Solitary fibrous tumor of the vulva: a case report

¹Department of Gynecology and Obstetrics, Regional Hospital of Menzel Temime, 8080, Menzel Temime, Nabeul, Tunisia, ²Faculty of Medicine of Sousse, University of Sousse, 4000, Sousse, Tunisia, ³Faculty of Medicine of Sfax, University of Sfax, 3029, Sfax, Tunisia, ⁴Faculty of Medicine of Monastir, University of Monastir, 5000, Monastir, Tunisia, ⁵Regional Hospital of Nabeul, Anatomical Pathology Laboratory, 8000, Nabeul, Tunisia, ⁶Faculty of Medicine of Tunis, University of Tunis El Manar, 1007, Tunis, Tunisia

^&Corresponding author
Aymen Khalfaoui, Department of Gynecology and Obstetrics, Regional Hospital of Menzel Temime, 8080, Menzel Temime, Nabeul, Tunisia

Introduction    

Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm first described in the pleura by Klemperer and Rabin in 1931 [1]. Initially thought to be exclusively pleural, it has since been identified in various extrapleural locations, including the soft tissues, head and neck, retroperitoneum, and abdominal organs [2]. These tumors originate from fibroblasts within the submesothelial connective tissue and are typically slow-growing with low malignant potential. However, SFTs exhibit variable biological behavior, with some cases demonstrating local recurrence or distant metastasis [3]. Histologically, they are characterized by spindle-shaped cells in a collagenous stroma with a "patternless" architecture, and their diagnosis is supported by immunohistochemical markers such as CD34, STAT6, and BCL2 [4]. Although nearly 100 extrathoracic locations have been documented, SFTs of the female genital tract remain exceedingly rare, with only a few reported cases involving the uterus, ovary, vagina, and vulva [5]. Due to their rarity, the clinical presentation, optimal management, and prognosis of gynecological SFTs are not well-defined, and no standardized treatment guidelines exist. Complete surgical excision is the primary treatment, but close follow-up is essential given the tumor´s unpredictable behavior [6]. Here, we report a rare case of solitary fibrous tumor of the vulva, highlighting its clinical, histopathological, and immunohistochemical features, and providing a review of the literature to enhance understanding and guide management of this uncommon condition.

Patient and observation     

Patient information: a 36-year-old female patient, with no significant medical or surgical history, presented to our department with a progressively enlarging vulvar mass. She had a history of two full-term vaginal deliveries. The mass, which had been present for two years, recently increased in size and became symptomatic, causing dyspareunia and dysuria. There was no prior history of fever, systemic symptoms, or weight loss. No relevant family or genetic history was noted.

Clinical findings: on physical examination, a well-circumscribed, rubbery, mobile mass measuring 6 x 5 cm was observed on the vulva (Figure 1, Figure 2). The lesion was non-ulcerated and non-tender, with no signs of inflammation. The mass was freely mobile concerning the deeper tissues, and no abnormalities were detected in the accessible pelvic lymph nodes.

Timeline of current episode: two years prior to consultation: the patient noticed a painless vulvar mass. Recent months: the mass increased in size and became symptomatic (dyspareunia, dysuria). Consultation at our department: physical examination and diagnostic assessment were performed. Diagnostic workup: imaging and biopsy were conducted. Definitive diagnosis: solitary fibrous tumor (SFT) confirmed histologically. Surgical intervention: local excision performed. Follow-up: no recurrence observed over four months post-surgery.

Diagnostic assessment: laboratory tests, including hemogram and renal function tests, were within normal limits. Beta-human chorionic gonadotropin (β-hCG) testing was negative. Pelvic ultrasound showed no abnormalities. Due to financial constraints, the patient declined pelvic magnetic resonance imaging (MRI). Under local anesthetic, a percutaneous needle biopsy was carried out. A mesenchymal proliferation of spindle and epithelioid cells with eosinophilic cytoplasm was discovered by histopathological analysis. The stroma had focal myxoid remodeling, was hyalinized, and was heavily vascularized (Figure 3). There was no necrosis and the mitotic index was 2 mitoses per 10 high-power fields (HPF). According to immunohistochemistry, the tumor cells tested negative for STAT6 and positive for CD34 (Figure 4). Based on these findings, the diagnosis of solitary fibrous tumor (SFT) of the vulva was confirmed. According to the risk stratification criteria established by Deminico et al. [7], this case was classified as low risk, with an excellent prognosis (Table 1).

Therapeutic interventions: the patient underwent complete local excision of the mass. Histopathological analysis of the excised specimen confirmed a solitary fibrous tumor with negative surgical margins, ensuring complete removal.

Follow-up and outcome of interventions: following tumor excision, the patient's urinary and vaginal symptoms resolved completely. A post-operative full-body scan revealed no evidence of residual disease or metastasis. At the four-month follow-up, no signs of local recurrence were observed.

Patient perspective: the patient expressed relief at finally receiving a diagnosis after enduring discomfort for two years. Although she was initially apprehensive about surgery, she was satisfied with the outcome, as it significantly improved her quality of life. She reported a return to normal daily activities, free from the persistent urinary and sexual symptoms that had previously affected her well-being.

Informed consent: the patient provided written informed consent for the publication of this case report.

Discussion     

Solitary fibrous tumors are mesenchymal tumors that arise from connective tissue, particularly the pleura [2]. Hundreds of extra-thoracic sites have been described to date, includes locations in the female genital tract. They are uncommon [5]. Clinical data from 24 patients show a median age of 50 years (ranging from 22 to 75 years) and an average tumor size of 4.7 cm in diameter (ranging from 1.0 to 18.0 cm) [4]. The size of the tumor at diagnosis differed depending on the location; SFTs in the abdominal cavity's lower genital tract were noticeably smaller than those in the upper genital tract. This is because gynecologic symptoms caused by lower genital tract cancers typically lead to their early detection, or they may be found during normal gynecologic examinations. The tumor in this instance was 60 by 50 mm at diagnosis, and it caused dyspareunia and dysuria that persisted for two years (Figure 1).

Due to their rarity, relying exclusively on physical examination or radiological features to distinguish vulvar SFTs from other vulvar cancers, including squamous cell carcinoma, might be difficult. A poorly defined mass with low signal intensity on T1-weighted MRI scans, intermediate to high signal intensity on T2-weighted imaging, and contrast enhancement is the typical presentation of vulvar cancer [8]. In this case, the patient refused to undergo a pelvic MRI due to a lack of financial resources. Therefore, before starting treatment, a biopsy is essential to do a histological diagnosis. To prevent the need for further resection of nearby organs, it is important to detect and diagnose tumors early. Gynaecologists should therefore be vigilant about slow-growing solid tumors and not hesitate to conduct additional examinations.

In our case, histological findings after the biopsy of the mass revealed that the tumor was composed of a mesenchymal proliferation of spindle and epithelioid cells associated with dilated and branching vascular structures (hemangiopericytoma-like vascular pattern) (Figure 3). The tumor stroma was hyalinized with focal myxoid changes. Mitotic index: 2 mitoses/10 HPF with absence of necrosis. Our assessment of the histology study indicates that sufficient surgical margins were obtained. The tumor cells showed positive results for CD34 (Figure 4) but negative results for STAT6 in immunohistochemistry. While CD34 is found in 88% of instances, STAT6 expression is seen in the majority of cases, according to recent pathological research. Therefore, immunohistochemical analysis plays a crucial role in the diagnosis of SFTs. Surgery is generally considered the standard treatment for localized vulvar solitary fibrous tumor. However, there is no defined surgical approach for each individual case [3]. In this case, the clinical exam revealed that the tumor was confined to the subcutaneous layer and did not extend to the urethra the clitoris, or the underlying muscle layer. So, we opted for total excision of the mass according to the patient's wishes and after the biopsy (Figure 2). The histological exam confirmed a vulvar solitary fibrous tumor.

Although solitary fibrous tumors (SFTs) typically behave in a benign manner, achieving optimal primary excision is crucial. Residual tumors can potentially regrow locally, leading to challenges with secondary excision. Consequently, excessive excision may sometimes be performed, which can negatively impact the patient´s quality of life [6]. Demicco et al. [7] proposed a risk stratification model based on three factors: age (<55 years or ≥55 years), tumor size (<5 cm, 5 to <10 cm, 10 to <15 cm, or ≥15 cm), and mitotic count (0, 1-3, or ≥4 per 10 high-power fields). This model was developed through Cox proportional hazards regression analysis using data from 110 cases of solitary fibrous tumors (SFTs) [7] (Table 1). Based on the above three factors, three risk groups were identified: low, moderate, and high. In subsequent studies, they introduced a modified risk stratification model that included tumor necrosis as an additional variable. They reported that this revised model showed a stronger association with metastasis [9].

Based on the criteria, the current instance is deemed to be low risk. The effectiveness of adjuvant radiotherapy and chemotherapy in treating localized solitary fibrous tumors is the subject of debate. The interdisciplinary staff has determined that there is no reason for adjuvant treatment in our situation. Moreover, NAB2-STAT6 does not currently have a specific treatment. The association between the prognosis and the molecular subtypes of the NAB2-STAT6 fusion is still unknown (10). Comprehensive, long-term care is necessary because there is still a chance of malignant development. Imaging is necessary to determine the disease's severity.

It can be used to rule out a primary tumor (thoracic in order of frequency) where vulvar involvement could be a secondary site, and to carry out a local and distant extension assessment [1]. In our case, the patient underwent a full body scan with no abnormalities. These gynecological TFS have different prognoses. Nine gynecological TFS cases are described by Biedrzycki et al. [5] including one fallopian tube case, one paraovarian tumor case, one uterine location case, two vaginal tumor cases, and four vulvar location cases (4). They describe a 33-year-old patient who had TFS measuring 15 cm in a paraovarian site. At 72 months, the patient's condition advanced to bone metastases, followed by brain and liver metastases, and no negative criteria were found in the original study (4). A specific case is reported involving a 4590-gram uterine tumor that was linked to a paraneoplastic syndrome of recurrent hypoglycemia. The tumor's production of insulin-like growth factor 2 (ILGF) was the cause of this condition, and after two years of follow-up, no recurrence was observed (4). In our case, there was no tumor recurrence observed for 4 months after surgery. Nevertheless, long-term follow-up remains essential for continued vigilance.

Conclusion     

The vulvar SFT is quite uncommon. However, it's crucial to take the SFT into account when using an IRM or scanner to perform a differential diagnosis of a vulvar tumor. In order to get a diagnosis and develop a surgical plan, a percutaneous preoperative biopsy was helpful. A precise histological diagnosis of SFT has been made possible by the presence of tumoral cells that test positive for STAT6 and CD34. Remarkable functional and oncological outcomes were obtained with the help of vulvar tumor conservation surgery.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

Patient management: Aymen Khalfaoui, Houssem Ragmou. Data collection: Achref Wadday, Nesrine Tounsi, Imene Noomen. Manuscript drafting: Aymen Khalfaoui. Manuscript revision: Achref Wadday, Nesrine Tounsi, Emna Chelbi. All the authors have read and approved the final version of the manuscript.

Table and figures     

Table 1: risk stratification model

Figure 1: well-defined rounded mass in the vulvar fourchette measuring 6 x 5 cm: arrow: clinical photograph showing a mobile, rubbery, and well-circumscribed mass located in the vulvar fourchette

Figure 2: post-excision appearance of the vulvar fourchette: arrow: surgical site after complete excision of the mass, showing intact surrounding tissues with no signs of residual tumor

Figure 3: histopathological features of the solitary fibrous tumor with hemangiopericytoma-like vascular pattern

Figure 4: diffuse CD34 expression in the solitary fibrous tumor

References