Update: Spinal astrocytoma

Epidemiology

Spinal astrocytomas are the second most common spinal cord tumor overall, representing 40% ofintramedullary tumor.

They account for 60% of paediatric intramedullary tumours, making them the most common spinal cordtumour in children.

The peak incidence of spinal astrocytomas occurs in the third decade, with the mean age at presentation being 29 years. Males are somewhat affected more commonly than females (M:F = 3:2) 1) 2) 3).

Associations

There is an increased incidence in neurofibromatosis type 1.

Clinical presentation

Clinical presentation is similar to that of other intramedullary spinal tumours, with pain, weakness and sensory changes common. Bowel and bladder dysfunction are uncommon

Pathology

Spinal cord astrocytomas generally have a lower histologic grade than astrocytomas in the brain (see grading of astrocytomas). In adults, 75% are low-grade neoplasms. Up to 25% are anaplastic astrocytomas. Glioblastoma multiforme represent only 0.2-1.5% of spinal cord astrocytomas. In children younger than 3, 80% are either grade I or II 5.

All astrocytomas are characterised by hypercellularity and the absence of a surrounding capsule. In contrast to cord ependymomas, a cleavage plane is not present in most intramedullary spinal astrocytomas.

High grade tumours are more likely to demonstrate extensive leptomeningeal spread seen in up to 60% of spinal cord glioblastomas.

Radiographic features

General imaging features

The most common location of astrocytomas is the thoracic cord (67%), followed by the cervical cord (49%), and tumour may of course involve both regions. Involvement of the entire spinal cord (holocord presentation) may occur and is more common in children than in adults. Isolated conus medullaris involvement is seen only rarely (3%) and involvement of the filum terminale is rare (whereas this is the typical location of myxopapillary ependymomas).

Astrocytomas are typically long multisegment intramedullary masses that cause diffuse cord expansion. The average length of involvement is 4-7 vertebral body segments 5,7.

Plain film/CT

Can be often normal however as these tumours are slow growing bony remodelling is not infrequently visible, with posterior vertebral body scalloping or thinning of the pedicle or laminae. Scoliosis is also present in a reasonable number of patients, especially in children presenting with holocord involvement 5. These features are however less common than in spinal ependymomas.

On CT expansion of the cord is frequently visible, but due to the lower contrast resolution compared to MRI can be subtle. If contrast is administered contrast enhancement is frequently visible.

Myelography

May show non specific multisegmental cord enlargement, and may results in a block to normal flow of contrast past the lesion, although this is more common with ependymoma.

MRI

MRI is the diagnostic modality of choice: spinal cord astrocytomas are iso- to slightly hypointense on T1, hyperintense on T2 and commonly have associated cysts. They enhance less intensely 4).

As astrocytomas arise from cord parenchyma (rather than the central canal as is the case for ependymomas), they typically have an eccentric location within the spinal cord. They may be exophytic, and even appear largely extramedullary. They usually have poorly defined margins. Peritumoral edema is present in 37% 8. Intratumoural cysts are present in approximately 21% and peritumoral cysts are present in aproximately 16% 8.

Unlike ependymomas, haemorrhage is uncommon.

Reported signal characteristics include:

T1: isointense to hypointense

T2: hyperintense

T1 C+ (Gd)

vast majority enhance (used to thought that all enhance but this is not the case)

usually patchy enhancement

Differential diagnosis

The main differential diagnosis is a spinal ependymoma. Certain imaging features may help to differentiate between the two:

ependymoma

more common in adults

scoliosis and bony remodelling more common

central location in spinal canal

well-circumscribed

haemorrhage is common

may rarely present as a subarachnoid haemorrhage

hemosiderin staining especially at the superior and inferior margins (so-called hemosiderin capping) is common focal, intense homogeneous contrast enhancement more frequent and more prominent cysts (intratumoral and polar)

Treatment

There are currently no clear treatment guidelines for the management of spinal cord astrocytomas. Additionally there is no conclusive evidence for the surgical resection of these tumors, with some studies even demonstrating worse survival with surgery. However, most studies have examined patients treated prior to the routine use of magnetic resonance imaging and advanced microsurgical techniques.

Somatosensory and motor evoked potential monitoring are routinely used but it is unclear if they improve outcomes. The operating microscope and bipolar cautery are essential surgical tools; the ultrasound and ultrasonic surgical aspirator are useful surgical adjuncts. Laminectomy is performed on adults while laminoplasty is favored for pediatric patients.

Prognosis

Astrocytomas are generally faster growing than ependymomas and typically have a worse prognosis.

Outcome for low-grade astrocytomas is less favorable than that of ependymomas with regard to both recurrence and function though many have prolonged survival. There is no correlation of extent of resection and recurrence. Outcome for high-grade tumors is extremely poor; tumor progression is relentless; median survival is thirteen months in children and six months in adults 5).

Cord astrocytomas in children tend to be associated with a good prognosis, as they behave much like grade I cerebellar pilocytic astrocytomas and displace neural tissue rather than infiltrate it.


A retrospective review of 46 consecutive patients with spinal cord astrocytomas treated from 1992 to 2012. Univariate and multivariate analyses were used to identify variables associated with survival.

The majority of patients (67.4%) underwent surgical resection, with the remaining only receiving biopsy. Of those who underwent resection, only 12.5% of patients underwent gross total resection, all of whom had low-grade astrocytomas. Of all patients, 30.7% worsened compared with their preoperative baseline. The occurrence of worsening increased with high tumor grade (52.9% vs. 27.6%, P = 0.086) and an increased extent of resection (66.7% vs. 18.8%, P = 0.0069). Resection did not provide a survival benefit compared with biopsy alone (P = 0.53). Multivariate analysis revealed high-grade histology (hazard ratio, 11.3; 95% confidence interval, 2.41-53.2; P = 0.0021), tumor dissemination (hazard ratio, 4.24; 95% confidence interval, 1.22-14.8; P = 0.023), and an increasing number of tumor involved levels (hazard ratio, 1.31; 95% confidence interval, 0.99-1.74; P = 0.058) to be associated with worse survival.

As surgical intervention is associated with a higher rate of neurological complications and lacks a clear benefit, the resection of spinal cord astrocytomas should be reserved for select cases and should be used sparingly 6).

1) Harrop JS, Ganju A, Groff M, Bilsky M. Primary intramedullary tumors of the spinal cord. Spine (Phila Pa 1976). Oct 15 2009;34(22 Suppl):S69-77.
2) Horbinski C, Hamilton RL, Nikiforov Y, Pollack IF. Association of molecular alterations, including BRAF, with biology and outcome in pilocytic astrocytomas. Acta Neuropathol. Jan 1 2010;epub ahead of print.
3) Raco A, Piccirilli M, Landi A, Lenzi J, Delfini R, Cantore G. High-grade intramedullary astrocytomas: 30 years’ experience at the Neurosurgery Department of the University of Rome “Sapienza”. J Neurosurg Spine. Feb 2010;12(2):144-53
4) , 5) Houten JK, Cooper PR. Spinal cord astrocytomas: presentation, management and outcome. J Neurooncol. 2000 May;47(3):219-24. Review. PubMed PMID: 11016738.
6) Babu R, Karikari IO, Owens TR, Bagley CA. Spinal cord astrocytomas: a modern 20-year experience at a single institution. Spine (Phila Pa 1976). 2014 Apr 1;39(7):533-40. doi: 10.1097/BRS.0000000000000190. PubMed PMID: 24384651.

Leave a Reply