Retroperitoneal Leiomyoma as a Source of Pelvic Pain: A Case Report and Review of the Literature
Authors: Kumar Nimisha , Forgie Marie M. 
Published: July 2024

Purpose: Leiomyomas are benign growths originating from the myometrium of the uterus and the most common pelvic tumor in women. They are frequently a source of abnormal uterine bleeding and pelvic pain, but occasionally occur outside of the uterus. Retroperitoneal leiomyomas are exceedingly rare with only about 100 cases noted in systematic reviews and literature searches. Given its rarity, preoperative diagnosis can be challenging. Our purpose is to raise awareness of this condition by reporting a case of retroperitoneal leiomyoma as an unexpected source of pelvic pain and (2) reviewing literature for commonly seen patient presentations, preoperative diagnostic challenges, and management of retroperitoneal leiomyomas.

Case Report: Patient was a 34-year-old nulliparous woman who presented with pelvic cramping, rectal pressure, and dysmenorrhea and was found to have an adnexal mass of unclear origin on pelvic ultrasound and computed tomography. Follow-up magnetic resonance imaging (MRI) showed a heterogenous mass containing macroscopic fat next to the left ovary with possible “claw sign”, but also abutting the sigmoid colon. Ovarian mass was the preoperative suspected diagnosis based on imaging. Tumor markers were negative. Patient underwent a diagnostic laparoscopy and a 7-centimeter globular mass was noted retroperitoneally along the left pelvic side wall, completely separate from the uterus and adnexa. It did not appear to involve the ureter or sigmoid colon. Given clear visualization of surrounding structures, it was carefully resected from the pararectal space given likely source of pelvic pain. Pathology resulted as leiomyoma and endometriosis.

An English language PUBMED, MEDLINE, CINAHL search for retroperitoneal leiomyomas yielded 34 case reports available for review. Five of the cases were in the United States and 29 were international. One systematic review was identified that spanned cases from 1941-2007. These case reports were then reviewed for patient characteristics, imaging findings, treatment, and follow-up to summarize common findings.

Results: Pathophysiology of extrauterine fibroids - Retroperitoneal leiomyomas may originate as an unintended consequence of the power morcellation leading to seeding of cells sprayed during shredding. Extrauterine myomas in a patient without a history of morcellation is theorized to be a pedunculated fibroid that torses on itself, detaches from the uterus, attaches to other tissue, and then is sustained through neovascularization. They may also be of primary multifocal origin, rather than metastatic or parasitic. As with intrauterine leiomyomas, there is also a small risk (<0.01%) that the fibroid may be a leiomyosarcoma.

Patient characteristics - A systemic review of retroperitoneal leiomyoma case reports revealed a mean age of 46.27 years. Seventy percent of patients had never undergone gynecologic surgery, while 29% had a previous hysterectomy or myomectomy. Of patients that still had a uterus, 29% had concurrent uterine leiomyomas.

If symptomatic, these masses can present as nonspecific or bulk symptoms depending on size and location. These include fatigue, discomfort, back and/or pelvic pain, constipation, and urinary incontinence. Around 25% of patients may be asymptomatic.

Imaging findings - As in our above case, retroperitoneal leiomyomas can be difficult to diagnose on imaging. Imaging workup for pelvic pain with concern for a mass should begin with pelvic ultrasound. MRI can be useful as an imaging modality when ultrasound has poor delineation, rapid growth is noted, or malignancy is suspected. This can additionally be helpful for surgical planning if a diagnostic laparoscopy is planned for further evaluation. As in our patient, however, MRI can also be misleading. If encountered intraoperatively, extrauterine myoma should be part of the differential for a retroperitoneal mass.

Treatment - Complete surgical excision of the mass is recommended. Depending on imaging and patient risk factors for malignancy, referral to a gynecology oncology specialist can be considered.

Recurrence is rare, but long-term follow up is recommended for surveillance. As they have been shown to have estrogen and progesterone receptors, minimizing hormone usage can be beneficial. In the case of recurrence, long-term therapy with gonadotropin-releasing hormone agonists or aromatase inhibitors could be considered.

Conclusion: Preoperative diagnosis of extrauterine leiomyoma can be extremely difficult. This case was unique in that adnexal mass was the preoperative diagnosis. MRI can be useful as an imaging modality when ultrasound has poor characterization or is concerning for malignancy. If encountered intraoperatively, extrauterine myoma should be part of the differential for a pelvic mass. Complete excision is the definitive treatment for retroperitoneal myomas. Post-excision surveillance is recommended to screen for the rare possibility of recurrence.