Tuesday, April 10, 2012

Ultrasound modalities for assessment female lower urinary tract and pelvic floor structures (part1)


Ultrasound modalities for assessment female lower urinary tract and pelvic floor structures (part1)

Introduction

Modalities of sonographic urethrocystography
I-Transabdominal sonography

II-Endosonography Procedures
     A- Endoanal (Transrectal sonography)
     B-Vaginal ultrasonography (Vaginosonography)
     C-Intraurethral ultrasound
    
III-Introital sonography

IV- Perineal ultrasound (PU) (Perineosonography, Dynamic transperineal sonourethrocystography, Translabial, Vulvar or TP-USG)
Introduction
The mobility of BN and base is an important parameter when evaluating patients suffering from SUI or uterovaginal prolapse. For decades, radiological techniques such as lateral bead-chain cystourethrography and videocystourethrography (VCU) have been the “gold standard” for bladder base and neck assessment. However, they involve the use of expensive bulky equipment and expose the patient to radiation. Although ultrasound evaluation of the pelvis was first described in 1958, only recent dramatic technical improvements have made it possible to use sonography to assess the position of BN and its position relative to pubic symphysis, and to obtain results similar to those obtained with X-rays (Anastasi et al, 2002).

The major disadvantage of radiologic scanning and at same time the most limiting factor for long-term studies is the dose of radiation to patient’s gonads. Ovarian radiation doses are reported to range from 1.6 to 13mGy per examination (Gordon et al, 1989). Using standard VCU, the radiation dose to the ovaries is approximately 700mrad/minute (Araki et al, 1984).  This prompted several investigators to evaluate the use of ultrasound place of X-ray fluoroscopy in lower urinary tract (LUT) disorders (Koelbl et al, 1991).

The development of echo graphic transducers allows now to study Female Urinary Exertional Incontinence (FEUI) using different approaches (Vaginal, Transrectal and Perineal) (Fernandez et al, 1998).

Modalities of sonographic urethrocystography
I-Transabdominal sonography is used to assess adynamic changes in the urinary tract. In upper tract, ultrasound can detect hydronephrosis, renal stones, and renal parenchyma abnormalities. In lower tract, ultrasound is used to assess post void residual volume (PVR), sub urethral diverticula's, and bladder tumor (Platt, 1998). Measuring the bladder and PVR requires three diameters (height, width, and depth) in two perpendicular planes (transverse and sagittal). The bladder volume is estimated by using the formula: Volume (ml) = (H x W x D) x (0.7) (Eddie, 1999). Abdominal scans can at best demonstrate proximal portion of the urethra, or urethral axis must be inferred from intravesical position of the urethral catheter (Bhatia et al, 1987). Although the urethrovesical angle can be measured on abdominal scans with about the same accuracy as on X-ray films, difficulties can arise in obese patients and in women with pronounced genital prolapse and associated descent of BN behind the symphysis (Bernaschek et al, 1981).

The use of transabdominal sonography turned out to be a useful diagnostic tool for measuring the extent of the mobility of the bladder and the urethra to determine whether an anatomic defect is present (Koelbl et al, 1991)

II- Endosonography procedures
          The availability of endosonography probes with higher frequencies (range: 3.5:7 MHz) has overcome some of the difficulties associated with abdominal transducers, since they provide a sharper, better focused picture with good resolution and without interference from the symphysis or subcutaneous fat (Koelbl et al, 1991).

The main disadvantage of endosonography relates to the size and shape of the probe, which can cause displacement of anatomic structures (Brown et al, 1985).

A- Endoanal (Transrectal sonography)
Endoanal sonography is a well established method for the morphological diagnosis of anal sphincter damage (Tracy, 1999). The sagittal transrectal view gives an unrivaled view of the internal urethral orifice in most patients and that urethral funneling with straining could only be well seen with this approach (Kuo, 1998).

B- Vaginal ultrasonography (Vaginosonography)
Vaginosonography using high-frequency endoprobes (5-7MHz) with reduced external dimensions is a simple technique for imaging the LUT. Similar to rectosonography, experts have advocated its use for measuring the urethrovesical angle and observing dynamic processes in that region (Quinn et al, 1989).

Bladder neck descent exceeding 1cm from the rest position with cough or Valsalva’s maneuver represents abnormal hypermobility whether demonstrated by cystography (Siegel and Raz, 1988) or pelvic endosonography (Bergman et al, 1988 I). A vaginal probe alters the position and function of the LUT. The use of vaginal ultrasonography in the assessment of women with UI is not recommended (Wise et al, 1992).

C- Intraurethral ultrasound
This ultrasound analysis in vivo together with urodynamic measurements helps clarify the association of anatomy and function of the periurethral tissues, which in turn should lead to further progress in understanding female UI. Other methods such as perineal, introital, or intravaginal ultrasound also may be useful to determine urethral layers. The disadvantage of these techniques is that pictures are taken along a sagittal axis, which makes interpretation of sections lateral to the urethral axis (lumen) difficult (Schaer et al, 1998 I).
III- Introital sonography
          Introital sonography is intermediate between perineal scanning and vaginosonography (Koelbl and Bernascheck, 1990).
A standard front-viewing vaginal probe is applied over a small area in the introital region just behind the urethral orifice to scan the bladder, the urethrovesical junction, and the urethra. The longer shaft allows optimum freedom of motion for the examiner and patient, and the small transducer contact area does not interfere with voiding or urethral catheterization. Meanwhile the technique preserves all advantages of perineal scanning. The position of the urethrovesical junction with respect to the pubic symphysis (Upper edge, lower edge) can be determined at rest and during stress in every patient. Thus, excursion of BN, especially in patients with genuine SUI, can be visualized without effort (Koelbl et al, 1990) (Figures 1 and 2).
Figure 1  Introital sonography in a patient with SUI, showing a vertical descent of urethrovesical junction (small arrows) during coughing and a marked increase of retrovesical angle β. Image I, at rest; image II, during coughing; B, bladder, S, symphysis (Quoted from Koelbl et al, 1991).

Figure 2  Introital sonography of a patient with genuine SUI, showing a rotator descent of urethrovesical junction (small arrow) during coughing, with a marked increase of the retrovesical angle β and the angle of inclination α. Image I, at rest; image II, during coughing; B, bladder, S, symphysis (Quoted from Koelbl et al, 1991).

Figures 1 and 2 illustrate the typical introital sonographic appearance of the bladder, BN, vesicourethral junction and urethra. The whole length of the urethra, the angle of inclination and urethrovesical angle β were measured without effort.

 The image provided by such transducer is characterized by the cone-shaped field of view and the resulting geometrical distortion of the image itself (Sarnelli et al, 2003).        




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