Spinal Cord Primary Tumors

Background

Approximately 15% of all primary CNS tumors arise in the spinal cord. The distribution of spinal cord tumors is significantly different than that of the brain. Dural tumors, including schwannomas and menigiomas predominate, followed by ependymomas. Gliomas of the spinal cord are uncommon. The majority of primary spinal cord tumors occur between ages 10 - 40 years.

Spinal axis tumors (intra-dural) arise from the spinal cord (intramedullary) or from surrounding structures (extra-medullary). The most common extramedullary intradural tumors are schwannomas and meningiomas. These tumors arise from the nerve roots and from the dura. A spinal tumor can produce focal neurologic deficits and distal symptoms or both. Local effects pinpoint the tumor location along the spinal axis, and distant effects reflect spinal cord tract involvement.

Two thirds of all spinal cord tumors are extramedullary and 2/3 of these are schwannomas. The remaining 1/3 are meningiomas. Only about 10% are intramedullary.

Intramedullary Tumors

Only 10% of primary spinal cord tumors are intramedullary, the most common being astrocytomas followed by ependymomas. Intramedullary tumors more commonly affect children and young adults < 30 years old.

Most intramedullary astrocytomas are WHO Grade I/II (LGG) and are pilocytic or fibrillary astrocytomas.

Myxopalillary ependymomas tend to arise from the filum terminae. Meningiomas tend to arise from the arachnoid layer.

Hemangioblastoma is the 3rd most common intramedullary spinal cord tumor. It is seen in patients with von Hippel-Lindau syndrome. VHL syndrome patients account for 25% of all hemangioblastomas.

Extramedullary Tumors

Extramedullary tumors (menigiomas) tend to appear later in life, often at get 50 - 70 years and most frequently present in the thoracic spine.

Spinal Cord Tumor Signs

Clinical signs of spinal cord tumors
Site	Findings
Foramen Magnum	11th Nerve Palsy (Trapezius/spinal accessory n.) 12th Nerve Palsy (Tongue paralysis) ipsilateral arm weakness early cerebellar ataxia Neck Pain
Cervical Spine	I/L arm weakness progressing to leg and contralateral arm with time wasting and fasiculation of the I/L neck, shoulder and arm decreased pain and temperature sensation in the upper cervical dermatomes early cervical neck pain
Thoracic Spine	Abdominal muscle weakness unilateral nerve root pains sensory level pain or parasthesias with ipsilateral changes early progressing to bilateral presentation
Lumbosacral region	Sciatic pain or Root pain in goin region weakend proximal pelvic muscles impotence bladder paralysis decreased knee reflex, with brisk ankle jerk reflex
Cauda Equina	Unilateral pain in back and leg progressing to bilateral pain with large tumors paralysis of bladder and bowel

Spinal Cord Anatomy

The spinal cord terminates at L1-L2 in adults. In children the cord extends to L3-L4 (newborns). It is terminated by the filum terminae which anchors the dural sac to the coccyx. The conus medullaris is the tapered portion of hte spinal cord giving rise to the cauda equina.

Workup and Staging

Primary spinal cord tumors present primarily with pain. 75% have pain on presentation as a chief complaint. Symptoms have a long prodrome lasting months to years. A detailed neurologic exam and spinal cord imaging with MRI or CT myelogram are used in the initial work up of spinal cord tumors. Astrocytomas are eccentric or asymmetric expansions of the cord, while ependymomas are central lesions with symmetric expansion fo the cord. Ependymomas and HGG (glioblastoma, anaplastic astrocytomas) require imaging of the entire craniospinal axis.

Spinal cord lipomas appear brightly on MRI T1 without contrast, and disappear on fat suppresed sequences.

Treatment

Surgery

Surgery is the primary first step in management of spinal cord primary tumors. The maximum safe possible resection ± RT, or when safe resection is not possible, then radiotherapy alone as definitive treatment is used. The two main advantages of initial surgical resection are histologic confirmation of diagnosis and decompression of the cord.

Intracranial meningiomas recur much more frequently at 10% - 20% than spinal cord meningiomas at 5% after gross total resection. GTR is achievable in spinal cord meningiomas and ependymomas in more than 90% of cases. However spinal cord astrocytomas are far less likely to have a gross total resection with less than 1/3 completely resectable.

Radiotherapy

Radiotherapy is controversial in spinal cord tumors, even after subtotal resection. Most spinal cord tumors are meningiomas or low grade gliomas and have an indolent course. There is significant potential for radiation toxicity in spinal cord treatment. Standard radiation therapy treatments after subtotal resection for meningiomas and ependymomas are 50.4 Gy at 1.8 Gy/fraction or 1 Gy BID or stereotactic radiotherapy to 16 Gy at the 80% IDV in a single fraction.

Treatment of low grade astrocytomas of the spinal cord include observation only after gross total resection and radiation to 50.4 Gy at 1.8 Gy/fraction after subtotal resection. For High grade astrocytomas, the treatment is 54 Gy.

Retrospective studies at Princess Margaret Hospital published in 2006 demonstrated PFS was significantly influenced by radiation in low and intermediate grade tumors. This study was influenced by the fact that the radiation therapy group had fewer complete resections compared with the surgery group alone.

Garcia (1985) and Shaw (1986 Mayo) examined dose response in ependymomas. Garcia reported 23% overall survival in doses < 40 Gy while increasing the dose beyond 40 Gy resulted in improved OS to 83%. Shaw looked at 50 Gy and below and found a local failure for dose < 50 Gy of 35% compared with local failure improving to 20% with dose > 50 Gy.

Radiotherapy has been shown to be beneficial for myxopapillary ependymoma regardless of the extent of surgical resection.

Myxopapilliary ependymomas, which are commonly associated with the conus medullaris and filum terminae region, all benefit from radiation, regardless of the extent of surgical resection. The field for these tumors (and others in the the distal CNS) covers the thecal sac down to S2-3. Inferior margins for spinal cord tumors are 3 - 5 cm.

Craniospinal radiation for high grade ependymomas (anaplastic and ependymoblastoma (WHO Gr. III/IV) ) ± CSF seeding is often given according to the following schedule: CSI to 36 Gy followed by a boost to 50.4 Gy - 54 Gy for gross disease.

Note that the present CCG recommendations for children under 3 years old recommend delay of radiation until children are greater than three. For those older than three, CSI is indicated if CSF is positive Chang M+), MRI demonstrates imaging confirmation of leptomeningeal involvement or ependymoblastoma.

Toxicity and Constraints

L'hermitte sign is a shock like sensation in the extremeties on neck flexion. It occurs 2 - 6 months post radiation and results from transient demylination of the nerve tracts.

Radiation therapy myelopathy generally occurs 13 - 29 months after radiation. It presents with parasthesias followed by weakness followed by pain and temperature loss followed by loss of bowel and bladder function.

The lumbar cord has traditionally been thought to be the most radiosensitive, while the cervical cord is considered to be the least radiosensitive.

Spinal Cord astrocytomas usually relapse within 2 years, mostly with in field failures.

Ependymoma failures can occur very late. Failures after 12 years have been reported so > 10 years follow up is required after spinal cord ependymoma resection.

Radiation Oncology Synopsis