pitfalls

• Do not expose facet joints, because this may lead to delayed instability.

• With inadequate hemostasis, particularly for epidural bleeding, bleeding will become excessive once the dura is opened.

• Inadequate exposure may create the need for further bony resection when the dura is opened and will allow unnecessary entry of blood and osseous shavings into the dural sac.

Portals/Exposures Equipment

• Retractor with low-profile bar: provides area to attach dural or pial sutures

• Paraspinal muscle hooks: provide exposure and are away from surgical site

Procedure

Step 1

image Hemostasis is meticulously maintained, particularly in the epidural region, before opening the dura.

image The rostral and caudal extent of the spinal lesion are defined and assured to be within the bony opening.

image Based on preoperative images, a single dural suture is placed, through which traction is applied to draw the dura away from the spinal cord.

image A midline or lateral dural incision is made with a sharp instrument.

• Maintain the arachnoid plane if possible.
• The arachnoid is opened and spinal fluid allowed to flow freely and decompress the canal.

image Dural tack-up sutures bilaterally maintain the exposure of the spinal lesion and prevent blood products from entering the cerebrospinal fluid (Figure 19-6). In addition, the epidural space can be visualized with the use of hemostatic material (Surgicel; Ethicon, Somerville, N.J.).

image

FIGURE 19-6

Step 1 Pearls

• Fold the dural edges over hemostatic strips, which are packed into the epidural space with the tack-up sutures.

• Tack-up sutures to the lateral muscles provide greater access to the spinal canal.

Step 1 Pitfalls

• Inadequate exposure before opening the dura results in the potential for bone and blood products to enter the spinal canal.

Step 2

image An intraoperative microscope is brought into the surgical field.

• Provides illumination
• Higher magnification of field than standard loupes

image Dissection with microinstrumentation enables the surgeon to

• Define normal anatomy proximal and distal to the lesion
• Outline proximal and distal extent of pathologic lesion (Figure 19-7)
• Determine nerve root or parenchymal involvement
image

FIGURE 19-7, A-C

Step 2 Pearls

• The microscope should be balanced with the correct cross-table attachments.

• Add film or CD-ROM to the microscope if applicable.

• Remove all previous surgical tools from the field and replace with a microdissection instrument set.

Step 2 Pitfalls

• Overmagnification using the microscope may limit the field of view.

Step 2 Instrumentation/Implantation

• Operative microscope

• Microdissection instrument set

Step 3

image Extramedullary lesions

• Nerve sheath lesions should be dissected from the spinal cord, and entering and exiting nerve rootlets should be defined (Figure 19-8).
• Neurofibromas and schwannomas may follow the exiting nerve and have a “dumbbell” appearance on imaging studies.
♦ Opening the nerve sheath and debulking may provide for manipulation of the intracanal portion away from the spinal cord.
♦ A major goal is to remove intracanal portion to prevent or remove cord compression.
• Neurophysiologic stimulation provides data on nerve conduction and potential sequelae of sacrifice.
• Meningiomas are dural based and dissected out en bloc and resected.

image Intramedullary lesions

• Define the lesion with intraoperative ultrasonography.
• Plan the cordotomy incision and bipolar coagulation of dorsal vessels along the cordotomy section.
• Make an incision parallel to posterior columns along the midline raphe.
• Biopsy the lesion and send the specimen to the pathologist.
• Lengthen the cordotomy to the extent of the lesion to enable removal of rostral and caudal poles.
• Define the gliotic planes and infold the tumor into the dissected region.
• Cavitation of the tumor with collapsing of the edges of the tumor’s capsule into the cavitation defect affords minimal manipulation of the neural elements.
image

FIGURE 19-8

Step 3 Pitfalls

• Active bleeding in the surgical bed is consistent with residual tumor.

Step 3 Instrumentation/Implantation

• Intraoperative ultrasonography

• Microdissection tools

Step 4

image After resection of the lesion, the wound is confirmed to have no active bleeding.

image Exploration of the surgical bed for residual neoplasm is necessary to confirm gross total resection.

image Dura is closed with nonabsorbable suture.

image Before completion of the dural closure, saline is injected into the subarachnoid space to confirm a watertight closure.

image The wound is closed in multiple layers.

Postoperative Care and Expected Outcomes

image MRI images of surgical resection should be obtained to confirm the extent of resection and to serve as a basis for future comparisons.

image On contrast-enhanced images, the amount of residual tumor can be assessed and can help determine the postoperative course of treatment.

Evidence

Berhouma M, Bahri K, Houissa S, et al. Management of intramedullary spinal cord tumors: surgical considerations and results in 45 cases. Neurochirurgie. 2009;55:293-302.

Biswas A, Puri T, Goyal S, et al. Spinal intradural primary germ cell tumour—review of literature and case report. Acta Neurochir. 2009;151:277-284.

Brotchi J. Intrinsic spinal cord tumor resection. Neurosurgery. 2002;50:1059-1066.

Burger PC, Scheithauer BW. Tumors of the central nervous system. In: Rosai J, Sobin LH, editors. Atlas of Tumor Pathology, series 3, facs 10. Washington, DC: Armed Forces Institute of Pathology; 1994.

Cavalcanti DD, Martirosyan NL, Verma K, et al. Surgical management and outcome of schwannomas in the craniocervical region. J Neurosurg. 2010;114:1257-1267.

Constantini S, Miller DC, Allen JC, et al. Radical excision of intramedullary spinal cord tumors: surgical morbidity and long-term follow-up evaluation in 164 children and young adults. J Neurosurg Spine. 2000;93:183-193.

Dong-Ki Ahn, Hoon-Seok Park, Daw-Jung Choi, et al. The surgical treatment for spinal intradural extramedullary tumors. Clin Orthop Surg. 2009;1:165-172.

Epstein FJ, Farmer JP, Freed D. Adult intramedullary astrocytomas of the spinal cord. J Neurosurg. 1992;77:355-359.

Mechtler L, Cohen ME. Clinical presentation and therapy of spinal tumors. In Bradley WG, Daroff RB, Fenchel GM, Marsden CD, editors: Neurology in Clinical Practice: The Neurological Disorders, 2nd ed, Boston: Butterworth-Heinemann, 1996.

Osborn AG. Diagnostic Neuroradiology. St Louis: Mosby–Year Book; 1994.

Simeone FA. Intradural tumors. In Rothman RH, Simeone FA, editors: The Spine, 3rd ed, Philadelphia: WB Saunders, 1992.

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