Spinal astrocytoma

Spinal astrocytomas are the second most common spinal cord tumouroverall, representing 40% of intramedullary tumours ³. They account for 60% of paediatric intramedullary tumours, making them the most common spinal cord tumour in children ⁶.

This article specifically relates to spinal astrocytomas. For a discussion on intracranial astrocytomas and for a general discussion of the pathology refer to the main article: astrocytoma. Pilocytic astrocytomas and pleomorphic xanthoastrocytomas are also discussed separately.

Epidemiology

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) ⁵. 

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

Astrocytomas (both intracranial and spinal) arise from astrocytic glial cells.

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 ⁵. 

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 ⁵ (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

As astrocytomas arise from cord parenchyma (c.f. ependymomas that arise in the central canal), 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 ⁸)
  • usually patchy enhancement

Treatment and prognosis

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

Surgical excision is usually the treatment of choice, however due to the infiltrative nature of astrocytomas, resection is almost always histologically incomplete.

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.

Differential diagnosis

The main differential diagnosis is a spinal ependymoma. Certain imaging features may help to differentiate between the two, which are covered in this article:

• 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)

See also

• neoplasms of the spinal canal