The use of a 15-7-MHz 'small parts' linear transducer to evaluate the anal sphincter in female patients

Anorectal Anatomy and Function

Anatomy of pelvic floor muscles has long been controversial. Novel imaging modalities, such as three-dimensional transperineal ultrasound imaging, MRI, and diffusion tensor imaging, have revealed unique myoarchitecture of the external anal sphincter and puborectalis muscle. High-resolution anal manometry, high-definition anal manometry, and functional luminal imaging probe are important new tools to assess anal sphincter and puborectalis muscle function. Increased understanding of the structure and function of anal sphincter complex/pelvic floor muscle has improved the ability to diagnose patients with pelvic floor disorders. New therapeutic modalities to treat anal/fecal incontinence and other pelvic floor disorders will emerge in the near future.

High-frequency ultrasound imaging of the anal sphincter muscles in normal subjects and patients with fecal incontinence

INTRODUCTION

The current "gold standard" to diagnose anal sphincter morphology and disruptions utilizes low-frequency (3-9 MHz) ultrasound (US) imaging techniques that provide a general outline of the sphincter muscles, but not their microstructural details. High-frequency US transducers (7-15 MHz) have been used to study the muscle architecture (direction of muscle fascicles) in the limb muscle.

AIMS

The goal of our study was to visualize the microstructural anatomy of the anal sphincters, specifically the external anal sphincter (EAS), using high-frequency US imaging.

METHODS

Studies were conducted in asymptomatic female and male subjects and patients with fecal incontinence. US images were acquired using a low-frequency US (3-9 MHz) and high-frequency (7-15 MHz) US transducer. The latter was placed intra-anally to image the anal canal at 12, 9, 3, and 6 o'clock positions.

RESULTS

The low-frequency US images revealed the general outline of the anal sphincter muscles. On the other hand, high-frequency imaging visualized muscle fascicles and connective tissue inside the external anal sphincter (EAS). In FI patients, there was loss of muscle fascicles and alteration in the echo-intensity pattern in the region of damaged EAS suggestive of muscle fibrosis.

CONCLUSION

High-frequency ultrasound imaging is a powerful tool to visualize the microstructural details of the EAS. Our studies show that damage to the EAS muscle results in the alteration of its myoarchitecture, that is, loss of muscle fascicles and increase in the muscle connective tissue.

Female pelvic floor dysfunction--an imaging perspective

Female pelvic floor dysfunction encompasses a range of morbidities, including urinary incontinence, female pelvic organ prolapse, anal incontinence and obstructed defecation. Patients often present with symptoms covered by several specialties including gastroenterology, colorectal surgery, urology and gynecology. Imaging can therefore bring clinicians from multiple specialties together by revealing that we frequently deal with different aspects of one underlying problem or pathophysiological process. This article provides an interdisciplinary imaging perspective on the pelvic floor. Modern pelvic floor imaging comprises defecation proctography, translabial and endorectal ultrasound, and static and dynamic MRI. This Perspectives focuses on the potential use of translabial ultrasound, including 3D and 4D applications, for diagnosis of pelvic floor disorders. Over the next decade, pelvic floor imaging will most likely be integrated into mainstream diagnostics in obstetrics and gynecology and colorectal surgery. Using imaging to facilitate communication between different specialties has the potential to greatly improve the multidisciplinary management of complex pelvic floor disorders.

The diagnostic accuracy of endovaginal and transperineal ultrasound for detecting anal sphincter defects: The PREDICT study

AIM

To determine the accuracy and predictive value of transperineal (TPU) and endovaginal ultrasound (EVU) in the detection of anal sphincter defects in women with obstetric anal sphincter injuries and/or postpartum symptoms of faecal incontinence.

MATERIALS AND METHODS

One hundred and sixty-five women were recruited, four women were excluded as they were seen years after their last delivery. TPU and EVU, followed by endonanal ultrasound (EAU), were performed using the B&K Viking 2400 scanner. Sensitivity and specificity, as well as predictive values with 95% confidence intervals, for detecting anal sphincter defects were calculated for EVU and TPU, using EAU as the reference standard.

RESULTS

On EAU a defect was found in 42 (26%) women: 39 (93%) had an external (EAS) and 23 (55%) an internal anal sphincter (IAS) defect. Analysable images of one level of the EAS combined with an analysable IAS were available in 140 (87%) women for EVU and in 131 (81%) for TPU. The sensitivity and specificity for the detection of any defect was 48% (30-67%) and 85% (77-91%) for EVU and 64% (44-81%) and 85% (77-91%) for TPU, respectively.

CONCLUSION

Although EAU using a rotating endoprobe is the validated reference standard in the identification of anal sphincter defects, it is not universally available. However while TPU and/or EVU with conventional ultrasound probes can be useful in identifying normality, for clinical purposes they are not sensitive enough to identify an underlying sphincter defect.

Three-dimensional transperineal sonographic characteristics of the anal sphincter complex in nulliparous women

OBJECTIVE

To explore the morphological characteristics and normal biometry of the anal sphincter complex in nulliparous Chinese women using three-dimensional (3D) transperineal ultrasound.

METHODS

3D sonographic data from 55 nulliparous Chinese women (aged 19-38 years) who had no pelvic organ prolapse and no symptoms of pelvic floor dysfunction were retrieved from an image dataset and analyzed by offline post-processing. The morphological characteristics of the external and internal anal sphincters, puborectalis muscle and perineal body were assessed in the sagittal, coronal and axial views.

RESULTS

The external anal sphincter had three sonographic components: the circular main body, a subcutaneous part and an extension portion. It was significantly thinner at 12 o'clock than at the 3, 6 and 9 o'clock positions. The internal anal sphincter was seen as dark echolucent strips of equal thickness. In the mid-sagittal view, it started from the anal verge and ended at the anorectal junction. The perineal body was an ovoid structure covering the upper margin of the external sphincter, while the puborectalis muscle was banana-shaped in the sagittal view and was located behind the anorectal junction, extending downward along the inferior margin of the posterior external sphincter extension. Sonographic characteristics of the anal sphincter complex did not vary with age, weight, height or body mass index.

CONCLUSIONS

3D transperineal ultrasound clearly demonstrates the spatial relationships of each component of the anal sphincter complex. This should allow standardized measurement of the complex for investigations of its function.

Postpartum evaluation of the anal sphincter by transperineal three-dimensional ultrasound in primiparous women after vaginal delivery and following surgical repair of third-degree tears by the overlapping technique

OBJECTIVE

Intrapartum damage to the anal sphincter is an important factor in fecal incontinence. Recognized lacerations occur in 0.36-8.4% of vaginal deliveries, and occult sphincter damage in up to 35% of primiparous women. We examined the role of three-dimensional transperineal ultrasound (3DTUS) in the evaluation of the anal sphincter in primiparous women after vaginal delivery and after surgical repair of third-degree intrapartum tears by the overlapping technique.

METHODS

During 2004-2005 139 primiparous women without clinically recognized third- to fourth-degree anal sphincter tears were prospectively studied 24-72 h postpartum (Group 1) and 13 primiparous women were examined 48 h to 4 months following surgical repair of third-degree tears with the overlapping technique (Group 2). A 3D 5-9-MHz transvaginal probe was placed in the area of the fourchette and perineal body in transverse and sagittal planes and 2-4 volumes were stored. The parameters studied were: examination duration; continuity of the internal and external sphincters; occult sphincter damage; internal sphincter and external sphincter width-measured 1.5 cm from the distal margin of the anus-at the '12, 3, 6 and 9 o'clock positions'; length of the posterior internal sphincter.

RESULTS

Scanning was possible in all women and the stored volumes were adequate in 127/139 (91.4%) cases. Mean examination time was 3.5 min. In Group 1, occult sphincter defect was suspected in 10/127 women (7.9%). These patients were excluded from measurement calculations, leaving 117 cases for analysis. The internal sphincter was consistently visualized in all the remaining patients (n = 117), while the external sphincter was fully visualized in 99/117 women (84.6%), and partially visualized in the remainder. Mean internal sphincter thickness was 2.60, 2.55, 2.60 and 2.72 mm at the 12, 3, 6 and 9 o'clock positions, respectively, and mean internal sphincter length was 3.34 cm. Mean external sphincter thickness was 4.15, 4.20, 4.21 and 4.20 mm at the 12, 3, 6 and 9 o'clock measurement points. In Group 2, 3DTUS confirmed anatomic abnormalities in all the women in the area surrounding the 12 o'clock position. Evaluation of sphincter tears and their position and length was possible using the longitudinal view. Thinning of the internal sphincter in the area of damage and thickening on the opposite side, the 'half moon sign', sphincter discontinuity, thickening of the external sphincter in the area of repair and abnormality of mucous folds, seemed to be common signs of third-degree intrapartum sphincter tears, even after repair.

CONCLUSIONS

3DTUS is an accessible and promising method for postpartum sphincter evaluation, that is apparently well tolerated by patients. Reference data for sphincter anatomy representative of findings at transperineal ultrasound in primiparous women in the postpartum period have been established.