Urogenital anatomy in ischiopagus conjoined twins: A single-center cohort study, structured literature review, and proposal of a standardized descriptive system

Why clinicians should know about it

• Picked for Anatomy (top studies of the week, 8 November 2026): Documents urogenital anatomical variation and proposes standardized classification

Abstract

BACKGROUND: Ischiopagus conjoined twins are a rare subtype of conjoined twinning characterized by complex pelvic fusion and highly variable urogenital anatomy. Detailed descriptions of urinary and genital structures remain inconsistent in the literature, limiting comparative analysis and surgical planning. This study aimed to characterize the spectrum of urogenital anomalies in ischiopagus conjoined twins, identify anatomical patterns associated with morphologic subtype, review previously reported cases, and propose a standardized descriptive classification system. METHODS: A retrospective cohort study was conducted of ischiopagus conjoined twins managed at a single tertiary referral center between 1990 and 2024. Demographic, radiologic, operative, and urogenital anatomical data were reviewed. Anatomical findings were compared in terms of the lower limb configuration. A structured literature review of published ischiopagus cases was also performed. Based on institutional and published findings, a novel conjoined twin Anomaly Descriptive System (CADS) was developed to standardize the reporting of renal and genital anomalies. RESULTS: Twenty-one sets of ischiopagus twins (42 patients) were identified; complete anatomical data were available for 39 patients from 20 sets. Tetrapus was the most common subtype (60%), followed by tripus (35%) and dipus (5%). Crossing ureters were present in 74.4% of patients and occurred in all tripus twins with separate bladders. Shared bladder anatomy was identified in 20% of sets, while 25.7% demonstrated completely shared urethrae. Penile anomalies were significantly more frequent in tripus twins compared with tetrapus twins (100% vs. 33.3%, p = 0.003). Female reproductive anatomy demonstrated uterus didelphys in 61.9% and duplicated vaginas in 57.2% of cases. Literature review identified 67 previously reported cases but demonstrated substantial inconsistency and missing anatomical data, particularly regarding urethral and female reproductive anatomy. DISCUSSION: Renal preservation (two kidneys per twin) was higher in our cohort than reported in literature (83.8% vs. 49.3%). Moreover, bladder sharing was less common in our series. Complete urethral sharing was reported in 40.3% of literature cases but found in only 25.7% in our cohort. We observed a higher proportion of fully separate urethrae 53.8% vs 8.9% in the literature. CONCLUSIONS: Ischiopagus conjoined twins demonstrate highly variable but partially predictable urogenital anatomical patterns. Tripus morphology appears associated with increased genital complexity. The marked heterogeneity and incomplete reporting in published literature highlight the need for standardized anatomical documentation. The proposed CADS framework may facilitate clearer communication, operative planning, and future comparative research in this rare population.

Abstract as published, via PubMed.