Clinical relevance of isthmoceles according to imaging modality: A prospective cohort study

To evaluate the clinical relevance of imaging-detected isthmoceles and to determine whether defects identified by different imaging modalities represent distinct clinical phenotypes.

This prospective cohort study enrolled women with a history of at least one cesarean section who presented at least 6 months after their most recent procedure to a tertiary gynecology clinic. All participants underwent transvaginal ultrasonography (TVUS). Saline infusion sonohysterography (SIS) was performed in women without a defect on TVUS. Participants were categorized into three groups: TVUS-detected isthmocele, SIS-only isthmocele, and no isthmocele. Associations between imaging-defined groups and composite bleeding outcome were assessed using logistic regression.

A total of 682 women were included. Isthmocele was detected in 69.2% on TVUS and in 92.5% following the addition of SIS in TVUS-negative women. Postmenstrual spotting and intermenstrual bleeding differed significantly across groups (p = 0.015 and p = 0.013, respectively). In multivariable analysis, parity (OR 1.29; 95% CI 1.08-1.53; p = 0.004) and TVUS-detected isthmocele (OR 1.84; 95% CI 1.02-3.31; p = 0.042) were independently associated with composite bleeding, whereas SIS-only isthmocele was not (OR 1.26; 95% CI 0.66-2.38; p = 0.481). Among women with TVUS-detected isthmocele, niche length and depth showed weak associations with bleeding, whereas residual myometrial thickness did not.

TVUS-detected isthmocele was independently associated with bleeding symptoms, whereas defects identified exclusively by SIS were not. These findings suggest that SIS may detect anatomical variants of uncertain clinical relevance, raising concern for overdiagnosis when applied as a routine screening tool. TVUS may be considered the primary modality for identifying defects that may warrant clinical attention.