MRI of the Pelvic Floor

Rosemarie Forstner and Andreas Lienemann

Contents					7    Value of MRI Versus Conventional
1	Introduction\			408		Techniques\			424
2	Imaging Techniques\			408	References\				425
3    MRI Technique of the Pelvic Floor\				409
3.1	Indications\			409
3.2	Patient Preparation\			409
						Abstract
3.3	Patient Instruction\			409
						Pelvic floor dysfunction comprises disorders
3.4	Patient Positioning\			410
3.5	Organ Opacification\			410		related to pelvic		floor descent and pelvic
3.6	Sequence Protocols\			410		organ prolapse, urinary and fecal inconti-
4    MR Image Analysis\				415		nence, defecation disorders, or pelvic pain.
4.1	Bony Pelvis\			415		Although it may also occur in young age,
4.2  Pelvic Floor Muscles and Ligaments\				415		typically postmenopausal women suffer from
4.3  Assessment of Pelvic Organ Mobility:
						pelvic floor dysfunction that may signifi-
	Reference Lines\			417
4.4  Definition of Pathological Findings						cantly impair the quality of life. Its etiology is
	and Grading\			418		multifactorial, but female gender, increasing
5	Typical Findings\			419		age and childbirths have been recognized as
5.1	Anterior Compartment\			420		leading risk factors. MRI has emerged as an
5.2	Middle Compartment\			421		imaging technique to provide comprehensive
5.3	Posterior Compartment\			421
						information and has become an important
5.4	Levator Ani Muscle\			422
6    MRI of the Pelvic Floor in Asymptomatic						diagnostic tool for treatment planning and for
						tailoring the surgical approach in pelvic floor
	Females\			423
						pathologies.
						This chapter reviews MRI for evaluation of
						the pelvic floor. The first part focuses on
R. Forstner (*)						details of the examination technique, and pro-
Universitätsinsitut für Radiologie Landeskliniken						vides information to assess qualitatively and
Salzburg, Paracelsus Medical University,						quantitatively the pelvic floor. In the second
Müllner Hauptstr., 48, Salzburg, Austria						part typical imaging findings associated with
e-mail: [e-mail]
						pathologies within the three anatomical com-
A. Lienemann
						partments of the		pelvic floor are covered.
Radiologie Mühleninsel, Mühlenstrasse 4, Landshut
						Finally, strengths and limitations of MRI of
84028, Germany
e-mail: [e-mail]						the pelvic floor will be discussed.

Med Radiol Diagn Imaging (2017)

407

DOI 10.1007/174_2017_53, © Springer International Publishing AG

Published Online: 19 April 2017

408	R. Forstner and A. Lienemann

Abbreviations

MRI\	Magnetic resonance imaging
PCL\	Pubococcygeal line
POP\	Pelvic organ prolapse
US\	Ultrasonography
WI\	Weighted images

1\ Introduction

Pelvic floor dysfunction has become a major health care issue with the increasing ageing population. It is an umbrella term for different clinical disorders related to pelvic floor descent and pelvic organ prolapse, urinary and fecal incontinence, defecation disorders, or pelvic pain (Pannu et al. 2015). Pelvic floor dysfunction affects 30–50% of women, with approximately 10–20% of these becoming symptomatic and requiring surgery (Jundt et al. 2015). POP recurrence rates after surgery are high with a range between 30 and 70% (Tijdink et al. 2011). Although it may occur in young age, typically postmenopausal women suffer from pelvic floor dysfunction that may significantly impair the quality of life (Rogers and Fashokun 2016). Its etiology is multifactorial and associated with degradation of collagen, hormonal effects, obesity, multiparity, vaginal delivery, previous surgeries, constipation, muscle denervation, and menopause. But female gender, increasing age, and childbirths have been recognized as leading risk factors (Rogers and Fashokun 2016). Demographic developments in industrialized countries let expect the substantially increased need of imaging in patients with pelvic floor symptoms (Woodfield et al. 2010).

Among the imaging modalities MRI has emerged as an imaging technique to provide comprehensive information and has become an important diagnostic tool for treatment planning and for tailoring the surgical approach in pelvic floor pathologies (Pannu et al. 2015; El Sayed et al. 2016).

2\ Imaging Techniques

Imaging modalities to assess the pelvic floor comprise conventional fluoroscopic techniques, ultrasonography, and MRI. Fluoroscopic X-ray techniques include cystourethrography, defecography or evacuation or voiding proctography, and colpocystoproctography. The latter requires opacification of multiple organs such as rectum, vagina, and small bowel and instillation of contrast media into the bladder via a urinary bladder catheter (Kim 2011). This widely available technique is performed in physiological sitting position, but is limited with respect of radiation exposure and inability to directly visualize the pelvic floor (Flusberg et al. 2011).

Various approaches including transabdominal, transvaginal, endoanal, transperineal, and translabial sonography have been used to assess urinary or fecal incontinence. Wellknown advantages of this technique are short duration of exam, wide availability, and realtime imaging capabilities (Pannu et al. 2015). These, however, are outweighed by the small field of view, and its high operator dependence. Although its routine use is still limited, 3D and 4D US are emerging techniques to diagnose POP and are able to demonstrate pelvic musculature and fascias and otherwise difficult-to- assess mesh slings or implants (Dietz 2010). When performed by experts, good to excellent interobserver agreement can be achieved even in multicompartment ultrasound of the pelvic floor (Lone et al. 2016).

MRI has become the imaging method of choice to assess complex pelvic floor disorders, as it provides a comprehensive approach by combining static and dynamic MRI sequences (Maglinte et al. 2011). This technique has synonymously also been reported as dynamic MR, cine MR, MR defecography, MR proctography, or functional MR of the pelvic floor (Pannu et al. 2015; El Sayed et al. 2016). It was first introduced in 1991 by Yang et al. and Kruyt et al. They described movement of the bladder, vagina, and rectum in relation to the

MRI of the Pelvic Floor	409

pubococcygeal­ and symphysiosacral reference line in asymptomatic subjects and in patients. In 1993 Goodrich et al. recommended MRI for the preand postoperative evaluation of patients after pelvic floor surgery (Goodrich et al. 1993). Several consecutive publications­ showed at least equal results or its superiority compared to conventional colpocystoproctography and defecography (Gufler et al. 2004; Kelvin et al. 2000; Bump et al. 1996; Lienemann et al. 1996, 1997). Unfortunately for many years this technique showed inherent limitations in respect of standardization resulting in numerous variants of imaging techniques and protocols (El Sayed et al. 2016). A joint initiative of the ESUR and ESGAR pelvic floor working groups has overcome this problem and recommendations for the imaging technique and for reporting of pelvic floor disorders with MRI have been published in 2016 (El Sayed et al. 2016).

3\ MRI Technique of the Pelvic

Floor

3.1\ Indications

Pelvic floor dysfunction may manifest with symptoms related specifically to affected structures, e.g., with urinary symptoms (stress and urge incontinence, or obstructed voiding), with defecatory symptoms (constipation, fecal incontinence, difficult or incomplete defecation), as pelvic pain or as adverse effects on sexual function (Rogers and Fashokun 2016). Among these bowel symptoms, those typically arising from the posterior pelvic compartment are leading indications for MRI (El Sayed et al. 2016). A specialist survey enlisted in order of decreasing frequency rectal outlet obstruction, rectocele, recurrent pelvic organ prolapse, enterocele, and dyssynergetic pelvic floor syndrome as clinical symptoms best suited to be assessed by MRI (El Sayed et al. 2016). In the postoperative setting MRI may assist to elucidate postoperative complications and the causes

of failed POP repair by visualization of meshes, of relapsed POP, and of the integrity and movement of the pelvic floor muscles (Pannu et al. 2015; Alt et al. 2014).

3.2\ Patient Preparation

An overextended bladder may impair the diagnosis of pelvic floor dysfunction. This is why according to the recent recommendations the bladder should be emptied 2 h before the exam, which will result in a midfull bladder during the exam (El Sayed et al. 2016). Cleansing of the rectum prior to the exam is helpful, but joint recommendations do not exist. Devices, e.g., pessar rings or intravaginal diaphragms, have to be removed before the exam.

3.3\ Patient Instruction

Explaining the patient how to perform the required exercises is pivotal for a successful MRI study. Thus, optimally dedicated training for how to correctly perform the dynamic phases including straining, squeezing, and evacuation should precede the MR exam (El Sayed et al. 2016). As collaboration is pivotal, the patient has to be able to understand and follow the commands during the examination. Emptying of the rectum during the examination is required to assess the complex relationships in pelvic organ prolapse (Flusberg et al. 2011). This is why evacuation should be prolonged until complete defecation has been documented. Incomplete rectal evacuation results in a significantly lower sensitivity for the detection of pelvic floor defects by MRI compared to colpocystoproctography (Vanbeckevoort et al. 1999). If the patient is either too embarrassed to defecate inside the magnet or is unable to empty the rectum at all while lying supine, a triphasic approach may be performed with an additional post-toilet phase after the patient has evacuated in the bathroom (Kelvin et al. 2000).

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3.4\ Patient Positioning

In open-configuration MRI systems patients can be examined sitting on an MRI-compatible seat (Pannu et al. 2015; Lienemann et al. 1996). A physiological position for defecation cannot be achieved in close configuration systems where only horizontal positioning of the patient is feasible. In this case supine position is preferred to prone position, as it is more stable and convenient for the patient (Delemarre et al. 1994). Positioning with feed first will reduce claustrophobia. Furthermore, slight bending of the knees by a pillow underneath the knees and abduction of the hips will facilitate the process of defecation (Pannu et al. 2015; Bitti et al. 2014). Diapers and waterproof pads placed beneath the patient reliably prevent soiling of the table and help to improve the compliance (El Sayed et al. 2016; Lienemann et al. 1997; Healy et al. 1997a).

3.5\ Organ Opacification

On T2-weighted imaging fluid-filled structures like the bladder or small bowel loops exhibit high signal intensity. But other organs like the vagina, rectum, or anal canal show an intermediate to low signal intensity. To improve their visualization and their differentiation from adjacent tissues during the dynamic phases vaginal and rectal opacification by ultrasound gel is performed (Lienemann et al. 1997; Sprenger et al. 2000). Some authors also advocated the placement of thin catheters to outline the urethra and to fill the bladder with 60 mL of saline solution and contrast media (Kelvin et al. 2000; Hodroff et al. 2002). But it is important to be aware that the catheter might impede the movement of the urethra and a rectocele or enterocele may be masked by a full bladder or a cystocele blocking the genital hiatus.

Emptying the bladder 2 h before the MRI will result in a midfull bladder. Lack of rectal contrast may result in a suboptimal study (Pannu et al. 2015). This is why rectum opacification is performed to improve visualization of the anorectal junction and to diagnose rectoceles. Instillation

of 120–250 cm3 of ultrasound gel improves also assessment of intususceptions and of rectal evacuation. A larger amount of gel is likely to facilitate the defecation (Lienemann et al. 1997). In the ESUR/ESGAR recommendations no agreement on opacification of the vagina was obtained (El Sayed et al. 2016). But opacification with 20 cm3 of ultrasound gel allows visualization of the entire vagina and especially of the posterior fornix and its posterior vaginal wall (Lienemann et al. 1997). In addition, during Valsalva maneuver the gel in the vagina is emptied passively and thus the movement of the organ itself is not impeded (Hodroff et al. 2002).

3.6\ Sequence Protocols

Technical prerequisites include midto high-field MR systems, surface array coils, and upright or supine position of the patient (Pannu et al. 2015; El Sayed et al. 2016; Fielding et al. 1998; Fielding 2003; Lienemann 1998). Pivotal in MR imaging of pelvic floor disorders is the acquisition of both static and dynamic imaging techniques. Static images provide multiplanar high spatial resolution of the pelvic floor anatomy, particularly the muscles and ligamentous structures (El Sayed et al. 2016; Lienemann et al. 1997; Delemarre et al. 1994). Integrity of the anal sphincter complex, position and morphology of the pelvic organs, and perivaginal space can also be assessed (Pannu et al. 2015; Fielding 2003). Furthermore, incidental findings (e.g., Bartholini, Gartner or ovarian cysts, or uterine leiomyomas) may be seen (Lienemann 1998).

Dynamic MRIs are performed at rest, squeezing, under maximal stress of the pelvic floor, and during defecation and displayed in cine mode (Fig. 1). Thus pelvic floor mobility, integrity of the pelvic floor or pelvic floor weakness, and organ prolapses are best visualized (El Sayed et al. 2016).

T2W imaging of the pelvic is performed at rest in three planes. This is followed by a dynamic acquisition in midsagittal plane at rest during squeezing, maximum straining, and evacuation of the rectal gel. Technical details of the MRI

MRI of the Pelvic Floor	411
a	b

c

d

Fig. 1  Maneuvers of the dynamic series at rest (a), squeeze (b), straining (c), and defecation (d)

protocol as suggested by the ESUR/ESGAR recommendations are summarized in Table 1.

For the dynamic studies the midsagittal plane through the pelvis is the preferred slice orientation. It provides an excellent overview of all rel-

evant organs within the different compartments of the pelvis and of the bony frame (Lienemann 1998) (Figs. 2, 3, and 4). This view is similar to conventional cystography or evacuation proctography. Owing to the complexity of the pelvic

Table 1  Recommended MR imaging protocol by ESUR/ESGAR

											Numbers of
Plane			Sequence	Technique	TE(ms)	TR (ms)	mm	FOV (mm)	Matrix	Plane/angulation	slices
Static MRI sequences 2D MRI
		Sag.	T2WI	Turbo/fast spin	77–132	500–4210	4	200–300	256–448	Midsagittal	23
				echo
		Trans.	T2WI	Turbo/fast spin	88–132	500–7265	4	200–300	256–512	Perpendicular to	25
				echo						urethra
		Cor.	T2WI	Turbo/fast spin	80–132	500–7265	4	200–260	256–512	Parallel to urethra	26
				echo
Dynamic MRI sequences
Squeezing
		Sag.	T2WI	GEa	1.27–1.88	3.3–397.4	8	250–310	126–280	Midsagittal	1 or 3
Straining
		Sag.	T2WI	GEa	1.27–1.88	3.3–397.4	8	250–310	126–280	Midsagittal	1 or 3
Optional		Trans.	T2WI	GEa	1.6–80	5,0–1,200	5 or 6	250–310	126–280	Perpendicular to the	5
										urethra
Optional		Cor.	T2WI	GEa	1.6	5	5 or 6	300	256	Parallel to the urethra	5
MR-Defecography
		Sag.	T2WI	GEa	1.27–1.88	3.3–397.4	8	250–310	168–280	Midsagittal	1 or 3
Optional		Cor.	T2WI	GEa	1.27–1.6	5–397	4 or 8	257–350	154–256	Parallel to anorectum	5

With permission from El Sayed et al. (2016) aGE, ultrafast GE and balanced GE

412

Lienemann .A and Forstner .R

MRI of the Pelvic Floor	413
a	b

c

d

Fig. 2  Combined organ descent in a 40-year-old primiparous woman with stool outlet obstruction. T2-weighted functional MR images of the pelvis (a–c midsagittal; d transversal) obtained with the patient at rest (a) and during straining (b–d). (a) Normal position of the bladder (B), vagina (V), and uterus (U) above the pubococcygeal reference line (white line). The rectum (R) shows no anterior bulging. Vagina and rectum are filled with sonography gel. (b) During the first period of straining the anterior rectal wall is protruding in an anterior direction forming a deep rectocele (arrows). The bladder (B) and the uterus (U) descend only slightly. (c) After repeated straining and

defecation now the rectum (R) and the rectocele (arrow) are emptied. Therefore, given more space to slide into the genital hiatus, a large cystocele (B) and a descensus of the uterus (U) far below the PC line occur causing a compression of the rectal lumen. Note the relaxed levator ani muscle with a nearly vertical orientation. (d) In the axial plane (level of the pubic symphysis) a ballooning of the levator ani muscle (arrows) resulting from muscular weakness can be seen. The descending bladder (B), lower parts of the uterus (U), and the rectum (asterisk) are located between the two sides of the puborectal muscle

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a	b

Fig. 3  Multiparous 71-year-old woman with defecation disorder. Midsagittal T2-weighted MR images of the pelvis obtained with the patient straining repeatedly. (a) During the first straining episode the well-gel-filled rectum (R) shows an extensive bulging of the rectal wall in the anterior-perineal as well as in the posterior direction (white arrows). This anterior and posterior rectocele stabilizes the position of both the bladder (B) and the vaginal vault (asterisk), which stay at the level of the PC line.

Fig. 4  A 69-year-old female with a partial prolapse of the posterior vaginal wall during clinical examination. Midsagittal T2-weighted MR images obtained with the patient straining. A huge bulging of the anterior rectal wall in an anterior direction occurs. The depth of the rectocele can be measured as the distance between the tip of the rectocele (double arrow) and a parallel line along the anal canal (black line). The bladder (B) and the uterus (U) descend only slightly

Additionally, a thickening of the rectal mucosa (black arrows) is depicted marking a beginning intussusception. (b) After incomplete emptying of the rectocele and rectum (R) a large enterocele (E) has developed with mesenterial fatty tissue sliding down into the rectovaginal space. The sonography gel in the vagina has been evacuated passively. These findings are accompanied by a small cystocele with funneling of the urethra (arrow) and a vaginal vault descent (asterisk)