Magnetic resonance imaging of the male pelvic floor: the anatomical configuration and dynamic movement in healthy men

Mechanism of Action of the Transobturator Sling for Post-Radical Prostatectomy Incontinence: A Multi-institutional Prospective Study Using Dynamic Magnetic Resonance Imaging

OBJECTIVE

To compare the length of the membranous (functional) urethra in male patients who underwent the male transobturator sling (TOS) for postradical prostatectomy urinary incontinence (PPI). The TOS is in established use for treatment of PPI; however, the precise mechanism of action is unknown.

MATERIALS AND METHODS

This is a prospective case-controlled study on men undergoing male TOS surgery from 2008 to 2014. The comparison arm included patients without incontinence after radical prostatectomy. All participants underwent dynamic magnetic resonance imaging (MRI) at baseline and this was repeated after TOS placement for those who underwent the procedure. Three standardized points were measured using MRI and compared in both groups in addition to clinical measures.

RESULTS

Thirty-nine patients were enrolled and 31 patients completed the protocols. The controls (N = 14) had a longer vesicourethral anastomosis to urethra measured at the penile bulb (functional urethral length) distance compared to the pre-TOS group at rest (1.92 cm controls vs 1.27 cm pre-TOS, P = .0018) and at Valsalva (2.13 cm controls vs 1.72 cm pre-TOS, P = .0371). Placement of the sling (N = 17) increased the functional urethral length distance at rest (1.92 cm control vs 1.53 cm post-TOS, P = .09) and at Valsalva (1.94 cm post-TOS vs 2.13 cm control, P = .61), so that the difference was no longer statistically significant.

CONCLUSION

We identified that one possible mechanism in improvement in stress urinary incontinence post-TOS placement is the lengthening of the vesicourethral anastomosis to bulbar-urethra distance. This is the first such study utilizing dynamics MRI in post prostatectomy controls, incontinent pre-TOS, and post-TOS to assess and show these findings.

The clinical value of magnetic resonance defecography in males with obstructed defecation syndrome

BACKGROUND

The aim of the present study was to assess the relationship between symptoms of obstructed defecation and findings on magnetic resonance (MR) defecography in males with obstructed defecation syndrome (ODS).

METHODS

Thirty-six males with ODS who underwent MR defecography at our institution between March 2013 and February 2016 were asked in a telephone interview about their symptoms and subsequent treatment, either medical or surgical. Patients were divided into 2 groups, one with anismus (Group 1) and one with prolapse without anismus (Group 2). The interaction between ODS type and symptoms with MR findings was assessed by multivariate analysis for categorical data using a hierarchical log-linear model. MR imaging findings included lateral and/or posterior rectocele, rectal prolapse, intussusception, ballooning of levator hiatus with impingement of pelvic organs and dyskinetic puborectalis muscle.

RESULTS

There were 21 males with ODS due to anismus (Group 1) and 15 with ODS due to rectal prolapse/intussusception (Group 2). Mean age of the entire group was 53.6 ± 4.1 years (range 18-77 years). Patients in Group 1 were slightly older than those in Group 2 (age peak, sixth decade in 47.6 vs 20.0%, p < 0.05). Symptoms most frequently associated with Group 1 patients included small volume and hard feces (85.0%, p < 0.01), excessive strain at stool (81.0%, p < 0.05), tenesmus and fecaloma formation (57.1 and 42.9%, p < 0.05); symptoms most frequently associated with Group 2 patients included mucous discharge, rectal bleeding and pain (86.7%, p < 0.05), prolonged toilet time (73.3%, p < 0.05), fragmented evacuation with or without digitation (66.7%, p < 0.005). Voiding outflow obstruction was more frequent in Group 1 (19.0 vs 13.3%; p < 0.05), while non-bacterial prostatitis and sexual dysfunction prevailed in Group 2 (26.7 and 46.7%, p < 0.05). At MR defecography, two major categories of findings were detected: a dyskinetic pattern (Type 1), seen in all Group 1 patients, which was characterized by non-relaxing puborectalis muscle, sand-glass configuration of the anorectum, poor emptying rate, limited pelvic floor descent and final residue ≥ 2/3; and a prolapsing pattern (Type 2), seen in all Group 2 patients, which was characterized by rectal prolapse/intussusception, ballooning of the levator hiatus with impingement of the rectal floor and prostatic base, excessive pelvic floor descent and residue ≤ 1/2. Posterolateral outpouching defined as perineal hernia was present in 28.6% of patients in Group 1 and were absent in Group 2. The average levator plate angle on straining differed significantly in the two patterns (21.3° ± 4.1 in Group 1 vs 65.6° ± 8.1 in Group 2; p < 0.05). Responses to the phone interview were obtained from 31 patients (18 of Group 1 and 13 of Group 2, response rate, 86.1%). Patients of Group 1 were always treated without surgery (i.e., biofeedback, dietary regimen, laxatives and/or enemas) which resulted in symptomatic improvement in 12/18 cases (66.6%). Of the patients in Group 2, 2/13 (15.3) underwent surgical repair, consisting of stapled transanal rectal resection (STARR) which resulted in symptom recurrence after 6 months and laparoscopic ventral rectopexy which resulted in symptom improvement. The other 11 patients of Group 2 were treated without surgery with symptoms improvement in 3 (27.3%).

CONCLUSIONS

The appearance of various abnormalities at MR defecography in men with ODS shows 2 distinct patterns which may have potential relevance for treatment planning, whether conservative or surgical.

Magnetic resonance imaging-guided functional anatomy approach to prostate brachytherapy

PURPOSE

To provide an MRI based functional anatomy guide to prostate brachytherapy.

METHODS AND MATERIALS

We performed a narrative review of periprostatic functional anatomy and the significance of this anatomy in prostate brachytherapy treatment planning.

RESULTS

MRI has improved delineation of gross tumor and critical periprostatic structures that have been implicated in toxicity. Furthermore, MRI has revealed the significant anatomic variants and the dynamic nature of these structures that can have significant implications for treatment planning and dosimetry.

CONCLUSIONS

The MRI-based functional anatomy approach to prostate brachytherapy takes into account extent of disease, its relation to the patient's individual anatomy, and functional baseline to optimize the therapeutic ratio of prostate cancer treatment.

Normal anatomy of urethral sphincter complex in young Chinese males on MRI

PURPOSE

In this research, the normal anatomy of urethral sphincter complex in young Chinese males has been studied.

METHODS

The sagittal, coronal, and axial T2-weighted non-fat suppressed fast spin-echo images of pelvic cavities of 86 Chinese young males were studied.

RESULT

Urethral sphincter complex is a cylindrical structure surrounding the urethra and extending vertically from bladder neck to perineal membrane. Urethral striated sphincter covers the anteriolateral urethra like a hat from bladder neck to verumontanum, while it surrounds the urethra in a ring shape from verumontanum to perineal membrane and backwards ends in central tendon of the perineum. From bladder neck to perineal membrane, the thickness of urethral smooth sphincter decreases gradually, and it extends forward to surround urethra with urethral striated sphincter as a ring. The length of urethral striated sphincter is 12.26-20.94 mm (mean 16.59 mm) at membranous urethra: 27.88-30.69 mm (mean 28.99 mm) from verumontanum to perineal membrane. The thickness of striated sphincter at membranous urethra is 4.29-6.86 mm (mean 5.56 mm) for the muscle of the anterior wall and 2.18-2.34 mm (mean 2.26 mm) for the muscle of the posterior wall.

CONCLUSIONS

In this paper, we summarized the normal anatomy of urethral sphincter complex in young Chinese males with no urinary control problems.

Three-dimensional MRI of the male urethrae with implanted artificial sphincters: initial results

The aim of this study was to develop a method for simultaneous 3D visualization of a new type of artificial urethral sphincter (AUS) and adjacent urinary structures. Serial MR tomograms were acquired from seven men after AUS implantation. 3D reconstruction was performed by thresholding original (positive) and inverted (negative) image intensity and by subsequently fusing positive and negative images. Results show that the bladder, cuff and balloons of the AUS of originally high intensity were imaged in 3D by thresholding the positive datasets. The urethrae and corpora cavernosa penis of originally low intensity were displayed in 3D by thresholding the negative datasets. Fusion of the positive and negative datasets allowed simultaneous visualization of the AUS complex and adjacent urinary structures. All the structures of interest were also clearly seen by interactive multiplanar reformatting. Coronal tomographic datasets provided better 3D and reformatted 2D images than sagittal and transverse datasets. This technique offers a simple means for evaluating the complex urethral anatomy and the AUS, and has potential for improved 3D visualization of many other complex morphological and pathological conditions.

Comparison of day 0 and day 14 dosimetry for permanent prostate implants using stranded seeds

PURPOSE

To determine, using MRI-based dosimetry (Day 0 and Day 14), whether clinically significant changes in the dose to the prostate and critical adjacent structures occur between Day 0 and 14, and to determine to what degree any changes in dosimetry are due to swelling or its resolution.

METHODS AND MATERIALS

A total of 28 patients with a permanent prostate implant using 125I rapid strands were evaluated at Days 0 and 14 by CT/MRI fusion. The minimal dose received by 90% of the target volume (prostate D90), percentage of volume receiving 100% of prescribed minimal peripheral dose (prostate V100), external sphincter D90, and 4-cm3 rectal volume dose were calculated. An acceptable prostate D90 was defined as D90 >90% of prescription dose. Prostate volume changes were calculated and correlated with any dosimetry change. A paradoxic dosimetric result was defined as an improvement in D90, despite increased swelling; a decrease in D90, despite decreased swelling; or a large change in D90 (>30 Gy) in the absence of swelling.

RESULTS

The D90 changed in 27 of 28 patients between Days 0 and 14. No relationship was found between a change in prostate volume and the change in D90 (R2 = 0.01). A paradoxic dosimetric result was noted in 11 of 28 patients. The rectal dose increased in 23 of 28 patients, with a >30-Gy change in 6. The external sphincter D90 increased in 19 of 28, with a >50-Gy increase in 6.

CONCLUSION

The dose to the prostate changed between Days 0 and 14 in most patients, resulting in a change in clinical status (acceptable or unacceptable) in 12 of 28 patients. Profound increases in normal tissue doses may make dose and toxicity correlations using Day 0 dosimetry difficult. No relationship was found between the prostate volume change and D90 change, and, in 11 patients, a paradoxic dosimetric result was noted. A differential z-axis shift of stranded seeds vs. prostate had a greater impact on final dosimetry and dose to critical adjacent tissues than did prostate swelling. These findings challenge the model that swelling is the principal cause of dosimetric changes after implantation. Stranded seeds may have contributed to this outcome. On the basis of these findings, a change in technique to avoid placement of stranded seeds inferior to the prostate apex has been adopted. These results may not apply to implants using single seeds within the prostate.

A novel technique for approaching the endopelvic fascia in retropubic radical prostatectomy, based on an anatomical study of fixed and fresh cadavers

OBJECTIVE

To present the anatomical basis and details of a technique for an approach to the endopelvic fascia devised to preserve urinary continence.

PATIENTS, MATERIALS AND METHODS

For cross-sectional macroscopic observation, seven formalin-fixed specimens of the male pelvic contents including the pelvic wall were serially sectioned at a 5-mm thickness. Semi-serial sections from eight other specimens were examined histologically. Eight fresh cadavers were dissected to mimic the various steps in a retropubic radical prostatectomy. After approaching the endopelvic fascia in an anatomically determined manner to reach the paraprostatic space, the pubic bone was removed and nerves near the rhabdosphincter dissected. To assess the clinical implication of this approach, we examined the time to achieve continence in 23 consecutive patients who had a radical retropubic prostatectomy using the new technique.

RESULTS

Sectional macroscopic observation depicted the fascia of the levator ani as a definite structure adherent to but not fused with the lateral pelvic fascia. The thin fascia overlying the levator ani fascia and lateral pelvic fascia represented the true endopelvic fascia. Microscopically, the lower part of the fascia of the levator ani was rich in smooth muscle, which interdigitated with the framework of the rhabdosphincter. In fresh cadavers, the levator ani muscle was removed laterally still covered by its fascia, without visualizing the muscle fibres. Small branches from the pudendal nerve entered the rhabdosphincter. The mean (sd, range) distance from the lowest point of the endopelvic fascia to the point where the sphincteric branch entered the rhabdosphincter was 5.5 (1.8, 3-8) mm. The continence rate at 1, 3, 6 and 9 months after surgery using the new technique was 44%, 83%, 96% and 100%, respectively.

CONCLUSIONS

Preserving the fascia of the levator ani helps to protect the levator ani muscle, rhabdosphincter and pudendal nerve branches to the rhabdosphincter. In retropubic radical prostatectomy, this anatomical approach to the endopelvic fascia should preserve or allow the earlier recovery of urinary continence.

Topographic anatomy of the male perineal structures with special reference to perineal approaches for radical prostatectomy

AIM

Although perineal approaches for radical prostatectomy have recently gained renewed attention as excellent methods for minimally invasive surgery, the most commonly used techniques, Belt's and Young's approaches, have inadequacies regarding the topographical relationship between the rectourethral and levator ani muscles.

METHODS

Using macroscopic observations of sagittal slices of 27 male pelvises and smooth muscle immunohistochemical staining of semiserial sections of another eight pelvises, we investigated the topographical anatomy of the perineal structures and their interindividual variations in elderly Japanese men.

RESULTS

The inferomedial edge of the levator ani was located 5-15 mm lateral to the midsagittal plane in an area between the urethra and the rectum. The rectourethral smooth muscle had a superoinferior thickness of 5-10 mm and occupied a space between the right and left levator slings. The levator was adjacent to, or continuous with, the striated anal sphincters. A thick connective tissue septum, composed of smooth muscle, was evident between the rectal smooth muscle and the anal sphincter-levator ani complex.

CONCLUSION

Because the connective tissue septum guides the surgeon's finger upwards towards the rectoprostatic space, Belt's approach appears relatively easy; however, rectal injury can sometimes occur if the surgeon loses this guidance. In contrast, if the levator edge is identified as the first step in Young's approach, the rectourethral muscle can be precisely divided, leaving a 3-5-mm margin from the rectum and sphincter-levator complex. Clinical investigations are now required to modify Young's approach based on the present results.

Individual variations in aging of the male urethral rhabdosphincter in Japanese

Although the degenerative changes with aging of the male urethral rhabdosphincter (URS) have been investigated, its individual morphological variations are still unclear. To provide an anatomical basis for clinical evaluation of the individual URS function in the aged, we investigated the structural differences in the URS of 25 elderly Japanese men using semiserial sections stained immunohistochemically and by hematoxylin-eosin. Before removal of the histological specimens, we dissected the ischioanal fossa and labeled several structures by carbon particles to allow proper orientation during the histological observations. In addition, macroscopic slices (10 mm thickness) made from five other male pelves were examined and, when necessary, followed by routine histological procedure to confirm the gross observations. An extended circular URS (over (1/2) circumferential configuration) was found in 15/25 cadavers, but showed very limited height (proximal-distal length) and thickness. A more restricted URS, including even a thin, arc-like pattern, was observed in the remaining cadavers. The attachment of the URS to the smooth muscle layer was loose and usually clearly separated. Continuation between the URS and deep transverse perineal muscle was sometimes observed. The thick fascia of the levetor ani, with high content of smooth muscles, usually provided the lateral or dorsal insertions of the URS. Our results in elderly Japanese subjects suggest that the sphincteric action is weak or incomplete. We suggest that the elderly URS maintains continence by retracting the urethra backward and upward with the aid of the levator sling, rather than the real sphincteric action expected in younger men.

Practical surgical anatomy for radical prostatectomy

Practical guidelines in surgical anatomy for radical prostatectomy can be summarized as follows: 1. There is significant individual variation in the anatomy of the male pelvis. 2. The prostate is covered anteriorly by a prominent detrusor apron. 3. Prostates vary with respect to size and shape. 4. BPH compresses and flattens the peripheral zone. 5. In reality, the puboprostatic ligaments are pubovesical ligaments. 6. The dorsal vein complex of the penis is a neurovascular plexus of veins, arteries, and nerves situated primarily ventral to the prostate and urethra. 7. The urethra from the verumontanum to the penile bulb is sphincteric, with its smooth muscle and elastic tissue components primarily responsible for postprostatectomy urinary continence. 8. Multiple micropedicles tether the neurovascular bundles along the entire posterolateral aspect of the prostate.

The dispute about the external sphincter and the urogenital diaphragm

PURPOSE

Basic scientific facts, such as anatomical structures, are rarely subjected to critical reappraisal. Nevertheless, several clinical phenomena exist which are inconsistent with the description of the anatomy of the so-called external sphincter muscle and urogenital diaphragm.

MATERIALS AND METHODS

We performed a global examination of the anatomy of the entire lower urinary tract in 50 male autopsy specimens. For comparison magnetic resonance imaging of the same regions was performed on 12 healthy patients.

RESULTS

Direct comparison of the results of both methods revealed the exact same topography of the bladder neck. The external sphincter or musculus sphincter urethrae is an independent morphological unit separated from the surrounding pelvic floor muscles by connective tissue.

CONCLUSIONS

The musculus transversus perinei profundus or deep transverse perineal muscle, which is believed to constitute the major element of the urogenital diaphragm, does not exist. There is histomorphological evidence that the external sphincter consists of a striated (musculus sphincter urethrae transversostriatus) and smooth muscle (musculus sphincter urethrae glaber) component.