Radiologic studies of the lower urinary tract and pelvic floor





Introduction


Pelvic floor disorders (PFDs), including urinary incontinence (UI), pelvic organ prolapse (POP), and anorectal disorders, are prevalent conditions that have a significant negative impact on women’s quality of life. The main approach to evaluating these conditions starts with a detailed history and physical examination, along with evaluation of pelvic muscle function, strength, and integrity. The pelvic floor anatomy may be described as comprising an anterior, a middle, and a posterior compartment. The bladder and urethra comprise the anterior compartment; the vagina and uterus comprise the middle compartment; and the rectum, anal canal, and sigmoid comprise the posterior compartment.


Because of the complexity of PFDs, physical examination can have limitations, especially when the severity of symptoms does not correlate with examination findings. Imaging diagnostic evaluations such as dynamic anorectal physiologic tests, magnetic resonance imaging (MRI), and ultrasound imaging, among others, serve as adjunct tools to physical examination. Radiographic imaging can complement the evaluation of PFDs by revealing clinically occult abnormalities in patients with a complex presentation. Although imaging plays a limited role in the evaluation of a straightforward case, it is valuable and informative in complex cases and when multiple compartments of the pelvic floor are involved. Many imaging modalities have been used to evaluate the pelvic floor, including x-ray, computed tomography (CT), MRI, barium contrast defecography, and pelvic floor ultrasound.


In this chapter we will review various imaging modalities used in clinical practice and in research to investigate PFDs.


Plain film of the abdomen


A plain film of the abdomen is not appropriate for evaluation of pelvic floor dysfunction. It is, however, useful as a scout film with an intravenous pyelography (IVP) and may be of benefit in the evaluation of urinary calculi. With the introduction of newer, nonionizing imaging techniques, other modalities are preferred when evaluating PFDs. A plain film can help with the evaluation of upper and lower urinary tract urolithiasis. Figs. 13.1 A and B show plain films of a right ureteral stone and multiple ureteral stones, respectively. Plain films are also valuable in evaluating the position of ureteral stents ( Fig. 13.2 ).




Fig. 13.1


Plain x-ray films of right kidney stones ( A ) and multiple bladder stones ( B ).





Fig. 13.2


Plain x-ray film of bilateral ureteral catheters.


Intravenous pyelography, computed tomography urogram, and retrograde pyelography


IVP is still frequently used to evaluate the urinary tract, even with the emergence of newer technologies. Advantages of this imaging modality include safety, low cost, wide availability, and its ability to provide information on the functional status of the urinary collecting system. Disadvantages to IVP include the exposure to iodine dye and radiation, and it is contraindicated in pregnancy, in those with congestive heart failure, and in those with renal insufficiency.


IVP is a mainly historic technique that is now infrequently used in the evaluation of the urinary tract. IVP is most commonly used in the setting of an acute trauma to assess bilateral renal moieties. Computed tomography urogram (CTU) has gradually replaced IVP in the evaluation of the urinary collecting system and is currently the gold standard for evaluation of hematuria, urinary stone detection, and characterization of renal masses. Two of the most common indications for CTU are the evaluation of ureteral obstruction as a result of stones, gynecologic or genitourinary malignancy, pelvic mass, or POP and the evaluation of postoperative complications after gynecologic surgery.


Diagnosing collecting system injury is essential to identifying cases that may require surgical management. Although many collecting system injuries may spontaneously resolve, the persistence of urine extravasation may require a urinary diversion with a percutaneous nephrostomy tube, double-J ureteral stent, or surgical treatment (see Chapter 24 ). Because collecting system injuries may be occult on arterial and venous phase imaging, the use of delayed contrast excretory phase imaging is vital in the setting of a suspected renal injury following trauma. The main diagnostic sign of a ureteric injury is visualization of contrast extravasation (shown as urinary ascites in Fig. 13.3 ), although more elusive findings may include mild ureteral dilation, deviation, or delayed function ( Fig. 13.4 ).




Fig. 13.3


Computed tomography urogram demonstrating urinary ascites from a ureteric injury.



Fig. 13.4


Computed tomography urogram demonstrating right ureteral obstruction secondary to suture ligation at the time of hysterectomy.


If the IVP and CT results are inconclusive, retrograde pyelography is indicated. Retrograde pyelogram is the most accurate, dedicated imaging test to evaluate the location and degree of ureteric injury, especially in cases where cystoscopy is also indicated. At the time of cystoscopy, the contrast medium is injected into the upper urinary tract through a ureteral catheter under fluoroscopy (fluoroscopy is a modification of x-ray which is used to image the continuous movement of internal structures) ( Fig. 13.5 ). Disadvantages of retrograde pyelogram include a higher rate of infection compared with the anterograde approach, and the possibility of systemic absorption of contrast extravasation. See Chapters 24 and 40 for more information on the indications, technique, and interpretation of retrograde pyelography. The integrity of the renal collecting system may also be evaluated by anterograde pyelography ( Fig. 13.6 ). However, this approach is only indicated when there is an indication for percutaneous puncture of the renal pelvis, such as at the time of percutaneous nephrostomy to relieve an obstructive or infected renal collection system.




Fig. 13.5


Retrograde pyleography demonstrating a left ureterovaginal fistula.



Fig. 13.6


Antegrade pyleography or nephrostogram.


Cystography and voiding cystourethrography


Cystography may be considered in the evaluation of bladder integrity in the setting of traumatic injury to the pelvis. Historically, cystography was done with plain films, but today it is most commonly done with CT (i.e., CT cystography). Cystography is also a useful tool in the evaluation of fistulas between the bladder and adjacent organs and in the setting of assessing bladder integrity after a cystotomy repair. This method may be useful to identify vesicovaginal, vesicoenteric, or vesicouterine fistulas, although small fistula tracts may be too small to be radiologically apparent ( Fig. 13.7 ).




Fig. 13.7


Computed tomography cystography showing vesicovaginal fistula in a patient after hysterectomy. Extravasation of contrast into the vagina is noted.


A voiding cystourethrogram (VCUG) is a dynamic radiologic study used to evaluate bladder and urethral abnormalities with voiding. Currently its main clinical application is in the evaluation of vesicoureteral reflux. Historically, this test has also been used in the evaluation of bladder or urethral diverticuli. This test is no longer recommended for routine evaluation of urethral diverticula, because it incurs the risk of radiation exposure and has a limited sensitivity as low as 65%. Upright VCUG has also been used to evaluate cystoceles and urethral hypermobility in pre- and postoperative patients, although it is rarely used in clinical practice today. Current limitations of this examination in pelvic floor dysfunction include patient exposure to radiation, patient discomfort, and the fact that imaging is confined to just the anterior compartment and lacks visualization of surrounding structures.


Fluoroscopy and defecography


Fluoroscopy is a modification of x-ray examination that is used to visualize the continuous movement of internal structures. Many imaging modalities have previously been used to evaluate the pelvic floor, including CT, MRI, and barium defecography.


Defecography, or fluoroscopic proctography, is an established method used to dynamically evaluate the mechanics of rectal emptying. Defecography is able to image dynamic physiologic rectal emptying under radiographic guidance. However, owing to the physiologic nature of the emptying mechanism, this evaluation is dependent on the voluntary control of the pelvic floor and passive emptying of the rectum from the patient’s point of view. A normal defecography study is conducted in three phases: rest, evacuation, and recovery. In the resting phase (with normal sphincter function), the anal canal should be closed. Measurements of the anorectal junction (ARJ) and the anorectal angle (ARA) are obtained during the resting phase. Evacuation is initiated by pelvic floor descent, which begins the defecation process. This is characterized by a descent of the ARJ from rest to opening of the rectal canal, normally occurring within a few seconds. When the canal is empty, it empties quickly, normally within 30 seconds. At this time, anatomy or mechanical abnormalities are evaluated following significant straining/Valsalva. The recovery phase follows evacuation and is typically shown by the return of tone to the internal sphincter and levator ani. At this time, the anal canal is closed, the ARA becomes more acute, and the ARJ and pelvic floor elevate to return to their resting positions. A notable advantage of defecography is that it enables patients to replicate their symptoms, because it requires patients to be upright, thereby replicating a more physiologic positioning for rectal emptying. In addition, organs of the anterior and posterior compartments of the pelvic floor can be examined, so that a patient can be evaluated for anterior and posterior prolapse concomitantly. See for a detailed demonstration of the indications, technique, and normal and abnormal findings of defecography. Overall, defecography is useful for evaluating the interaction between rectal evacuation, the pelvic organs, and the pelvic floor musculature. The most significant disadvantage is that it requires multiple organs to be opacified, thereby exposing patients to a high level of radiation. See Chapter 28 for additional discussion on the use of defecography in the evaluation of constipation and rectal evacuation disorders.


Ultrasound


Techniques


The basic structures to include for the pelvic floor ultrasound examination include the pubic symphysis, the urethra, the bladder, the vagina, the uterus (if present), the endoanal canal, the levator plate, and the levator ani muscle complex. The integrity of the levator ani muscle complex is usually evaluated by documenting its insertion at the inferior portion of the pubic symphysis and measuring the dimensions of the levator hiatus. More than one modality may be required for proper identification of all relevant anatomic structures. All ultrasound modalities should include a two-dimensional (2D) assessment of the pelvic floor and a dynamic assessment with imaging at rest (static assessment) and then with squeeze and Valsalva maneuvers (dynamic assessment), followed by three-dimensional (3D) and four-dimensional (4D) assessments if available. Lastly, an evaluation of the anal sphincter may be performed. Indications for pelvic floor ultrasound are listed in Box 13.1 .



Box 13.1

(From AIUM/IUGA practice parameter for the performance of Urogynecological ultrasound examinations. Int Urogynecol J 30, 1389–1400 (2019). doi.org/10.1007/s00192-019-03954–5 .)

Indications for Pelvic Floor Ultrasound





  • Urinary incontinence



  • Recurrent urinary tract infections



  • Persistent dysuria



  • Symptoms of voiding dysfunction



  • Symptoms of pelvic organ prolapse



  • Obstructed defecation



  • Anal incontinence



  • Vaginal discharge or bleeding after pelvic floor surgery



  • Pelvic or vaginal pain after pelvic floor surgery



  • Dyspareunia



  • Vaginal cyst or mass



  • Synthetic implants (slings, meshes, and bulking agents)



  • Levator ani muscle assessment after childbirth



  • Obstetric perineal injury



  • Obstetric anal sphincter injury



  • Perineal cyst or mass




Perineal ultrasound and introital ultrasound


For perineal ultrasound, the patient is placed in the dorsal lithotomy position (with hips flexed and abducted). If stirrups are not available on the examination table, the patient may be placed on the lateral position. The patient is asked to empty her bladder before the examination or to have a moderate amount of urine in the bladder without discomfort. Requirements for 2D perineal ultrasound include a B-mode capable 2D ultrasound system and a 3.5- to 6-MHz transducer. A curved abdominal transducer is placed on the perineum/vulva. The transducer may be covered with a non—powdered glove or transducer cover. Ultrasound gel is applied to the transducer, and it is then placed firmly on the perineum. The examination is started with midsagittal images of the pelvis, which are obtained at rest, during squeeze, and with the Valsalva maneuver. Midsagittal images of the pelvic organs are demonstrated (bladder, vagina, uterus, and rectum) with relation to the pelvic floor at the level of the pubic symphysis ( Fig. 13.8 ). From the midsagittal view, the following structures should be identified from ventral to dorsal: symphysis pubis (SP), urethra, bladder neck, vaginal canal, uterus, cervix, anorectal canal, and the central portion of the puborectalis muscle. The examiner can visualize in real-time and measure the degree of pelvic prolapse at rest and with Valsalva maneuvers. The bladder neck undergoes subjective and objective evaluation for hypermobility. Findings of pelvic floor dyssynergia may be noted as a paradoxical movement of the pelvic floor during these maneuvers; similarly, an atonic pelvic floor is characterized by a lack of levator plate movement with prompted squeeze. Observation of coordinated pelvic floor lift by ultrasound may be indicative of pelvic floor dysfunction. Parting the labia and varying the degree of pressure of the transducer may improve image quality. By rotating the transducer 90 degrees, one can obtain a coronal view, and by placing a dorsal inclination on the transducer, the anal canal and sphincter complex can be visualized and examined. Once adequate images are obtained, the transducer is removed from the perineum and cleaned.




Fig. 13.8


A , A schematic diagram and (B) , the ultrasound image showing a midsagittal view on two-dimensional transperineal ultrasound (Voluson E6 with RAB 4-8 MHz transducer [GE Healthcare, Wauwatosa, WI]). A , Anal canal; V , vagina; u , urethra; U , uterus; B , bladder; S , symphysis pubis.

( A from Dietz HP. Pelvic floor ultrasound: a review. Am J Obstet Gynecol . 2010;202:321. With permission.)


The 2D images can be integrated into 3D volume data either by freehand acquisition of images or by using a transducer equipped with a motor to allow for automatic acquisition of images. To perform the examination, the patient is placed in the same position as described for 2D ultrasound. The 3D-capable transducer is placed firmly on the perineum, maintaining a midsagittal orientation. The transducer is then held in place while the images are obtained at rest, during squeeze, and with the Valsalva maneuver. The 3D postprocessing of the images can be performed with the appropriate software. The 4D imaging entails the real-time acquisition of data to produce and save image cineloops. To perform 4D ultrasound, images are recorded during a prompted maneuver such as a squeeze or maximal Valsalva maneuver. This allows for instant acquisition of ultrasound volumes, optimized versions of which may then be viewed in orthogonal planes or rendered views ( Fig. 13.9 A and B).




Fig. 13.9


A , Translabial three-dimensional ultrasound images in the midsagittal plane ( left ) and oblique axial plane ( right ) showing identification of the plane of minimal hiatal dimensions on Valsalva maneuver. The horizontal line in the image on the left illustrates the identification of the plane of minimal hiatal dimensions in the midsagittal plane and is equivalent to the vertical line in the image on the right . The dotted line in the image on the right illustrates the minimal hiatal area on Valsalva, which was measured at 19 cm 2 , indicating normal distensibility of the hiatus.

(From Dietz HP, Shek C, De Leon J, Steensma AB. Ballooning of the levator hiatus. Ultrasound Obstet Gynecol . 2008;31:676.) B , Tomographic ultrasound imaging in the C (axial) plane for assessment of levator integrity. Slice 1 is the caudal slice; slice 8 is the most cranial slice. The arrows indicate the symphysis pubis. (From AIUM/IUGA practice parameter for the performance of urogynecological ultrasound examinations: developed in collaboration with the ACR, the AUGS, the AUA, and the SRU. Int Urogynecol J . 2019;30:1389.)




Introital pelvic floor ultrasound requires an endocavitary front fire transducer. Similar steps are performed by obtaining images of the pubic symphysis, urethra, vagina, and anal canal with an initial midsagittal view. This will allow for an initial static image of the urethrovesical junction and ARA. A dynamic assessment of the pelvic floor is obtained by having the patient perform squeeze and Valsalva maneuvers, followed by a 3D assessment of the levator ani complex, if the 3D modality is available. Lastly, the anal sphincter complex may be imaged in the axial plane, specifically noting the integrity of the external anal sphincter (EAS) and internal anal sphincter (IAS) ( Fig. 13.10 ).




Fig. 13.10


Transperineal view showing an intact anal sphincter complex. EAS , External anal sphincter; IAS , internal anal sphincter.


Endovaginal ultrasonography.


Endovaginal ultrasound (EVUS) of the pelvic floor also begins with a 2D static and dynamic assessment of the pelvic floor. An endocavitary transducer such as a high-resolution, multifrequency, 9- to 16-MHz transducer is used (linear array 360-degree 3D transducer or radial array 360-degree 3D transducer). EVUS is routinely performed with the patient in the dorsal lithotomy position with a comfortable amount of urine in the bladder ( Fig. 13.11 A and B). To perform the exam, the transducer is inserted into the vagina in a neutral position, avoiding excessive pressure on the surrounding structures. Typically it is performed at rest, with a Valsalva maneuver, and during pelvic floor muscle contraction.




Fig. 13.11


A , Schematic of placement of three-dimensional (3D) endovaginal transducer. B , 3D endovaginal ultrasound volume.




During the 2D assessment, the transducer is introduced into the vagina until the urethrovaginal junction is visualized. At this time, any anterior compartment, including the urethra or bladder neck, can be visualized, and any dynamic maneuvers, such as squeeze or Valsalva, can also be performed. Note that these movements can be impeded by the presence of the transducer in the vaginal canal. The transducer may then be advanced to visualize the urethrovesical junction, and it is at this time that the 3D volume acquisition, if available, can be started. The scan starts at the urethrovesical junction and continues until 6 cm caudally to include the perineal body as an anatomic landmark. Postprocessing may be performed on the scanner, but is easier to carry out using the free software, which can be installed on any computer. shows an example of 3D postprocessing of a 3D volume from an EVUS and includes measurements of minimal levator hiatus, the ARA, and levator ani integrity. This allows for the volume to be exported to an external drive and viewed and analyzed at any time. The software allows manipulation of the 3D cube in the x, y, and z planes, as well as linear, angle, area, and volume measurements ( Fig. 13.12 ). As with other ultrasound modalities, the 3D volume obtained is useful in visualizing levator ani muscle integrity or defects, for describing and measuring vaginal masses, and for localizing and characterizing slings, mesh, and other foreign bodies ( Fig. 13.13 ).




Fig. 13.12


Three views of urethra diverticulum on the x, y, and z planes using three-dimensional endovaginal sonography.



Fig. 13.13


Three-dimensional ultrasound showing anterior mesh and two midurethral slings.


Transrectal ultrasonography.


Endoanal ultrasound is useful for the evaluation of anal sphincter defect or pathology and is performed with a high-resolution, multifrequency, mechanical 360-degree rotational transducer. This method has been regarded as the “gold standard” in the evaluation of the anal sphincter complex. The patient is placed in the lithotomy, lateral, or prone position. Some clinicians prefer the left lateral position when performing this ultrasound. If in lithotomy position, the transducer is inserted gently at a 45-degree angle until the levator plate is visualized posteriorly. Irrespective of patient positioning, the transducer should be positioned so that the anterior aspect of the anal canal is superior on the screen, at the 12 o’clock position. The distal end of the transducer should be at the level of the puborectalis muscle or 6 cm into the anal canal. The mechanical rotational transducer, once activated, automatically obtains 3D images. In addition to obtaining detailed views of the anal sphincter complex, this method may be useful in imaging the pelvic anatomy of individuals with a short or absent vagina. The IAS is a continuous smooth muscle hypoechoic ring, the EAS is a striated muscle hyperechoic ring, and the conjoint longitudinal muscle consists of a mixed echogenicity layer between the two sphincters ( Fig. 13.14 ).




Fig. 13.14


Example of a normal three-dimensional endoanal ultrasound. EAS , External anal sphincter; IAS , internal anal sphincter.


Applications of ultrasound in evaluating disorders of the lower urinary tract and pelvic floor


Anterior compartment


The anterior compartment of the pelvis is often assessed with transperineal ultrasounds and EVUSs. Considering the inherent displacement of adjacent tissue with EVUS, transperineal ultrasound may be preferred for visualizing bladder neck descent, urethral hypermobility, cystocele, and cystourethrocele. On transperineal and introital ultrasound, the position of the urethrovesical junction at rest and at maximal Valsalva may be measured relative to the central line of the SP or its inferoposterior margin. It is recommended to use the posterior inferoposterior margin of the SP as a reference. On Valsalva, the bladder neck and proximal urethra are noted to rotate in the inferior and posterior directions. The distal urethra remains stable because of its tethering to the SP and pelvic side walls. There is no standard measurement to define hypermobility of the urethra, but movement cutoffs of 20, 25, or 30 mm have been proposed. However, there is no current standard definition for urethral hypermobility on ultrasound, and similar measurements have been found in asymptomatic nulliparous women. Perhaps an observation of greater importance is hypomobility of the urethra. A fixed or hypomobile urethra considerably increases the risk of failure after placement of a midurethral sling. In a study by , repeat sling surgery for UI in patients with limited urethral mobility diagnosed by either Q-tip test or ultrasound was associated with a four times greater risk of sling failure. Similarly, also noted that patients treated with tension-free vaginal tape who had decreased bladder neck mobility of 10 mm or less on ultrasound had a two-fold higher risk of failure from the procedure. Clinically, the finding of urethral hypomobility increases the risk of sling failure and may prompt consideration of other treatment options.


A 3D EVUS can be used to provide a detailed anatomic depiction of anterior compartment structures, including the trigone, the compressor urethra, and the urogenital sphincter. The examiner is also able to measure the components of the urethral complex, including urethral width, length, and volume. Ultrasound is also an excellent tool for visualizing vaginal cysts and masses, including Skene’s gland cysts, urethral diverticula, and Garner’s duct cysts.


The female urethra is a complex organ that plays a central role in UI, and thus normal anatomy, innervation, position, and proper relation to the surrounding pelvic floor structures ensure its normal function. Signs and symptoms of pelvic floor dysfunction often overlap with signs and symptoms of urethral diverticula, ectopic ureters, urethral tumors, and periurethral cystic lesions. Ectopic ureters and ureteroceles are usually diagnosed in childhood and rarely present in adults. Nevertheless, these conditions should be considered in patients with urinary tract infections or UI, as surgery can correct these disorders. EVUS has been used in the diagnosis of ectopic and dystopic ureters. Moreover, on rare occasions ultrasound is helpful in distinguishing pathology mimicking anterior vaginal wall prolapse, such as a vaginal cyst, vaginal myoma, Skene’s gland cyst, or urethral diverticulum.


Urinary incontinence


Various ultrasound techniques and findings have been taken into account in the evaluation of UI. One of the initial steps in the evaluation of UI involves the measurement of a postvoid residual, which may be accomplished with ultrasound, allowing for the estimation of bladder volume in millimeters. Evaluation of the bladder neck in the context of UI was one the first procedures to be performed by perineal ultrasound. Findings such as urethral hypermobility and bladder funneling have been noted in association with UI but may also be observed in asymptomatic women with normal urethral sphincters and in women with urge incontinence. Currently there is insufficient evidence that ultrasound evaluation is of significant clinical benefit in the standard evaluation of UI.


Urethral and periurethral abnormalities


A urethral diverticulum is a localized outpouching of the urethral mucosa into the surrounding nonurothelial tissues. This is an uncommon condition that is found mainly in adult women, and it is a diagnosis that is often overlooked in patients presenting with elusive lower urinary tract symptoms (e.g., UI, dysuria, dyspareunia, vaginal mass). The delay in diagnosis of this condition can lead to chronic morbidity, including urethral calculus formation, chronic or recurrent urinary tract infections, or, rarely, malignant transformation. Previously, contrast-enhanced radiography (e.g., voiding cystourethrography, retrograde double-balloon positive pressure urethrography) was used to evaluate women for urethral diverticulum. However, these procedures are invasive and technically difficult, and the contrast-dependent studies are only able to visualize diverticula that are patent enough to allow filling with contrast material. Therefore the preferred imaging techniques are MRI or ultrasound ( Fig. 13.15 ).


Nov 27, 2021 | Posted by in GYNECOLOGY | Comments Off on Radiologic studies of the lower urinary tract and pelvic floor
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