Introduction/Background Soft tissue tumors arising from peripheral nerve sheath tumors (PNSTs) may ocasionally be observed in the pelvic retroperitoneum during gynecologycal examination. These are usually benign, although a very low risk of malignant transformation has been reported. The purpose of this study was to describe the clinical and sonographic characteristics of benign, retroperitoneal, pelvic PNSTs.

Methodology A retrospective, single, gynecologic oncology center study conducted between 1 January 2018 and 31 August 2022. All ultrasound images, clips, and final specimens of benign PNSTs were reviewed to describe: (1) the ultrasound appearance of the tumors using standardized terminology on a predefined ultrasound assessment form, (2) the origin of the tumors in relation to nerves and pelvic anatomy, and (3) the correlation between ultrasound features and histotopograms.

Results Five women (mean age 53 years) with benign, retroperitoneal, pelvic PNSTs were identified: four with schwannomas and one with a neurofibroma, all of which were sporadic and solitary. All patients had good quality ultrasound images and clips and final biopsies of surgically excised tumors, except for one patient managed conservatively with a tru-cut biopsy. In four of these cases, the findings were incidental. All five PNSTs measured 31–50mm, were solid, moderately vascular tumors, with non-uniform echogenicity, well-circumscribed by hyperechogenic epineurium, and had no acoustic shadowing. They contained small, irregular, anechoic, cystic spaces (n = 3), and hyperechoic areas (n = 4).

Conclusion Accurate preoperative diagnosis of these tumors may avoid the potential risks of surgery, especially collateral nerve and vascular damage. However, no ultrasound features reliably differentiated schwannomas from neurofibromas. In fact, they overlap with those of malignant tumors. Ultrasound-guided biopsy can be used to diagnose these tumors, which may be subsequently monitored with ultrasound surveillance.

Disclosures On ultrasound, benign PNSTs were solid, non-uniform, moderately vascular tumors without acoustic shadowing. Most were round and contained small, irregular, anechoic, cystic spaces, and hyperechoic areas, consistent with degenerative changes on pathology. All tumors were well-circumscribed by a hyperechogenic rim composed of epineurium. This may support the development of a novel field using ultrasound to evaluate the pelvic nerves.