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Year : 2021  |  Volume : 64  |  Issue : 4  |  Page : 847-849
A case of solitary fibrous tumor of urinary bladder

1 Department of Histopathology and Cytology, Apollo Main Hospitals, Chennai, Tamil Nadu, India
2 Department of Urology, Chennai Urology and Robotics Institute, Chennai, Tamil Nadu, India

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Date of Submission28-Jul-2020
Date of Decision05-Sep-2020
Date of Acceptance02-Oct-2020
Date of Web Publication20-Oct-2021

How to cite this article:
Krishnamurthy S, Menon M, Parameswaran A, Sivaraman A. A case of solitary fibrous tumor of urinary bladder. Indian J Pathol Microbiol 2021;64:847-9

How to cite this URL:
Krishnamurthy S, Menon M, Parameswaran A, Sivaraman A. A case of solitary fibrous tumor of urinary bladder. Indian J Pathol Microbiol [serial online] 2021 [cited 2021 Nov 28];64:847-9. Available from: https://www.ijpmonline.org/text.asp?2021/64/4/847/328582

Mesenchymal tumors of the bladder are rare, and among these, Solitary fibrous tumors are distinctly unusual. SFTs were first described by Klemperer and Rabin et al. as pleural-based lesion.[1] The recognition of lesions with similar morphology in extra-pleural sites led to documentation of their presence in the deep soft tissue, pelvis, retroperitoneum, serosal surfaces, and in the head and neck region including the orbit and meninges. The overlapping morphology with “hemangiopericytoma'' and the common CD34 positivity on immunohistochemistry led to the realization that these were two ends of the spectrum of a common entity.[1] Westra W H et al. in the year 2000, described five cases of SFT in the lower genital tract of which two cases were in the urinary bladder. These were the first w cases in the urinary bladder.[2] Thereafter, only 30 urinary bladder SFTs have been reported in the bladder in the English literature.[3]

A 30-year-old lady was referred to the urologist by her family physician for evaluation of a bladder mass detected in the course of a routine pelvic ultrasound. The patient reported that she had had urgency and straining to void urine on and off for the past 2 month. Computed tomography (CT) showed a hypodense lesion in the urinary bladder with intense postcontrast enhancement, along the right lateral wall, measuring 3.0 × 2.3 cm [Figure 1]. On MRI, the lesion was well defined in T1-weighted images, hyperintense in T2, and measured 2.6 × 2.0 cm, indenting the serosa. A CT-guided biopsy of the lesion was performed. Microscopic examination revealed a cellular spindle cell lesion arranged in short fascicles and with a pericytomatous vasculature. The tumor cells exhibited ovoid bland nuclei, wavy eosinophilic cytoplasm, and interstitial collagenous stroma; and scattered ectatic blood vessels were noted [Figure 2]a. Mitoses were not evident. The histopathology was reported as a spindle cell lesion with the possibility of solitary fibrous tumor being raised. Immunohistochemistry showed strong and diffuse positivity for CD34, diffuse nuclear staining for STAT6, and membranous staining pattern for CD99 [Figure 2]b, [Figure 2]c, [Figure 2]d. Desmin S100 and c-Kit (CD117) were negative.
Figure 1: Axial computed tomography with contrast depicting a well-defined enhancing lesion in the right lateral bladder wall. (White arrow)

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Figure 2: (a) Solitary fibrous tumor, core biopsy: High-power view showing ovoid to spindle-shaped nuclei with dispersed chromatin and ectatic vasculature. (H and E, ×400) (b) Tumor cells are diffusely positive for CD34 (IHC, ×400). (c) Strong and diffuse nuclear staining for STAT6 (IHC, ×400). (d) Membranous staining for CD99. (IHC, ×400)

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The patient underwent a robotic partial cystectomy; the mass was noted to involve the right lateral wall of urinary bladder [Figure 3]a, [Figure 3]b, [Figure 3]c, [Figure 3]d. Gross examination of the excision specimen revealed a tan brown nodular mass covered by mucosa on one aspect and adherent perivesical fat on the other. On sectioning, a circumscribed whitish firm lesion measuring 2.4 × 2.3 × 2.0 cm was noted. Histology revealed urinary bladder wall with a circumscribed nodular lesion interdigitating between the smooth muscle bundles composed of spindle-shaped cells with interstitial hyalinization with a “patternless pattern” [Figure 4]a, [Figure 4]b, [Figure 4]c, [Figure 4]d. Few storiform foci were observed. Ectatic blood vessels with a branched appearance were seen. No cellular atypia, necrosis, or increase in mitoses was noted. The lesion extended from the submucosa into the perivesical adipose tissue. Circumferential and perivesical margins were free of tumor. The postoperative course was uneventful at 6 months follow-up.
Figure 3: (a–d):Intracorporeal view of the bladder mass (white arrow) during robotic-assisted partial cystectomy. Bladder mucosa (asterisk)

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Figure 4: Microscopic aspect of SFT, excision specimen. (a and b) “Patternless” architecture with variable cellularity and hyalinised blood vessels. (H and E, ×100) (c) Fibrous area with collagenous stroma (H and E, ×400). (d) Tumor insinuating in between the detrusor muscle. (H and E, ×100)

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   Discussion Top

Histological features that typify SFTs are variable cellularity including both fibrous and cellular areas, a “patternless pattern” with interstitial collagenization and hemangiopericytoma type “staghorn” vasculature.[1] The criteria for malignancy is similar in pleural and extrapleural sites, which includes high cellularity, mitoses of four or more per ten high-power fields, hemorrhage, necrosis, and cellular pleomorphism.[4] The differential diagnosis is broad and includes many benign and malignant mesenchymal tumors. Based on the hemangiopericytomatous pattern of vasculature, alternating hypo and hypercellular areas, and the site, gastrointestinal stromal tumor, low-grade dedifferentiated liposarcoma, deep fibrous histiocytoma, and vascular lesions enter into the differential diagnosis. Most of the SFTs are positive for CD34 (90–95%) and CD99 (70%),[5] but are generally negative for S-100, actin, desmin, and keratin. Molecular genetics studies have identified NAB2-STAT6 gene fusion in a majority of SFTs. STAT 6 by immunohistochemistry, a surrogate marker for this fusion, is a highly sensitive and specific marker.[5] In a study by Doyle et al., which included 231 cases of benign and malignant tumors including 60 SFTs, 98% of SFTs showed strong and diffuse nuclear expression of STAT6. All the other tumors were negative with the exception of three dedifferentiated liposarcomas and one deep fibrous histiocytoma, which though positive had a weak staining intensity.[6] Our case had typical features of SFT, lacking atypia or pleomorphism and with diffuse and strong expression of CD34 and STAT 6 on immunohistochemistry. The tumor cells were negative for S100, C kit (CD117), and desmin. According to a risk stratification model in a study by Demicco EG et al., age less than 55 years, size less than 5 cm and absence of mitosis are predictive of low risk tumors with metastases free and disease specific survival rate at 5 and 10 years of 100%.[7] Our patient falls under this low-risk category. The most common approach in the management of SFT is complete resection with tumor-free margins.[5] Hence, a conservative minimally invasive robotic treatment approach was justified in this patient as the tumor lent itself to complete resection (partial cystectomy). The diagnosis on needle biopsy enabled planning the appropriate surgery. Although uncommon, the possibility of SFT should be considered in the differential of spindle cell lesions of the urinary bladder. Long-term follow-up is recommended in these patients as 5–10% of histologically benign cases behave aggressively, with recurrence and metastases.[5]

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   References Top

Goldblum JR, Folpe AL, Weiss SW, Enzinger FM. Enzinger and Weiss's Soft Tissue Tumours. 6th ed. Philadelphia, PA: Saunders/Elsevier; 2014. p. 1002-17.  Back to cited text no. 1
Westra WH, Grenko RT, Epstein J. Solitary fibrous tumor of the lower urogenital tract: A report of five cases involving the seminal vesicles, urinary bladder, and prostate. Human Pathology 2000;31:63-8.  Back to cited text no. 2
Sun S, Tang M, Dong H, Liang C, Yan T, Li J, et al. Solitary fibrous tumor involving urinary bladder: A case report and literature review. Transl Androl Urol 2020;9:766-75.  Back to cited text no. 3
England DM, Hochholzer L, McCarthy MJ. Localized benign and malignant fibrous tumors of the pleura. A clinicopathologic review of 223 cases. Am J Surg Pathol 1989;13:640-58. Erratum in: Am J SurgPathol 1991;15:818.  Back to cited text no. 4
Hornick JL. Practical Soft Tissue Pathology: A Diagnostic Approach: A Volume in the Pattern Recognition Series. 2nd ed. Philadelphia, PA: Elsevier; 2019. p. 38-42.  Back to cited text no. 5
Doyle LA, Vivero M, Fletcher CD, Mertens F, Hornick JL. Nuclear expression of STAT6 distinguishes solitary fibrous tumor from histologic mimics. Mod Pathol 2014;27:390-5.  Back to cited text no. 6
Demicco EG, Park MS, Araujo DM, Fox PS, Bassett RL, Pollock RE, et al. Solitary fibrous tumor: A clinicopathological study of 110 cases and proposed risk assessment model. Mod Pathol 2012;25:1298-306.  Back to cited text no. 7

Correspondence Address:
Suganthi Krishnamurthy
Department of Histopathology and Cytology, Mezzanine Floor, Apollo Hospitals, 21, Greams Lane, off Greams Road, Chennai - 600 006, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/IJPM.IJPM_901_20

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]


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