Abstract

Background: Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms that infrequently involve the central nervous system, particularly the spine. Spinal SFTs are typically intradural extramedullary lesions that mimic common tumors such as meningiomas or schwannomas. Our case highlights how an atypical spinal SFT was diagnosed on magnetic resonance (MR) and successfully resected.

Case Description: A 55-year-old female with a history of chronic nocturnal low back pain and multiple falls presented with urinary incontinence alone. The spinal MR imaging (MRI) revealed an intradural, extramedullary, lobulated contrast-enhancing lesion at T7. The lesion was resected utilizing a hemi-laminectomy/tubular retractor. Postoperatively, the patient recovered normal function, and the MR confirmed gross total tumor excision. The histopathology confirmed a solitary fibrous tumor (central nervous system [CNS] World Health Organization grade 1), composed of spindle cells in a collagenous stroma with thin-walled, staghorn-like vessels. Immunohistochemistry showed focal vimentin positivity and negative STAT6 staining, supporting a lowgrade SFT diagnosis. Eighteen months later, the MRI showed enhancement at the surgical site but without a clear mass; an open biopsy confirmed normal inflammatory changes, but no tumor recurrence.

Conclusion: Spinal SFTs are exceedingly rare neoplasms that can mimic more common spinal tumors, and early diagnosis with surgical biopsy and immunohistochemical confirmation is essential to ensure accurate management.

Keywords: Central nervous system, World Health Organization grade 1, Extramedullary lesion, Hemangiopericytoma, Solitary fibrous tumor, Spinal tumor, Staghorn vasculature

INTRODUCTION

Solitary fibrous tumors (SFTs) of the spine are rare mesenchymal neoplasms that are distinct entities in the 2021 World Health Organization (WHO) classification of central nervous system tumors. Previously grouped with hemangiopericytomas (HPCs), the updated terminology reflects the shared molecular signature characterized by NAB2-STAT6 gene fusion. These tumors may arise from the meninges and often present with non-specific clinical symptoms, including localized pain and progressive neurological deficits. Although diagnosis can be challenging, histopathological confirmation using STAT6 immunostaining is often diagnostic. Complete surgical resection remains the mainstay of treatment, but long-term surveillance is necessary due to the risk of recurrence.[ 9 - 11 ]

CASE DESCRIPTION

A 55-year-old female presented with chronic nocturnal low back pain, multiple falls over the past 3 months, and chronic urinary incontinence; she had no other focal neurological deficits. The thoracic spine magnetic resonance (MR) showed an intradural extramedullary lobulated well-defined lesion at the T7. It was isointense on T1, hyperintense on T2, and homogeneously enhanced with contrast. It was right-sided and traversed the right T7/8 neural foramen; although it displaced the cords, there was no cord edema [ Figure 1 ].

Figure 1:

Magnetic resonance imaging of the thoracic spine showing an intradural extramedullary lobulated lesion at T7 level. (a) Axial T1-weighted contrast-enhanced image. (b) Sagittal T1-weighted contrast-enhanced image. (c) Axial T2-weighted image showing hyperintensity. (d) Sagittal T2-weighted image demonstrating cord displacement without edema.

Surgery

Using fluoroscopy, a right-sided T7/8 hemi-laminectomy without fusion was performed through a tubular retractor [ Figure 2 ]. The lesion is well-defined, red-greyish in color, soft in consistency, and very vascular. It was excised in piecemeal fragments. The patient had an uneventful full postoperative recovery [ Figure 3 ]. The MR imaging (MRI) 18 months later showed enhancement at the surgical site; she underwent an open biopsy that ruled out tumor recurrence.

Figure 2:

Schematic diagram demonstrating intraoperative localization and placement of a tubular retractor system during thoracic spine surgery.

Figure 3

Postoperative magnetic resonance imaging images confirming complete excision of the lesion. (a) Axial T1-weighted contrast-enhanced image. (b) Sagittal T1-weighted contrast-enhanced image. (c) Axial T2-weighted image. (d) Sagittal T2-weighted image.

Histopathology

The histopathologic diagnosis was consistent with SFT, central nervous system (CNS) WHO grade 1. Hematoxylin and eosin-stained section (×10) showed a spindle cell tumor embedded in a pink collagenous stroma with prominent thin-walled, dilated, staghorn-like (HPC-like) [ Figure 4 ]. The tumor was characterized by oval/spindle cells with bland nuclei surrounding the ectatic thin-walled branching vessels. There were no mitotic figures or necrosis [ Figures 5 and 6 ].

Figure 4:

Hematoxylin and eosin stain (×10) showing spindle cell tumor embedded in pink collagenous stroma with prominent thin-walled, dilated, staghorn-like vasculature.

Figure 5:

Higher magnification hematoxylin and eosin (20X) staining demonstrating oval to spindle-shaped tumor cells with bland nuclei surrounding ectatic thin-walled branching vessels.

Figure 6:

Hematoxylin and eosin (40X) section showing absence of mitotic figures and necrosis in the tumor cells.

Immunochemistry

The immunohistochemistry stain revealed the tumor was only focally positive for Vimentin, while negative for STAT6, EMA, PR, GFAP, S100, SOX10, Inhibin, Melan-A, Caldesmon, SMA, CKAE1/AE3, CK7, CK8/18, TLE-1, C99, and CD45. STAT6 was negative in our case, but the morphology was typical for SFT, and other differential diagnoses were ruled out with immunostaining [ Figure 7 ]. The negative immunohistochemistry for STAT6 should not rule out a diagnosis of SFT, as it can be lost in some dedifferentiated tumors. Although this tumor does not show dedifferentiated or malignant features, further studies are needed to explore if STAT6 can be negative in low-grade SFTs.

Figure 7:

Immunohistochemistry stain (40X) showing negative STAT6 nuclear expression in tumor cells.

CD34 was limited to the vasculature in our case [ Figure 8 ]. The exact staining pattern in SFT can vary from diffuse to focal or even absent. The Ki-67 proliferation index was low [ Figure 9 ].

Figure 8:

CD34 immunostain highlighting vascular channels but absent staining in tumor cells (20X).

Figure 9:

Ki-67 immunostaining (20X) demonstrating a low proliferation index in the tumor.

DISCUSSION

SFT is a rare mesenchymal neoplasm that represents 1% of all CNS lesions.[ 9 ] The 2021 WHO classifies SFTs into three grades based on mitotic activity and necrosis to predict prognosis.[ 10 ] Thoracic involvement is most frequent, followed by cervical and lumbar regions.[ 4 ] SFTs are often misdiagnosed as meningioma, schwannoma, metastatic tumors, or other spinal neoplasms.[ 2 ] On MRI, they are well-defined, dural-based, lobulated, or oval masses, exhibiting T1 isointensity and variable T2 signal intensities that markedly homogeneously or heterogeneously enhance.[ 4 , 12 ] They may show flow voids due to hypervascularity.[ 4 ] However, unlike meningiomas, SFTs more commonly cause bone erosion and exhibit increased vascularity.[ 12 ] Table 1 summarizes key references discussing the diagnostic, imaging, histological, and management aspects of solitary fibrous tumors (SFTs).

Table 1:

Summary table of key references.

Histology and immunohistochemistry

Histologically, SFTs consist of spindle cells interspersed with thick collagen bands and thin-walled, staghorn-shaped vessels.[ 3 , 7 ] Immunohistochemical analysis shows diffuse nuclear expression of STAT6, reflecting the NAB2-STAT6 gene fusion, along with CD34 positivity.[ 3 ] Negative staining for EMA, S-100, and GFAP helps distinguish SFTs from fibrous meningiomas and schwannomas.[ 7 ] Notably, STAT6 negativity has been reported in some rare cases despite classic histopathological features.[ 5 ]

Surgery

Gross total surgical resection offers the best chance for disease control and is more achievable in intradural versus extradural lesions.[ 1 ] Complete en bloc resection with dural removal is sometimes recommended to minimize recurrence risk.[ 5 ]

Role of adjuvant therapy

The role of adjuvant therapy in spinal SFTs is controversial. Radiotherapy may reduce tumor recurrence following subtotal resection or high-grade tumors, while in other cases, there is no significant survival benefit.[ 6 , 8 ] Chemotherapy is generally ineffective, though antiangiogenic agents have shown some promise in controlling metastatic disease.[ 8 ]

Long-term surveillance with MR

Long-term surveillance with MRI is crucial to look for delayed recurrent lesions.[ 12 ] Predictors for recurrence include: subtotal resection, high mitotic index, and necrosis.[ 5 ] PET imaging may facilitate early detection of recurrence and/or metastases.[ 7 ]

CONCLUSION

Spinal SFTs are exceedingly rare neoplasms that can mimic more common spinal tumors, and early diagnosis with surgical biopsy and immunohistochemical confirmation is essential to ensure accurate management.

Ethical approval:

The research/study approved by the Institutional Review Board at Prince Sultan Medical Military City, number E-2125, dated July 30, 2023.

Declaration of patient consent:

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that they have used artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript or image creations.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

References

1. Dufour H, Métellus P, Fuentes S, Murracciole X, Régis J, Figarella-Branger D. Meningeal hemangiopericytoma: A retrospective study of 21 patients with special review of postoperative external radiotherapy. Neurosurgery. 2001. 48: 756-62 discussion 762-3

2. Fiorenza V, Ascanio F, Ferlito E, Lo Duca B, Librizzi D. Primary intra and extradural solitary fibrous tumor of thoracic spine with paravertebral intrathoracic spread: Case report and review of the literature. Interdiscip Neurosurg. 2020. 21: 100746

3. Fritchie KJ, Jensch K, Moskalev EA, Caron A, Jenkins S, Link M. The impact of histopathology and NAB2-STAT6 fusion subtype in classification and grading of meningeal solitary fibrous tumor/hemangiopericytoma. Acta Neuropathol. 2019. 137: 307-19

4. Kim HJ, Lee S, Park S, Cho H, Jung H, Choi J. MRI characteristics of spinal solitary fibrous tumors. Eur Spine J. 2023. 32: 2261-9

5. Kimura Y, Shitara S, Nakamura H, Hirata H, Watanabe M, Saito T. Histological predictors of recurrence in spinal solitary fibrous tumors. Brain Tumor Pathol. 2023. 40: 23-31

6. Li Z, Deng Y, Li Z, Wang T, Gao J, Zhou W. Primary epidural hemangiopericytoma of the thoracic spine: Case report and literature review. J Clin Neurosci. 2019. 60: 142-7

7. Mammucci P, Sardaro A, Ferrari C, Nardulli M, D’Alessandro V, Rubini G. Intracranial solitary fibrous tumor: A “new” challenge for PET imaging. Diagnostics (Basel). 2022. 12: 1863

8. Moore MG, Ross DA, Sonneland PR, Meguro K, McCutcheon IE, Gokaslan ZL. Solitary fibrous tumors of the spine. Neurosurg Focus. 2003. 14: E2

9. Ng HK, Li L, editors. Mesenchymal, non-meningothelial tumours involving the CNS. WHO classification of central nervous system tumours. Lyon, France: IARC; 2021. p. 299-338

10. WHO Classification of Tumours Editorial Boa, editors. Central Nervous System Tumours. Lyon, France: IARC; 2021. p. 1-584

11. Yoshida A, Tsuta K, Ohno M, Yoshida M, Narita Y, Kawai A. STAT6 immunohistochemistry is helpful in the diagnosis of solitary fibrous tumors. Am J Surg Pathol. 2014. 38: 552-9

12. Zhang Y, Wang L, Liu J, Li T, Zhao X, Sun Y. Imaging pitfalls in spinal solitary fibrous tumors. Radiol Case Rep2022;. 17: 4563-67