Objectives
Ultrasound is the first-line imaging modality of the pelvis in the pediatric and adolescent gynecology (PAG) population. Ultrasound findings in pre- and postpubertal PAG patients differ from those in adults. Diagnostic models for adnexal pathology have not been validated in this cohort. The primary aim of this study was to evaluate normative findings and the incidence of pathology in this cohort. The secondary aim was to assess the performance of expert opinion alone, as well as using retrospective application of the International Ovarian Tumor Analysis (IOTA) simple rules (SRs) and benign descriptors (BDs) in those found to have an adnexal mass.

Methods
This was a retrospective review of pelvic ultrasound examinations performed in patients < 18 years of age from January 2017 to July 2021 in one expert center in the UK. Analysis was performed on three age groups: neonatal (aged < 1 year), premenarchal (aged ≥ 1 year) and postmenarchal. The study was locally approved as an audit (GRM_082). Expert review of images of ovarian masses was performed using retrospective application of the IOTA-SRs and IOTA-BDs.

Results
In total, data on 1429 pelvic ultrasound examinations were retrieved, of which 116 were excluded, resulting in the inclusion of 1313 ultrasound images (1145 patients). The median age at the first ultrasound scan was 2 days after birth in the neonatal group (n = 20), 8.8 years in the premenarchal group (n = 124) and 16.1 years in the postmenarchal group (n = 961). The status of menarche was unknown in a further 40 patients. Normative ultrasound findings were in keeping with those in the existing literature. Uterine anomalies were seen in 14 (1.2%) patients. Endometrial pathology was rare, with five cases of gestational trophoblastic disease. The most frequent indication for ultrasound scan for each group were a known medical condition in neonates (n = 11 (55.0%)), suspected precocious puberty in premenarchal girls (n = 38 (30.6%)) and abnormal vaginal bleeding in postmenarchal girls (n = 504 (52.4%)). Polycystic ovarian appearances were described in 150 (15.6%) postmenarchal girls. Adnexal pathology was identified in 102 (8.9%) participants on initial ultrasound: four neonates, three premenarchal and 95 postmenarchal patients. Benign cystadenomas and hemorrhagic cysts were the most common adnexal mass type in all groups. Final outcomes were available for 79/95 masses in the postmenarchal group, none of which were malignant. The IOTA-SRs, IOTA-BDs, expert opinion and standard ultrasound reporting could characterize as benign 96.2%, 87.3%, 98.7% and 77.2% of the masses, respectively, all with a specificity of 100%. Eleven patients underwent 12 surgeries overall (three oophorectomies, six cystectomies and three cyst aspirations), with 11 out of 12 masses classified as benign based on retrospective expert assessment.

Conclusions
Ultrasound is effective for assessment of the female pelvis in the PAG population. Adnexal masses are common, but few require surgical intervention and most resolve expectantly. The IOTA-BDs and IOTA-SRs maintain their performance in this population. Larger studies are required for the prospective validation of diagnostic models which may aid a fertility-sparing approach to care. © 2024 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.