Shelley O’Sullivan1 , Vincent Tse2 , Stephanie The3 , Lewis Chan2 and Peter Stewart4
(1)
Ultrasound, Philips Healthcare Australia, Epping Road, North Ryde, NSW, 2113, Australia
(2)
Department of Urology, Concord Repatriation General Hospital, Sydney, NSW, Australia
(3)
Department of Women’s and Children’s Health Pelvic Floor Unit, Westmead Hospital, Sydney, NSW, Australia
(4)
Department of Colo-Rectal Surgery, Concord Repatriation General Hospital, Sydney, NSW, Australia
Shelley O’Sullivan
Email: shelley.osullivan@philips.com
Vincent Tse
Email: vincent.tse@sydney.edu.au
Stephanie The
Email: wdu@optusnet.com.au
Lewis Chan (Corresponding author)
Email: lewis.chan@sswahs.nsw.gov.au
Peter Stewart
Email: pstewart@bigpond.com.au
3D pelvic floor ultrasound imaging has an emerging role in the assessment and management of pelvic floor disorders. Whilst many patients with voiding dysfunction, incontinence and pelvic organ prolapse can be assessed utilizing dynamic 2D imaging as shown in the previous chapters, there is increasing interest in the use of 3D/4D ultrasound imaging in complex pelvic floor dysfunction. Furthermore, advances in ultrasound equipment and transducer technology has brought this modality within reach of many clinicians.
Potential applications of 3D ultrasound in pelvic floor dysfunction include assessment of sling and mesh complications, pelvic organ prolapse, obstetric pelvic floor injuries, fecal incontinence and complex perianal sepsis/fistulae.
Principles of 3D Ultrasound
With 3D ultrasound imaging a series of sagittal images (or axial images in some endocavity 360° transducers – see Case 4) are collected which make up a volume data set (Fig. 9.1a, b). This can then be manipulated and reconstructed in different planes to obtain extra information not easily available from 2D imaging. The acquisition of a 3D volume dataset can be automated within the mechanics of the 3D transducer (either mechanical or electronic steering of the ultrasound beam) or less commonly by freehand movement (a ‘sweep’) of the transducer.
Fig. 9.1
(a, b) 3D volume acquisition. A series of sagittal (a) or axial (b) images are acquired by the transducer to obtain a 3D volume dataset
2D greyscale ultrasound imaging allows the operator to image the organ or region of interest in two planes (the sagittal and transverse planes). The ability to acquire a 3D ultrasound dataset (volume) allows reconstruction of the axial plane which is generally not able to be obtained in 2D imaging. This process is called multi-planar reconstruction, similar to the process of reconstructing images in sagittal and coronal planes on a CT scan.
The ability to perform volume rendering allows the user to reconstruct a 3D image which may help in diagnosis. There are also powerful algorithms that allow real-time updating of the 3D reconstructed image, producing a so-called ‘4D’ capability (the fourth dimension being time). These processes require considerable computing/post-processing of the echo information and together with the physical limits of ultrasound (e.g. Pulse repetition frequency, field of view, lines of sight, etc. – see Chap. 1) can lead to lower resolution of the reconstructed image.
Technique of 3D Volume Acquisition and Analysis
3D Definitions and instrumental controls:
· Pixel – A term used to describe the basic unit of 2D information displayed on an ultrasound image. Each pixel is assigned a series of gray scale X and Y Values.
· Voxel – A term used to describe the basic unit of 3D information, as it has an additional vector of Z attached to it, to specify its location in the 3D volume. It is assigned the same series of gray scale values X, Y and the additional Z.
· MPR (Multi planar reconstruction – Figs. 9.2 and 9.3) – MPR consists of the three planes that make up the 3D data set. They are positioned 90° from each other and labeled X, Y and Z. When one plane is manipulated, the other planes on view will change accordingly. Figure 9.4 illustrates the three MPR planes during 3D volume analysis. By convention the top left box is the acquisition plane, which is the sagittal plane in the example. This is the plane that was used initially to acquire the data set. The top right box is the orthogonal view to the acquisition plane. In the above case it’s the transverse view. The bottom left box is the coronal or C-plane view which is derived from the combination of acquisition and orthogonal views. This is the plane which is not generally possible on 2D imaging.
Fig. 9.2
Multiplanar reconstruction – the 3D ultrasound volume dataset can be analysed by manipulating the three planes (X, Y, Z) at right angles to each other
Fig. 9.3
MPR – 3D volume obtained by endoanal 3D transducer
Fig. 9.4
Cross hair – this is a marker of the intersection of each plane. The intersecting point of the cross hair on each view represents the same point within the volume data set
· Cross Hair – This is a marker of the intersection of each plane (Fig. 9.4). The intersecting point of the cross hair on each view represents the same point within the volume data set. Each plane rotates around the corresponding line that makes up the cross hair.
· ROI – Region of Interest (Fig. 9.5). This is the user defined area on 2D imaging that is used to produce a 3D data set.
Fig. 9.5
Region of Interest (ROI). This is the user defined area on 2D imaging that is used to produce a 3D data set. The white triangular shaped area is the ROI box
· Trim Line – In Fig. 9.5 the solid horizontal line is the trim line. Anything above this line will not be included in the 3D data set. Therefore, this line should be moved to the very top of the image so that information is not cut out of the data set.
· Acquisition – This is the process of sweeping, pivoting or performing live 2D that will record a 3D volume.
· Angle – This determines the range (thickness of the 3D volume) over which the acquisition will occur. Larger angle settings results in a larger volume acquired (Fig. 9.6).
Fig. 9.6
Sweep angle – this determines the range (thickness of the 3D volume) over which the acquisition will occur
Technique of 3D Data Acquisition (See Tips 9.1)
1.
2.
3.
4.
5.
6.
7.
Reconstructing the Data Set
1.
2.
3.
4.
5.
6.
7.
8.
Case 1 Persisting Voiding Dysfunction Post Sling Division
A 52 year old female presents having underwent excision of a suburethral segment of sling for voiding difficulties following a synthetic mid urethral sling. Urodynamics showed poor flow with protracted void and elevated voiding pressures. Postoperatively she had only mild improvement and complained of persisting symptoms of poor flow and incomplete bladder emptying. Transperineal 3D ultrasound scan was performed to assess residual sling position (Fig. 9.12).
Fig. 9.12
(a, b) Transperineal 3D ultrasound images in patient with persisting voiding dysfunction post sling division demonstrating insufficient division of the sling (arrows) with a segment of sling continuity (b)
Comments – (Also See Chap. 5)
The differential diagnosis of persisting symptoms post treatment of voiding dysfunction due to an obstructive sling procedure include residual/recurrent obstruction or hypocontractile (underactive) bladder. 3D ultrasound can be used to assess the adequacy of sling division. The images (Fig. 9.12a, b) showed there was insufficient division of the sling with a segment of sling continuity. The patient underwent re-exploration and excision of the residual sub-urethral mesh segment.
Figure 9.13 demonstrates a patient who had recurrence of voiding dysfunction 6 months following sling division. The X-plane image showed the effect of scar contraction with insufficient separation of the sling segments following simple division of the obstructive sling. This patient subsequently underwent re-exploration and excision of a sub-urethral segment of sling.
Fig. 9.13
Recurrent voiding dysfunction post sling division – the X-plane (transverse) image (right image) shows the effect of scar contraction with insufficient separation of the sling (arrow) segments following division of the obstructive sling
Case 2 Persisting Incontinence Despite 2 Sling Procedures
A 47 year old female presents with persisting urinary stress incontinence despite the placement of a transobturator mid urethral sling, and subsequent placement of another synthetic mid-urethral sling. 3D pelvic floor ultrasound scan was performed to assess sling positions.
The image (Fig. 9.14) shows the value of 3D Pelvic floor ultrasound in identification of sling location relative to the urethra in complex cases where there is prior sling surgery especially in planning further treatment. The two slings have been placed in the same position. Urodynamic study demonstrated intrinsic sphincteric deficiency with low leak point pressures and little urethral mobility (see Chap. 5). The patient subsequent underwent excision of the suburethral portions of the slings and placement of a pubo-vaginal fascial sling at the level of proximal urethra.
Fig. 9.14
Persisting incontinence despite two slings. The ultrasound image showed that the two slings have been placed in the same position at level of mid urethra
Case 3 Dysuria and Hematuria, Previous Sling and Bulking Agent
A 75 year old female presents with dysuria and two episodes of macroscopic haematuria. She had a background of a transobturator mid urethral sling procedure that did not improve her incontinence She subsequently underwent two injection procedures of a bulking agent (Macroplastique), which eventually improved her urinary continence. Cystoscopy showed urethral erosion of the injectable implant at the level of proximal urethra. Transperineal 3D pelvic floor ultrasound was performed to further evaluate the extent of the synthetic injected material which extended from proximal to mid urethra adjacent to the sling (Fig. 9.15).
Fig. 9.15
MPR view of patient with a mid-urethral sling and injection of bulking agent. The Macroplastique® implant is echogenic and can be seen in the sagittal and transverse planes (arrows)
Comments
The images showed the Macroplastique (silicone microspheres) material, which is typically quite echogenic. The implant extended from proximal to mid urethra adjacent to the sling and is best appreciated on the axial reconstruction (Z plane) in Fig. 9.16.
Fig. 9.16
Axial reconstruction demonstrating the Macroplastique® bulking agent (M) and the mid-urethral sling
The patient eventually decided to continue an expectant approach as she was reluctant to undergo further surgery to remove the implant due to the likelihood of requiring urethral reconstruction, possible fascial sling procedure and the risk of developing a fistula.
Case 4 Chronic Anal Pain, Intersphincteric Fistula
A 55 year old female presented with 12 month history of chronic anal pain. There was no bleeding or alteration of bowel habits. There was mild tenderness anteriorly on right side on digital examination. The 3D endoanal ultrasound images (Fig. 9.17) showed a trans-sphincteric abscess with fistula through the lower part of the anal canal with well preserved sphincter proximal to the fistula. She underwent a LIFT (ligation of intersphincteric tract) procedure with good outcome.
Fig. 9.17
Trans-spincteric abscess with fistula (arrow) through the lower part of the anal canal with well preserved sphincter proximal to the fistula
Apart from assessment of ano-rectal abscess and fistulae, endoanal ultrasound with 3D reconstruction can assist in the assessment of ano-rectal malignancy both in preoperative staging and in cases of recurrent tumour following surgery. Figure 9.18 shows a reconstructed 3D image of anal squamous cell carcinoma showing extent and depth of invasion. Figures 9.19 and 9.20 are cases of locally advanced rectal carcinoma; in one case there was tumour involving the capsule of the prostate and the other shows lymph node metastases.
Fig. 9.18
Squamous cell carcinoma (T)
Fig. 9.19
Locally advanced rectal carcinoma involving capsule of the prostate
Fig. 9.20
Locally advanced rectal carcinoma (T) with lymph node metastases (arrow)
Case 5 Symptomatic Pelvic Organ Prolapse (POP)
A 61 year old lady presents with bothersome vaginal bulge symptoms. These symptoms were especially prominent at the end of a long day at work where she had to stand up for long periods of time. It was often associated with lower back pain that tended to subside when she lay down. She also complained of urinary frequency, urgency and sensation of incomplete bladder emptying. Vaginal examination revealed a POP-Q Stage 3 cystocele with associated vault prolapse.
Comments
The key feature of a cystocele is its low position relative to the inferior border of the symphysis pubis, either at rest or straining. There may also be distortion of the urethra with hypermobility, bladder neck opening and rotational descent. The 3D axial images at rest and on Valsalva demonstrates descent of the cystocele with widening of the levator haitus (Figs. 9.21 and 9.22)
Fig. 9.21
Cystocele- 3D volume datasets with patient at rest (a) and on maximal Valsalva (b). Note Nabothian cyst in cervix seen in sagittal and axial views (arrow). Adjusting the display colour map such as using the ‘chroma’ setting in these images may assist in demonstrating some pathologies
Fig. 9.22
Coronal reconstruction image of pelvic floor in patient with cystocele (c)
3D Pelvic Floor Ultrasound in Assessment of Pelvic Organ Prolapse
Advances in 3D ultrasound imaging has opened up new opportunities for studying the functional anatomy of the pelvic floor. 3D pelvic floor ultrasound is especially useful in the assessment of pelvic organ prolapse (POP) and can be performed by transperineal (translabial) or transvaginal approaches. Whilst POP is routinely assessed by clinical examination, 2D/3D pelvic floor ultrasound can clearly demonstrate to the pelvic floor surgeon which pelvic viscera are involved in the prolapse and the degree (stage) of prolapse. The imaging findings can add to the clinical examination findings and assist the surgeon in deciding what type of reconstruction is most suitable for the patient. Occasionally, what is seen at physical examination may represent clinical understaging (a ‘false-negative’) of the actual prolapse present. This is due to levator co-activation which can prevent the maximal extent of the prolapse from presenting at the bedside [1]. This phenomenon can often be seen on ultrasound and may be due to a generalized defensive reflex [2].
One of the pathophysiological factors in POP is levator avulsion (LA), thought to be predominantly related to obstetric trauma [3, 4]. 3D imaging is of particular importance in the assessment of this entity as the levator ani muscle is well demonstrated in the axial plane (Figs. 9.23 and 9.24). Dietz et al. [3] have reported in uro-gynaecological patient cohorts that the presence of LA is associated with a twofold increased risk of Stage 2 or above POP (mainly cystocele and uterine prolapse). Furthermore when LA is identified, it is often associated with paravaginal defects and may have implications regarding surgical reconstructive approach (Fig. 9.25). Shek et al. reported that in patients undergoing native tissue cystocele repair, the presence of LA on pelvic floor ultrasound is associated with an increased risk of treatment failure/recurrence [5]. However, levator defects are not associated with urinary symptoms or voiding dysfunction [6].
Fig. 9.23
Coronal reconstruction of pelvic floor in patient with stress incontinence cured by a mid-urethral synthetic sling. U urethra, V vagina, R rectum, PF pelvic floor muscle
Fig. 9.24
Levator tear (arrow) in patient with urinary incontinence but no pelvic organ prolapse
Fig. 9.25
Levator tear (blue arrow) with paravaginal defect in patient with stress incontinence cured by mid-urethral sling
3D pelvic floor ultrasound is also useful in understanding what happens when surgery fails, especially if there has been placement of synthetic meshes. Shek et al. demonstrated on 3D imaging that POP recurrence after anterior mesh reconstruction can occur dorsal to the mesh, implying dislodgement of the mesh arms [7].
If a patient presents with de novo dyspareunia after mesh repair, 3D ultrasound may also be useful in assessing the configuration and location of the mesh in addition to clinical vaginal examination. The mesh may appear crenulated and folded on ultrasound, corresponding to induration or firm bands palpable on clinical examination. Identification of such findings may reflect on technical issues during mesh placement and assist in planning surgical correction/mesh removal.
Tips 9.1 How to Acquire Good 3D Images
Technique of acquiring 3D volume datasets during transperineal imaging
· The results of 3D data analysis depend on the quality of image data acquired
· A high quality 2D image acquisition will allow good 3D data capture
· Use the same gain adjustments (TGC, LGC, Gain, ROI) settings to optimize image before performing 3D acquisition
· Keep patient relaxed and comfortable to minimize unintended pelvic floor activation especially in assessment of pelvic organ prolapse
· Use lots of sonographic gel and ensure good contact between perineum and transducer (but not excessive pressure to distort anatomy)
· Start in mid-sagittal plane
References
1.
Dietz HP. Why pelvic floor surgeons should utilize ultrasound imaging. Ultrasound Obstet Gynecol. 2006;28:629–34.CrossRefPubMed
2.
van der Velde J, et al. Vaginismus, a component of a general defensive reaction. An investigation of pelvic floor muscle activity during exposure to emotion-inducing film excerpts in women with and without vaginismus. Int Urogynecol J Pelvic Floor Dysfunct. 2001;12:328–31.CrossRefPubMed
3.
Dietz HP, Simpson JM. Levator trauma is associated with pelvic organ prolapse. BJOG. 2008;115(8):979–84.CrossRefPubMed
4.
Steensma AB, Konstantinovic ML, Burger CW, de Ridder D, Timmerman D, Deprest J. Prevalence of major levator abnormalities in symptomatic patients with an underactive pelvic floor contraction. Int Urogynecol J. 2010;21(7):861–7.CrossRefPubMedCentralPubMed
5.
Dietz HP, Chantarasorn V, Shek KL. Levator avulsion is a risk factor for cystocele recurrence. Ultrasound Obstet Gynecol. 2011;37(4):500.CrossRef
6.
Dietz HP, Steensma AB. The prevalence of major abnormalities of the levator ani in urogynaecological patients. BJOG. 2006;113(2):225–30.CrossRefPubMed
7.
Shek KL, Dietz HP, Rane A, Balakrishnan S. Transobturator mesh for cystocele repair: a short to medium term follow-up using 3D/4D ultrasound. Ultrasound Obstet Gynecol. 2008;32(1):82–6.CrossRefPubMed