Martinetti C., Bergaglio C., Migone S., Verardo I., Morcaldi D., Rollandi L, Listo E., Urru A., Gerboni M., Schettini D, Rosa F., Gandolfo N.
The aim of this educational poster is to depict the principal indications, the correct technique and semeiotics of MR Defecography in male pelvic floor evaluation. The normal MR anatomy is described providing anatomic landmarks specific for male anatomy useful in correctly identifying pelvic floor structures. Afterwards, radiological features of the most frequent pelvic floor diseases in male population are illustrated, including MRI evaluation of their surgical treatments.
INTRODUCTION Pelvic floor disorders are less common in men than in women but can lead to an important impairment of everyday quality of life. The most important risk factors for male pelvic floor disorders are previous surgery (primarily radical prostatectomy), pelvic radiotherapy, pelvic floor injuries, obesity, age, muscle atrophy, smoking, and chronic constipation (1,2). As for the female population MR Defecography provides both anatomical and functional information about pelvic floor disorders, allowing a correct diagnosis and grading the severity of pathologies to guide proper therapy. MR Defecography can also be used in the evaluation of postsurgical complications related to prostatectomy, first of all urinary incontinence. Radiologists should know the normal male pelvic floor anatomy and remember the physiological anatomical changes during maximum strain and defecation to correct report images findings. The knowledge of standard measurements is essential, even if most of them have not been validated yet for male pelvic floor. The interpretation of MR Defecography should therefore be done considering the context of clinical information. ANATOMY OF THE MALE PELVIC FLOOR (Figure 1,2,3) The pelvic floor is a dynamic and synergic muscle-elastic system that guarantees the stability of pelvic organs and ensures their function. The correct knowledge of its anatomy is essential to understanding its function and therefore also its dysfunction. It is characterized by support structures and suspension structures (ligaments). SUPPORT STRUCTURES In male support structures are organized in three layers, from superficial (caudal) to deep (cranial): - the superficial perineal pouch, - the urogenital diaphragm - the pelvic diaphragm. The superficial perineal pouch consists of three muscles: - the bulbospongiosus muscle - the ischiocavernosus muscle - the superficial transverse perinei muscle Role: these structures help the maintenance of urinary continence and the rigidity during penile erection and ejaculation and provide support to pelvic and perineal structures. The simultaneous contraction of the superficial transverse perineal muscles stabilizes the perineal body and fixes the central tendinous portion of the perineum. The urogenital diaphragm is formed by: - the deep transverse perinei muscle, - the external sphincter urethrae, - the compressor urethrae muscles - a muscular membrane that divides the superficial perineal pouch from the upper pelvis. Role: it is important for the stabilization of the pelvis during movements and for the closure of urethra during intra-abdominal pressure increasing. In the urogenital diaphragm there are two separate openings: one for the membranous urethra and one for deep dorsal vein of the penis. The pelvic diaphragm is constituted by: - the pubococcygeus-puborectalis complex, - iliococcygeus muscles. Together these muscular structures are also known as the levator ani. Role: the levator ani elevates the anal sphincter during contraction. The obturator internus, while not officially part of the pelvic floor musculature, contributes to the support of the pelvic organs. The role of the puborectalis muscle is the preservation of urinary continence because it elevates the bladder neck and compresses it against the pubic symphysis, and the control of the anorectal angle, ensuring the anal continence with its contraction and the evacuation when relaxed. In the pelvic diaphragm there is only one opening: the anorectal hiatus. SUSPENSION STRUCTURES (ligaments) The male urethral suspensory mechanism is made by three ligaments: - anterior pubourethral ligament, - intermediate pubourethral ligament, - posterior puboprostatic ligament. Male urethra is 20 cm long in men and is divided into four tracts: preprostatic, prostatic, membranous and spongy (divided into bulbar and penile urethra). The penile suspensory ligamentous system is formed by three components: - the fundiform ligament of penis - the suspensory ligament of penis - the arcuate pubic ligament. Role: to keep the stability of the penis and to maintain its straight position during the erection phase. MRI OF THE MALE PELVIC FLOOR MRI defecography (MRD) is considered the imaging of choice in the evaluation of the pelvic floor disorders (3,4). It provides a panoramic and detailed study of pelvic floor anatomy and also depicts functional data during straining and evacuation phases. INDICATIONS The principal indications for MRD in male population are urinary incontinence, sexual disfunction, anorectal disorders and pre-operative planning for pelvic floor surgical repair. TECHNIQUE According to the Pelvic Floor Disorders Consortium, the same MRI technique can be used for both sexes (3). Previous enema is needed, the evening and few hours before examination. Patients should be positioned in sitting or supine position and rectal distension with contrast medium is necessary: ultrasound gel is widely used (about 60-250 ml) and rectum is filled by hand injection with a catheter tip syringe. The patient should be aware of the different dynamic phases to ensure his best cooperation. The exam protocol consists in: - a static evaluation of pelvic floor anatomy, using two-dimensional high resolution T2-Weighted Images (T2-WI) oriented on the three orthogonal planes of the space, - a dynamic evaluation, performing steady state sequences (e.g. FISP, GRASS, FFE, PSIF, SSFP, T2-FFE) or balanced state free precession sequence (e.g. trueFISP, FIESTA, B-FFE) in sagittal plane, during squeezing, straining and evacuation phases. Dynamic sequences require breath holding and should not exceed 20 seconds each. The evacuation phase should be repeated until the rectum is emptied to exclude rectal intussusception (2-3 minutes) (4) PRINCIPAL LANDMARKS (Table1) In the evaluation of pelvic floor diseases, different points of reference and measurements are required for correctly diagnose and grade pelvic organ prolapse to determine which patients need surgery. Actually, not all the principal landmarks used in Female MR defecography have been validated in men and validation studies in literature are based only on small series. Moreover, male pelvis presents anatomically different dimensions from the female one: it is narrower and deeper. For all these reasons, it is important to carefully interpret MR imaging findings in reporting Male MRI Defecography and always correlate with clinical data. The principal measurements to check in MRI Defecography must be drawn using midsagittal images both at rest and at maximal strain, usually during the defecation phase. In male MRD there are some sex-specific landmarks to check, principally related to the prostate gland and the urethra, considering the high prevalence of urinary disorders associated posterior compartment symptoms. Below the measurements and their definition (Figure 4, Figure5, Figure 6): • The Pubo-coccygeal line (PCL) According to Pelvic Floor Disorders Consortium (3), it is the reference line most widely used and represents the level of the pelvic floor. It is a line that connects the inferior edge of the pubic symphysis to the last coccygeal joint. The descent of pelvic organs can be measured in centimeters using the perpendicular distance from the PCL. In the anterior compartment, the reference points are the most posterior-inferior aspect of the bladder base and the prostate apex. In the posterior compartment, the landmark is the anterior aspect of the anorectal junction. • The H line It is a line drawn from the inferior edge of the pubic symphysis to rectal posterior wall at the level of the anorectal junction. It corresponds to the anteroposterior length of the levator hiatus. The normal value in men has still not been validated; in women the reference standard is 5cm means a hiatal enlargement. The latero-lateral widening of the levator hiatus could also be measured in axial plane, at rest and during maximal strain (Figure 6). The normal value at rest is 3,3 ±0,4 cm, while during maximal strain it should be among 4,5 ±0,7cm. • The M line It is a perpendicular line from the PCL to the posterior tip is of the H line and it is used for grading the levator hiatus descent. A normal M line in men can be considered of approximately 1.2 cm during maximum strain (5). Measurement of the H and M lines provides the severity of pelvic floor relaxation at maximal strain during defecation. • The anorectal angle It is the angle between the central axis of the anal canal and the posterior wall of the distal rectum. Physiologically this angle decreases during squeezing (becomes more acute) due to the shortening of the puborectalis muscle and the elevation of the anorectal junction and increases during straining and defecation because of the relaxation of the puborectalis muscles and the levator plate. The normal anorectal angle in men at rest can be considered at about 101° (5), while the changes of this angle during contraction and defecation have still not been validated: in women anorectal angle decrease and increase measure approximately 15°–20°. • The puboprostatic angle Sex-specific; it is the angle between the pubic symphysis and the axis of the bladder neck. This angle normally increases during micturition along with the descent of the bladder neck and the rotation of the prostate gland around the pubic symphysis. It should not widen during the Valsalva maneuver or defecation. Normal values during micturition range from about 34° to 57° before and after voiding, as shown in a study using MRI cystography (6). It is important to remember that it could be affected by the size of the prostate. In the interpretation of MRI Defecography, the size of the prostate gland should be reported and the values of puboprostatic angle should be checked at rest and during defecation, indicating as abnormal a significant difference between the two phases (>20°). • The prostatic-urethral angle It is the angle between the proximal and distal prostatic urethra. Normal value at rest should be less than 34°: higher values are related to bladder outlet obstruction and increased urinary retention in patients with benign prostatic hyperplasia (7). • The length of the membranous urethra It is the distance from the entry of the urethra into the penile bulb up to the external sphincter and/or prostatic apex, measured on a coronal plane. It is considered an important prognostic factor of continence after radical prostatectomy (RP). PATHOLOGICAL FEATURES – Male Pelvic Floor Disorders In men there are two functional compartments, the anterior, or genitourinary compartment, and the posterior, or anorectal compartment. Posterior Compartment Posterior compartment disorders are quite similar between male and female population. The most common male posterior compartment dysfunctions are rectocele, rectal intussusception, anal incontinence and functional defecatory disfunction. - Ano-rectal junction descent: DEFINITION: It represents pelvic floor relaxation. MEASURE: it is measured as the perpendicular distance from PCL (M line), and it can be classified as mild (2-4cm), moderate (4-6cm) and severe (greater than 6cm), even if these values have not been validated for men. - Rectocele (Figure 7): DEFINITION: it is the abnormal bulging of the rectal wall, and could be anterior (the most common), lateral or posterior. Anterior rectocele is frequently associated with ano-rectal junction descent (in about 4-17% of men) (8), especially as a complication of prostatectomy. It results in symptoms of incomplete evacuation even if in men can be occult because of the absence of clinical evidence as vaginal wall bulging in women. MEASURE: It should be quantified on sagittal images, at rest and during maximum strain/defecation, by measuring the distance from the anterior rectal wall protruded and the point of expected normal anterior rectal margin. Normal values in men have not been validated, but the grading scale used in women can be applied: small (4cm). - Rectal intussusception DEFINITION: it is defined as the invagination of the rectal wall into the rectal lumen, anal canal, or, through the anal sphincter muscle, outside the anus. These three possibilities configure an intra-rectal, intra-anal or extra-anal intussusception. The latter is considered the true complete rectal prolapse (Figure 8). It is also be classified as partial, if the mucosa only prolapses, or full thickness, if all the wall layers are interested. In men frequently it begins at the detachment point of rectal wall from Denonvillier fascia, underling the important support function of this structure. It is important to remember that, and it can be associated also with non-surgical pathologies such as irritable bowel syndrome, chronic constipation and pelvic floor dyssynergia (a paradoxical contraction of the levator ani muscles during defecation). MEASURE: It should be evaluated on sagittal images, looking for wall folds, best shown with a complete rectal emptying; incomplete defecation could lead to underestimate the intussusception. - Anal incontinence can be observed as the inability to retain the rectal contrast medium and as pelvic floor descent. MRI also can be used to identify sphincter tears or anal sphincter atrophy in men with anal incontinence (9). - Functional defecatory dysfunctions (Figure 9) DEFINITION: The main disorder is the so-called pelvic floor dyssynergia, defined as an incoordination between abdominal and pelvic floor muscles during defecation. It seems to be caused by a traumatic injury to the pelvic floor neuromuscular system. Normally the increase of intra-abdominal pressure is followed by puborectalis and external anal sphincter muscles relaxation to ensure the widening of the anorectal angle. In dyssynergia the puborectalis muscle contracts, the levator plate moves up and there is a paradoxical narrowing of the anorectal angle. Anorectal manometry is the gold standard for the diagnoses; MRD can confirm. MEASURE: it is evaluated on sagittal images, during defecation. It is important to look for signs of abdominal pressure increase, such as bladder compression or the descent of anorectal junction, to make sure patient understanding and not to interpretate voluntary contraction as dyssynergia. The main MR features during defecation are: the lack of pelvic floor descent, a narrow anorectal angle and prolonged incomplete evacuation. The static anatomic images could show the hypertrophic puborectalis and external anal sphincter muscles. ANTERIOR COMPARTMENT (genitourinary) Bladder prolapse is less frequent in men rather than in women and usually it happens after prostatic surgery, involving the bladder neck. The excessive prostate descent during straining can be caused by an injury of the puboprostatic ligament; however, the significance of an abnormal prostate descent in male pelvic floor disorders is still unknown. Anterior compartment disorders are categorized in urinary and sexual dysfunctions. Urinary dysfunctions include the so-called LUTS, Lower Urinary Tract Symptoms, and urinary incontinence. The term LUTS (Lower Urinary Tract Symptoms) refers to storage, voiding and post-micturition symptoms that can occur both in men and in women. In men, the most common cause of LUTS is benign prostate hyperplasia that brings to bladder outlet obstruction. Other conditions that can cause LUTS include detrusor muscle weakness or hyperactivity, infection (prostatitis or urinary tract infection) and neurological disease with neurogenic bladder overactivity. MR defecography has a minor role in this kind of pathologies; an adequate micturition study can be done performing MR voiding cystourethrography. Essential is a correct urologist indication. During reporting the MR Defecography is still important to do a complete anatomical evaluation and check for prostate gland dimensions. Urinary incontinence can be functional, due to elderly or disability that prevent the mobility and the ability to go to the toilet, or stress-induced, a urinary leakage after a sudden pressure on the bladder due to an exertion (laugh, cough, sneeze, or work out). The rule of imaging in functional incontinence is minor, basically aimed at looking for complication or ruling out other causes of incontinence. Stress-induced incontinence occurs frequently after radical prostatectomy (RP) or after prostate radiation therapy. MRI can be used in the preoperative setting to understand the probability of urinary incontinence occurrence after surgery, allowing to choose the more advisable surgical technique. In this context, several studies have tried to identify the factors that are linked to a better postoperative quality of life. In particular, the most useful measurement to evaluate in preoperative MRI is the membranous urethra length (MUL): a longer MUL is considered an important prognostic factor of continence after RP (10). Indeed, the 10%–40% of the functional membranous urethra is covered by prostatic apex and the aim of the surgery is to spare of the intraprostatic portion of membranous urethra. Even a close relation between the levator ani and the membranous urethra can affect recovery of continence. (11) Last, but not least a greater prostate volume is also associated with an increased risk of incontinence after RP. (12) MRI post-surgical evaluation of anterior compartment Anatomical changes after surgery or radiotherapy, especially in pelvic floor musculature and bladder neck, can be well depicted by MR Defecography. Thickness of the puborectalis muscle and the movement of the bladder neck upward and forward have been correlated with the possibility to recover urinary continence. MRI is also useful in the evaluation of correction therapy for urinary incontinence. Severe stress urinary incontinence unresponsive to physiotherapy and drugs is treated with the placement of bulking agents, slings and artificial urethral sphincters. Bulking agents are injected in the submucosa of the urethra, often in multiple sites, using a dedicated needle and a transurethral or periurethral approach. The common materials are silicon, collagen, carbon-coated microbeads and calcium hydroxylapatite. The role of MR is to verify their correct placement and to detect their complications. Silicon is T2-hyperintense and is hardly distinguishable from recently injected collagen; collagen afterwards becomes isointense to hypointense on T1WI and T2WI due to phenomena of water resorption and degradation of the collagen. Carbon-coated microbeads appear T1 and T2WI-hypointense, while calcium hydroxylapatite is T2WI hypointense and due to its calcium content is radiopaque at CT. It is fundamental to distinguish the presence of bulking agents from a urethral diverticulum or a tumoral lesions. Contrast medium could be useful in the differential diagnosis (bulking agents do not enhance) (13). Urethral slings are considered in patients who can undergo surgery and have a residual continence. These devices are strips to be placed around urethra and are divided in compressive and reposition sling. Compressive slings squeeze the urethra against the pubis, and the pressure on the urethra can be readjusted over time (adjustable sling) or standard (non-adjustable sling) (14). Reposition slings pulls in and up the bulbous urethra. Sling displacement can be a cause of failure of the device and can be evaluated using MRI. These devices are made of polypropylene, invisible at MRI: their presence is identifiable only by the indentation on the urethral bulb, that is important to correct localize (15, 16). The artificial urinary sphincter is a prosthetic device that surrounds the urethra to create an occlusion. It is formed by a control pump, an inflatable cuff e a pressure-regulating balloon filled with saline solution or diluted iodinated contrast agent. The cuff can be placed in the bulbar urethra or in the bladder neck. The balloon is placed in the prevesical space, while the pump is in the scrotum. At rest, the cuff is inflated to close the urethra to obtain continence, while during micturition the pump is squeezed by the patient, and the cuff is released. Then the cuff automatically come back in the rest condition. At MRI, the cuff and the balloon that contain fluid are hyperintense in T2-weighted sequences, while the pump and the plastic tubing are hardly visible because of susceptibility artifacts. Several complications can occur after the placement of this device. MRI and CT can detect a malposition of the balloon, its migration in adjacent structures and a kinking or a disconnection of the tubing, especially when the system is filled with iodinated contrast. Another complication is the erosion of the urethra by the cuff, often associated with infection, that can present with perineal erythema, pain and abscess. However, cystoscopy is the imaging of choice of AUS dysfunction (17). REFERENCES 1- Lakhoo J., Khatri G., Elsayed R., et al. MRI of the Male Pelvic Floor Radiographics 2019 39:7, 2003-2022 DOI: https://doi.org/10.1148/rg.2019190064 2- MacLennan A., Taylor A., Wilson D. et al. The prevalence of pelvic floor disorders and their relationship to gender, age, parity and mode of delivery, An international Journal of Obstetrics and Gynaecology, 2005 107: 1460-1470. DOI: https://doi.org/10.1111/j.1471-0528.2000.tb11669.x 3- Gurland B, Khatri G., Ram R. et al, Consensus Definitions and Interpretation Templates for Magnetic Resonance Imaging of Defecatory Pelvic Floor Disorders: Proceedings of the Consensus Meeting of the Pelvic Floor Disorders Consortium of the American Society of Colon and Rectal Surgeons, the Society of Abdominal Radiology, the International Continence Society, the American Urogynecologic Society, the International Urogynecological Association, and the Society of Gynecologic Surgeons. American Journal of Roentgenology, 2021 217:800–812 DOI: https://doi.org/10.2214/AJR.21.26488 4- El Sayed R., Alt C., Maccioni F., et al, Magnetic resonance imaging of pelvic floor dysfunction - joint recommendations of the ESUR and ESGAR Pelvic Floor Working Group. European Journal of Radiology, 2017 27, 2067–20852 DOI: 10.1007/s00330-016-4471-7 5- Goh V., Halligan S., Kaplan G., et al. Dynamic MR imaging of the pelvic floor in asymptomatic subjects. American Journal AJR American Journal of Roentgenology 2000;174(3):661–666. DOI: 10.2214/ajr.174.3.1740661. 6- Hocaoglu Y., Roosen A., Herrmann K., et al. Real-time magnetic resonance imaging (MRI): anatomical changes during physiological voiding in men. British journal of Urology Int 2012;109(2):234–239. DOI:10.1111/j.1464-410X.2011.10255.x 7- Guneyli S, Ward E, Peng Y, et al. MRI evaluation of benign prostatic hyperplasia: Correlation with international prostate symptom score. Journal of Magnetic Resonance Imaging 2017;45(3):917– 925) DOI: 10.1002/jmri.25418 8- Cavallo G, Salzano A, Grassi R, et al. Rectocele in males: Clinical, defecographic, and CT study of singular cases. Dis Colon Rectum 1991;34(11):964–966. DOI: 10.1007/BF02049958 9- Fielding JR. Practical MR imaging of female pelvic floor weakness. RadioGraphics 2002;22(2):295–304. DOI: https://doi.org/10.1148/radiographics.22.2.g02mr25295 10- Lamberg H, Shankar P., Singh K. et al. Preoperative Prostate MRI Predictors of Urinary Continence Following Radical Prostatectomy, Radiology 2022, 303:1, 99-109 https://doi.org/10.1148/radiol.210500 11- 11. Von Bodman C., Matsushita K, Savage C., et al. Recovery of Urinary Function after Radical Prostatectomy: Predictors of Urinary Function on Preoperative Prostate Magnetic Resonance Imaging, Journal of Urology 2012 187: 945-950 doi: 10.1016/j.juro.2011.10.143 12- Tienza A, Hevia M, Benito A, et al. MRI factors to predict urinary incontinence after retropubic/laparoscopic radical prostatectomy. International Urology and Nephrology 2015;47(8):1343–1349 DOI: 10.1007/s11255-015-1019-8 13- Bridges M., Petrou S., Lightner D. Urethral Bulking Agents: Imaging Review, Genitourinary Imaging, 2005, 85:257–264 https://doi.org/10.2214/ajr.185.1.01850257 14- Abranches-Monteiro L., Hamid R., D’ancona C., and al. The International Continence Society (ICS) report on the terminology for male lower urinary tract surgery. Neurourology Urodynamics. 2020. 39(8):2072-2088. DOI: 10.1002/nau.24509 15- Collado Serra A., Pelechano Gomez P., Martin I., et al., Magnetic resonance imaging as an assessment tool following intervention with an AdVance XP suburethral sling for postprostatectomy urinary incontinence, Neurourology Urodinamics, 2019, 38(6):1616-1624.DOI: 10.1002/nau.24023 16- Kahokehr A., Selph J., Belsante M. et al., Mechanism of Action of the Transobturator Sling for Post-Radical Prostatectomy Incontinence: A Multi-institutional Prospective Study Using Dynamic Magnetic Resonance Imaging, Urology, 2018, 116:185,192 https://doi.org/10.1016/j.urology.2018.01.053 17- Chorney E., Ramchandani P., Jaffe W., et al. CT and MR Imaging Features of Artificial Urinary Sphincters, Penile Prostheses, and Other Devices in the Male Lower Genitourinary Tract, Radiographics, 2018, 38:3, 794-805 https://doi.org/10.1148/rg.2018170087
Figure 1. Schematic illustration of male pelvic floor anatomy.
Figure 2. MRI rappresentation of male pelvic floor anatomy; axial T2 WI on the right; Coronal T2 WI on the left showing the corrisponding axial plane.
Figure 3. The images show principal anatomic strutures of male pelvic floor visible on coronal plane; a schematic rappresentation on the left; T2 WI on coronal plane on the right.
Figure 4. Summary Table of the principal measurements to check on MRI Male Defecography.
Figure 5. The image shows the principal landmarks in Male MRI Defecography to evaluate on mid-saggital and coronal plane T2 WI.
Figure 6. The image shows how to measure the latero-lateral widening of the levator hiatus, on T2WI, axial plane, at rest (A) and during maximal strain (B). Normal value at rest is 3,3 ±0,4 cm, while during maximal 4,5 ±0,7cm.
Figure 7. Mid-sagittal T2 WI show an example of pathological descent of anorectal junction during maximum strain (B) and defecation (C), with the development of an anterior rectocele (green star in C).
Figure 8. Mid-sagittal T2 weighted image, acquired during defecation, shows an example of pathological descent of the ano-rectal junction under the PCL associated with an extra-anal intussusception, the true complete rectal prolapse, with rectal mucosa prolapsed beyond external anal sphincter (arrow).
Figure 9. Mid-sagittal T2 WI show an example of pelvic floor dyssynergia: there is a pathological narrowing of the anorectal angle, from 75° at rest (A) to 53° and 42° at maximum strain (B) and during defecation (C); the puborectalis muscle is contracted and appears hypertrophic (arrow in C) and the levator plate is moved up. In C the bladder compression is shown (black star), as a sign of abdominal pressure increase, to make sure it is a real evacuation phase.
MR Defecography is the technique of choice in the evaluation of pelvic floor diseases, that even in men can lead to debilitating and less-known conditions. Therefore, is crucial for the radiologist to know normal male pelvic floor anatomy and function and recognize MR features important to describe for guiding treatment.