Scrotal Size Index: a novel anatomical classification of scrotal morphology in inflatable penile prosthesis surgery

Pump-related complications remain a significant cause of dissatisfaction and reoperation following inflatable penile prosthesis (IPP) implantation. Despite their clinical importance, scrotal anatomy is currently assessed subjectively, without a standardized method to guide pump placement and surgical decision-making. This study aimed to develop a simple, objective classification system for scrotal morphology and to evaluate its association with intraoperative surgical decisions and pump-related outcomes following IPP surgery.

A retrospective cohort study was conducted including patients who underwent primary 3-piece IPP implantation via a penoscrotal approach between 2018 and 2024. Dependent scrotal length was measured intraoperatively using a ruler from the penoscrotal junction to the most dependent point of the empty scrotum and recorded for all patients. Based on these measurements, patients were categorized according to the proposed Scrotal Size Index (SSI). Associations between SSI categories, intraoperative surgical variables, and pump-related outcomes were analyzed. Primary outcomes included the relationship between SSI categories and operative variables, including cylinder length, rear tip extender (RTE) utilization, and the need for intraoperative pump- or tubing-related adjustments. Secondary outcomes included pump-related complications within 12 months, including malposition, migration, patient-reported accessibility difficulties, and revision surgery.

A total of 210 patients were included. The mean dependent scrotal length was 7.25 ± 1.56 cm. Distribution analysis demonstrated distinct clustering of measurements (P < .001), supporting categorization into 3 anatomical groups: Small (<6 cm), medium (6-9 cm), and large (>9 cm), corresponding to the proposed SSI. The distribution of patients across these categories was 26.2%, 57.1%, and 16.7%, respectively. Significant differences in IPP-related variables were observed among SSI categories. Mean cylinder length increased from 16.2 ± 1.6 cm in the small group to 18.1 ± 1.7 cm in the medium group and 21.9 ± 1.9 cm in the large group (P < .001). Mean RTE length similarly increased from 0.9 ± 1.0 cm to 2.1 ± 1.1 cm and 3.0 ± 1.2 cm, respectively (P < .001), with corresponding increases in RTE utilization (32.7%, 65.0%, and 82.9%; P < .001).

Scrotal morphology appears to be associated with prosthesis-related operative variables during IPP implantation. The proposed SSI offers a simple and reproducible framework for objective anatomical assessment and may assist intraoperative planning. Further prospective studies are required to determine its utility in predicting pump-related outcomes and to establish its clinical validity.