Radiation Oncology: A Question-Based Review

Primary Spinal Cord Tumor

Boris Hristov and Timothy A. Chan

image Background

At what level does the spinal cord (SC) end in adults? Newborns?

1.     Adults: L1-2

2.     Newborns: L3-4

What is the filum terminale?

The filum terminale is the filamentous process that anchors the dural sack inferiorly to the coccyx.

What is the conus medullaris?

The conus medullaris is the inf/tapering portion of the SC.

What % of all primary CNS malignancies arise in the SC?

~15% of all primary CNS malignancies arise in the SC.

What is the age range for primary SC tumors?

Primary SC tumors occur in the age range of 10–40 yrs.

Are most primary SC tumors intra- or extradural?

Intradural. If extradural, SC tumors are most likely to be metastatic, not primary.

Are most primary SC tumors intra- or extramedullary?

Two thirds of primary SC tumors are extramedullary.

What are the most common and 2nd most common intradural/extramedullary primary SC tumors?

Two thirds are schwannomas, and one third are meningiomas.

What % of primary SC tumors are intramedullary?

10% of primary SC tumors are intramedullary.

What are the most common intramedullary SC tumors, and what age group do they typically affect?

Astrocytomas > ependymomas; children/young adults (<30 yo)

What type of tumor typically arises at the filum terminale?

Myxopapillary ependymomas arise at the filum terminale.

From what anatomic portion of the meninges do mengiomas arise?

Meningiomas arise from the arachnoid layer.

What is a common age range and location for SC meningiomas?

SC meningiomas most often occur at age 50–70 yrs, with most presenting in the thoracic spine.

What grade is most common for primary SC astrocyomas?

~90% are low grade/WHO grades I−II (pilocytic/fibrillary).

What is the 3rd most common intramedullary SC tumor, and with what syndrome can it be associated?

Hemangioblastoma is the 3rd most common intramedullary SC tumor, with ~25% of cases associated with von Hippel-Lindau syndrome.

image Workup/Staging

What is the most common presenting Sx of primary SC tumors, and over what time frame do Sx present?

Primary SC tumors most commonly present with pain (75%), with Sx presenting over mos to yrs (long prodrome).

What is particularly important as part of the workup for a SC tumor?

Detailed neurologic exam and SC imaging (MRI or CT myelogram)

What is the difference between astrocytomas and ependymomas on MRI (location/appearance)?

1.     Astrocytoma: eccentric/asymmetric expansion of SC

2.     Ependymoma: central/symmetric expansion of SC

What is the MRI appearance of SC lipomas?

On MRI, SC lipomas appear bright on T1 without contrast, and signal disappears on fat suppression.

Which primary SC tumors require imaging of the entire craniospinal axis?

Ependymomas, glioblastoma multiforme, and anaplastic astrocytomas

image Treatment/Prognosis

What is the Tx paradigm for primary SC tumors?

Primary SC tumor Tx paradigm: max resection +/− RT or definitive RT alone

What are the 2 main advantages of upfront surgical resection?

Histologic confirmation and decompression of the cord

After GTR, which meningiomas—spinal or intracranial—have higher rates of recurrence?

Intracranial meningiomas have a 10%−20% recurrence rate, while spinal meningiomas have ~5% recurrence rate.

What is the most important predictor for recurrence for meningiomas/ependymomas?

Extent of resection is the most important predictor for recurrence. There are few recurrences after GTR.

In what % of SC meningioma/ependymoma pts is GTR achievable?

GTR is achievable in >90% of pts. (Retrospective series: Gezen F et al., Spine 1976Peker S et al., J Neurosurg Sci 2005)

In what proportion of SC astrocytoma pts is GTR possible?

GTR is possible in fewer than one third of pts.

Why is RT controversial for most SC tumors, even after STR?

Most SC tumors are indolent (slow growing), and there is potential for SC toxicity with RT.

What RT options are available after STR for meningioma/ependymoma?

Standard EB to 50.4 Gy (1.8 Gy/fx or 1 Gy bid) or stereotactic body RT, 16 Gy to 80% IDL (Bhatnagar AK et al., Technol Cancer Res Treat 2005)

What Tx options are available for SC astrocytomas?

1.     Low grade: observe after GTR/50.4 Gy after STR

2.     High grade: 54 Gy

What retrospective studies support use of RT in SC astrocytomas?

Rodrigues GB et al., IJROBP 2000 (Princess Margaret Hospital) and Abdel-Wahab M et al., IJROBP 2006: PFS was significantly influenced by RT in low- and intermediate-grade tumors; however, the RT group had fewer complete resections as compared with the surgery alone group (13% vs. 53%; p = 0.01).

What data supports the RT dose response for SC ependymomas?

1.     Garcia DM, IJROBP 1985: <40 Gy, 23% OS; >40 Gy, 83% OS

2.     Mayo data (Shaw EG et al., IJROBP 1986): 35% LF for <50 Gy vs. 20% for >50 Gy

For what type of SC tumor has adj RT been shown to be beneficial, regardless of extent of resection?

1.     Adj RT has been shown to be beneficial with myxopapillary ependymoma.

2.     MDACC data (Akyurek S et al., J Neurooncol 2006): +/− 50.4 Gy RT 10-yr LC GTR/STR (55%/0%) vs. GTR + RT/STR + RT (90%/67%), all SS

What RT schedule is often used for high-grade ependymomas +/+ CSF spread?

CSI to 36 Gy + boost to 50.4−54 Gy gross Dz

What anatomic region needs to be covered with RT in caudal ependymomas?

The thecal sac down to S2-3 needs to be covered.

What are the typical sup-inf RT margins for SC tumors?

The typical sup-inf margin required for SC tumors is 3–5 cm.

image Toxicity

What is the L–hermitte sign? When does it occur, and to what is it due?

The L–hermitte sign is shocklike sensations in the extremities upon neck flexion. It occurs within 2–6 mos of RT from demyelination of the nerve tracts.

When does RT myelopathy occur, and what is the temporal sequence of onset for neurologic deficits?

RT myelopathy occurs 13–29 mos after RT, with paresthesia → weakness → pain/temperature loss → loss of bowel/bladder function.

Within what time frame do SC astrocytoma pts usually relapse?

Relapse in SC astrocytoma pts usually occurs within 2 yrs (most in-field).

How long of a follow-up is required after SC ependymoma resection?

>10 yrs follow-up is required, as late recurrences (>12 yrs) have been reported in 5%−10% of pts.

What region of the SC has traditionally been thought to be most sensitive to RT? Least sensitive?

The lumbar SC is thought to be most sensitive to RT, while the cervical cord is thought to be least sensitive.