Solitary fibrous tumor of the posterior fossa: a rare and atypical case report

Abstract

Introduction:

Solitary fibrous tumor (SFT) is an uncommon mesenchymal neoplasm of fibroblastic origin. Intracranial SFTs account for less than 1% of primary central nervous system tumors, and posterior fossa location is exceptional. Although often slow-growing and histologically bland, intracranial SFTs have an intermediate biological potential due to delayed recurrence and extracranial metastases. We report a posterior fossa SFT mimicking a common extra-axial lesion.

Case presentation:

A 60-year-old woman presented with a 1-year history of progressive headaches, vomiting, and right-sided weakness. Examination revealed right hemiparesis, cerebellar dysfunction, and central facial palsy. MRI showed a large right posterior fossa extra-axial mass compressing the fourth ventricle and causing obstructive hydrocephalus. She underwent a posterior suboccipital craniectomy with gross total resection. Histology showed patternless spindle-cell proliferation with staghorn vessels and collagenous stroma. Immunohistochemistry was positive for CD34, STAT6, and vimentin and negative for EMA, S-100, and GFAP, confirming SFT. Postoperatively, she developed hydrocephalus requiring ventriculoperitoneal shunting (Clavien–Dindo grade IIIb). At 3 months, her neurological status improved, and MRI showed no recurrence.

Discussion:

This case highlights the diagnostic difficulty of a posterior fossa SFT, which may mimic a meningioma or other extra-axial tumors. Atypical features included a rare infratentorial location, obstructive hydrocephalus, and postoperative cerebrospinal fluid diversion despite complete resection. STAT6 immunostaining remains central, especially where molecular testing is unavailable.

Conclusion:

Posterior fossa SFT is rare, characterized by benign-appearing histology yet unpredictable behavior. Complete resection, immunohistochemical confirmation, hydrocephalus management, and long-term radiological surveillance are essential.

Introduction

Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm of fibroblastic origin that can arise at many anatomical sites, including the central nervous system (CNS)^[1^]. In the 2021 World Health Organization classification of CNS tumors, SFT and hemangiopericytoma are unified within the same pathological spectrum because they share the characteristic NAB2-STAT6 fusion, which can be detected indirectly by nuclear STAT6 immunohistochemistry^[1,2^].

Intracranial SFTs account for less than 1% of primary CNS tumors and are most often dural-based extra-axial masses^[1,3^]. Posterior fossa involvement is particularly uncommon. Because older reports often used the term hemangiopericytoma and because posterior fossa, cerebellopontine angle, and skull-base lesions are sometimes grouped together, the exact prevalence of posterior fossa SFTs is difficult to determine^[3,4^]. The available literature is mainly composed of isolated case reports and small series, including cases with posterior cranial fossa and cerebellopontine angle presentations^[5^].

HIGHLIGHTS

• Posterior fossa solitary fibrous tumors are exceptionally rare and may mimic meningiomas.

• Immunopositivity for STAT6 and immunopositivity for CD34 are key diagnostic markers.

• Complete microsurgical resection remains the main treatment goal.

• Postoperative hydrocephalus may require ventriculoperitoneal shunting.

• Long-term follow-up is required because late recurrence can occur.

This case is relevant because posterior fossa confinement can cause early neurological compromise and obstructive hydrocephalus, while imaging may mimic common extra-axial tumors. In resource-limited settings, histology and STAT6 immunohistochemistry are essential when molecular testing is unavailable^[1,4^].

This case report is written in line with the revised SCARE guidelines^[6^].

Case presentation

Patient information and clinical findings

A 60-year-old woman with no notable past medical history presented with a 1-year history of gradually progressive headaches. The headaches were initially mild and partially responsive to standard analgesics but later became persistent and refractory to medication. They were associated with occasional vomiting and progressive heaviness and weakness on the right side of the body. No smoking, alcohol use, relevant occupational exposure, or family history of CNS tumors was identified in the available clinical record.

On admission, the patient was alert and fully oriented, with a Glasgow Coma Scale score of 15/15. Neurological examination revealed right hemiparesis, right-sided kinetic and static cerebellar dysfunction, and central facial palsy. The remainder of the cranial nerve examination was unremarkable, with no dysphagia, dysarthria, or dysphonia.

Timeline

The patient’s clinical timeline is summarized in Table 1.

Table 1.

Clinical timeline.

Time point	Event
1 year before admission	Progressive headaches with intermittent vomiting.
Weeks to months before admission	Progressive right-sided heaviness and weakness.
Admission	Neurological examination showed right hemiparesis, cerebellar signs, and central facial palsy. MRI demonstrated a right posterior fossa extra-axial mass with obstructive hydrocephalus.
Surgery	Posterior suboccipital craniectomy and microsurgical gross total resection.
Postoperative day 4	Clinical deterioration due to progressive hydrocephalus; programmable VP shunt placed. Complication classified as Clavien-Dindo grade IIIb.
3-month follow-up	Neurological improvement and MRI showing no residual or recurrent tumor.

Diagnostic assessment

Brain MRI (Fig. 1) revealed a well-circumscribed extra-axial mass in the right posterior fossa, centered near the right cerebellar hemisphere. The lesion was isointense on T1-weighted images, hyperintense on T2-weighted images, and showed strong homogeneous enhancement after gadolinium administration. It exerted mass effect on the fourth ventricle, resulting in obstructive hydrocephalus without evidence of trans-ependymal cerebrospinal fluid flow. No marked perilesional edema was observed.

Figure 1.

Axial magnetic resonance imaging (MRI) showing an extra-axial lesion of the right cerebellar hemisphere on T1-weighted images without contrast (A), T2-weighted images (B), and contrast-enhanced T1-weighted images (C).

Preoperative differential diagnoses included meningioma, hemangiopericytoma/SFT, and other extra-axial posterior fossa tumors. Histopathology and immunohistochemistry were required for confirmation.

Therapeutic intervention

The patient underwent a posterior suboccipital craniectomy under general anesthesia. She was positioned prone, and the lesion was approached through a midline posterior fossa route directed toward the right cerebellar hemisphere. The procedure was performed using microsurgical techniques and operative magnification. Intraoperatively, the tumor was extra-axial, firm, and moderately hemorrhagic, with a well-defined plane of cleavage from the adjacent cerebellar parenchyma. Careful circumferential dissection allowed complete removal while preserving adjacent cerebellar and neurovascular structures. Preoperative embolization was not performed because the lesion was surgically accessible and it was not indicated by the angiographic workup. Operative time and blood loss were not quantified; bleeding was moderate and controllable.

No major intraoperative complications occurred. Immediate postoperative CT confirmed complete resection (Fig. 2). During postoperative monitoring, the patient experienced a deterioration in consciousness on postoperative day 4 due to progressive hydrocephalus. A programmable ventriculoperitoneal shunt was inserted under general anesthesia. This postoperative reintervention was classified as Clavien-Dindo grade IIIb.

Figure 2.

Follow-up computed tomography scan confirming complete removal of the lesion.

Pathological findings

Histopathological examination (Fig. 3) showed a patternless proliferation of spindle-shaped cells embedded in a collagenous stroma, with branching staghorn-like vascular channels. No significant nuclear atypia or necrosis was identified. Immunohistochemistry demonstrated strong positivity for CD34, STAT6, and vimentin and negative staining for S-100, EMA, and GFAP, supporting the exclusion of schwannoma, meningioma, and glial tumors. These morphological and immunophenotypic findings confirmed the diagnosis of SFT. The original pathological report did not provide a mitotic count or Ki-67 proliferative index. Consequently, formal WHO grading could not be completed, and the proliferative assessment was limited. Molecular testing for NAB2-STAT6 fusion was not available.

Figure 3.

Histological section of a solitary fibrous tumor showing spindle cells and collagenous stroma (H&E, 200×).

Follow-up and outcomes

At 3-month follow-up, the patient remained neurologically stable, with significant improvement in hemiparesis and cerebellar signs. Follow-up MRI demonstrated no residual tumor, local recurrence, or new intracranial lesion; the fourth ventricle was patent and hydrocephalus had resolved. Because this interval documents only early local control, a structured long-term surveillance plan was established, consisting of neurological examination and serial brain MRI at 6-month intervals initially, and annually thereafter, with earlier reassessment if new neurological symptoms develop.

Patient perspective

The patient reported improvement in headaches, balance, and right-sided weakness after surgery and shunt placement. She expressed satisfaction with the clinical improvement and agreed to the publication of the case and accompanying images following anonymization.

Discussion

Intracranial SFT is a rare extra-axial mesenchymal tumor, particularly uncommon in the posterior fossa. Symptoms are usually caused by mass effect rather than tumor-specific biology. In this patient, headache, vomiting, cerebellar signs, hemiparesis, and hydrocephalus reflected compression of posterior fossa structures and obstruction of the fourth ventricle ^[4,7^].

The present case is atypical for several reasons. First, the infratentorial posterior fossa location is rare compared with the more frequent supratentorial dural-based sites. Second, the lesion radiologically resembled a meningioma because it was extra-axial, well-circumscribed, and strongly enhancing. Third, despite complete resection, the patient developed clinically significant postoperative hydrocephalus requiring shunting. These features make the case educational for neurosurgeons, radiologists, and pathologists, particularly in environments where rare extra-axial tumors may initially be managed as meningiomas.

Radiological differentiation between SFT and meningioma remains challenging. Intracranial SFTs usually present as well-defined, enhancing extra-axial masses^[8^]. Features that may favor SFT over meningioma include lobulated contours, heterogeneous signal, prominent flow voids, bone erosion rather than hyperostosis, and a less consistent dural tail^[9,10^]. However, these signs are not reliable in every patient. In our case, homogeneous enhancement and well-defined margins were misleading and supported meningioma in the differential diagnosis, emphasizing the need for pathological confirmation.

Histopathology and immunohistochemistry are the diagnostic cornerstones. Classic features include spindle cells in a patternless arrangement, collagenous stroma, and branching staghorn-like vessels. Strong nuclear STAT6 expression is a useful surrogate for NAB2-STAT6 fusion and is highly supportive of SFT^[1,3,11^]. CD34 and vimentin positivity further support the diagnosis, while EMA, S-100, and GFAP negativity help exclude meningioma, schwannoma, and glial tumors. In this case, the absence of significant atypia and necrosis indicated bland morphology; however, bland histology does not exclude delayed recurrence or metastasis. Because the mitotic count was unavailable, formal WHO grading could not be completed; the missing Ki-67 index further limited prognostic assessment^[2,7^].

Gross total resection remains the primary treatment whenever safely achievable. Complete removal is associated with better local control than subtotal resection, although recurrence can still occur and may be delayed^[4,12,13^]. Tumor vascularity is an important operative consideration. Preoperative embolization may be useful for large or highly vascular lesions, but it is not required in every case and should be individualized according to vascular anatomy, accessibility, and available expertise. In our patient, complete resection was achieved without embolization despite moderate but controllable intraoperative bleeding^[2,7,9^]. Adjuvant radiotherapy is generally considered on an individualized basis, particularly after subtotal resection, recurrence, or aggressive pathological features; it does not replace long-term surveillance^[4,13^].

Postoperative hydrocephalus is a clinically important complication after posterior fossa tumor surgery. In the present case, clinically significant hydrocephalus progressed despite gross total resection and caused deterioration in consciousness on postoperative day 4. Definitive cerebrospinal fluid diversion with a programmable VP shunt was therefore required and classified as Clavien-Dindo grade IIIb. This course illustrates that removal of the obstructing mass does not always result in immediate normalization of cerebrospinal fluid dynamics. At 3 months, the patient had improved neurologically, the fourth ventricle was patent, and hydrocephalus had resolved on MRI.

Compared with reported posterior cranial fossa and cerebellopontine angle SFTs, this case reinforces recurrent themes: preoperative mimicry of common extra-axial tumors, reliance on immunohistochemistry for definitive diagnosis, operative concern regarding vascularity, and the need for prolonged follow-up^[5,8,14^]. Its additional educational value lies in documenting postoperative hydrocephalus requiring a grade IIIb intervention despite radiologically complete resection. The absence of recurrence at 3 months should therefore be interpreted as early local control rather than evidence of cure.

Large language models may be used in healthcare writing; transparent reporting remains important^[15^].

Several limitations should be acknowledged. Follow-up was limited to 3 months and therefore could not address late local recurrence or extracranial metastasis. The absence of NAB2-STAT6 molecular testing and of a mitotic count precluded molecular confirmation and formal grading; the missing Ki-67 index further limited proliferative assessment. Operative time and estimated blood loss were not quantified.

No intraoperative photographs were available; therefore, radiological and pathological illustrations constitute the main visual documentation. Despite these limitations, the case remains clinically relevant because it combines a rare posterior fossa localization, meningioma-like imaging, complete microsurgical resection, postoperative hydrocephalus requiring shunting, and immunohistochemical confirmation using STAT6.

Conclusions

Posterior fossa SFT is exceptionally rare and can mimic more common extra-axial tumors such as meningiomas. Although an SFT may appear histologically bland, this does not eliminate the risk of delayed recurrence or metastasis. Complete microsurgical resection, STAT6/CD34 immunohistochemical confirmation, prompt management of postoperative hydrocephalus, and structured long-term clinical and radiological surveillance are essential. In the absence of mitotic index and Ki-67 data, prognostic interpretation should remain cautious.

Ethical approval

Trauma and Burn Center does not require ethical approval for reporting individual cases or case series. The report was prepared in accordance with institutional standards and patient confidentiality was preserved.

Consent

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Sources of funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author contributions

All authors contributed to patient management, data collection, manuscript preparation, critical revision, and approval of the final version.

Conflicts of interest disclosure

The authors declare that they have no conflicts of interest.

Research registration unique identifying number (UIN)

Not applicable.

Guarantor

Mohamed Aziz Hermassi.

Provenance and peer review

Not applicable.

Data availability statement

All relevant data are included in this article. Additional anonymized information may be available from the corresponding author upon reasonable request.