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Original Research |
1 Department of Radiology, Academic Medical Center, G1-228, Meibergdreef 9, 1105
AZ Amsterdam, The Netherlands.
2 Department of Clinical Epidemiology & Biostatistics, Academic Medical
Center, Amsterdam, The Netherlands.
3 Department of Colorectal Surgery, Academic Medical Center, Amsterdam, The
Netherlands.
4 Department of Colorectal Surgery, University Medical Center Utrecht, Utrecht,
The Netherlands.
Received September 12, 2006;
accepted after revision March 28, 2007.
Address correspondence to A. C. Dobben
(a.c.dobben{at}amc.uva.nl).
Abstract
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SUBJECTS AND METHODS. Thirty fecal incontinent patients with an EAS defect were included. The severity of incontinence was evaluated pre- and postoperatively using the Vaizey incontinence score. Patients underwent endoanal MRI and endoanal sonography before and after sphincter repair. We evaluated the association between preoperatively assessed EAS measurements with outcome and postoperatively depicted residual defects, atrophy, tissue at overlap, and sphincter overlap with clinical outcome.
RESULTS. After surgery, the mean Vaizey score in 30 patients (97% females; mean age, 50 years) had improved from 18 to 13 (p < 0.001). MRI showed that baseline measurement of preserved EAS thickness correlated with a better outcome (r =0.42; p = 0.03). Clinical outcome did not differ between patients with and those without a persistent EAS defect (p = 0.54) or EAS atrophy (p = 0.26) depicted on MRI. Patients with a visible overlap and less than 20% fat tissue had a better outcome than patients with nonvisible, fatty overlap (decrease in Vaizey score, 7 vs 2 points, respectively; p = 0.04). Sonography showed that patients with a persistent EAS defect had a worse outcome than those without an EAS defect (17 vs 10 points, respectively; p =0.003).
CONCLUSION. Endoanal MRI was useful in determining EAS thickness and structure, and endoanal sonography was effective in depicting residual EAS defects.
Keywords: anal sphincter repair • endoanal MRI • endoanal sonography • fecal incontinence • sphincteroplasty
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It is unclear why some patients with fecal incontinence do not benefit from EAS surgery. Hypotheses have pointed to postsurgical breakdown of the repair; scarring; pudendal neuropathy, related either to the initial injury or to the subsequent repair; and changes associated with aging [10]. The relationship between pudendal neuropathy, as measured by prolonged latency at pudendal nerve motor latency testing, and the outcome of anal sphincter repair is still controversial [10]. Endoanal MRI can depict EAS atrophy, so clinicians do not have to assume atrophy on the basis of only pudendal nerve latencies [11-13]. In one study [14], investigators found that extreme atrophy of the EAS detected on MRI was a predictor for poor outcome of anterior anal sphincter repair. Several other studies showed that postoperatively persistent EAS defects depicted on endoanal sonography were associated with a poor clinical outcome after anterior anal sphincter repair [15-18] and that patients may undergo a second or even third sphincter repair [19]. Ternent and colleagues [20] showed that the size of an EAS defect postoperatively determined using endoanal sonography significantly correlated with change in continence after sphincter repair.
Anorectal physiology tests can give us only a partial understanding of the origin of sphincter repair failures. Therefore, we wanted to further investigate the role of endoluminal imaging. We accordingly set up a study to investigate prospectively whether preoperative endoluminal imaging can identify factors that can be used to predict the outcome of sphincter repair and whether postoperative endoluminal imaging findings are associated with poor outcome.
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Inclusion criteria were fecal incontinence complaints for 6 months or longer; a Vaizey incontinence score of at least 12 [22]; and failure of conservative treatment based on standardized, specialized pelvic floor physiotherapy, dietary recommendations, or antidiarrhetics. The Vaizey score contains items about the type (gas, fluid, or solid) and frequency of fecal incontinence and additional items that address alterations in lifestyle, the need to wear a pad or plug, the use of constipating medications, and the presence of urge incontinence. The total Vaizey score ranges from 0 (complete continence) to 24 (complete incontinence).
Excluded were patients younger than 18 years, patients diagnosed with an
anorectal tumor less than 2 years earlier, patients with a previous ileoanal
or coloanal anastomosis, patients with chronic diarrhea (always fluid stools
3 times per day), overflow incontinence, proctitis, soiling (leakage of
fecal material out of the anus after normal defecation that led to perineal
eczema), and rectal prolapse. For the exclusion of patients with a rectal
prolapse, all patients underwent evacuation proctography.
Consecutive patients were included. In patients with a relevant EAS defect in whom physiotherapy had failed as an initial therapy, overlapping anterior anal sphincter repair was considered the next available treatment option. A relevant EAS defect was defined as an EAS defect in the axial plane of more than 1 hour depicted on endoanal MRI, endoanal sonography, or both. Excluded from surgery were patients with extreme generalized EAS atrophy detected on endoanal MRI [12, 14].
Endoluminal Imaging
Because the current endoluminal imaging techniques are endoanal sonography
and endoanal MRI, patients underwent both before and after surgery. The
results of each technique were compared with the findings at surgery. Surgery
acted as the reference standard for all patients, and the investigators
concluded that both imaging techniques can be used to depict surgically
repairable anterior EAS defects
[23].
Associations between patient age, the size of EAS defects, the thickness of EAS, atrophy, sphincter overlap, tissue at overlap, and the improvement or lack thereof after repair were evaluated.
Endoanal sonography—Endoanal sonography was performed on a sonography scanner using a radial endoscopic probe (7.5- or 10-MHz transducer) and a sonolucent plastic cone while the patient lay in the left lateral position with the knees bent at 90° [19, 24, 25]. The endoscopic probe was introduced into the anal canal, positioned at the upper aspect of the puborectalis sling, and slowly withdrawn until all levels perpendicular to the anal canal had been scanned.
The images were evaluated by one of four observers from different hospitals, all of whom are experts in the field with a considerable amount of experience in interpreting endoanal sonography images (i.e., 10-14 years).
The pre- and postoperative presence of an EAS defect, the extent of that defect, and the presence of atrophy were assessed.
An EAS defect preoperatively was defined as a discontinuity of the muscle ring (i.e., anatomic defect) or was characterized as the loss of normal architecture with an area of amorphous texture that usually had low reflectiveness (i.e., functional defect, scar tissue) [18].
A residual EAS defect postoperatively was defined as a complete hypoechogenic gap in the region of the repair with separated fibers of the EAS and no evidence of overlapping sphincters [17, 20] or as no decrease in the extent of the EAS defect compared with the defect depicted at baseline.
The extent and location of a defect were indicated in hours (1-12 hours) on a clock face using axial images. The orientation was as follows: the 12-o'clock position was anterior; 3 o'clock, left lateral; 6 o'clock, posterior; and 9 o'clock, right lateral.
Atrophy was judged on its reflection of the outer interface (i.e., border of EAS and subadventitial fat) and its reflection pattern and length.
Because EAS thickness cannot be accurately measured using conventional endoanal sonography due to the difficult delineation of the outer border of an EAS, sphincter thickness was evaluated only using endoanal MRI.
Findings were evaluated unblinded to patient outcome.
Endoanal MRI—Endoanal MRI was performed on a 1- or 1.5-T unit (Gyroscan ACS-NT, Philips Medical Systems; Horizon EchoSpeed, GE Healthcare) using a rectangular receive-only coil with a diameter of 19 mm [13, 19, 26, 27].
Scanning parameters were optimized for the MRI machines used on the basis of extensive previous experience. The following T2-weighted fast spin-echo sequences were used according to a standardized imaging protocol that was established during joint meetings: TR range/TE range, 2,500-3,500/70-90; echotrain length, 10; fields of view, 10 x 10 cm (axial) and 16 x 16 cm (coronal); imaging matrix, 256 x 512; 3-mm slice thickness; 0.3-mm interslice gap; and 2 excitations. Axial images and coronal images with a slice orientation perpendicular and parallel to the anal sphincter and endoanal coil were obtained.
Because this study concerns a pilot study identifying factors playing a role in surgical outcome, images were analyzed by just one reviewer; that reviewer is a highly experienced radiologist and is the most experienced reviewer available in evaluating abdominal MRI (12 years) and endoanal MRI (1,000 examinations).
The pre- and postoperative presence of an EAS defect, the extent of that defect, EAS thickness, and atrophy were assessed. In addition, the extent of sphincter overlap and the EAS structure were evaluated at a postoperative stage.
An EAS defect preoperatively was defined as a discontinuity of the muscle ring (i.e., anatomic defect) or was recognized by a hypointense deformation of the normal pattern of the muscle layer due to replacement of muscle cells by fibrous tissue (i.e., functional defect, scar tissue) [26, 28].
A residual EAS defect was defined as a full-thickness discontinuity of more than half of the anterior external sphincter or as no decrease in the extent of the EAS defect compared with the defect depicted at baseline.
The extent and location of a defect were indicated in hours (1-12 hours) on a clock face using axial images. The orientation was as follows: the 12-o'clock position was anterior; 3 o'clock, left lateral; 6 o'clock, posterior; and 9 o'clock, right lateral.
EAS thickness was measured (normal on endoluminal imaging = 4 mm) [29] anteriorly at the 12-o'clock position, at the right lateral (9-o'clock) position, and at the level of 1 cm superior to the anal verge. The 9-o'clock position was chosen because the most anterior EAS defects do not extend to 9 o'clock. The anterior postsurgical measurement included sphincter overlap. Longitudinal measurements of the anterior sphincter length (in millimeters) were also obtained in the axial plane by scrolling through the images calculating the total sphincter length, starting at the caudal sphincter to the cranial sphincter end (normal on endoluminal imaging: men, 27 mm; women, 15 mm) [29]. The longitudinal measurement was checked in the longitudinal plane when appropriate. The advantage of measuring the longitudinal dimension in the axial plane is that the axial plane is the most optimal plane for the identification of the inferior sphincter edge.
Atrophy was defined as thinning of the EAS or replacement of sphincter
muscle by fat [26,
28]. Subsequently, atrophy was
graded as none (no thinning or fat replacement), mild (< 50% thinning or
fat replacement [or both]), or moderate ( 50% thinning or fat replacement
[or both]).
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The postsurgical EAS structure was evaluated qualitatively by scoring percentages (by units of 10) of muscle, fat, and scar tissue at the level of the anterior sphincter overlap. Muscle was defined as tissue with low signal intensity and a structured orientation of fibers; fat, as high signal intensity; scar tissue, as very low signal intensity and disordered architecture [26].
The findings were evaluated unblinded to patient outcome.
Overlapping Anterior Anal Sphincter Repair
The decision to perform surgery was made by a participating surgeon based
on imaging findings (e.g., extent of the EAS lesion at endoanal imaging and
degree of sphincter atrophy), complementary clinical information (e.g.,
clinical examination and the severity of fecal incontinence), and findings
from anorectal physiology testing. Overlapping anterior anal sphincter repair
was performed as previously described
[30,
31] at eight participating
centers by one of eight experienced colorectal surgeons with 6-25 years'
experience in colorectal surgery.
After surgery, the severity of fecal incontinence was determined with the Vaizey incontinence score and endoluminal imaging was repeated, similar to the procedures at baseline.
Statistical Considerations
Changes in the Vaizey incontinence scores after surgery from baseline were
tested for significance using Wilcoxon's test for paired data.
The Mann-Whitney test was used to evaluate the association of factors with the outcome of surgery.
Spearman's correlation coefficients were used to evaluate the association between the size of an EAS defect and the change in the Vaizey score before and after surgery. Also, Spearman's correlation coefficient was used to determine any correlation between EAS measurements (thickness and length) before surgery and outcome of surgery; and between postsurgery EAS tissue structure (fat, scar, or muscle) and outcome of surgery on endoanal MRI.
For all statistical tests, a p value of less than 0.05 was considered to indicate statistical significance. We used SPSS (version 11.5, 2002; SPSS) for Windows (Microsoft) to perform statistical analysis of our data.
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The median interval between clinical assessment, preoperative imaging, and surgery was 10 months (range, 5-21 months). The follow-up period for clinical assessment ranged from 1 to 20 months (median, 4.7 months) after surgery and for imaging, from 3 to 18 months (median, 4.5 months) after surgery.
Clinical Outcome
The mean ± SD Vaizey score changed significantly after surgery from
18 ± 3 to 13 ± 6 (p < 0.001), resulting in a mean
improvement of 25% for all included patients. In 10 patients (33%), the Vaizey
score improved less than 5% or showed deterioration; in 13 patients (43%), the
Vaizey score improved 5-50%; and in seven patients (23%), it had improved more
than 50% (Fig. 1). The latter
were all patients without previous anorectal surgery in their medical history
in contrast to the other patients with minor improvement (seven of 13
patients) or those with no improvement (three of 10 patients).
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Imaging
Normal anatomy of the sphincter complex on endoanal sonography and endoanal
MRI is shown in Figures 2A and
2B.
Endoanal Sonography
Preoperative—There were 26 patients with an EAS defect
depicted on endoanal sonography. The size of the EAS defect was not associated
with clinical outcome (p = 0.79)
(Table 2). Neither mild nor
moderate generalized EAS atrophy was depicted on endoanal sonography.
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Postoperative—In 11 patients, endoanal sonography depicted a residual EAS defect (Fig. 3A). The postoperative Vaizey score was significantly worse in patients with a postoperative EAS defect compared with patients without an EAS defect (17 ± 4 vs 10 ± 6, respectively; p = 0.003). The size of a residual EAS defect after surgery was not significantly associated with the change in the incontinence score (p = 0.55) (Table 3). Endoanal sonography was not able to depict mild or moderate EAS atrophy.
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Endoanal MRI
Preoperative—Endoanal MRI depicted an EAS defect in 24
patients. The size of the EAS defect was not associated with clinical outcome
(p = 0.19).
There was no significant difference in change in the Vaizey score between patients with and those without generalized EAS atrophy (p = 0.15) or between patients with mild and moderate EAS atrophy depicted at baseline (p = 0.46) (Table 4).
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Postoperative—We had to exclude the postsurgery MR data of one patient from our analysis because of extensive susceptibility artifacts.
In 13 patients, endoanal MRI depicted a residual EAS defect (Fig. 3B). There was no significant difference in clinical outcome between patients with and those without a residual EAS defect (p = 0.54) or between patients with and those without EAS atrophy (p = 0.26). No significant difference could be found between patients with visible anterior sphincter overlap (Figs. 4A and 4B) compared with patients in whom sphincter overlap was not depicted (p = 0.46) (Table 5).
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EAS thickness and height had changed significantly from the baseline measurements to the postsurgery measurements (Table 6). Preserved EAS thickness at the 9-o'clock position was significantly correlated with a better surgical outcome (r = 0.42; p = 0.03; Fig. 5). None of the other sphincter measurements was associated with surgical outcome.
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There was no significant correlation between the amount of fat (r = 0.03), scar (r = 0.13), or muscle (r = 0.04) depicted at endoanal MRI and surgical outcome, as measured with the Vaizey score, unless sphincter overlap interacted with fat. Patients with clearly visible overlap and less than 20% fat tissue (n = 15) had a significantly better surgical outcome than patients (n = 10) with a fatty anterior EAS in whom overlap could not be visualized (mean ± SD decrease in Vaizey score, 7 ± 6 versus 2 ± 5 points, respectively; p = 0.04).
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Our results show that patients with a residual EAS defect depicted on endoanal sonography had a significantly worse clinical outcome at short-term follow-up after overlapping anterior anal sphincter repair. As other investigators have reported in many other studies [32, 33], we found that a persistent EAS defect on endoanal sonography was associated with a poor surgical outcome. In contrast to the results of earlier studies [20, 34], our results did not reveal a relation between the size of an EAS defect postoperatively depicted on endoanal sonography and the change of Vaizey fecal incontinent score after surgery.
Until now, denervation of the EAS muscle postoperatively has been determined by pudendal nerve terminal motor latencies [14, 20, 35-39]. In view of the lack of correlation between pudendal nerve terminal motor latencies, fiber density, and outcome, the use of neurophysiologic evaluation has been questioned [40]. A consequence of prolonged pudendal nerve latencies is EAS atrophy. Endoanal MRI is able to accurately depict EAS atrophy. The fact that we could not find a relation between postoperatively depicted atrophy and surgical failure contradicted our prior expectations. It is plausible that the exclusion from surgery of patients with extreme generalized atrophy narrowed the disease spectrum to such an extent that it was difficult to show that relation.
This study showed that advanced age ( 65 years) was associated with a
poor surgical outcome. The associations between age and the results of
sphincter repair have not been elucidated yet
[2]. Although in the literature
there is a trend toward younger patient age being associated with a favorable
outcome
[41-44],
the results of this study show a significant difference in outcome only when
patients are 65 years or older.
A number of potential limitations of this study should be considered. The depiction of residual EAS defects on endoanal MRI was insufficient. This deficiency can be explained by the lack of observer experience in evaluating postsurgical anatomy using endoanal MRI. Furthermore, there are no fixed diagnostic criteria for endoanal MRI to evaluate postsurgical status. In this pilot study, we evaluated postsurgical anatomy after a relatively short follow-up period (median follow-up, 4.5 months) because scar tissue may become very hypointense only 1-2 years after surgery. It is possible that scar tissue was incorrectly identified as muscle on MRI, thus leading to misdiagnosis of defects. We suggest performing a larger study with a longer follow-up period to improve our understanding of postsurgical scar tissue.
Clinical outcome was studied in terms of changes in the Vaizey incontinence score, which is a subjective measurement instrument. Assigning a grade to characterize the degree of fecal incontinence is difficult; several incontinence scoring systems have been developed [22, 45, 46]. The Vaizey score is the most complete scoring system [22, 47]. The results of a previous study showed that this scoring system is reproducible and correlates well with the physician's clinical impression [22, 48]. Despite this fact, subjective elements may have introduced bias or imprecision in evaluating surgical outcome.
Because this study was a pilot study, the patient group was small. Due to the limited number of patients, we must be careful in drawing conclusions. Both the MR images and sonography images were assessed by one observer. Consequently, no reproducibility data are available yet.
In conclusion, the results of our study showed that preoperatively performed endoluminal imaging findings might function as a potential predictor of surgical outcome and that certain postoperative findings on endoluminal imaging are associated with poor surgical outcome. Endoanal MRI is predominantly useful in determining EAS thickness and structure, and endoanal sonography is predominantly effective in the postoperative assessment for depiction of residual EAS defects. Probably the best cost-benefit ratio can be obtained by having patients undergo endoanal MRI preoperatively to evaluate for the presence of EAS defects, atrophy, and thickness, respectively, to select patients as candidates for surgery. At the postoperative stage, it is presumably most efficient to perform endoanal sonography only if surgery has failed. If available, endoanal sonography can be used to identify residual sphincter defects.
Additional research is needed to answer remaining questions about failure of anterior anal sphincter repair.
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