1. Kwofie M1, Moritani T1, Vijapura C1, Kademian J1, Kirby P2
Imaging of Solitary Fibrous Tumor/Hemangiopericytoma Spectrum in Brain, Head & Neck, and Spine—Pathological Correlations
Kwofie M1, Moritani T1, Vijapura C1, Kademian J1, Kirby P2
1: Department of Diagnostic Radiology, University of Iowa Hospitals and Clinics, Iowa City, IA
2. Department of Pathology, University of Iowa Hospitals and Clinics, Iowa City, IA

2. INTRODUCTION
Intracranial solitary fibrous tumors (SFT) and hemangiopericytomas (HPC) are generally part of a histologic spectrum of fibroblastic-type mesenchymal neoplasms, unlike soft tissue counterpart
Based on recent genetic analysis (NAB2-STAT6 fusion gene), intracranial SFT/HPC are considered a true counterpart of soft tissue SFT/HPC
HPC of the CNS have a recurrence rate reaching >92% compared to soft tissue SFT

3. INTRODUCTION
Accurate diagnosis on imaging has implications for management
Intracranial HPCs are rare as they represent 2 to 4% of meningeal tumours in large series, thus comprising less than 1% of all intracranial tumours
histogenesis of intracranial HPC has been a matter of controversy for a long time

4. INTRODUCTION Intracranial HPC frequently misdiagnosed as meningioma
General agreement that intracranial HPC is more aggressive than meningioma (greater local recurrence, extraneural metastases, irregular or polylobulated borders, bone erosion)

5. PURPOSE OF EXHIBIT
To describe imaging findings of SFT/HPC in the brain, head & neck, and spine
To describe pathologic correlations
To discuss differential diagnosis

6. APPROACH Review SFT/HPC cases at UIHC from 2012 to 2016
Review CT and MRI of cases
Review pathology of cases
Compare to recent literature review

7. CASES: EPIDEMIOLOGY
Sample: living cases SFT/HPC from 2012 to 2016 at UIHC
N: 15
# Male: 6
# Females: 9
Mean Age: 58
Age range: 36-89
# still alive: 14

8. CASES: SYMPTOMS AND LOCATION
At least 3 cases were recurrent disease

9. CASES: PATHOLOGY
Cases 8-11 diagnosed as SFT/HPC spectrum

10. HISTOPATHOLOGY
SFTs are typically composed of juxtaposed hyper- and hypocellular spindle cell proliferation, dense collagenous stroma, and numerous thin-walled blood vessels with a staghorn configuration, a histologic hallmark of hemangiopericytoma or SFT

11. HISTOPATHOLOGY SFT have
cellular component (monotonous appearance and thin-walled branching vessels),
fibrous component (alternating fibrous areas and hyalinized thick-walled vessels), or
both components with variable degrees
cellular variant of SFT is indistinguishable from hemangiopericytoma

12. IMMUNOHISTOCHEMISTRY
Fibrous SFT
Strong CD34 positivity
Bcl-2 and vimentin positivity and
S100, actin, and keratin negativity
cellular variant of SFT/HPC
weaker CD34 positivity

13. CASES: IMAGING FINDING
On MRI,
low T2 signal correlates with fibrous content, and
high T2 correlates with cellular component
Multicystic changes and flow voids may be seen
Signal characteristics on diffusion-weighted imaging (DWI) and low apparent diffusion coefficient (ADC) correlate with cellularity.
Perfusion-weighted image shows an early enhancement pattern.

14. CASES: IMAGING FINDING
On CT, SFT/HPC are
generally mildly or moderately hyperdense and
enhancing corresponding to cellular or fibrous component

15. CASES
54-year-old female with dizziness. Left temporal solitary fibrous tumor WHO grade 2. (A) Axial CT showing a hyperdense medial portion of the lesion. (B) Coronal T2 shows variable high T2 signal in the lateral portion of the lesion consistent with cellular components and cystic changes. (C) and (D) Axial and sagittal T1 post contrast, respectively show enhancement. (E) and (F) DWI and ADC, respectively, show focal area of diffusion restrict in the medial aspect of lesion.

16. CASES
54-year-old female with dizziness. Left temporal solitary fibrous tumor WHO grade 2.
Tissue fragments show a cellular proliferation of oval to spindled, relatively uniform cells in a swirling pattern, separated by parallel bundles of collagen. Occasional thin-walled, dilated vessels are identified within the cellular proliferation.  The neoplastic cells stain positively for vimentin, CD34, CD99, F13a and BCL-2, and negatively for synaptophysin, chromogranin, CD45, CD20, CD3, EMA, pankeratin and S100.

17. CASES
55 year-old female with history of headaches and depression. Left temporal anaplastic hemangiopericytoma, WHO grade 3. (A) Axial T2 show lesion with multicystic changes. (B) Axial T1 with low signal in areas of cystic changes. (C) Sagittal T1 post contrast enhancement of the solid components. (D) and (E) DWI and ADC, respectively, with focal area of diffusion restriction in the posterior aspect of lesion.

18. CASES
55 year-old female with history of headaches and depression. Left temporal anaplastic hemangiopericytoma, WHO grade 3.
Sections show fragments of cellular tissue containing numerous vascular spaces of varying size and shape with occasional vascular spaces demonstrating a staghorn-type architecture.  The intervening stroma is densely cellular, demonstrating spindled to ovoid cells with occasional pleomorphic nuclei with a haphazard orientation.  Focal areas demonstrate a more solid appearance containing numerous small vascular spaces and there are other areas that have greater fibrous stroma associated with the cells.  Dense fibrous tissue is present along the edge of some fragments, consistent with dura.  Only rare bits of brain parenchyma are seen along the edges of some fragments, but no brain invasion per se is identified. Mitoses are greater than 5 per 10 high power fields in some areas. There are focal aggregates of lymphocytes and a few aggregates of foamy macrophages.  At the edge of one fragment, there is focal necrosis associated with hemorrhage.  

19. CASES
55 year-old female with history of headaches and depression. Left temporal anaplastic hemangiopericytoma, WHO grade 3.
 The reticulin stain shows varying degrees of reticulin deposition throughout the tumor.  Vimentin demonstrates diffuse positivity. Immunohistochemical stains for CD31 and CD34 highlight the previously described vascular spaces.  In addition, CD34 is focally positive within a minority of tumor cells.  Factor XIIIa demonstrates scattered positivity within tumor cells and CD57 stain demonstrates rare positivity within tumor cells.  Staining for EMA shows minimal weak staining and an immunostain for progesterone receptor shows a very rare weakly positive nuclei. Staining for S100, SMSA and pankeratin stains are negative within the cells of interest.

20. CASES
43 year-old male with bipolar affective disorder and suicide attempts. Intraventricular solitary fibrous tumor WHO grade 2. (A) Axial CT shows hyperdense periphery of the lesion. (B) Axial T2 with low and high T2 components corresponding to fibrous and cellular components within the lesion. (C) Axial T1 shows flow voids within lesion. (D) Axial T1 post contrast shows more enhancement of the cellular components compared to the fibrous component. (E) DWI showed partially restricted diffusion with decreased ADC (ADC not shown). (F) MR spectroscopy showing low NAA (N-acetyl aspartate) peak consistent with tumor of non neuronal origin, and increase MI peak which may help distinguish SFT/HPC from meningioma. MI: myo-inositol; chol: choline.

21. CASES: IMAGING FINDING
43 year-old male with bipolar affective disorder and suicide attempts. Intraventricular solitary fibrous tumor WHO grade 2. Sections show monomorphous tumor composed of closely packed, randomly oriented spindle cells with intervening fibrocollagenous to hypocellular stroma with interspersed staghorn-type blood vessels. The nuclei are oval to elongated with moderately dense chromatin and inconspicuous nucleoli. The mitotic activity is up to 1 mitosis/10 high power field. No necrosis, atypia or increased cellularity is seen. There is no bone invasion.

22. CASES: IMAGING FINDING
89 year-old female with a mass in the right brow and diplopia. Right sinonasal malignant solitary fibrous tumor/hemangiopericytoma intermediate grade (FNCLCC grade 2/3). (A) Coronal CT shows erosion of adjacent bone. No calcification within lesion. (B), (C) Coronal T2 andT1 show high and low signals within lesion. (D) Coronal T1 post contrast shows relative enhancement of the periphery of the lesion. (E) DWI shows high signals in the T2 high component and low in fibrous component due to T2 dark through. (F) and (G) H&E stain showing fibrous (F) and cellular components (G), respectively.

23. CASES
89 year-old female with a mass in the right brow and diplopia. Right sinonasal malignant solitary fibrous tumor/hemangiopericytoma intermediate grade (FNCLCC grade 2/3). The mitotic count is 14/10 HPFs.  No necrosis is identified. Immunohistochemical studies reveal the precursor solitary fibrous tumor to be strongly positive for CD34, with loss of CD34 expression in the more cellular component, consistent with the above diagnosis.  Desmin is focally positive while pankeratin is negative.

24. CASES
56 year-old male with L3 spinal tumor. Benign solitary fibrous tumor. (A) Axial CT lumbar spine at L3 level showing isodense mass with remodeling of the left L3 poster elements. (B) Axial T2 shows predominantly low T2 signal within lesion. (C) Coronal T1 shows normal bone marrow signal. (D) Axial T1 post contrast shows enhancement within lesion.

25. CASES
56 year-old male with L3 spinal tumor. Benign solitary fibrous tumor. The tumor focally expressed CD34 with no significant expression of S100, neurofilament, SMSA, SMM, EMA, MUC4, beta-catenin (nuclear), or KIT.

26. DIFFERENTIAL DIAGNOSIS
Meningioma (has calcifications, hyperostosis, broader dural tail favors meningioma)
metastasis, and
other primary benign or malignant tumors

27. DISCUSSION AND CONCLUSION
Intracranial SFT and HPC continue to be regarded as different entities while soft tissue HPC is considered to be SFT in the latest version of the WHO CNS tumor classification.
Intracranial HPC have a recurrence rate reaching >92% compared to soft tissue SFT possibly secondary to genetic difference in NAB2-STAT6
Intracranial SFT/HPC form a histopathologic spectrum
Imaging findings such as low T2 and high T2 signals correlates with fibrous, cellular and cystic content of SFT/HPC and are helpful in diagnosis

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