Huge retroperitoneal leiomyoma: a case report of a massive 35 cm tumor presenting with vague abdominal pain.

Introduction and importance: Leiomyoma is the most common benign tumor in females, typically occurring in the uterus. Primary retroperitoneal leiomyoma (PRL) is an exceptionally rare variant that originates from local smooth muscle tissue outside the female reproductive tract. Due to its rarity, it often presents a diagnostic challenge, mimicking more aggressive retroperitoneal malignancies. Case presentation: A 45-year-old woman presented with a 1-year history of nonspecific abdominal pain. CT imaging identified a massive unilocular mass in the right retroperitoneal space. Surgical exploration was performed to resect the giant tumor. Histopathology confirmed the diagnosis of leiomyoma. The patient's postoperative course was unremarkable, and she was discharged in good clinical status. Clinical discussion: PRLs are often asymptomatic until they reach a significant size, leading to late discovery. Radiologically, they can be difficult to distinguish from leiomyosarcomas. Surgical excision is the primary treatment and is necessary for a definitive diagnosis. While these tumors are histologically benign, their location makes complete resection vital to prevent local recurrence and alleviate pressure on adjacent structures. Conclusion: PRL is a rare but important differential diagnosis for retroperitoneal masses. Despite their benign nature, these cases require precise surgical management and close long-term follow-up due to the potential risk of malignant transformation or recurrence. This case adds to the limited literature on giant primary retroperitoneal tumors.