MR defecography: comparison of HMO system measurement between supine and lateral decubitus patient position

Abstract

Background

Pelvic floor dysfunction (PVD), a prevalent clinical issue impacting quality of life, can be effectively assessed using magnetic resonance defecography (MRD) with the patient either supine or in the lateral decubitus position.

Purpose

To compare the measurement value and grading in dynamic MRD within the closed-magnet system of PFD patients performed in supine versus lateral decubitus position using the H line, M line, and organ prolapse (HMO) classification system.

Material and Methods

During 2017–2019, 100 patients with PFD underwent MRD during defecation in both supine and lateral decubitus positions. MR images were measured and graded by two blinded radiologists. The mean value of each HMO parameter and grading severity were compared between supine and lateral positions. Image quality (IQ) between two positions was also evaluated. Paired t-test and Wilcoxon ranked test were performed for significant difference. P < 0.05 was considered statistically significant.

Results

For HMO measurement, M-line, levator plate angle (LPA), urethral hypermobility (UH), uterine prolapse, and peritoneocele had significantly higher mean values when measured in the lateral decubitus position than in the supine position. For grading, M-line, uterine prolapse, and peritoneocele also had more grading severity in the lateral decubitus than supine position with statistical significance (P = 0.002, 0.004, and 0.001, respectively). Only anterior rectocele had a mean value and grading severity in the supine more than the lateral position (P = 0.003 and P = 0.005). IQ in the supine was better than in the lateral decubitus position (P < 0.001).

Conclusion

MRD in lateral decubitus showed a more severe degree of PFD in most parameters based on the HMO grading system irrespective of inferior imaging quality.

Keywords

Magnetic resonance defecography pelvic floor dysfunction HMO system supine position lateral decubitus position

Introduction

Pelvic floor dysfunction (PFD) is the result of the ligament, fascia, or muscle impairment that supports the urinary bladder, uterus, and bowel, which may result in pelvic pain, urinary and fecal incontinence, long-term constipation, voiding difficulty, and sexual dysfunction (1). The risk factors of PFD are increasing age (2), postmenopausal status (3), pregnancy (4), connective tissue disorders (5), chronic obstructive pulmonary disease (COPD) (6), and obesity (6 –8). Most cases are seen in elderly female patients, with more than 50% experiencing urinary stress incontinence (9 –11), while approximately 40% of postmenopausal women aged 50–79 years have been reported to have some degree of pelvic organ prolapse based on clinical symptoms and pelvic examination (12). The lifetime risk of women who will have one or more surgical interventions for urinary incontinence or pelvic organ prolapse by the age of 80 years is approximately 11% (13,14). In low-income countries, previous reports showed that prevalence of pelvic organ disorder was approximately 19.7%, urinary incontinence 28.7%, and fecal incontinence 7% (15). Clinical examination is sufficient for many cases with anterior compartment issues and is limited in the assessment of complex multicompartmental cases and for cul-de-sac hernias (15).

Magnetic resonance defecography (MRD) is a minimally invasive imaging test (16) that can be used to anatomically evaluate all pelvic organ compartments and their function simultaneously (17,18). This information can then be used for further surgical planning (19). MRD can either be performed on an open or closed MR system. An open system allows evacuation and assessment in a seated position, which is more physiological, but this type of magnet is not widely available (20,21). Conventional closed MRI is more ubiquitous, but the assessment is in non-physiological lying position (22) with MRD in a closed system generally performed only in the supine position (23). We observed that some patients cannot defecate in the supine position during scans. As an alternative, MRD can be performed in the lateral decubitus position, which aligns with the standard position for anorectal manometry. Rao et al. (24) found that approximately one-third of patients displayed dyssynergia in the supine position during anorectal manometry, and more than half were unable to complete the balloon expulsion test (BET) or the silicone stool test (FECOM). Hence, we introduced the lateral decubitus position for patients who have difficulty defecating in the supine position and found that more patients were able to successfully defecate in the lateral position. Nevertheless, the performance of MRD in the lateral position has not yet been established.

In 2018, Schawkat et al. demonstrated that there were similar grades of pelvic floor descent in the lateral position similar to the supine position (25). However, this study did not provide detailed information on the measurement of the H line, M line, and organ prolapse (HMO) system. Therefore, the aim of the present study was to investigate the performance of MRD in the lateral decubitus position and compare HMO system measurements between supine and lateral decubitus using a conventional closed MR device.

Material and Methods

Patients

This study was approved by the Institutional Review Board (no. 149/62). The requirement for informed consent was waived owing to the retrospective nature of the study.

Between September 2017 and May 2019, a total of 128 patients were recruited into this study. The inclusion criteria were patients age >15 years who underwent MRD in both the supine and left lateral decubitus positions. A total of 28 patients were excluded due to poor image quality (n = 5) and dyssynergic defecation (n = 23). The exclusion of patients with dyssynergic defecation was necessary as they were not able to defecate in both positions; therefore, we could not obtain any distinct measurements from those patients. The remaining 100 patients who underwent MRD in both the supine and lateral decubitus positions were included.

The patient was asked to void 1 h before the scan to ensure moderate bladder filling and subsequently 300 mL of ultrasound gel was instilled into the rectum and 30 mL into the vagina via a 24-Fr rectal tube on the MR table in the left lateral decubitus position, followed by diaper wear to avoid leakage (26).

MR defecography

MRD was performed on a single 1.5-T scanner (MAGNETOM Aera; Siemens, Erlangen, Germany) with surface phased-array coils wrapped around the pelvis. First, all patients were scanned in the supine position to perform the static sequences using the following protocol: (i) thin slice sagittal T2-weighted (T2W) imaging; (ii) thin slice axial oblique and (iii) coronal oblique T2W imaging with a small field of view (FOV) oriented orthogonal and parallel to anal canal long axis with slice thickness 3 mm and no gap; (iv) axial view of the whole pelvis in T1-weighted imaging; and (v) axial view of whole pelvis in T2W imaging with fat suppression (FS).

The dynamic sequences were then performed using balanced steady state free precession (bSSFP, TRUFI sequence in Siemens) in the mid-sagittal plane in both the supine and lateral decubitus positions, including pubic symphysis, urinary bladder, vagina, anorectum, and coccyx to evaluate pelvic floor relaxation during defecation. These sequences were performed using the cine loop mode (TR/TE = 4.26/1.77 ms; FOV = 40 × 40 cm; matrix = 256 × 256; slice thickness = 8 mm). The imaging sequence in the defecation phase always began with three trials in the supine position, followed by scans in the left lateral decubitus position until adequate defecation was achieved. There was no knee or pillow support in either the supine or lateral decubitus position. This protocol was consistently followed for all patients. Each defecation phase took 70 seconds to perform.

Image interpretation

MR images were independently measured and graded by two radiologists with 6 and 12 years of experience in abdominal imaging. MR images were evaluated in the mid-sagittal plane of the pelvic image during maximal straining/defecation. Each position was assessed separately over a 6-week interval to reduce recall bias. The HMO classification system measurements were made as follows (Fig. 1): H-line, M-line, levator plate angle (LPA); anorectal angle (ARA); urethral hypermobility (UH); cystocele; uterine/vaginal prolapse; enterocele; peritoneocele; and anterior rectocele.

Fig. 1.

Reference points of the HMO system. The PCL is drawn from the inferior border of the pubic symphysis (A) to the last coccygeal joint (B). The H line (H) represents the anteroposterior hiatal width that extends from point A to the posterior aspect of the puborectalis muscle (C). The M line (M) is the perpendicular distance from the posterior end of H line (C) to the PCL and measures pelvic floor descent. The LPA is the angle between the PCL and levator plate. The ARA is the angle between the posterior border of the distal rectum and the central axis of the anal canal. ARA, anorectal angle; LPA, levator plate angle; PCL, pubococcygeal line.

The severity of the HMO system was graded as mild, moderate, and severe (Table 1).

Table 1.

Severity grading of the HMO system.

HMO parameters	Mild degree (cm)	Moderate degree (cm)	Severe degree (cm)
H-line	6–8	8–10	>10
M-line	2–4	4–6	>6
Cystocele	1–3	3–6	>6
Uterine/vaginal prolapse
Enterocele	<3	3–6	>6
Peritoneocele
Anterior rectocele	<2	2–4	>4

Image quality

The image quality (IQ) was assessed by imaging artifacts and resolution as well as the visualization of these reference structures on mid-sagittal images, i.e. inferior border of pubic symphysis, last coccygeal joint, anorectal junction (ARJ), bladder base, and the most anteroinferior aspect of the cervix (or posterosuperior vaginal apex in patients who have undergone hysterectomy).

The IQ score was classified into five grades as follows: 5 = excellent, all reference structures clearly seen, no motion or susceptibility artifacts; 4 = good, minimal motion artifacts but no effect on reference structures; 3 = satisfactory, having motion artifacts causing minimal effect to reference structures; 2 = moderate, with motion artifacts causing unclear identification of one reference structure; and 1 = poor, unclear identification of more than one reference structure.

Statistical analysis

Statistical analysis was performed using SPSS version 22 (IBM Corp., Armonk, NY, USA). Demographic data are shown as mean ± SD. The intraclass correlation coefficient (ICC) was used to define the level of inter-observer agreement. The scale used for interpretation of ICC statistics was as follows: 0.75–1.0 = excellent; 0.60–0.74 = good; 0.40–0.59 = fair; and <0.4 = poor (27). We used the average mean value of each parameter in both positions between the two readers for the statistical analysis. The mean difference was calculated by the mean value in the supine position minus the mean value in the lateral decubitus position. The Wilcoxon signed-rank test and paired t-test were applied to compare the supine and lateral decubitus positions. P < 0.05 was considered statistically significant.

Results

Effects of position on HMO classification

A total of 100 patients (13 men, 87 women; mean age = 56.7 ± 15.0 years) were included for analysis. The indications for MRD in both groups were difficult defecation, solitary rectal ulcer syndrome (SRUS), PFD, and others (rectal intussusception, mucous bloody stool, and loose anal sphincter). Patient characteristics and indications for MRD are shown in Table 2. For inter-observer agreement, there were fair to excellent agreements of the supine position (ICC = 0.59–0.94) and lateral decubitus position (ICC = 0.56–0.99) (Table 3). Seven parameters—H-line, M-line, cystocele, uterine/vaginal prolapse, enterocele, peritoneocele, and anterior rectocele—had excellent inter-observer agreement in the supine position (ICC = 0.78–0.94) while only five parameters—H-line, uterine/vaginal prolapse, enterocele, peritoneocele, and anterior rectocele—had excellent agreement in the lateral decubitus position (ICC = 0.81–0.99). ARA, LPA, and UH had fair to good agreement in both the supine and lateral decubitus positions (ICC = 0.59–0.73 and 0.56–0.63, respectively). M-line, ARA, LPA, and cystocele had better agreement in the supine position than the lateral decubitus position, whereas UH, uterine/vaginal prolapse, enterocele, and peritoneocele had better agreement in the lateral decubitus position than the supine position, for which all ICCs were statistically significant (P < 0.001).

Table 2.

Patient characteristics and indication for MRD in 100 patients.

Characteristic	Number of patients
Female	87
Male	13
Age (years)	56.7 ± 15.0 years
Indication for MR defecography
Difficult defecation	54
Solitary rectal ulcer syndrome	12
Pelvic floor descent	28
Others*	6

Values are given as n or mean ± SD.

*Other: rectal intussusception, mucous bloody stool, and loose anal sphincter.

Table 3.

ICC, mean, and mean difference of HMO parameters between the supine and lateral decubitus positions.

Parameters	ICC		Supine	Lateral decubitus	Mean difference*	P value
Parameters	Supine	Lateral decubitus	Supine	Lateral decubitus	Mean difference*	P value
H-line (cm)	0.82	0.81	7.46 ± 1.32	7.47 ± 1.32	−0.01 ± 0.94	0.890
M-line (cm)	0.78	0.73	4.17 ± 1.24	4.43 ± 1.22	−0.26 ± 0.98	0.009^†
ARA (°)	0.73	0.62	128.49 ± 16.80	128.54 ± 14.18	−0.05 ± 13.42	0.973
LPA (°)	0.65	0.56	44.12 ± 11.78	49.48 ± 11.30	−5.36 ± 10.84	<0.001^†
UH (°)	0.59	0.63	68.99 ± 31.04	78.94 ± 32.43	−9.95 ± 28.54	0.001^†
Cystocele (cm)	0.91	0.73	1.20 ± 1.41	1.37 ± 1.22	−0.17 ± 1.84	0.355
Uterine prolapse (cm)	0.80	0.97	0.76 ± 1.26	1.08 ± 1.34	−0.32 ± 1.01	0.002^†
Enterocele (cm)	0.94	0.99	0.18 ± 0.76	0.19 ± 1.35	−0.01 ± 1.51	0.955
Peritoneocele (cm)	0.82	0.98	0.84 ± 2.07	1.36 ± 2.23	−0.52 ± 1.65	0.002^†
Anterior rectocele (cm)	0.87	0.89	1.84 ± 1.09	1.57 ± 1.03	0.27 ± 0.89	0.003^†

Values are given as mean ± SD unless otherwise indicated.

*Mean difference = mean value in supine position (cm) – mean value in lateral decubitus position (cm).

^†Statistically significant.

ARA, anorectal angle; ICC, intraclass correlation coefficient; LPA, levator plate angle; UH urethral hypermobility.

The results of the HMO measurement are shown in Table 3. All parameters except anterior rectocele had higher mean values when measured in the lateral decubitus position than in the supine position (Fig. 2). Five parameters—M-line, LPA, UH, uterine prolapse, and peritoneocele—had a statistically significant difference of mean values between the lateral decubitus and supine positions (P < 0.05), while only anterior rectocele had a higher mean value when measured in the supine position (P = 0.003) (Fig. 3).

Fig. 2.

A 52-year-old woman with a history of pelvic floor descent underwent MRD in (a) the supine position and (b) the lateral decubitus. Mid-sagittal TRUFI images, HMO measurement of supine image (a) demonstrated H-line = 6.4 cm (mild degree), M-line = 4.4 cm (moderate), uterine prolapse = 1.3 cm (mild). Measurement in the lateral decubitus position demonstrated H-line = 7.5 cm (mild), M-line = 5.4 cm (moderate), cystocele = 1.1 cm (mild), and uterine prolapse = 2.6 cm (mild). No cystocele was observed in the supine position. Image quality in this patient was scored as 5 in both the supine and lateral decubitus positions. MRD, magnetic resonance defecography.

Fig. 3.

A 55-year-old woman with a history of difficult defecation underwent MRD in (a) the supine and (b) lateral decubitus positions. Peritoneocele and enterocele are observed in both positions, with measurements higher in the lateral position than in the supine position. In contrast, the measurement of the anterior rectocele is greater in the supine image (2.9 cm; moderate degree) compared to the lateral decubitus image (2.4 cm; moderate degree). MRD, magnetic resonance defecography.

In terms of severity, the majority of patients exhibited consistent grading in both positions across all parameters (59%–90%). However, among those with different grades, most parameters showed a higher prevalence of more severe grading in the lateral decubitus position compared to the supine position, except for the H-line and anterior rectocele. Significant differences were observed for the M-line, uterine prolapse, peritoneocele, and anterior rectocele (Table 4). The remaining parameters (H-line, cystocele, and enterocele) showed no significant differences. The details of grading changes for each parameter in the 100 patients of the study are shown in Table 5.

Table 4.

Number of patients of severity grading in supine and lateral decubitus positions.

Parameter	No. of patients		Sum of ranks*		P value*
Parameter	Lateral < supine	Lateral > supine	Lateral < supine	Lateral > supine	P value*
H-line	12	14	156.0	195.0	0.29
M-line	9	28	180.5	522.5	0.002^†
Cystocele	11	19	180.0	285.0	0.112
Uterine prolapse	7	21	101.5	304.5	0.004^†
Enterocele	4	6	21.0	34.0	0.251
Peritoneocele	11	30	204.0	657.0	0.001^†
Anterior rectocele	26	10	483.0	183.0	0.005^†

*Calculated by Wilcoxon ranked test.

^†Statistically significant.

Table 5.

Details of grading changes between the supine and lateral decubitus positions for each parameter in 100 patients.

Grading	H-line	M-line	Cystocele	Uterine prolapse	Enterocele	Peritoneocele	Rectocele
Same	74	63	70	72	90	59	64
Different	26	37	30	28	10	41	36
Supine < lateral	12	28	19	21	6	30	10
Change 1 grade	12	27	19	21	2	18	9
Change ≥2 grades	0	1*	0	0	4*^†	12*^†‡	1*
Supine > lateral	14	9	11	7	4	11	26
Change 1 grade	13	8	10	7	2	8	23
Change ≥2 grades	1^§	1**	1**	0	2^§††	3^§**	3^α

Values are given as n. Supine < lateral position = *none to moderate, ^†none to severe, ^‡mild to severe. Supine > lateral position = ^§moderate to none, **severe to mild, ^††severe to none.

For the M-line, 28 (28%) patients demonstrated higher grading in the lateral position compared to the supine position (P = 0.002). Notably, 27 cases exhibited a change of only one grade, while one case showed a two-grade change, transitioning from no pelvic floor descent in the supine position to moderate descent in the lateral position. Nine patients had lower grading in the lateral decubitus position compared to the supine position.

Concerning uterine prolapse, seven patients displayed lower grading in the lateral decubitus position compared to the supine position, while 21 patients exhibited higher grading in the lateral position (P = 0.004). Among these, all 21 patients experienced a one-grade change.

In the case of peritoneocele, 11 patients had lower grading in the lateral decubitus position compared to the supine position, whereas 30 patients demonstrated higher grading in the lateral position (P = 0.001). Within this group, 18 cases had a one-grade change, eight cases experienced a two-grade change (from none to moderate in seven cases, and from mild to severe in one case), and four cases showed a three-grade change from none to a severe degree.

Conversely, anterior rectocele exhibited higher grading in the supine position for 26 patients. Among them, 23 cases underwent a one-grade change, and three cases showed a moderate degree in the supine position with no rectocele observed in the lateral position. In contrast, 10 patients displayed higher grading in the lateral position compared to the supine position (P = 0.005).

In total, 16 patients underwent various surgical procedures, including the Manchester operation (for uterine prolapse repair), rectal repair, rectopexy, colpopexy, total hysterectomy, and sphincteroplasty after MRD. Among them, six cases (37.5% of surgical cases) exhibited a higher grading in the lateral position compared to the supine position. Three cases showed a one-grade change, and three cases showed a two-grade change (transitioning from no pelvic floor descent (n = 1) and no peritoneocele (n = 2) to a moderate degree). In total, 84 patients had no surgical intervention; of them, only three patients were treated by pelvic floor muscle training (PFMT).

Effects of position on image quality

In addition, the IQ from the supine position was better than from the lateral position (Fig. 4). Most cases in the supine position (89%) had IQ scored as good to excellent (score 4–5), 10% were satisfactory (score 3), and 1% was moderate (score 2). This case with moderate IQ showed an unclearly identified anterior cervical lip, while in the lateral position 56% of cases were scored as good to excellent, 33% were satisfactory, and 11% were moderate IQ (P < 0.001). Most of these cases with moderate IQ exhibited motion artifacts, which resulted in poor visualization of one reference structure: the last coccygeal joint (n = 7); anterior lip of uterine cervix (n = 2); vaginal apex (n = 1); and urinary bladder base (n = 1).

Fig. 4.

Mid-sagittal images in (a) the supine and (b) lateral decubitus positions show different IQs. There is minimal motion artifact on the supine image, but the reference points are still well-identified, with a score of 4. (b) The lateral position image had motion artifacts, which cannot well visualize the last coccygeal joint (arrow), thus it was scored by 3 (moderate IQ). IQ, image quality.

Discussion

Currently, MRD is a widely employed diagnostic tool in clinical centers for assessing PFD and assisting in treatment planning (28). Many institutions commonly utilize conventional closed-magnet devices, which have limited the physiological assessment of defecation. Despite this limitation, closed-magnet MRI remains capable of evaluating pelvic floor descent in both the supine and lateral decubitus positions. To date, only one study has explored the comparative performance of dynamic MRD in these two positions. Schawkat et al. (25) reported a significantly more severe grade of descent in the anterior compartment during the lateral decubitus position compared to the supine position, with no significant differences noted in the middle and posterior compartments. In contrast, our study reveals more pronounced grades of pelvic floor descent in both the middle and posterior compartments.

Our study is based on the hypothesis that body position may affect the ability and force of defecation, resulting in variations in measurements and grading of pelvic floor descent. In the lateral decubitus position, patients can flex their hips and knees more than in the supine position during examination, which may facilitate straining and the defecation process. Notably, the severity of anterior rectocele was greater when measured in the supine position than in the lateral position. We observed the coexisting anterior and middle compartment organ prolapse i.e. cystocele, uterine/vaginal prolapse, peritoneocele, and enterocele in these cases with more grading of descent in lateral position (Table 3). These lead to rectovaginal space widening that may hinder the anterior bulging of rectum and result in an underestimation of anterior rectocele in the lateral position (Fig. 3). Moreover, the patients also slightly flex their hip joints in the lateral decubitus position causing decreased space in the pelvic cavity. The anterior rectal wall in the lateral decubitus position may be off-midline due to gravity, causing a partially seen anterior wall in the mid-sagittal image, which may cause more measure in supine position.

Nevertheless, the inter-observer agreement and IQ score in the lateral position was lower than in the supine position. According to the studies on pelvic tilt measurement by Karabag et al. (29) and Le Huec et al. (30), we measured the degree of pelvic tilt in supine and left lateral decubitus positions. We observed that in the lateral position, most patients have anterior pelvic tilt, while fewer patients have posterior pelvic tilt, which may result in some moderate IQ cases, making it difficult to accurately identify all anatomical reference points (pubic symphysis, last coccygeal joint, ARJ, bladder neck, or lower border of the cervix) in the mid-sagittal image (Fig. 4). However, neither had poor IQ in our study. Moreover, during the defecation phase, the pelvis seemed to move in the lateral position more notably than that in the supine position, leading to pronounced motion artifacts. ARA, LPA, and UH had moderate agreement in both positions, since some cases had intussusception or redundant posterior rectal wall leading to imprecise ARA measurement. For UH, the criterion for diagnosis was anterior angulation of the urethra by more than 30° from its resting axis on sagittal images obtained during straining or defecation (1). Accordingly, measuring the degree of urethral axis in different images (from resting to defecation phases) can affect measurement variables.

To our knowledge, this is the first study using the HMO classification system to compare the supine and lateral decubitus positions in MRD. Our study's strengths include the large number of patients using a single MRI scanner to evaluate various parameters of HMO measurement, which is widely used, allowing consistent standardization and grading of various forms of PFD. Each patient underwent MRD in both positions.

The present study has some limitations. The study was a non-randomized, retrospective study and there was no gold standard reference, such as a correlative surgical report, because most patients (84%) were treated conservatively, there was no report grading pelvic organ descent, and some patients were lost follow-up. Therefore, there is a lack of analysis on the clinical significance of the degree of grading in the lateral decubitus position being severe. However, we found that 6/16 (37.5%) cases that underwent surgical treatment for pelvic floor descent showed a higher grading in the lateral decubitus position compared to the supine position; however, due to the small number of patients, statistical significance could not be evaluated. Iacobellis et al. reported that the sitting position in an open MR device more correctly diagnosed and graded pelvic organ descent than the supine position in a closed MR system (23). Accordingly, a comparison between the sitting and lateral decubitus positions would be of interest for future studies.

In conclusion, our results show that MRD in the lateral decubitus position showed a more severe degree of pelvic floor disorder in most parameters based on the HMO grading system irrespective of inferior image quality.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Kewalee Sasiwimonphan

Thitinan Chulroek

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