CNS & pituitary tumors

Other tumors

Solitary fibrous tumor



Last author update: 27 April 2023
Last staff update: 11 October 2023

Copyright: 2002-2024, PathologyOutlines.com, Inc.

PubMed Search: Solitary fibrous tumor pathology

Brenndan Crumley, M.D., M.P.H.
Katherine Schwetye, M.D., Ph.D.
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Cite this page: Crumley B, Schwetye K. Solitary fibrous tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cnstumorsft.html. Accessed April 14th, 2024.
Definition / general
  • Solitary fibrous tumors (SFTs) of the CNS are spindle cell neoplasms with a wide range of histopathologic appearances and a pathognomonic NAB2::STAT6 fusion mutation with a characteristic immunophenotype
Essential features
  • Spindle cell neoplasm that ranges in stromal collagenization and cellularity, often with a patternless pattern or dilated staghorn vessels
  • Most common in the dura (especially the tentorium) but very rare compared to other primary meningeal tumors (Acta Neuropathol 2019;137:307)
  • Pathognomonic NAB2::STAT6 fusion mutation that separates it from other tumors with similar microscopic appearances (Acta Neuropathol 2019;137:307)
  • Positive IHC includes STAT6 (nuclear), CD34 and CD99
  • Good prognosis but metastasis is possible, even with low grade tumors (Acta Neuropathol 2019;137:307)
Terminology
  • Recent changes to the CNS WHO classification system have made solitary fibrous tumor the sole name for this entity (Neuro Oncol 2021;23:1231)
  • Formerly called solitary fibrous tumor / hemangiopericytoma (SFT / HPC) and angioblastic meningioma
  • Hemangiopericytoma has been removed from the most recent WHO CNS tumor classification
ICD coding
  • ICD-O: 8815/1 - solitary fibrous tumor
  • ICD-10 codes no longer listed by the WHO
  • ICD-11: 2F7C & XH7E62 - neoplasms of uncertain behavior of connective or other soft tissue & solitary fibrous tumor, NOS
  • ICD-11: 2B5Y & XH1HP3 - other specified malignant mesenchymal neoplasms & solitary fibrous tumor, malignant
Epidemiology
Sites
  • Affects the dura most frequently (mainly found in the tentorium)
  • Other sites include falx, other dural sites, skull base, cerebellum and pineal gland
Pathophysiology
  • Pathognomonic NAB2::STAT6 fusion mutation on 12q13
  • Exact pathogenesis of this neoplasm has not been fully elucidated apart from its spindle cell / fibroblastic nature
Etiology
  • No known familial association
Diagrams / tables

Images hosted on other servers:

Intracranial SFT vascular permeability

Clinical features
  • Patients most commonly present with symptoms related to mass effect
Diagnosis
  • Patients are given a preliminary, often nonspecific diagnosis from CNS imaging
  • Found either during a primary workup or incidentally as part of a separate workup
  • Typically made by (immuno)histologic examination but can be supplemented with molecular testing for the NAB2::STAT6 mutation
Laboratory
  • Minority of cases present with hypoglycemia due to IGF1 production but this is nonspecific (Hum Pathol 1996;27:858)
Radiology description
  • Common: dural tail sign (nonspecific) and clear demarcation from surrounding tissue
  • Some cases will show a lack of obvious demarcation
  • Isodense on noncontrast T1 weighted images but bright on T1 with contrast and T2 weighted images
  • Meningiomas may also show a dural tail sign and similar enhancement patterns but are more likely to show intratumoral calcification and spoked wheel vessels (Neuroradiology 2021;63:1215)
Radiology images

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MRI of spinal SFT

MRI of parieto-occipital SFT

MRI of expansive SFT

PET / CT after SFT resection


Vividly enhancing mass, various images

Extra-axial mass, various images

Tumor mass in the left cerebellum

Resection cavity with residual tumor tissue

Prognostic factors
Case reports
Treatment
  • All tumors are treated with total resection
  • Higher grade tumor treatment is often supplemented with adjuvant radiation
  • Patients may be monitored for many years and even decades to evaluate for recurrence and metastasis
Clinical images

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Spinal SFT during resection

Gross description
  • Discrete mass, often contiguous with dura, white to brown
  • Gross appearance varies based on the relative amount of stromal collagen and tumor cellularity
  • Some tumors can lose their dural attachment and infiltrate surrounding tissue (Ann Diagn Pathol 2003;7:169)
Gross images

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SFT metastatic to liver

Frozen section description
  • Characteristic feature: spindled cells without a single / discrete architecture (patternless pattern)
  • Enlarged vascular spaces (staghorn vessels) can suggest SFT
  • Typical frozen diagnosis: spindle cell neoplasm, with differential to include SFT, meningioma and possibly other (schwannoma, etc.) depending on location
Intraoperative frozen / smear cytology images

Contributed by Brenndan Crumley, M.D., M.P.H. and Katherine Schwetye, M.D., Ph.D.
Typical SFT

Typical findings

Spindle cells

Spindle cells

Spindled neoplastic cell aggregate

Spindled neoplastic cell aggregate



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Squash prep

Microscopic (histologic) description
  • Essential: patternless pattern of spindle cells, often solid but can also have papillary and other architectures, arranged around branching hyalinized vessels
  • Varying amounts of stromal collagen and overall cellularity
  • Nuclei are bland, without features seen in mimicking neoplasms
  • WHO grading criteria:
    • < 5 mitoses/10 high power fields (HPF) = grade 1
    • ≥ 5 mitoses/10 HPF = grade 2
    • ≥ 5 mitoses/10 HPF with necrosis = grade 3
  • Often has staghorn vasculature
Microscopic (histologic) images

Contributed by Brenndan Crumley, M.D., M.P.H. and Katherine Schwetye, M.D., Ph.D.
Hypercellular neoplasm, patternless pattern

Hypercellular neoplasm, patternless pattern

Neoplasm, haphazard spindle cells

Neoplasm, haphazard spindle cells

Hypercellularity and staghorn vessels

Hypercellularity and staghorn vessels

Characteristic CD34 positivity

CD34 positivity can be focal

STAT6 nuclear positivity

STAT6 nuclear positivity

Virtual slides

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Fibrous dural mass

Occipital dural mass

Occipital dural mass, CD34

Occipital dural mass, reticulin

Cytology description
  • Lower grade tumors will show the characteristic patternless pattern but there is not a standardized list of cytology criteria for SFT diagnosis (J Pathol Transl Med 2019;53:192)
  • Higher grade tumors can show sheets of monotonous cells with heterochromatic nuclei, often with rhabdoid cells and eosinophilic cytoplasm (J Pathol Transl Med 2019;53:192)
Positive stains
Negative stains
Molecular / cytogenetics description
  • NAB2::STAT6 fusion mutation can be detected by sequencing, RT PCR or a proximity ligation assay
  • NAB2 and STAT6 are close to each other on chromosome 12q, which can make genetic analysis difficult and the WHO considers a positive STAT6 immunostain to be sufficient for diagnosis in most cases (Nat Genet 2013;45:131)
Molecular / cytogenetics images

Images hosted on other servers:

NAB2::STAT6 mutation analysis results

NAB2::STAT6 RT PCR and sequencing

Videos

General overview of solitary fibrous tumors (not specific to CNS tumors) by Dr. Jerad Gardner

Sample pathology report
  • Brain, tentorium, resection:
    • Solitary fibrous tumor, CNS WHO grade 1 (see comment)
    • Comment: Sections show a neoplasm composed of bland spindle cells within a heavily collagenized stroma, with 3 mitoses in 10 high power fields. A panel of immunohistochemical stains is strongly positive for CD34 and STAT6 (nuclear), with focal positivity for SMA and is negative for EMA and SSTR2A. These findings are consistent with a solitary fibrous tumor.
Differential diagnosis
Board review style question #1

This STAT6 stained slide is taken from the excision of an intracranial neoplasm. Which of the following stains should be negative in this neoplasm?

  1. ALDH1
  2. CD34
  3. SMA
  4. SSTR2A
Board review style answer #1
D. SSTR2A. A is incorrect because ALDH1 stains are often positive in solitary fibrous tumors, with ALDH1 acting as a CD34 surrogate. B is incorrect because CD34 stains are positive in the vast majority of solitary fibrous tumors, with loss of expression seen in some higher grade tumors. C is incorrect because SMA can be expressed on the periphery of solitary fibrous tumors. SSTR2A is correct because this marker's positive staining in some meningiomas and complete lack of staining in solitary fibrous tumors can help distinguish between the two diagnostic entities.

Comment Here

Reference: Solitary fibrous tumor
Board review style question #2

What is the most common location of the extra-axial, STAT6 positive CNS neoplasm seen in this image?

  1. Cerebellum
  2. Pineal gland
  3. Spinal cord
  4. Tentorium
Board review style answer #2
D. Tentorium. A, B and C are incorrect because while solitary fibrous tumors can be found in the cerebellum, pineal gland and spinal cord, it is not their most common location. D is correct because solitary fibrous tumors are most common in the dura, and the dural site they are most common in is the tentorium.

Comment Here

Reference: Solitary fibrous tumor
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