Solitary fibrous tumour of the dura

Solitary fibrous tumours of the dura are rare dural masses, histologically identical to solitary fibrous tumours found elsewhere and now believed to be closely related to haemangiopericytomas, a fact reflected in the current (2016) WHO classification of CNS tumours. They are composed of spindle cells thought to be of mesenchymal origin. They usually occur in middle-aged individuals and symptoms depend on the size of the mass and its location.

On imaging, these tumours are similar to meningiomas, appearing as extra-axial well circumscribed solid masses with vivid contrast enhancement. 

Solitary fibrous tumours occur in older middle-aged individuals (mean 47-56 years of age), without a convincing gender predilection, although some reports have found increased incidence in females 1,2

Clinical presentation is nonspecific and identical to other dural masses (e.g. meningioma). Symptoms depend on the size of the mass and its location. Headache is the most common presenting complaint 1

Rarely, solitary fibrous tumours result in non-islet cell tumour hypoglycemia (NICTH) as a result of secretion of insulin-like growth factor-2 (IGF-2) 3. Rarer still is acromegaly 3

In the latest (2016) update to the WHO classification of CNS tumourshaemangiopericytomas and solitary fibrous tumours of the dura are considered to be one entity with variable morphology, although both terms are retained to reflect the very different imaging and clinical features 4,5. This reflects the current understanding of this tumour; in fact, the term haemangiopericytoma has fallen out of favour outside of the CNS. 

Grading

Although this is an area of some debate with alternative grading systems having been proposed, usually, solitary fibrous tumours of the dura are considered WHO grade I (whereas haemangiopericytomas are considered WHO grade II or III) 5

Having said that, a proportion (5.8%) of solitary fibrous tumours appear malignant, with high mitotic rate, necrosis and haemorrhage 1

Macroscopic appearance

These are well-circumscribed and firm 5

Microscopic appearance

Typically, solitary fibrous tumours demonstrate areas thick bands of collagen separating areas of hypercellularity and hypocellularity. Staghorn vessels, classically seen in haemangiopericytomas, are also commonly seen 5

Immunophenotype

The immunohistochemical appearance of solitary fibrous tumours is not surprisingly the same as that of haemangiopericytomas, characterised by 1,2,5:

  • CD34: positive
  • vimentin: positive
  • STAT6 protein: relocation of this protein to the nucleus
  • EMA: usually negative
  • PS100: negative

The radiographic appearances are those of a well-circumscribed mass arising from the dura (supratentorial convexity, falx and tentorium and posterior fossa). Unlike solitary fibrous tumours of the spinal cord, which most frequently arise from the cord itself and not the theca 2, parenchymal tumours of the brain are very rare.

CT

Solitary fibrous tumours are well circumscribed and isodense to hyperdense compared to adjacent brain. They may demonstrate calcifications, and may erode bone if abutting it 1

MRI

These tumours are similar to meningiomas, appearing as extra-axial well-circumscribed masses, with the following signal characteristics 1,2

  • T1
    • typically, intermediate signal similar to brain
  • T2
    • heterogeneous signal
    • iso- to hypointense (the best clue to the diagnosis)
    • flow voids commonly seen
  • T1 C+
    • vivid diffuse heterogeneous contrast enhancement of low T2 signal components
    • dural tail may be seen, but is much less common than in meningiomas
  • DWI / ADC: regions of restricted diffusion are frequently seen
  • MRS
  • MR perfusion: elevated rCBV
Angiography

Prominent tumour blush, with feeding vessels varying, depending on the location of the tumour. Importantly, in addition to meningeal supply, these tumours can receive blood supply from pial vessels 1.

Surgical resection, if complete, is usually curative. Recurrence rates are variably reported as low to relatively high; up to 50% in one series 2. If incomplete or recurrence occurs, then radiotherapy may be employed 1

The differential of solitary fibrous tumours of the dura is essentially that of other dural masses, and common entities to be considered include 1,2

The most useful feature that helps in making a preoperative diagnosis is the propensity for solitary fibrous tumour to be low signal on T2. Importantly, lymphoma, Erdheim-Chester disease and melanocytic lesions may also have low T2 signal. Meningiomas may also be low on T2, usually in the setting of mineralisation/calcification; thus reviewing other sequences (T2*) or CT is useful. 

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Article Information

rID: 37075
Synonyms or Alternate Spellings:
  • Solitary fibrous tumor of the dura
  • Solitary fibrous tumor of the brain
  • Solitary fibrous tumour (SFT) of the dura
  • Dural SFT

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    Case 2: on the left olfactory groove
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