PATHOGENESIS

 

 

Intradural tumors are rarely the result of metastatic spread of malignant cells. The main categories of intradural tumors are intradural extramedullary and intradural intramedullary. Some tumors will exhibit characteristics of both intramedullary and extramedullary or exophytic growth.

 

Intradural tumors of the spine are less common than primary or metastatic tumors of the bone or epidural space. Their surgical removal requires delicate technique and maximal avoidance of injury to the spinal cord and nerve roots.

 

The most common types of tumor that are found in the intradural extramedullary space are benign meningioma, schwannoma, and neurofibroma.

 

Teratoma is a more rare intradural tumor that often is both intramedullary and extramedullary.

 

The most common intramedullary tumors are spinal cord ependymoma, hemangioblastoma, lipoma, astrocytoma, and glioblastoma. They are rarely exophytic except for ependymomas that occur at the conus medullaris.

 

Nerve sheath tumors (schwannoma, neurofibroma) usually present with radicular symptoms, and myelopathic symptoms develop once the tumor has enlarged to the point where it is causing compression of the spinal cord.

 

In the lumbar spine (below the conus medullaris), intradural extramedullary tumors commonly cause radicular symptoms (pain, paresthesias, weakness), and low back pain can develop and rapidly progress to an excruciating level when the tumors grow to occupy the majority of the spinal canal.

 

Intradural intramedullary tumors can cause axial or radicular pain, but the most common presentation is myelopathy. The progression is typically very slow over many months, unless the pathology is the malignant glioblastoma of the spinal cord. A careful preoperative evaluation must eliminate other pathology of the spinal cord parenchyma such as sarcoidosis, transverse myelitis, multiple sclerosis, etc.

 

PATIENT HISTORY AND PHYSICAL FINDINGS

 

Presenting symptoms of both intramedullary and extramedullary spinal cord tumors include axial or appendicular/radicular pain. The pain is usually persistent when either active or at rest.

 

Myelopathic symptoms present as numbness, tingling (paresthesias), gait instability, small motor/hand incoordination (cervical), increasing urinary voiding frequency, difficulty voiding, and general motor weakness.

 

Upper motor neuron signs such as hyperreflexia, Hoffman sign, spreading of reflexes, myoclonus, and Babinski signs are typical.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Magnetic resonance imaging (MRI) is the imaging technology of choice for intramedullary and extramedullary spinal cord tumors. Contrast enhancement is necessary.

 

Intramedullary tumors have fairly characteristic appearances on MRI.

 

 

Astrocytomas will demonstrate variable contrast enhancement and almost never have a solid, homogenous area of enhancement.

 

Ependymomas consistently have a homogenously enhancing mass within the parenchyma of the spinal cord (FIG 1A).

 

T1-weighted images will show low intensity within the tumor mass that enhances brightly on contrast administration.

 

Often, T2-weighted images will demonstrate surrounding edema within the spinal cord.

 

Hemangioblastomas typically have a cystic area of low signal intensity on T1-weighted images with a smaller contrast-enhancing nodule on the inside wall of the cyst.

 

Intramedullary lipomas will be nonenhancing and exhibit the typical high signal on T1- and T2-weighted images as seen in bodily adipose tissue.

 

Extramedullary tumors such as meningiomas will usually enhance positively with contrast in a very homogenous pattern, and often, a “tail” of enhancement will be seen in the location of attachment to the dura (FIG 1B,C).

 

Schwannomas and neurofibromas can have homogeneous or heterogeneous enhancement patterns. Some schwannomas will exhibit little to no enhancement, but this is less common.

 

For patients that cannot undergo an MRI (eg, those with pacemakers, defibrillators, spinal cord stimulators), computed tomography (CT) myelography can be used and can delineate an area of spinal cord swelling or even myelographic block that would indicate the location of intramedullary tumors. Extramedullary tumors are usually well outlined by CT myelography.

 

NONOPERATIVE MANAGEMENT

 

Asymptomatic patients with minimal or no upper motor neuron signs can be watched closely with serial neurologic and MRI examination.

 

Patients with lumbar intradural tumors that are asymptomatic can similarly be watched carefully, but one needs to make sure that even subtle signs of lower motor neuron bladder dysfunction are in fact not present.

 

 

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FIG 1 • A. Ependymoma on contrast-enhanced MRI. B,C. T1-weighted MRIs with and without contrast, respectively. Intradural extramedullary meningioma enhanced with contrast. Note dural tail sign (arrows in B).

SURGICAL MANAGEMENT

Intradural Extramedullary Tumors

 

The indications to proceed with surgical resection of intradural tumors of the spine include severe, progressive axial or radicular pain; progressive weakness due to nerve root compression or involvement; and myelopathic symptoms of an upper motor neuron bladder, spastic gait disturbance, incoordination of the upper extremities, generalized weakness, and sensory loss or disturbance.

 

Preoperative Planning

 

Surgery for intradural extramedullary tumors is usually done via a posterior approach. Preoperative intravenous antibiotics with good central nervous system (CNS) penetration such as Nafcillin or Ancef are administered within 1 hour of the skin incision.

 

Positioning

 

Patients with tumors located between the skull base and the upper thoracic spine (approximately T4-T5) are positioned on chest rolls with the head in the table-mounted, three-pin headholder.

 

A slightly flexed position is used for most cervical tumors.

 

If posterior fusion with instrumentation is planned, a more neutral sagittal position is preferred. A urethral catheter is placed in most cases.

 

Intradural Intramedullary Spinal Cord Tumors

Preoperative Planning

 

The most common tumor type encountered within the parenchyma of the spinal cord is ependymoma, astrocytoma, hemangioblastoma, and lipoma.

 

The presenting symptoms of intramedullary tumors are less radicular and mostly myelopathic.

 

Deep axial or radicular pain is uncommon. Numbness, spasticity, disturbance of bladder function, and quadriparesis are most commonly the presenting symptoms.

 

Needle biopsy is not recommended due to the risk of spinal cord injury and hemorrhage. Therefore, open biopsy and resection is the standard practice for primary intramedullary tumors.

 

Patients should be counseled extensively regarding the much higher risk and expectation of new postoperative deficits compared with extramedullary tumors.

 

Almost all patients will experience some degree of new or increased sensory or motor disturbance as a result of removal of an intramedullary spinal cord tumor.

 

In the early postoperative state, it is difficult to ascertain what new deficits will be transient and which changes may be permanent. Most patients, however, experience improvement of new neurologic findings over time.

Some patients will have new permanent deficits, and in some patients, there will be progressive neurologic deficits as seen in patients with a malignant, incompletely resected astrocytoma of the spinal cord. Often, these tumors respond poorly to radiation therapy and chemotherapy.

 

Positioning

 

Positioning and laminar bone removal is essentially identical to that performed for extramedullary tumors.

 

The dural opening is usually made in the midline regardless of the eccentricity of the tumor within the spinal cord.

 

Although the techniques of internal debulking and tumor capsule dissection are fairly consistent with all solid extramedullary tumors, the strategies of resection for intramedullary tumors varies with tumor type.

 

MRI characteristics of the tumor preoperatively usually allow the surgeon to anticipate whether there is going to be a demarcation between tumor capsule and spinal cord tissue (as with ependymoma), or whether there is going to be a diffuse blending of tumor tissue with the spinal cord tissue at the periphery of the tumor (astrocytoma, lipoma), or whether there is a large cystic area containing a smaller mural nodule of tumor (hemangioblastoma).

 

 

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TECHNIQUES

• Microsurgical Resection of Intradural Extramedullary Tumors Incision and Exposure

  After the skin preparation, a midline incision is made and a subperiosteal exposure of the spine is accomplished.

  The dural opening for most intradural extramedullary tumors will usually need to include a lamina above and below the pathology, so the number of laminae to be removed is usually clear from the sagittal and axial MRI or CT myelogram images.

  The dural opening is usually midline, but the opening can be paramedian in patients with tumors eccentric to one side.

  Large schwannomas and neurofibromas will often be visible upon exposure as a dura-covered mass extending out and expanding the neural foramen. In these cases, the dural opening is often lateral, with a T-shape extension of the midline opening.

  As with all tumors located in or extending out laterally to the neural foramen, the location of the vertebral artery must be clearly known from preoperative imaging studies. This artery is most commonly displaced anteriorly and can remain patent.

  In such cases, the vertebral artery can almost always be spared following resection.

  For tumors in which the vertebral artery is encased within the mass of the tumor, consideration can be given to preoperative endovascular test occlusion and subsequent obliteration via coiling/embolization.

  Resection

  For extramedullary tumors such as schwannoma, neurofibroma, and meningioma, the essential techniques of tumor removal consist of internal debulking of the tumor, delicate dissection of the tumor capsule from the pial surface of the spinal cord, and meticulous sparing and protection of surrounding nerve rootlets.

  An ultrasonic aspirator is most useful for internal debulking of these tumors. The surgeon must be careful to avoid going through the capsule of the tumor.

  It is helpful to pause from resection every few minutes and three-dimensionally reassess the extent of tumor mass remaining by careful palpation and manipulation of the tumor capsule and remaining tumor mass using microinstruments.

  All three of these tumor types typically allow for successful peeling of the final capsule off of the pial surface of the spinal cord.

   

  In cases in which the tumor capsule is very adherent to the pial surface or to the surface of posterior or ventral nerve rootlets, the surgeon may elect to leave behind that material and coagulate it with bipolar cautery.

   

  With large, ventral dural-based (meningioma) or nerve root sleeve tumors, it is usually necessary to cut the denticulate ligaments at the equator of the spinal cord. This should be done at several levels so that manipulation of tumor does not result in excessive torquing of the spinal cord tissue in a small area.

   

  Microscopic monofilament suture (eg, 6-0, 8-0 Prolene [Ethicon, Somerville, NJ]) can be placed through the base of the denticulate ligaments to provide a means of gently rotating the spinal cord.

   

  If rotation is necessary to gain access to large ventral tumors, then the denticulate ligament should be released over several levels (not just in the vicinity of the tumor).

   

  Blood pressure should be maintained at normal levels and consideration can be given to using motor evoked potentials and somatosensory evoked potentials.

   

  Changes in potential readings during rotation of the spinal cord can allow the surgeon to release the traction to help prevent injury.

   

  In removal of a meningioma, the surgeon should assess the location of the dural attachment and decide whether dural resection and patching is possible or whether coagulation (alone) of the area is best.

   

  Ideally, resection of the area of dura from which the tumor arose provides the best protection against recurrence. Local fascia or lyophilized bovine pericardium or synthetic materials can be used for sewing in a patch.

   

  With final removal of a schwannoma, all nerve fibers that are not the source of the tumor are carefully dissected off the capsule and preserved. Those that clearly enter the bulk of the tumor are cut and removed with the tumor.

   

  Prior to final closure, meticulous inspection for bleeding is performed. One should limit the amount of bipolar coagulation of pial blood vessels. Often, holding a thrombin-soaked collagen sponge with gentle pressure over a small bleeding venule or arteriole is sufficient to stop microscopic hemorrhage.

   

  The dural is then closed with a running (locking or unlocked) monofilament or braided nylon or Prolene suture. Interrupted dural closure is also acceptable. Fibrin glue or other synthetic glue products are often used to reinforce the suture closure.

   

  The adjuvant use of external lumbar cerebrospinal fluid draining is up to the judgment of the surgeon and may be helpful particularly in cases where weeping of cerebrospinal fluid is seen despite a good suture closure of the dura.

• Microscopic Resection of Intramedullary Tumors Incision and Exposure

 

One important decision involves where to enter the spinal cord. For tumors that come to the pial surface, it is obviously safest to enter there.

 

Many tumors, however, have normal spinal cord tissue between the tumor and the pial surface. They may be eccentric to one side.

 

For centrally located tumors, a midline myelotomy should be considered (TECH FIG 1).

 

For eccentric tumors that do not come to the surface, the dorsal root entry zone should be considered.

 

Ultrasound can be helpful in assessing the location and outline of the tumor. The pia is coagulated using microbipolars at low

 

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settings, and a no. 11 blade scalpel or microscissors are used to open the pial layer.

 

 

 

TECH FIG 1 • Initial dissection of the arachnoid, preparing for midline myelotomy. Note dural tack-up sutures.

 

 

Microinstruments are then used to gently tease open the tissue from inside out, working up and down along the extent of the tumor and respecting the cephalocaudal orientation of the long tracts.

Resection

 

With an ependymoma, the tumor capsule will be a distinctly different color (gray-red) than the surrounding white spinal cord parenchyma (TECH FIG 2A).

 

When a portion of the tumor capsule has been exposed, the capsule is coagulated and incised with a no. 11 blade scalpel.

 

The ultrasonic aspirator and hand instruments such as cupped forceps or micropituitary rongeur are used to internally debulk the tumor tissue.

 

A portion can be sent for frozen section analysis.

 

The important step in internal debulking of an ependymoma is making sure that one does not penetrate the capsule because there is often normal tissue ventral and lateral to the capsule (TECH FIG 2B).

 

 

 

TECH FIG 2 • A. Myelotomy complete, exposing tumor mass within parenchyma of the spinal cord. Small pia-arachnoid sutures can be seen superiorly and inferiorly holding open myelotomy. B. Final portions of tumor being removed with normal spinal cord tissue at base of cavity within spinal cord. C. Tumor removed, pial sutures released.

 

 

With this tumor type, there is almost always a ventrally located artery supplying the tumor that one will encounter and need to coagulate as the final, ventral portions of the capsule are resected (TECH FIG 2C).

 

Small Cottonoid patties (Codman, Warsaw, IN) are very useful in “claiming territory” as the capsule becomes soft and floppy. Multiple Cottonoids placed between the capsule and the tumor tissue serve as further protection against instrument damage. Gross total removal of an ependymoma is often feasible.

 

With a spinal cord astrocytoma, the demarcation between tumor tissue and spinal cord parenchyma is often difficult.

 

The goals of surgery are different from an ependymoma removal where gross total resection can be achieved.

 

With an astrocytoma, the surgeon must carefully judge the appearance of the tumor tissue under the microscope. Clearly abnormal tissue that is more yellow or gray can usually be safely removed without devastating consequences.

 

Once the demarcation is no longer clear, one should consider avoiding further tumor removal.

 

In cases where the frozen section results show a high-grade (malignant) astrocytoma or glioblastoma, then the prognosis is very poor and the risk of creating devastating neurologic loss may not be of value to the patient.

 

Spinal cord lipomas are usually solid, bright yellow tissue and easily distinguished from normal spinal cord parenchyma.

In rare cases, the tumor mass may be discovered to be in liquid, oily form rather than solid tissue. These tumors usually are visible on the pial surface and can even be exophytic, but ventrally and laterally, the fatty tissue can blend in with the normal parenchyma. Thus, gross total resections may not be possible without the increased risk of neurologic injury. Often, a small rim of lipomatous tissue is left behind.

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With cystic hemangioblastomas, the surrounding spinal cord tissue does not necessarily have to be opened along the entire extent of the cystic cavity.

Attention is paid to where the mural nodule of tumor is located.

The myelotomy should be performed closest to the level where the nodule is located, and often, only a portion of the cystic cavity is exposed that allows adequate visualization of the tumor.

Vessels identified under magnification that are feeding and draining the tumor are coagulated and cut, and the tumor can often be dissected off of the wall of the cystic cavity.

The fluid of the cavity typically drains out spontaneously after working and irrigating during tumor removal. Meticulous hemostasis (as always) is confirmed prior to dural closure.

 

 

 

PEARLS AND PITFALLS

 

• The essence of surgery for removal of intradural extramedullary tumors is internal debulking of the tumor and careful dissection of tumor capsule from the pial surface of the spinal cord.

   

• In removing intradural intramedullary tumors of the spinal cord, preoperative knowledge of the anatomic characteristics such as the presence of a cyst, the sharpness of demarcation on imaging of the tumor, the presence of a mural nodule, etc. all help guide the surgeon in deciding the location of the initial myelotomy and the approach to the tumor.

   

• With ventral tumors, multiple levels of release of the denticulate ligaments is helpful.

   

• When dissecting or manipulating normal or tumor tissue, use fine, slow movements to minimize tissue trauma.

   

• Always dissect during the initial myelotomy with the idea of the cephalocaudal orientation of the long tracts.

   

• Avoid using coagulation on normal pial vessels (gently apply Gelfoam sponge [Baxter Healthcare Corp., Hayward, CA] and micro-Cottonoid and most bleeding will stop in tiny vessels).

   

• Frequently zoom out and take in the larger picture of how far along the tumor resection has progressed.

   

• The “backside” or “side walls” of the tumor or tumor capsule will come up faster than you think; avoid breaching that final layer of tumor tissue and injuring normal tissue on the blind side of the tumor.

 

 

 

 

POSTOPERATIVE CARE

Intensive care unit observation of immediate postoperative patients is recommended following resection of an intradural intramedullary or extramedullary spinal cord tumor so that blood pressure can be monitored, and frequent neurologic examinations can be performed to identify those rare patients with a complication such as a postoperative epidural or intramedullary hemorrhage.

The use of corticosteroids is at the discretion of the surgeon.

External cerebrospinal fluid diversion via a lumbar intrathecal drain may be used.

 

Patients with cervical or upper thoracic tumors can be nursed in a partially upright or sitting position as this will decrease the cerebrospinal fluid pressure in the area of the dural closure.

Lower thoracic (and lumbar) tumor patients are often kept at flat bed rest, although no guidelines exist for this issue, and the decision is at the discretion of the surgeon.

Progressive mobilization and ambulation can begin very soon after surgery or a period of bed rest.

 

COMPLICATIONS

The most concerning complication is quadriplegia, and this may occur even when very delicate handling of spinal cord and tumor tissue has been performed. This complication can sometimes not be avoided, but short amplitude, delicate movements of the microinstruments; maintenance of normal blood pressure and oxygenation; and preservation of normal arteries, arterioles, veins, and venules are of great importance.

Postoperative intramedullary hemorrhage is rare and meticulous confirmation of hemostasis while under the microscope is essential.

Cerebrospinal fluid leak is a more common complication. Attention to watertight closure suturing technique is important, and many surgeons use various forms of fibrin glue or synthetic materials to help seal the suture closure.

In patients with thin or easily torn dura and/or leaking of cerebrospinal fluid through the suture holes, postoperative external cerebrospinal fluid drainage via a lumbar intrathecal catheter can be helpful. Three to 5 days of drainage in those patients is commonly practiced.

 

 

 

SUGGESTED READINGS

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1. Angevine PD, Kellner C, Hague RM, et al. Surgical management of ventral intradural spinal lesions. J Neurosurg Spine 2011;15(1): 28-37.

    

2. Boström A, von Lehe M, Hartmann W, et al. Surgery for spinal cord ependymomas: outcome and prognostic factors. Neurosurgery 2011;68(2):302-308.

    

3. Kucia EJ, Bambakidis NC, Chang SW, et al. Surgical technique and outcomes in the treatment of spinal cord ependymomas, part 1: intramedullary ependymomas. Neurosurgery 2011;68(1 suppl): 57-63.

    

4. Kucia EJ, Maughan PH, Kakarla UK, et al. Surgical technique and outcomes in the treatment of spinal cord ependymomas: part II: myxopapillary ependymoma. Neurosurgery 2011;68(1 suppl):90-94.