A case of solitary fibrous tumor of urinary bladder

Abstract

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 2a]. 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 2b-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)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)The patient underwent a robotic partial cystectomy; the mass was noted to involve the right lateral wall of urinary bladder [Figure 3a-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 4a-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)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