The development of the external urethral sphincter in humans

OBJECTIVE: To assess the hypothesis that during fetal development, the external urethral sphincter changes from a concentric sphincter of undifferentiated muscle fibres to a transient ring of striated muscle which regresses caudo-cranially in the posterior urethra during the first year of life, when the sphincter assumes its omega-shaped configuration. MATERIALS AND METHODS: The anatomy and development of the external urinary sphincter was assessed in human males and females during fetal life. Plastic-embedded sections (transverse, sagittal and frontal planes; 300-700 microm) of the pelvis of 31 females and 31 males (9 weeks of gestation to newborn) were stained with azure II/methylene blue/basic fuchsin and viewed at x 4-80. The sections of interest were taken from the bladder neck to the perineum. The sections of the membranous urethra were reconstructed three-dimensionally using a computer program. RESULTS: In both male and female an omega-shaped external sphincter was apparent in all specimens at > 10 weeks of gestation. In the early fetal period (ninth week), there was undifferentiated mesenchyme; in this period the mesenchyme was more dense in the anterior part and loose in the posterior part of the urethra. In females, there was a close connection between the urethra and the anterior wall of the vagina. CONCLUSION: The omega-shaped configuration of the external urethral sphincter was recognisable from 10 weeks of gestation in both sexes. There was no suggestion of a change from a cylindrical to an omega-shaped sphincter in the fetal period to birth. Also, a transient 'tail' posterior to the sphincter was not apparent. The rectovesical septum was well developed in neonates. There is no reason to assume that the development of the septum leads to an apoptosis of muscle cells in the posterior part of the external sphincter in males after birth. The anatomical development of the external sphincter does not explain transient outlet obstruction during fetal life. The function of the muscle may change during development because of neuronal maturation.     

The relationship between external anal and external urethral sphincter activity in continent women

The relationship between the external anal sphincter and the periurethral sphincter muscles is an unresolved issue. Recordings of the external anal sphincter (EAS) are commonly used to indicate the responses of the urethral sphincter during urodynamic evaluations and in biofeedback procedures for the treatment of urinary incontinence. This study examined the validity of using anal sphincter training to teach control of the external urethral sphincter. Subjects were 5 continent women, aged 37–51 years, who reported being free of all urologic symptoms. Using visual biofeedback of anal sphincter pressure, subjects were trained to voluntarily contract the sphincter to four amplitudes: 5, 10, 15, and 20 mmHg (6.8, 13.6, 20.4, and 27.2 cmH₂O). Then they were guided through a series of controlled anal sphincter contractions, while the response of the urethral sphincter was measured using surface electrodes embedded in a Foley catheter. At each of four bladder volumes, subjects performed 16 contractions (four contractions at each of the four amplitudes). The order of contractions was counterbalanced, using a Latin square design. The results show a strong, statistically significant, monotonic relationship between the magnitude of anal sphincter contraction (pressure) and the level of urethral sphincter electromyographic (EMG) activity. The results support the use of the external anal sphincter as an indicator of urethral sphincter activity for the purpose of conducting biofeedback in the treatment of urinary incontinence.     

男性尿生殖膈的MRI与解剖对照研究

目的 探讨尿生殖膈MRI影像学的表现特点. 方法 选择4例健康男性尸体盆腔局部离断标本及15名健康男性志愿者,分别进行MRI检查,对照男性盆腔解剖切片与盆腔MRI扫描图像,在MRI图像中找到正常尿生殖膈结构. 结果 解剖标本显示尿生殖膈两侧附于耻骨下支和坐骨支,在前缘和后缘两层结构互相融合.断层切片显示尿生殖膈上筋膜及尿生殖膈下筋膜分别位于最上方和最下方,其间可见会阴深横肌.冠状位MRI影像表现为“三明治”样三层结构,并且可以显示其全程,三层结构显示清晰.15名志愿者采取同样方位及参数的MRI序列进行扫描,图像中尿生殖膈同样呈“三明治”样结构.10例行小视野T2WI及脂肪抑制序列扫描,与常规T2WI序列扫描比较,应用小视野T2WI及脂肪抑制序列可以更清晰地显示尿生殖膈的三层结构. 结论 常规MRI可以显示男性尿生殖膈结构,小视野扫描可以更清晰地显示其结构.     

Fatigue rate of the external anal sphincter

Aim Studies of skeletal muscle show that fatigue rate corresponds to the proportion of fast‐twitch and slow‐twitch fibres that are present in the muscle. Limited work has been done on the fatigue rate of the external anal sphincter. We have prospectively studied fatigability of the external anal sphincter in women with faecal incontinence and women with normal bowel control. Method Anorectal manometry was measured by a station‐pull technique using a water‐filled microballoon. Fatigue rate was calculated from anal pressure measurements taken every 0.1 s over a 20‐s squeeze. Results Women with faecal incontinence (n = 88, median ?12 cmH₂O/min) were less susceptible to fatigue than women with normal bowel control (n = 36, median ?43 cmH₂O/min) (P < 0.01). The external anal sphincter was less susceptible to fatigue with increasing age (P < 0.01, r = 0.499). In women with normal bowel control and in women with faecal incontinence fatigue rate was negatively correlated with maximum squeeze pressure (P < 0.01, r = ?0.287; P < 0.01, r = ?0.579). Conclusion The external anal sphincter was less susceptible to fatigue with increasing age. Women with faecal incontinence have a weaker but more fatigue‐resistant external anal sphincter. This might correspond to a higher proportion of slow‐twitch muscle fibres. Histological studies are needed to examine this hypothesis.     

Non-neurogenic neurogenic bladder: The relationship between intravesical pressure and the external sphincter electromyogram

We retrospectively reviewed the urodynamic studies of 14 patients: 3 males and 11 females, previously diagnosed clinically and urodynamically as having non-neurogenic neurogenic bladder. The mean age of the patients was 10 years (range 4–24 years). We identified 3 urodynamic features in this patient population that are distinct from those seen in patients with true detrusor-external sphincter dyssynergia: (1) quieting of the external sphincter electromyogram (EMG) immediately prior to the onset of a detrusor contraction, (2) quieting of the EMG during the upslope of a detrusor contraction, and (3) augmented EMG activity during the downslope of the detrusor contraction. Although both involve incoordinate bladder and pelvic floor/external sphincter activity, a simple cystometrogram with EMG may allow reliable differentiation between true detrusor-external sphincter dyssynergia and non-neurogenic neurogenic bladder.     

Histomorphological analysis of the urogenital diaphragm in elderly women: a cadaver study

The objective of this study was to describe the histomorphological structure of the urogenital diaphragm in elderly women using a modern morphometric procedure. Biopsies were taken from the posterior margin of the urogenital diaphragm of 22 female cadavers (mean age, 87 years) using a 60-mm punch. Hematoxylin/eosin and Goldner sections were analyzed with the Cavalieri estimator. The mean thickness of the urogenital diaphragm was 5.5 mm. The main component was connective tissue. All biopsies contained smooth muscle. Eighteen biopsies contained more smooth muscle than striated muscle. In six of 22 biopsies, no striated muscle was found. The ratio of striated to smooth muscle to connective tissue was 1:2.3:13.3. Muscle fibers were dispersed in all parts of the urogenital diaphragm. The urogenital diaphragm of elderly women mainly consists of connective tissue. Smooth muscle was also found but to a lesser extent. The frequently used English term “perineal membrane” for the urogenital diaphragm is justified and well describes our findings in elderly women.     

Electrically evoked activity in the human external anal sphincter

Following electrical stimulation of perianal skin, short latency evoked electromyographic (EMG) responses from the external and sphincter have been interpreted as the electrophysiological correlate of the anal reflex. Delayed responses in patients with idiopathic faecal incontinence have been interpreted as evidence for denervation of the external anal sphincter. Electrically evoked responses were studied in normal subjects, either before and during spinal anaesthesia (n = 8), or before and during competitive neuromuscular blockade (n = 4), instituted for operative purposes. Short latency responses persisted unchanged in either latency or duration during spinal anaesthesia whereas long latency responses were completely abolished. Both short and long latency responses were abolished during competitive neuromuscular blockade. Short latency responses are not spinal reflex in nature, but due to stimulus activation of alpha-motoneuronal terminal branches. Delayed responses in incontinent patients cannot be interpreted as evidence for pudendal neuropathy. Long latency (i.e. greater than 40 ms) responses demand a functional sacral spinal cord and represent the true anal reflex. Their wide range of latency in normal subjects suggests this measurement will be of little use in confirming the presence or absence of pudendal neuropathy, and that other measures of neuropathy may be more appropriate.     

Significance of electromyographic changes in the external urinary sphincter

The diagnostic role of electromyography of external urinary sphincter is well established in neurologically compromised patients. A brief historical review and methodology is described. For those who are not familiar with this modality, the character and clinical significance of abnormal potentials has been described. The coordination of bladder and sphincter mechanism and its abnormality is explained. Our experience with various neurological disorders is listed. It includes myelodysplasia, transverse myelitis, multiple sclerosis, herpes zoster, Parkinson disease, and some cerebral disorders. Any apparent statistical difference is due to the highly selected nature of the cases.     

Delayed external sphincter repair for obstetric tear

In some patients with faecal incontinence due to an obstetric tear of the external and sphincter there is additional weakness of the anal sphincter muscles from damage to the innervation of these muscles during delivery. Of 19 patients who required surgical repair of an obstetric sphincter tear some months or years after injury, 9 (47 per cent) had evidence of pudendal nerve damage at pre-operative anorectal physiological investigation. The result of surgical repair was excellent or good in eight of the ten patients in whom there was no evidence of nerve damage, while this was the case in only one of the nine patients with nerve damage. These results are significantly different (P = 0.018). Thus the functional result of delayed anal sphincter repair after obstetric lesions is partly dependent upon whether the nerve supply is intact. Pre-operative physiological evaluation can give information on the probability of a successful surgical result.