Imaging in gynecological disease: clinical and ultrasound characteristics of benign retroperitoneal pelvic nerve sheath tumors.

OBJECTIVE: To describe the clinical and sonographic characteristics of benign, retroperitoneal, pelvic peripheral nerve sheath tumors (PNST).

METHODS: This was 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 by the authors to describe (1) the ultrasound appearance of the tumors using the terminology of the International Ovarian Tumor Analysis (IOTA), Morphological Uterus Sonographic Assessment (MUSA) and Vulvar International Tumor Analysis (VITA) groups 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. A review of literature on benign, retroperitoneal, pelvic PNSTs with preoperative ultrasound examination was performed.

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. Size range for the five PNSTs was from 31-50 mm. All five PNSTs were solid, moderately vascular tumors, with non-uniform echogenicity, well-circumscribed by hyperechogenic epineurium, and had no acoustic shadowing. Most of the masses were round (n = 4 (80%)), and contained small, irregular, anechoic, cystic spaces (n = 3 (60%)), and hyperechoic areas (n = 4 (80%)). A literature search identified 47 cases of retroperitoneal schwannomas and neurofibromas, the characteristics of which were compared with the cases in our series.

CONCLUSIONS: On ultrasound, benign PNSTs were solid, non-uniform, moderately vascular tumors without acoustic shadowing. Most were round, containing 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. No imaging characteristics reliably differentiated between schwannomas and neurofibromas. In fact, they overlap with the ultrasound appearance of malignant tumors. Hence, ultrasound-guided biopsy plays a pivotal role in diagnosis, and if confirmed as benign PNSTs, these tumors can undergo ultrasound surveillance. This article is protected by copyright. All rights reserved.