Meningeal haemangiopericytoma (historical)

Haemangiopericytomas of the meninges are rare tumours of the meninges, now considered to be an aggressive form of solitary fibrous tumours of the dura. They often present as large and locally aggressive dural masses, frequently extending through the skull vault. They are difficult to distinguish on imaging from the far more common meningioma but are treated similarly with surgical resection with or without radiotherapy to reduce the risk of recurrence, which is high. 

The remainder of the article presents a historical perspective of this entity. For an updated discussion, please refer to solitary fibrous tumours of the dura.

Terminology

Haemangiopericytomas have been enigmatic tumours with a long and checkered history of changing name and classification. 

They were previously classified as angioblastic subtype meningiomas, then considered to arise from smooth muscle perivascular pericytes of dural capillaries (pericytes of Zimmerman) ³.

It has since been shown that these lesions actually arise from fibroblasts and are in the spectrum of the solitary fibrous tumours of the dura ⁴. This is further supported by the fact that both entities share a similar genetic alteration: genomic inversion of 12q13 locus resulting in the fusion of NAB2 and STAT6 genes, the latter expressed and able to be assessed using immunohistochemistry techniques ⁶. 

This resulted in the term being abandoned throughout the body, but for some time it tenaciously persisted in the CNS classification on account of what was felt to be distinctive imaging features. 

In the revised 4^th edition (2016) of the WHO classification of CNS tumours, it ceased to be a distinct entity but the term remained in use under the compound diagnosis "solitary fibrous tumour/haemangiopericytoma" ⁶. 

In the 5^th edition (2021) the term was finally officially retired ⁷. Solitary fibrous tumours grade 2 or 3 are equivalent to haemangiopericytomas ⁷.  

Epidemiology

Haemangiopericytomas accounted for less than 1% of all intracranial tumours ¹. They were typically encountered in younger adults (30-50 years) with up to 10% being diagnosed in children ³. There is a slight male predilection (M:F = 1.4:1) ^3,6. 

Clinical presentation

Clinical presentation was usually due to mass effect and will vary depending on location. Headache, seizures, focal neurological dysfunction may all be presenting features ³. Additionally, in up to 20% of cases, these tumours can metastasise systemically, typically to liver, lung, and bone ^1,3,6.

Pathology

Solitary fibrous tumours of the dura can be graded from WHO grade 1 to 3 with what traditionally has been termed haemangiopericytomas being grade 2 or 3 ⁶.

Microscopic appearance

Haemangiopericytomas were highly cellular tumours with frequent mitoses (grade II <5 per 10 HPF; grade III ≥5 per 10 HPF) and often with areas of necrosis ⁶.  The cells are separated by a limited amount of delicate reticulin fibres and have numerous "staghorn" vessels, the latter a feature shared by solitary fibrous tumours of the dura ⁶. 

Immunophenotype

Ideally, the diagnosis is confirmed by assessing for STAT6 expression by immunohistochemistry or identifying NAB2-STAT6 fusion ⁶. Haemangiopericytomas had a number of useful immunohistochemical markers ⁶: 

• STAT6: positive

• CD34: positive

• vimentin: positive

Ki-67 proliferation index is typically around 10% ⁶. 

Radiographic features

Haemangiopericytomas were almost always solitary, usually supratentorial masses, often lobulated in contour. They were highly vascular and had a tendency to erode adjacent bone ³.

Another common location was the posterior fossa in the posterior occipital region.

CT

• vivid enhancement

• erosion of adjacent bone

• no hyperostosis

• no calcification

MRI

Features on various sequences included:

• T1: isointense to grey matter

• T1 C+ (Gd)

  • vivid enhancement

  • heterogeneous

  • may have a narrow base of dural attachment

  • dural tail sign is seen, more commonly in grade II tumours

• ​T2

  • isointense to grey matter

  • multiple flow voids on MRI (need to distinguish from the spoke-wheel appearance of meningioma)

  • adjacent brain oedema frequently present

• MR spectroscopy

  • high myoinositol ³

  • absent alanine peak (present in meningiomas) ³

• DWI/ADC

  • intermediate restricted diffusion (less than meningioma) 

  • minimum ADC ~1100 (+/- 130) x 10^-6 mm²/s 

Angiography (DSA)

• external carotid, internal carotid, and vertebral artery supply common

• highly vascular

• corkscrew arteries

• fluffy tumour stain

• lack of early draining veins ³

• useful for pre-operative embolisation

• assessment of dural venous sinus involvement 

Treatment and prognosis

Total surgical excision was recommended, with pre-operative catheter embolisation helpful in limiting blood loss ³. Adjuvant radiotherapy to reduce the incidence of recurrence has also been advocated ^1,3.

Differential diagnosis

The main differential diagnosis was that of meningioma although all other dural masses should be considered. Distinguishing a haemangiopericytoma from a meningioma was difficult as they have similar appearances on both CT and MRI.

• meningioma

  • older patients (>50 years of age)

  • smoother

  • central vascular spoke-wheel vascular supply

  • less likely to erode adjacent bone

  • more likely to cause hyperostosis

  • more likely to be multiple

  • very unlikely to metastasise

  • usually, have a broad dural attachment and dural tail

  • MRS: alanine peak, absent myoinositol peak

  • immunohistochemistry: EMA positive, CD34 and STAT6 negative