Meningeal hemangiopericytoma (historical)

Meningeal haemangiopericytomasHaemangiopericytomas of the meninges  areare rare tumours of the meninges, now considered to be an aggressive versionsform 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 a generalcurrent discussion of non-meningeal haemangiopericytomas, please refer to solitary fibrous tumours of the general article on haemangiopericytomadura.

EpidemiologyTerminology

Haemangiopericytomas account for less than 1% have been enigmatic tumours with a long and checkered history of all intracranial tumours ¹. They are 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) ^3,6changing name and classification. 

Clinical presentation is 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 metastasize systemically, typically to liver, lung, and bone ^1,3,6.

Pathology

HaemangiopericytomasThey were previously classified as angioblastic sub-type meningiomas, then considered to arise from smooth muscle perivascular pericytes of dural capillaries (pericytes of Zimmerman)³,but the most.

More recent studies suggest that these lesions are actually arising from fibroblast 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. In fact,

This resulted in the 2016 updateterm 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 4th edition (2016) of the WHO classification of CNS tumours, it ceased to be a distinct entity but the two entities have been combinedterm remained in use under the compound diagnosis "solitary fibrous tumour/haemangiopericytoma" ⁵⁶. 

Solitary fibrous tumours of the dura are WHO I grade one lesion, whereas haemangiopericytomas arecan be graded from WHO grade II1 to 3 with what traditionally has been termed haemangiopericytomas being grade 2 or III (anaplastic) tumours3 ⁶. 

Microscopic appearance

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

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

CT

• vivid enhancement
• erosion of adjacent bone
• no hyperostosis
• no calcification

MRI

Features on various sequences includeincluded:

• 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
  • intermediate restricted diffusion (less than meningioma) 
  • minimum ADC ~1100 (+/- 130) x 10^-6 mm²/s 

Angiography

• ECA, ICA and vertebral 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 iswas 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 iswas that of meningioma although all other dural masses should be considered. Distinguishing a haemangiopericytoma from a meningioma can bewas 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 metastasize
  • usually, have a broad dural attachment and dural tail
  • MRS: alanine peak, absent myoinositol peak
  • immunohistochemistry: EMA positive, CD34 and STAT6 negative