Effectiveness of hysteroscopic resection of a uterine caesarean niche can be predicted: a prospective cohort study

This study aimed to develop and validate a model for the preoperative prediction of the effectiveness of hysteroscopic resection of a uterine cesarean niche in patients with postmenstrual spotting. The predictive model was developed in a primary prospective cohort consisting of 208 patients with niche treated by hysteroscopic resection. Multivariable logistic regression analysis was performed to develop the predictive model, which incorporated preoperative menstrual characteristics and magnetic resonance imaging (MRI) findings. Surgical efficacy was defined as a decrease in postmenstrual spotting duration of at least 3 days at the 3-month follow-up compared with baseline. The predictive model was presented with a nomogram, and the performance was assessed with respect to its calibration, discrimination, and clinical use. Internal validation was performed using tenfold cross-validation. The predictive factors in the final model were as follows: preoperative menstrual duration, thickness of the residual myometrium (TRM), length, TRM/thickness of the adjacent myometrium ratio, angle γ, area, and presence of a lateral branch of the niche. The model showed good performance in predicting the effectiveness of hysteroscopic niche resection. Incorporating the preoperative duration of the menstrual period and MRI findings of the niche into an easy-to-use nomogram facilitates the individualized prediction of the effectiveness of a hysteroscopic niche resection by 26 Fr resectoscope, but multicenter prospective studies are needed to validate it.

Appendix S1 MRI image acquisition and measurement procedure of niche.
Magnetic resonance imaging (MRI) was done on a 1.5 Tesla (Siemens Avanto, Erlangen, Germany) system with an actively shielded whole-body superconducting magnet. All the MRI were performed before the surgery, consist of T1-weighted (T1W) and T2-weighted (T2W) imaging sequences in sagittal and coronal planes of niche. Niche was diagnosed if a high signal intensity mass was seen in the normal myometrium of the anterior wall of lower segment uterus in the T1-weighted and T2-weighted images. Imaging measurement was performed by 2 observers who were blind to clinical effect and prior MRI reports with the Siemens Syngo MR software package.

The image measurement procedure
All measurements were conducted in sagittal and coronal planes. The length, depth and area of the niche should each be measured in the sagittal plane in which it is largest. TRM should be measured in the sagittal plane in which the niche has the smallest TRM. Width was measured in the coronal plane in which it is largest.
(1) Length (l) was measured from the upper rim to the lower rim of niche (Figure S1-a1); (2) Depth (d) was defined as the vertical distance between the base and the apex of the defect (Figure S1-a2); (3) TRM was defined as the distance from the serosal surface of the uterus to the apex of the niche (Figure S1-a1); (4) TAM was defined as the total thickness adjacent to the niche next to the base of the defect (Figure S1-a1); (5) The degree of severity of the defect was based on the ratio of the myometrial thickness at the scar to the thickness of adjacent myometrium. Severe defect was a ratio of <50% and mild defect was a ratio of ≥50%; (6) The distance between the lower point of niche to the internal cervical os (d1, Figure S1-a2); (7) The distance between the lowest demarcation of niche to the internal cervical os (d2, Figure   S1-a2).  13 (10, 14) Preoperative dysmenorrhea score (0-10) 0 (0, 3) Preoperative chronic pelvic pain score (0-10) 0 (0, 3)

Which symptom improvement is most important to you
postmenstrual spotting 45 (90%) dysmenorrhea 3 (6%) chronic pelvic pain 2 (4%) The minimal days of shortening in postmenstrual spotting duration to be satisfied (day). ≥2 Data are reported as mean ± standard deviation or median (interquartile range, IQR) or as n (valid percentage) MRI=magnetic resonance image; TRM=thickness of the residual myometrium; TAM=thickness of the adjacent myometrium; TRM/TAM= the ratio of myometrial thickness at the scar to the thickness of adjacent myometrium Angle α was defined as the angle of the upper margin of the defect; Angle β was defined as the angle of lower margin of the defect; Angle γ was defined as the angle of the apex of the defect; Angle θ was defined as angle between the cervical axis and the axis of uterine corpus A: the endpoint of upper edge of niche on MRI; B: the endpoint of lower edge of niche on MRI; C: the apex of niche on MRI