Solitary fibrous tumor of the spinal cord

Solitary fibrous tumours of the spinal cord are are uncommon spindle-cell cell neoplasms of probable mesenchymal origin, most commonly arising from the spinal cord without dural attachment. 

They are histologically identical to solitary fibrous tumours located elsewhere, most commonly arising from the pleura. 

The remainder of this article largely focuses on solitary fibrous tumours arising from the spinal theca.  For a more general discussion of these tumours please refer to the article on solitary fibrous tumours of the dura. 

Epidemiology

The median age at the time of diagnosis is 48 years ¹. There is no reported sex predilection.

Clinical presentation

The most commonly reported presentations are back pain or radicular pain, and presentation is similar to other intramedullary or intradural masses. 

Pathology

Solitary fibrous tumours of the dura were first described in 1996 and are rare. Prior to their classification as a distinct entity, solitary fibrous tumours were diagnosed as fibrous meningiomas or hemangiopericytomas.

Classically, solitary fibrous tumours are distinguished by the absence of any single diagnostic feature. The characteristic microscopic appearance is a "patternless" growth pattern, with bland spindle cell cytology, alternating hyper- and hypocellular areas, keloidlikekeloid-like hyalinization, and a frequently prominent branching vasculature often described as "hemangiopericytoma-like" ². Myxoid changes have been reported in SFTs, particularly in the spinal cord lesions, but pure myxoid variants are extremely rare ³. Tumour cells stain positive for the stem cell marker CD34. Due to their histologic variability, solitary fibrous tumours may mimic other tumours ².

Most cases of extrapleural SFTs are benign, however, malignant CNS solitary fibrous tumours have been reported ¹. Histological features associated with “aggressive” extrapleural solitary fibrous tumorstumours may be seen in up to 10% of extrathoracic tumours and include hypercellularity, moderate to- marked cytological atypiasatypia, necrosis, more than four mitoses per 10 high-power fields and/or an infiltrative margin ². However, whilst these features are associated with clinical aggressiveness, they are not by themselves reliable predictors of such behaviour. Like pleural solitary fibrous tumours, the behaviour of extrathoracic tumours is unpredictable.

Radiographic features

In contrast to intracranial solitary fibrous tumours which arise most frequently from the dura, spinal solitary fibrous tumours of the spinal cord are most commonly parenchymal (intramedullary) although both intradural extramedullary and intramedullary location is encountered ^1,6. These intramedullary tumours do not, therefore, demonstrate a dural attachment ¹. Intradural/ extramedullary and extradural extension of intramedullary lesions has been reported ⁷.

CT

There are no specific appearances on CT. These tumours typically appear as relatively well-defined masses with demonstrate heterogenousheterogeneous enhancement. Rarely, calcification or necrosis may be visible ⁷.

MRI

Solitary fibrous tumours of the cord are usually well-circumscribed and encapsulated ³. Signal characteristics are typically:

• T1 - isointernseisointense to hypointense
• T2 - markedly hypointense
  • T2 hypointensity helps distinguish solitary fibrous tumours from other spinal cord tumours
  • T2 hypointensity is thought to be due to the presence of abundant collagen fibres ⁵
  • peritumoural oedema may be seen
• T1 C+ (Gd) - avid and homogeneous enhancement

Differential diagnosis

• spinal astrocytoma
  • hyperintense on T2 weighted images
  • ill-defined
  • patchy irregular contrast enhancement
  • eccentric location within the spinal cord
• spinal ependymoma
  • hyperintense on T2 weighted images
  • haemorrhage is common
  • often associated with prominent cysts (tumoural and polar)
• spinal ganglioglioma
  • hyperintense on T2 weighted images
  • mixed signal intensity on T1 weighted images
  • typically involve long segments of the spinal cord, often extending for greater than eight vertebral body segments
  • commonly eccentric in location
  • approximately half contain tumoural cysts
  • peritumoural oedema is uncommon
  • patchy or no enhancement
  • calcification is common (low signal with blooming on GRE)
• spinal hemangioblastoma
  • iso-hyperintense on T2 weighted images
  • focal flow voids on T2 weighted images
  • an associated tumour cyst or syrinx is common
  • haemosiderin capping may be present
• spinal paraganglioma
  • hyperintense on T2 weighted images
  • usually located inferior to the conus
  • the characteristic “salt-and-pepper” appearance of neck and skull base
  • aragangliomasparagangliomas may be seen
• spinal intramedullary metastases
  • hyperintense on T2 weighted images
  • extensive peritumoural oedema

Treatment and prognosis

The prognosis of spinal solitary fibrous tumours remains unclear. The treatment of choice is complete surgical resection. Whilst this is curative in most cases, recurrence has been reported. The role of postoperative radiotherapy in atypical or incompletely resected CNS solitary fibrous tumours has not been established ^1,5.