Giant solitary fibrous tumor of the pelvis invading the rectum and bladder: a rare case report in an adolescent

Background: Pelvic solitary fibrous tumor is a rare spindle-cell tumor arising from mesenchymal tissue, usually benign. However, its malignant form is an extremely rarer, and more aggressive disease. Our review of previous literature found that it has not been reported in adolescents younger than 18 years. Herein, we describe a case of pelvic giant solitary fibrous tumor with rectum and bladder invasion in a 16-year-old girl and summarize the diagnosis and treatment experience to further improve the existing management of solitary fibrous tumor. Case Description Retrospectively analyzed a 16-year-old girl admitted to our department with irregular menstruation and increased menstrual bleeding for 2 months. A computed tomography scan of the abdomen demonstrated an 11.2×7.5×8.9 cm isodense space-occupying lesion in the pelvis. Contrast-enhanced computed tomography showed heterogeneous enhancement, which was considered a tumor of mesenchymal origin. Pelvic mass resection, bladder repair, and right ureteral stent placement were performed. It was confirmed that the mass invaded the upper rectal and the right bladder wall during the operation. After complete resection of the tumor, malignant solitary fibrous tumor was diagnosed in combination with histopathology and immunohistochemistry. The patient survived well with no tumor metastasis or recurrence in 4 months of postoperative follow-up. Conclusion This case report suggests that pelvic solitary fibrous tumor is rarely seen clinically. Because of its non-specific clinical manifestation and imaging, definite diagnosis is mainly based on histopathology and immunohistochemistry. Complete resection of the tumor is the first-line treatment, and most patients have a good prognosis.