Assessing Vaginal Wall Elasticity via Shear-Wave Elastography Using a Transrectal Linear Array High-Frequency Probe in Premenopausal versus Postmenopausal Women: A Cross-Sectional Feasibility Study

Abstract

Objectives

This study aims to evaluate the feasibility of transrectal high-frequency linear array shear wave elastography (SWE) for assessing vaginal wall elasticity in women and to investigate potential differences in segmental elasticity values between premenopausal and postmenopausal populations.

Methods

This cross-sectional study included 228 women (164 premenopausal and 64 postmenopausal) who underwent gynecological ultrasound examinations at Hubei Maternal and Child Health Hospital from December 2024 to January 2025. Transrectal linear array high-frequency ultrasound examinations were performed by two ultrasound technicians. Tissue stiffness was assessed using Young’s modulus measurements obtained from six standardized vaginal wall segments: upper, middle, and lower regions of both anterior and posterior walls. Inter-rater reliability was assessed by calculating the intraclass correlation coefficient (ICC).

Results

Linear mixed-effects modeling adjusting for age and BMI demonstrated that postmenopausal women exhibited significantly higher Young’s modulus values (kPa) in the middle anterior wall (14.59 ± 3.93 vs 12.88 ± 3.87 kPa; adjusted P = 0.003, FDR q = 0.009) and middle posterior wall (14.87 ± 4.09 vs 13.28 ± 4.25 kPa; adjusted P = 0.013, FDR q = 0.026) compared with premenopausal women. Intra-group analysis revealed a significant proximal-to-distal stiffness gradient along the anterior wall in both premenopausal (P < 0.001) and postmenopausal (P = 0.001) groups, whereas the posterior wall displayed spatial homogeneity (P > 0.10). Inter-observer reliability was excellent, with ICCs ranging from 0.83 (0.68–0.94) to 0.95 (0.88–0.98) (P < 0.001).

Conclusion

Transrectal SWE is a reliable, non-invasive method for evaluating segment-specific vaginal elasticity. Our study showed that postmenopausal tissue stiffening is localized to the middle vaginal canal rather than pan-vaginal, with an anterior proximal-to-distal elasticity gradient. While these findings advance understanding of regional biomechanical specialization, future large-scale, age-matched, and multicenter studies are required to validate these results and establish clinical diagnostic thresholds.

Introduction

The growing global population of older adults highlights the critical importance of addressing women’s health during and after the menopausal transition.¹ Menopause is defined as the physiological cessation of menses resulting from declining ovarian follicular function and systemic estrogen levels.² In estrogen-responsive tissues such as the vagina, postmenopausal hypoestrogenism induces structural and biomechanical alterations, including mucosal thinning, loss of elastin fibers, degraded extracellular matrix architecture, and decreased compliance.^3–5 When these physiological tissue changes become symptomatic, they are clinically recognized as Genitourinary Syndrome of Menopause (GSM).⁶ GSM is a comprehensive clinical syndrome encompassing bothersome genital symptoms (dryness, burning, irritation), sexual symptoms (lack of lubrication, dyspareunia), and urinary symptoms (urgency, dysuria, recurrent urinary tract infections) that affect 27–84% of postmenopausal women.⁶ Crucially, while menopause represents the underlying physiological and hormonal state, GSM refers specifically to the symptomatic clinical presentation.

Timely assessment of vaginal tissue biomechanics across menopausal stages is key to understanding the physiological transition that creates vulnerability to GSM. Lower estrogen levels trigger profound alterations in the extracellular matrix, characterized by collagen degradation and loss of elastin fibers, which reduces tissue elasticity (the capacity of the tissue to deform reversibly under mechanical load) and increases tissue stiffness (the structural resistance of the tissue to deformation).⁷ Historically, research on vaginal tissue composition relied on invasive biochemical assays⁸ or ex vivo mechanical testing.⁹ Advances in shear wave elastography (SWE)¹⁰ enable the non-invasive, quantitative assessment of intrinsic tissue stiffness via Young’s modulus (E). Young’s modulus directly quantifies material stiffness by calculating the ratio of applied stress to resultant strain (E=σ/ε), where higher modulus values signify greater stiffness and reduced elasticity.¹¹ However, traditional transvaginal probes are limited by their inability to precisely control probe pressure against the vaginal wall and their susceptibility to operator-dependent variability, potentially leading to measurement errors. These limitations highlight the need for alternative approaches that can accurately and effectively assess vaginal tissue composition.

The development and application of transrectal linear array high-frequency probes (TLAHP) represent a significant advancement in gynecological imaging, providing enhanced visualization of pelvic organ microstructures and improving diagnostic capabilities.¹² High-frequency probes and linear arrays offer better image quality and resolution, enabling more detailed visualization of structures such as the vaginal walls.¹² Recent work by Huang et al (2023) demonstrated the technical feasibility of using TLAHP combined with SWE to evaluate vaginal wall parameters.¹³ As an extension and rigorous clinical validation of this approach, the present study builds on their foundational work in three key ways. First, while Huang et al evaluated a feasibility cohort (n=87), we evaluated a significantly larger, well-powered sample (N=228) to establish robust baseline biomechanical values. Second, whereas prior work found no significant difference in globally averaged elasticity between premenopausal and postmenopausal cohorts, we conducted detailed segment-specific profiling (anterior vs posterior; proximal-to-distal gradients) to determine whether localized tissue alterations account for menopausal biomechanical differences. Third, we performed a formal two-observer inter-rater reliability analysis (ICC) to validate the operator reproducibility of this transrectal elastographic protocol. Specifically, we hypothesized that postmenopausal women would demonstrate significantly higher Young’s modulus values (E, indicating increased tissue stiffness and reduced tissue elasticity) compared to premenopausal women in a segment- and compartment-specific manner across the vaginal wall.

Materials and Methods

Study Design and Participants

This cross-sectional study consecutively recruited patients who presented for routine gynecological or pelvic floor ultrasound examinations at Hubei Maternal and Child Health Hospital between December 2024 and January 2025. Primary clinical indications for ultrasound included routine health screening, assessment of pelvic floor dysfunction or uterine/adnexal conditions, and evaluation of non-acute pelvic discomfort. Inclusion criteria were as follows: (1) age ≥ 18 years; (2) female; (3) receiving TLAHP in the study hospital; (4) physical and cognitive ability to comply with examination requirements. Exclusion criteria were as follows: (1) current pregnancy or lactation; (2) history of abortion (induced or spontaneous) within the preceding 3 months; (3) use of hormonal therapy within the last 6 months; and (4) inability or refusal to provide informed consent.

A total of 260 women were screened for eligibility; 12 were excluded for meeting exclusion criteria, and 12 declined participation. Furthermore, 8 examinations were excluded due to technically unsuccessful SWE acquisitions (defined as poor acoustic contact, persistent motion artifacts, or incomplete color-fill within the regions of interest). Consequently, 228 patients completed TLAHP ultrasound examinations and were included in the final analysis, comprising 164 premenopausal women (mean age ± SD: 37.77±7.06 years) and 64 postmenopausal women (mean age ± SD: 57.61±6.50 years). This study was conducted in accordance with the Declaration of Helsinki, and the study protocol was approved by the Ethics Committee of Hubei Maternal and Child Health Hospital (No. 2022 ICE 058). All participants were fully informed of the study’s purpose, procedure, benefits, and risks, and provided written informed consent before enrollment.

Menopausal status was operationally defined before enrollment. Postmenopausal status was defined as the natural cessation of menses for at least 12 consecutive months (≥12 months of continuous amenorrhea) not attributable to other physiological or pathological causes, or documented surgical menopause (eg, prior bilateral oophorectomy).^14,15 In women with ambiguous menstrual histories or prior hysterectomy with ovarian conservation, postmenopausal status was confirmed by serum follicle-stimulating hormone (FSH) levels >40 IU/L and estradiol levels <30 pg/mL.^14,15 Premenopausal status was defined as having regular, predictable menstrual cycles without vasomotor symptoms or clinical indicators of perimenopausal transition.^14,15

Procedures and Measurements

All examinations were conducted by two ultrasound technicians (Z.S. and X.Q.Q.) with over five years of experience in obstetric and gynecological ultrasound examinations. TLAHP was performed using a transvaginal dual-plane high-frequency probe (ELC13-4U, Nuewa R9G Mindray, China) with frequency ranges of 3.2–12.8 MHz (linear array). Patients were instructed to empty their bladders and bowels 15 minutes before examination. Examinations were conducted with the patient in the standard lithotomy position. The dual-plane probe, covered with a double-layer sterile condom, was gently inserted into the rectum while maintaining a neutral orientation. Under high-frequency linear array mode (3.2–12.8 MHz), the vaginal sagittal plane was visualized with the probe’s orientation marker at the 12 o’clock position, ensuring the beam was perpendicular to the vaginal wall. Images were required to clearly display the urethra, anterior/posterior vaginal walls, and vaginal gas line (Figure 1). The examiner maintained a steady hand while activating the dual-image real-time display function. Two-dimensional ultrasound and corresponding elastography images were acquired after stabilizing the elastography for at least 3 seconds.

Figure 1.

Transrectal B-mode ultrasound visualization of female pelvic anatomy. Sagittal B-mode ultrasound image obtained using a high-frequency linear array transrectal transducer, demonstrating anatomical orientation and spatial relationships of the pelvic floor structures. U urethra, V vagina, bl bladder, pd perineal body.

We identified the midpoint of the vagina at the level of the bladder neck and defined a 1 cm range above and below this midpoint for analysis. The trigone was selected as a reproducible anatomical reference visible during transrectal imaging.¹⁶ We analyzed the vaginal wall by dividing it into six regions of interest (ROIs): upper, middle, and lower segments of both anterior and posterior vaginal walls (Figure 2). The size of each ROI was specified as 2 mm in diameter. Quantitative tissue characterization was performed using SWE to determine Young’s modulus (E), also known as the modulus of elasticity, a measure of a material’s stiffness or resistance to elastic deformation under stress.¹¹ In this context, elasticity refers to the vaginal wall’s ability to undergo reversible deformation without permanent structural alteration. Stiffness represents the structural resistance of a vaginal tissue segment to mechanical deformation under acoustic stress. Young’s modulus is typically expressed as E = σ(stress)/ε(strain) and reported in kilopascals (kPa), with a high value indicating greater stiffness and a low value indicating greater elasticity.¹¹

Figure 2.

Shear-wave elastography (SWE) measurement mapping of the vaginal wall. A representative transrectal SWE color-coded elastogram demonstrating quantitative regions of interest (ROIs 1–6) across six distinct anatomical segments: ROI 1: middle anterior segment; ROI 2: middle posterior segment; ROI 3: upper anterior segment; ROI 4: upper posterior segment; ROI 5: lower anterior segment; ROI 6: lower posterior segment.

Inter-Observer Reliability Protocol

To evaluate inter-observer reliability, a randomly selected subset of participants (n=30) underwent independent ultrasound scanning and quantitative SWE measurements by both operators (Z.S. and X.Q.Q.) during the same visit. The examination order between the two observers was randomized. A 10-minute rest period was enforced between the two examinations to allow tissue recovery and prevent probe-induced strain artifacts. Both observers were fully blinded to each other’s elastographic measurements as well as the clinical and menopausal status of the participants. Each observer independently re-positioned the probe, acquired new image planes, and measured Young’s modulus across the six standardized ROIs. All measurements per ROI were repeated three times by the operating examiner, and the mean value of these three acquisitions was recorded for statistical analysis.

Statistical Analysis

Sample Size and Power Calculation

Sample size determination was guided by expected effect sizes from preliminary shear-wave elastography literature on vaginal tissue elasticity.¹⁶ Given the achieved cohort (164 premenopausal vs 64 postmenopausal), α = 0.05 (two-sided), and an SD of ≈4.0 kPa, the study provided 80% power to detect segmental between-group differences of ≥1.65 kPa (90% power: ≥1.91 kPa).

Statistical Modeling, Confounder Adjustment, and Multiplicity Correction

Continuous variables are expressed as Mean ± Standard Deviation (SD) or Median (Interquartile Range [IQR]) based on normality testing via Shapiro–Wilk tests. To account for repeated, correlated measurements across six vaginal regions within each participant, a Linear Mixed-Effects Model (LMM) was fitted with a random intercept for each patient. Fixed effects included Menopausal Status (premenopausal vs postmenopausal), Compartment (anterior vs posterior), Segment (upper, middle, lower), and their two- and three-way interactions. Potential confounding factors—including age and BMI—were included as fixed covariates. To control for Type I error inflation due to multiple pairwise comparisons across the six anatomical matrix regions, P-values were adjusted using the Benjamini-Hochberg False Discovery Rate (FDR) method (q-values reported).

Inter-Observer Reliability

Inter- observer reliability for quantitative SWE measurements was assessed using intraclass correlation coefficients (ICCs) with 95% confidence intervals (95% CIs). The ICC was modeled using a two‑way random‑effects model for absolute agreement based on averaged-measures ICC(2,k), calculated from the mean values of three consecutive acquisitions obtained by each independent observer.¹⁷ ICC values were interpreted as follows: < 0.50, poor reliability; 0.50–0.75, moderate reliability; 0.75–0.90, good reliability; and > 0.90, excellent reliability.¹⁷ A p-value <0.05 was considered statistically significant.

All statistical analyses were conducted using SPSS version 20.0 (IBM Corp., Armonk, NY, USA). P<0.05 or q<0.05 was considered statistically significant.

Results

Participant Characteristics

A total of 228 women completed the transrectal ultrasound and SWE protocol and were included in the final analysis. The overall pooled mean age was 43.34 ± 11.28 years, and the overall pooled body mass index (BMI) was 22.67 ± 2.79 kg/m². The cohort comprised 164 premenopausal women (37.77 ± 7.06 years; BMI: 22.65 ± 2.87kg/m²) and 64 postmenopausal women (57.61 ± 6.50 years; BMI: 22.71 ± 2.58 kg/m²). As expected, age differed significantly between groups (t = 20.21, P < 0.001), whereas BMI was comparable (t = 0.15, P = 0.881) (Table 1).

Table 1.

Demographic and Clinical Baseline Characteristics of the Study Population

Parameter	Total Sample (N = 228)	Premenopausal (n = 164)	Postmenopausal (n = 64)	t	P value
Age (years), mean ± SD	43.34 ± 11.28	37.77 ± 7.06	57.61 ± 6.50	20.21	< 0.001
BMI (kg/m2), mean ± SD	22.67 ± 2.79	22.65 ± 2.87	22.71 ± 2.58	0.15	0.881

Notes: Values are mean ± SD. P values were derived from Welch’s two-sample t-test comparing the premenopausal and postmenopausal groups.

Abbreviations: BMI, body mass index; SD, standard deviation.

Inter-Group Differences in Segmental Elasticity

Quantification of tissue elasticity (E, kPa) across the six anatomical sampling sites revealed distinct regional elevations in postmenopausal women compared to premenopausal controls (Table 2). In unadjusted analyses, postmenopausal status was associated with significantly higher tissue stiffness in the middle anterior (14.59 ± 3.93 vs 12.88 ± 3.87 kPa, P = 0.003), middle posterior (14.87 ± 4.09 vs 13.28 ± 4.25 kPa, P = 0.012), and lower posterior (15.02 ± 4.01 vs 13.74 ± 4.26 kPa, P = 0.039) walls, whereas the remaining segments showed no unadjusted significant differences (P ≥ 0.076). Following multivariable linear mixed-effects modeling with participant-level random intercepts (adjusting for age and BMI) and FDR correction for repeated spatial measurements, postmenopausal tissue stiffening remained localized to the middle anterior (β =1.68 ± 0.56 kPa, adjusted P = 0.003, FDR q = 0.009) and middle posterior (β=1.52 ± 0.60 kPa, adjusted P= 0.013, FDR q = 0.026) segments. In contrast, elevation in the lower posterior wall retained a trend toward stiffening (β=1.24 ±0.61 kPa, adjusted P=0.043) but did not cross the FDR multiplicity threshold (q=0.065).

Table 2.

Inter-Group Comparisons of Segment-Specific Vaginal Wall Elasticity (Young’s Modulus, Ē, in kPa) Between Premenopausal and Postmenopausal Women

Anatomical Location/Segment	Mean ± SD (kPa)		Unadjusted		Adjusted Model		FDR q value
	Premenopausal (n = 164)	Postmenopausal (n = 64)	Difference (kPa)	t	β ± SE	P value
Anterior vaginal wall
Lower segment	14.48 ± 3.71	15.55 ± 4.20	1.79	0.076	1.02 ± 0.58	0.079	0.095
Middle segment	12.88 ± 3.87	14.59 ± 3.93	2.97	0.003	1.68 ± 0.56	0.003	0.009*
Upper segment	12.88 ± 3.75	13.81 ± 4.04	1.59	0.114	0.89 ± 0.57	0.118	0.118
Posterior vaginal wall
Lower segment	13.74 ± 4.26	15.02 ± 4.01	2.08	0.039	1.24 ± 0.61	0.043	0.065
Middle segment	13.28 ± 4.25	14.87 ± 4.09	2.56	0.012	1.52 ± 0.60	0.013	0.026*
Upper segment	13.78 ± 4.17	14.69 ± 4.51	1.41	0.161	0.81 ± 0.63	0.201	0.201

Notes: Values for the premenopausal and postmenopausal groups are presented as mean ± SD in kilopascals (kPa).

Intra-Group Compartmental Differences and Spatial Gradients

Paired-sample comparisons between corresponding anterior and posterior wall segments, as well as proximal-to-distal segmental gradients within each group, are detailed in Table 3. Across the full cohort (N=228), the upper anterior wall exhibited significantly lower elasticity than the corresponding upper posterior wall (13.14 ± 3.85 vs 14.04 ± 4.28 kPa; mean difference: −0.90 kPa, paired t = −3.45, P = 0.001, FDR q = 0.002). Conversely, in the lower segment, the anterior wall was significantly stiffer than the posterior wall (14.78±3.88 vs 14.10±4.22 kPa; mean difference: +0.68 kPa, paired t = 3.66, P < 0.001, FDR q = 0.001), while no significant compartment difference was observed at the middle segment (P = 0.108).

Table 3.

Intra-Group Comparisons and Spatial Elasticity Gradients Across Vaginal Wall Compartments (Young’s Modulus, Ē, in kPa)

Menopausal Group	Segment	Elasticity, Mean ± SD (kPa)		Paired Comparison (Anterior vs Posterior)				Segmental Gradient ANOVA (F, P value)
		Anterior Wall	Posterior Wall	Mean Difference (kPa)	t	P value	FDR q value
All participants (n = 228)	Lower	14.78 ± 3.88	14.10 ± 4.22	+0.68	3.66	< 0.001	0.001*	F = 26.77, P < 0.001* (anterior)
	Middle	13.36 ± 3.95	13.73 ± 4.26	−0.37	−1.61	0.108	0.130	F = 3.85, P = 0.146 (posterior)
	Upper	13.14 ± 3.85	14.04 ± 4.28	−0.90	−3.45	0.001	0.002*
Premenopausal (n = 164)	Lower	14.48 ± 3.71	13.74 ± 4.26	+0.74	2.94	0.004	0.008*	F = 19.11, P < 0.001* (anterior)
	Middle	12.88 ± 3.87	13.28 ± 4.25	−0.40	−1.43	0.156	0.156	F = 2.01, P = 0.135 (posterior)
	Upper	12.88 ± 3.75	13.78 ± 4.17	−0.90	−2.79	0.006	0.009*
Postmenopausal (n = 64)	Lower	15.55 ± 4.20	15.02 ± 4.01	+0.53	1.22	0.228	0.228	F = 7.33, P = 0.001* (anterior)
	Middle	14.59 ± 3.93	14.87 ± 4.09	−0.28	−0.70	0.489	0.489	F = 0.31, P = 0.738 (posterior)
	Upper	13.81 ± 4.04	14.69 ± 4.51	−0.88	−2.37	0.021	0.042*

Notes: Values for the anterior and posterior walls are presented as mean ± SD in kilopascals (kPa).

Subgroup analyses demonstrated consistent patterns. In the premenopausal group (n=164), tissue stiffness was significantly lower in the upper anterior vs upper posterior segment (12.88 ± 3.75 vs 13.78 ± 4.17 kPa, P = 0.006, FDR q = 0.009) and significantly higher in the lower anterior vs lower posterior segment (14.48±3.71 vs 13.74±4.26 kPa, P = 0.004, FDR q = 0.008). In the postmenopausal group (n = 64), the upper anterior wall maintained significantly lower elasticity than its posterior counterpart (13.81 ± 4.04 vs 14.69 ± 4.51 kPa, P = 0.021, FDR q = 0.042), whereas lower segment compartmental differences were attenuated (P = 0.228).

One-way repeated-measures ANOVA revealed a distinct spatial stiffness gradient along the anterior vaginal wall in all participant subsets, characterized by a progressive increase in Young’s modulus from the upper (proximal) to the lower (distal) segment (F = 26.77, P<0.001 for total population; F= 19.11, P < 0.001 for premenopausal group; F = 7.33, P =0.001 for postmenopausal group). In contrast, the posterior vaginal wall showed a homogeneous elasticity profile without significant proximal-to-distal gradients across premenopausal (F = 2.01, P = 0.135), postmenopausal (F = 0.31, P = 0.738), or pooled cohorts (F = 3.85, P = 0.146).

Inter-Rater Reliability

Table 4 shows the ICC values measured by two physicians for each segment of the vaginal wall. The ICC ranged from 0.83 (0.68–0.94) to 0.95 (0.88–0.98) (p < 0.001), indicating good to excellent inter-rater reliability. These findings suggest that the two physicians are highly consistent in measuring vaginal wall elasticity using the linear array probe.

Table 4.

Inter-Observer Reliability of Transrectal Shear-Wave Elastography Measurements (Young’s Modulus, Ē, in kPa)

Operator	Anterior Wall, Mean ± SD (kPa)			Posterior Wall, Mean ± SD (kPa)
	Lower	Middle	Upper	Lower	Middle	Upper
First operator	14.14 ± 3.68	14.05 ± 2.89	13.14 ± 2.33	13.57 ± 2.57	12.69 ± 1.90	12.50 ± 2.78
Second operator	14.57 ± 2.66	13.48 ± 2.44	12.39 ± 2.28	13.57 ± 2.34	12.36 ± 1.70	12.10 ± 2.14
ICC (95% CI)	0.85** (0.71–0.95)	0.86** (0.66–0.95)	0.83** (0.68–0.94)	0.95** (0.88–0.98)	0.86** (0.66–0.95)	0.88** (0.71–0.95)

Notes: Values for the first and second operators are expressed as mean ± SD. ** P < 0.001. Model: two-way random-effects model for absolute agreement, ICC (2,k).

Abbreviations: ICC, intraclass correlation coefficient; CI, confidence interval; kPa, kilopascals.

Discussion

Significant alterations in vaginal biomechanics during the menopausal transition—including reduced tissue compliance and diminished elasticity—are biologically hypothesized to be associated with estrogen decline.¹⁸ Such alterations are thought to contribute to the pathophysiology of genitourinary syndrome of menopause (GSM),⁴ which negatively affects quality of life and overall well-being in aging women, necessitating timely and accurate diagnosis. Current diagnostic tools are limited by invasive procedures, measurement errors, or ethical issues. To overcome these limitations, our study introduced an innovative application of rectal high-frequency ultrasound sound touch elastography for vaginal wall assessment and compared vaginal elasticity between premenopausal and postmenopausal women. Inter-group comparison of vaginal elasticity indicators showed that the postmenopausal group had significantly higher stiffness and lower elasticity than the premenopausal group. Intra-group comparative analysis of segmental elasticity between anterior and posterior vaginal walls across different menopausal status groups revealed distinct patterns. In addition, the ICC values demonstrated good to excellent inter-rater reliability. These findings demonstrated the feasibility and reliability of the Linear Array High-Frequency Probe in assessing vaginal tissue elasticity.

The dual-plane transducer system of the Linear Array High-Frequency Probe, originally developed to evaluate prostatic and rectal conditions,¹⁹ uses two ultrasound probes integrated into a single system. This includes a linear array probe that generates rectangular beams along the probe’s lateral aspect and a convex array probe that emits fan-shaped beams from its superior aspect. By utilizing the high-frequency linear array probe positioned within the rectal lumen, our protocol achieves optimal technical conditions for vaginal wall evaluation. It ensures perfect acoustic beam perpendicularity to the anterior vaginal wall, clear sagittal plane visualization of vaginal anatomy, and complete vaginal imaging with moderate bladder filling. Most importantly, the transrectal approach avoids compression of the vaginal wall, which can distort elasticity measurements. This novel approach represents significant progress in pelvic floor imaging, offering several key advantages over conventional techniques: (1) standardized probe positioning that minimizes operator-dependent variability, (2) consistent measurement conditions unaffected by variable probe pressure, and (3) improved reliability in segmental vaginal elasticity quantification. Rectal probe positioning creates a stable acoustic window that allows reproducible measurements while maintaining the natural biomechanical state of the vaginal wall. By ensuring reliable, reproducible measurements, this technique provides data for understanding the underlying mechanisms of pelvic floor disorders and their relationship with hormonal factors. Furthermore, this technique avoids the ethical constraints associated with tissue sampling and overcomes the technical limitations of existing imaging modalities.

Our findings demonstrate segment-specific alterations in vaginal wall stiffness following menopause. Following multivariable adjustment for covariates using an LMM and FDR correction, postmenopausal women exhibited localized, statistically significant elevations in tissue stiffness (Young’s modulus) predominantly restricted to the middle anterior wall and middle posterior wall. While unadjusted analyses suggested broader pan-vaginal stiffening, rigorous confounder control confirms that menopausal biomechanical degradation is concentrated within the middle vaginal canal. These localized biomechanical changes align with prior histological and tissue-level studies proposing that menopausal status and chronological aging jointly contribute to structural alterations, potentially mediated by estrogen withdrawal, extracellular matrix degradation, loss of vascular elasticity, and age-related collagen cross-linking.^20,21 However, because this study did not explicitly quantify serum estrogen levels, hypoestrogenism remains a plausible biological hypothesis rather than a confirmed direct mechanism for the observed regional stiffening.

Our results directly build upon and extend the technical foundation established by Huang et al (2023),¹³ who demonstrated the feasibility of transrectal high-frequency SWE across a six-region matrix. While Huang et al reported no significant differences between pre- and postmenopausal women when aggregating measurements into a composite, globally averaged elasticity score, our segment-specific framework offers a plausible explanation for this disparity. By modeling each anatomical site independently with linear mixed effects and FDR control, we identified that menopausal stiffening is not pan-vaginal but highly focal, localized specifically to the middle anterior and middle posterior walls. Aggregating values across non-significant distal and proximal segments inherently dilutes these localized elevations. Thus, evaluating regional elasticity at segment-specific resolution is a primary novel contribution of our study, uncovering localized biomechanical alterations otherwise masked by global averaging. Furthermore, our primary novel contribution is the identification of compartment-specific (anterior vs posterior) and proximal-to-distal elasticity gradients, supported by a substantially larger cohort (N = 228) and rigorous two-observer inter-rater reliability testing (ICCs up to 0.95).

Comparative analysis between vaginal compartments revealed distinct spatial heterogeneity across both premenopausal and postmenopausal cohorts. In both groups, the upper anterior wall exhibited significantly lower Young’s modulus values (higher compliance) than its posterior counterpart. In contrast, distal compartmental differences were present in premenopausal women—where the lower anterior wall was significantly stiffer than the lower posterior wall—but attenuated following menopause. These variations likely reflect underlying histomorphological distinctions between the anterior wall mucosa and the thicker, smooth muscle-rich posterior wall.²² The posterior wall’s superior structural reinforcement provides enhanced load-bearing capacity, potentially explaining structural variations observed during clinical physical examinations.²²

Furthermore, our intra-group evaluation established a significant, progressive proximal-to-distal stiffness gradient along the anterior vaginal wall across all participant subsets, characterized by lowest Young’s modulus values proximally (upper segment) and highest values distally (lower segment). Conversely, the posterior vaginal wall exhibited spatial biomechanical homogeneity without significant longitudinal gradients. The distal stiffening of the anterior wall corresponds to known regional specialization in pelvic architecture, where distal muscular and fibrous structures provide the mechanical support required for vaginal introitus and pelvic floor stability.²³ Conversely, greater proximal compliance facilitates the vaginal elongation and tissue distensibility needed during physiological strain.²⁴ Similar distal-reinforcement patterns observed in mammalian biomechanical models suggest a conserved functional architecture that balances introital structural support with proximal elasticity.²⁴

Our research presents several key methodological advancements in vaginal biomechanics assessment. Applying rectal linear array high-frequency ultrasound provides a non-invasive yet quantitative approach to evaluate menopause-related tissue changes. This innovative technique offers practical clinical advantages, including ease of operation and reliable reproducibility for assessing vaginal wall elasticity. However, several limitations remain. First, because this study used an observational, cross-sectional design, direct causality between menopausal transition and altered tissue elasticity cannot be inferred. Although multivariable linear mixed-effects modeling controlled for key clinical covariates, independent menopausal effects cannot be completely uncoupled from chronological age or other unmeasured factors, such as parity, obstetric history, subclinical vascular changes, and tissue-level inflammatory markers. Second, serum hormone levels (eg, estradiol) were not explicitly quantified in this cohort, and diagnostic performance for related clinical conditions—such as GSM or pelvic organ prolapse—was not formally established. As a result, hypoestrogenism and age-related tissue remodeling remain plausible biological hypotheses rather than demonstrated mechanisms for the observed regional stiffening. Third, because our findings are derived from a single-center cohort, external generalizability remains to be verified. Rigorous multi-center external validation, longitudinal tracking across the menopausal transition, and benchmarking against gold-standard histological or ex vivo mechanical reference methods are strictly required before considering any routine clinical implementation. Finally, because SWE measurements were not directly benchmarked against histological or ex vivo mechanical gold-standard reference methods, we cannot make statements about absolute diagnostic accuracy or tissue validity. Our findings demonstrate technical feasibility, high inter-observer reliability, and sensitivity to regional stiffness differences. Still, the formal diagnostic accuracy and clinical validity of transrectal shear-wave elastography remain to be established in future comparative studies.

Conclusion

Transrectal high-frequency linear array shear-wave elastography provides a reliable, non-invasive method for evaluating segment-specific vaginal wall elasticity. By applying a linear mixed-effects framework with multiplicity control, this study demonstrated that postmenopausal tissue stiffening is localized to the middle vaginal canal rather than pan-vaginal, while also characterizing distinct compartment-specific differences and a proximal-to-distal elasticity gradient along the anterior wall. Although these regional biomechanical insights contribute to our fundamental understanding of vaginal architectural specialization, future large-scale, age-matched, and multicenter studies are needed to validate these findings and establish standardized clinical diagnostic thresholds.

Disclosure

The authors report no conflicts of interest in this work.