Chapter 1 Anorectal Anatomy: The Contribution of New Technology

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Chapter 1

Anorectal Anatomy: The

Contribution of New Technology

Andrew P. Zbar

Introduction

Recent imaging utilizing direct coronal and sagittal images, as well as recon- structed axial anatomical images, has largely clariﬁed the disposition of the sphincters in humans and the relevant gender differences (1,2). Despite these studies, there is no uniform consensus regarding their anatomic nomenclature (3). Recent attempts to incorporate matched images obtained by three-dimensional (3D) reconstructions of the anal canal with attendant level-orientated physiologic readings, where morphologically demonstrable and separable recognizable muscle groups have been equated with resting and squeeze contributions to recorded pressures (4), have provided results that are somewhat contradictory to manometric reports, particularly in what is represented by the anal high-pressure zone (5). In this chapter, an outline of basic anorectal embryology is provided, along with an anatomical description of the internal anal sphincter (IAS), external anal sphincter (EAS)–puborectalis complex, the longitudinal muscle, and the rectogenital septum of relevance to the colorectal surgeon based on anatomical dissections and recent imaging. The speciﬁc pharma- cology of the IAS as it pertains to proctologic practice may be found in Chapter 4.

Anorectal Embryology for the Adult Coloproctologist

A working knowledge by the adult coloproctologist of current concepts in

anorectal embryology permits an understanding of congenital anorectal

anomalies and their surgical aftermath. For the adult surgeon, description,

diagnosis, and management of neonates and young children with congeni-

tal anorectal anomalies appears confusing. Little is known about the genetic

and teratogenic inﬂuences on hindgut development, and this is com-

pounded by an incomplete knowledge concerning normal anorectal growth

and its interrelationship with the developing pelvic musculature and inner-

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vation. Recent advances in whole embryo scanning electron microscopy and immunostaining have permitted 3D reconstruction of hindgut struc- tures in well-established animal models, allowing their re-characterization and providing avenues for working classiﬁcations of the main types of anomalies (6).

Classical descriptions of the developing rectum have been based upon early independent work by Tourneux (7) and Retterer (8) towards the end of the last century that postulated the formation of a primitive cloaca sub- divided by a urorectal septum into an anterior urogenital sinus and a pos- terior anorectal tract (Figure 1.1). Caudal continuity with a proctodeal anlage was separable from the ectoderm by a cloacal membrane whose abnormal development was believed to result from either craniocaudad arrest (resulting in some variant of anal/anorectal agenesis or an imperfo- rate anal membrane) or a disturbance in lateral fusion (producing an H- type complex rectourinary ﬁstula between the blind-ending rectal pouch and some portion of the urinary tract). Although the cloacal concept is useful in practical deﬁnition of low anomalies in the female (9), this sim- plistic view has been challenged by detailed studies largely performed in pig embryos with a high hereditary expressivity of anorectal malformations resembling those observed in humans (10). This misunderstanding about

Allantois

Cloacal Membrane

4mm Embryo Stage (4 weeks)

Hindgut

Trigone

Renal Blastema

Ureteric Bud 70mm Embryo Stage (male)

(12 weeks) Wolffian

Duct

Figure 1.1. Traditional concepts in cloacal development. (Left) At the 4-week stage, a common cloaca incorporates the allantois, hindgut, and Wolfﬁan ducts. The cloacal membrane joins the ectodermal edge and separation of the urorectal septum pro- ceeds in the craniocaudal and lateral directions. (Right) By the 12th week, the bladder and rectum are separated by the urorectal septum. The distal Wolfﬁan duct atrophies and the ureteric bud fuses with its contralateral partner to form the trigone (male). In the female, the Mullerian ducts intervene and fuse in a craniocaudal direction. The formed sinovaginal bulb represents the distal vaginal vault. In the male, these ducts atrophy and persist as the utriculus masculinus.

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the nature of the cloacal membrane and the urorectal septum has been com- pounded by the traditional concept originally proposed by Bill and Johnson that the rectum and anal anlage tends to migrate backwards relatively late in the course of embryonic growth (11). This view purported to explain the observed anal ectopia in both sexes, as manifested by the covered anus, perineal anus, and anocutaneous ﬁstula in the male and the anovestibular ﬁstula in the female. These anomalies present in association with a normally disposed sphincter complex and are dealt with satisfactorily via a perineal approach with excellent long-term functional outcomes. This traditional view of anorectal embryology provided a basic division of anomalies into high, intermediate, and low dependent upon their relationship to the levator plate and into those either communicating or not communicating with the genitourinary tract.

What has become evident from the work of van der Putte (10) and Kluth and Lambrecht (6) is that there is no embryological evidence of such a dorsal shift in the anal anlage, but rather a ventral outgrowth of the cloacal membrane (with a failure of normal posterior membrane development), as well as an impairment in the movement of the membrane from a vertical to a horizontal orientation (Figure 1.2). This “new” description has resulted

Hindgut Ureter

Wolffian Duct

Cloacal Membrane UR

X

Figure 1.2. Newer concepts in disposition of the cloacal membrane. The cloacal membrane re-orientates to a horizontal disposition with ventral outgrowth (movement by arrows of the dotted line). This pushes the anal anlage posteriorly at its ﬁxed point (marked as X), provided that the dorsal cloaca develops normally. The urorectal septum (UR) moves downward to separate the hindgut from the urogenital sinus.

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from the work of these groups using whole embryo scanning electron microscopy at different stages of gestation for on-line 3D assessment. Both studies failed to show either lateral septation of the cloacal elements or dorsal anal migration, as previously described (12,13). This work has been assisted by the presence of characterized animal models of anorectal mal- formations, most notably the Danforth SD-mouse mutant, which carries a gene affecting tail, rectal and urogenital development, and which pheno- typically demonstrates a range of anorectal anomalies that bear a striking resemblance to those observed in pigs and humans (14–16). This model has been re-examined recently using the new whole-embryo techniques (17).

In summary, improved genetic understanding of anorectal deformities will occur through mutational analyses of candidate loci in patients with recog- nizable syndrome complexes or co-existent dysganglionoses. New whole- embryo immunostaining and scanning has provided a different view of cloacal membrane development as the primary abnormality in many cases and has highlighted the inadequacy of conventional concepts of hindgut embryology as they pertain to observable categories of human anorectal malformations. Consequently, no simple classiﬁcation system for anorectal anomalies based upon embryological considerations currently exists (18).

The Internal Anal Sphincter

Historically, there have been many conﬂicting anatomical reports of the

IAS and its relationship to the EAS. Prior to 1950, it was believed that the

IAS was the main contributing inﬂuence to resting continence, although

subsequently it had been suggested that preservation of the EAS was crit-

ical in the maintenance of overall continence (19,20). Resting pressure

analyses in human subjects during general and spinal anesthesia indepen-

dently conducted by Duthie, Ihre, and von Euler had shown that the IAS

is the main contributor to resting anorectal pressure (21–23). Only recently

has it has become evident that IAS division or damage by itself may be

associated with troublesome soiling (24), and this ﬁnding may be allied to

those studies that have shown that resting anal function, anorectal sampling

(the ability to differentiate between ﬂatus and ﬂuid), and the presence of

the IAS-driven rectoanal inhibitory reﬂex (RAIR) are all impaired follow-

ing low anterior resection and coloanal anastomosis where there is exten-

sive endoanal manipulation (25). The restoration of both the anorectal

sampling mechanism and the return of the RAIR both correlate with clin-

ical improvement in functional outcome and less nocturnal incontinence

and urgency after this type of restorative rectal resection (26). In this

regard, incontinence has been shown to occur (although not be strictly pre-

dictable) after isolated IAS injury (27), with inherent differences in basal

IAS manometry and sphincter graphics in those patients prospectively fol-

lowed through their internal anal sphincterotomy for topically resistant

anal ﬁssure where differences were represented in those who remained

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continent and those who became incontinent based entirely on their IAS manometric pattern (5,28). Moreover, the inherent parameters of the RAIR (an IAS function) appear to be different in those patients with dif- ferent anorectal disorders (29–31) whereby a more rapid recovery is demonstrable in those cases where there is already fecal incontinence and EAS atrophy, implying that IAS function itself may differentially contribute towards continence defense where continence is already compromised.

Recently, endoanal ultrasound (US) [as well as magnetic resonance imaging (MRI)] has clariﬁed the expected age and gender variations of the IAS, as well as the IAS/EAS, disposition in what may be regarded as the constitutive overlap of these sphincter components (32). This effect has proved of clinical relevance where it has been shown in some patients that there is such poor constitutive overlap, particularly in chronic anal ﬁssure.

In these cases, injudicious internal anal sphincterotomy may render the distal anal canal relatively unsupported, leading to predictable postopera- tive leakage (33).

Although there are no longitudinal studies, there is ample evidence to show morphological increases in the IAS thickness with age, probably asso- ciated with degeneration in the muscle component and its replacement with ﬁbrous tissue (34). This effect has been equated with the development of passive leakage consequent upon isolated IAS degeneration (35). Although the exact morphological interrelationship between the IAS and the other sphincter musculature in health and disease remains to be determined, direct comparisons between endoluminal US and MRI cannot strictly be made because both modalities variably identify the intersphincteric space and US appears less capable of deﬁning the outer extremity of the EAS muscle.An overall greater IAS dimension determined by US may be indica- tive of the relationship of the IAS to variable components of the longitu- dinal muscle (vide infra, 36).

Overall, the physiological and clinical signiﬁcance of IAS integrity is increasingly being recognized, where all attempts are made to preserve the muscle by avoidance of excessive anal distraction, particularly in patients where continence is already compromised (37,38). This view recently has carried over to deliberate IAS preservation in anorectal surgery where normally the IAS is deliberately destroyed, most notably in high trans- sphincteric ﬁstula-in-ano, where resting pressures and continence appear to be maintained when cutting setons are rerouted through the intersphinc- teric space for attendant EAS division with concomitant IAS repair (39).

The External Anal Sphincter

Recent endoluminal imaging has clariﬁed the widely held view that the

EAS is represented by a three-tiered structure (1,40,41). This view owes

much to the original anatomical descriptions of the subcutaneous, superﬁ-

cial, and deep components of the EAS as espoused by Riolan and Santorini

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(42,43) and by von Holl (44), Milligan and Morgan (45), and Gorsch (46).

These new imaging modalities have permitted the abandonment of confusing systems of bi-tiered anatomical configurations as reported by Courtney (47), Fowler (48), and Wilson (49), as well as more recent often- quoted expositions (50). This also has cast doubt on the more controversial models of interconnecting muscle loops as proffered by Shafik (51). Some of the confusions of the component muscle parts of the EAS have arisen as a result of descriptions of encasing fascia that extended laterally and that are inserted into the perianal skin, a point of some importance in defining and classifying the spread and presentations of perirectal infections (52).

However, this area still requires considerable work because both endoanal and transvaginal imaging have failed to delineate adequately the anatomi- cal composition of the perineal body (53), a difﬁculty that may account for variation in the reported incidence of anterior postobstetric anal EAS defects following vaginal delivery (54). The “misimpression” provided by conventional unreconstructed endoanal ultrasonography of a shorter anterior EAS in women has resulted in a more complex and sophisticated view of a greater relative physiological contribution by the posterior puborectalis muscle. Given that there is a clear plane of cleavage between these two muscle entities (namely the puborectalis and the deep compo- nent of the EAS; 55), this area needs to be revisited in the dissecting room (56,57).

The Longitudinal Muscle and Distal Anal Supporting Structures

There is remarkably little data concerning the disposition of the anal lon- gitudinal muscle. It is evident during intersphincteric rectal dissection and has been demonstrated by routine endoanal ultrasonography (58) and endoanal MRI (59). This muscle is in direct contiguity with the outer muscle coat of the rectum and has been variously reported as supplemented by stri- ated musculature derived from the levator ani (45,60), the puboanalis (61), and the pubococcygeus (62), as well as by the levator muscle fascia (47,63).

The complexity of the intersphincteric musculofibrous contribution and the way it splits to attach to the perianal skin has formed the basis of Shafik’s classification of attendant perianal spaces and has given rise to his complex classification of perirectal sepsis (64).

The medial and lateral extensions of these bands and contributions

abound in a series of historical eponyms that are used in various texts. Com-

munications between the submucosal and intersphincteric planes have been

described (65,66), being labeled by Milligan and Morgan as the anal inter-

muscular septum, limiting the spread of rectal infection to the inferior ter-

mination of the IAS, as well as surrounding the lowermost border of the

subcutaneous portion of the EAS muscle (45). These fascial bands were

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considered of some clinical importance both in the understanding of the spread of perirectal infection and in their classification, being labeled by Parks as the mucosal suspensory ligament that medially confined the ductal system of the anal glands (and crypts) and that inferolaterally separated the perianal from the ischiorectal space (67–70). Extensions of this musculo- fascial band have been described as running submucosally for variable dis- tances, independently being labeled as the musculis canalis ani (71), Treitz’s muscle (72), the sustentator tunicae mucosae (73), and the musculus sub- mucosæ ani (74,75). Lateral extensions of the longitudinal muscle have been described by Courtney (47) as encircling the urethra and contributing to the rectourethralis muscle as the most medial fibers of the levator ani complex (76–78). This muscle is a principal landmark in the anterior aspect of the rectal dissection during perineal proctectomy by angulating the rectum, where division of the right and left columns of the rectourethralis muscle permits the rectum to fall backwards, protecting the prostate (or vagina) from inadvertent injury. The most caudal extensions of these fibers extend to the skin in a variably reported way, enclosing the perianal space and separating it from the ischiorectal fossa, with formation of the corru- gator cutis ani muscle bands extending into the perianal skin. This latter muscular component originally described by Ellis (79) has been attributed as part of the panniculus carnosus, and its existence in many cases has been questioned (48).

The Rectovaginal Septum

There has been a long-standing debate concerning the existence and

integrity of the rectovaginal septum. Several early anatomical studies, which

were entirely histologic in nature (where there were no correlative anatom-

ical dissections), were unable to deﬁne its presence (80,81). These fre-

quently quoted studies have been contradicted by the fetal and adult

cadaveric work of Uhlenluth et al. (82,83) and Nichols and Milley (84,85),

who were able to identify a deﬁnitive anatomic and histologic fascial struc-

ture between the rectum and the vagina in all dissections. More recently,

Fritsch and colleagues, revisiting this area using transparent plastinated

fetal and adult pelvic specimens with sectional radiographic [computed

tomography (CT) and MR] correlations, also were unable to demonstrate

visceral fasciae surrounding the pelvic organs (86–89), suggesting that the

disposition of pelvic connective tissue and the designation of potential

pelvic spaces bound by visceral and parietal pelvic fascia are actually less

complicated than previously reported in classical textbooks of anatomy and

embryology (90–93). Very recent comparative fetal and adult dissections by

Fritsch and her team speciﬁcally addressing the rectovaginal septum have

conﬁrmed its presence in plastinated specimens, showing it to be completely

developed in the newborn (94–98).

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These early studies recently have been confirmed by the cadaveric work of DeLancey, who showed the fibers of the rectovaginal septum running ver- tically and blending with the muscular wall of the vagina. He has suggested a multifaceted posterior vaginal support reliant upon the endopelvic fascia, levator ani muscle, and perineal membrane. Distally, the perineal membrane fibers are effectively horizontal and become parasagittal in the mid vagina, connecting the vaginal channel to the pelvic diaphragm. It has been sug- gested that these structures may become important in vaginal support in the pelvis if the main levator muscle is damaged or denervated (99,100).

Anatomically, it is believed that the rectovaginal septum represents the female analogue of the male rectovesical fascia first described by Denonvilliers in 1836 (101–105). The surgical importance of this fascia was first recognized by Young during radical perineal prostatectomy for cancer as a surgical landmark for urologists (106). Its anatomy was confirmed inde- pendently at the turn of the century by Cuneo and Veau (107) and Smith (108) and has been re-highlighted extensively in the dissection of the extraperitoneal rectum for rectal cancer. Recently our group has used macroscopic dissections on embalmed human pelves and plastination his- tology in both fetal and newborn pelvic specimens, showing that the recto- genital septum is formed by a local condensation of mesenchymal connective tissue during the early fetal period and that the longitudinal muscle bundles can be traced back to the longitudinal layer of the rectal wall. Immunohistochemical staining methods using mono- and polyclonal antibodies for tissue analysis and neuronal labeling (most notably PGP 9.5, S-100, Substance P, and Choline acetyl transferase) has revealed that auto- nomic nerve fibers and ganglia appear to innervate these muscle cells, sug- gesting that parasympathetic co-innervation of both the rectal muscle layers and the adjacent longitudinal muscle fibers of the septum is relevant in the function between the two structures and that the rectogenital septum has intrinsic sensory innervation that might be important in rectal filling and asymmetric rectal distension (109).

In recent years, Richardson has called attention to the presence of

“breaks” within this septum that are anatomically evident using a trans-

vaginal approach to rectocele repair, highlighting the importance of what

he has described as “defect-speciﬁc” rectocele repairs (110,111). In this

sense, although short-term follow-up data is coming out in the literature of

such repair types for symptomatic rectocele, it really represents a gyneco-

logical “rediscovery” of the importance of defect-speciﬁc repair, which has

been the cornerstone of the endorectal route (as advocated by the colo-

proctological fraternity) for many years. In Richardson’s cadaveric and clin-

ical operative work, he has described a taxonomy of fascial breaks, with the

most common type appearing as a transverse posterior separation above

the attachment of the perineal body, resulting in a low rectocele. The most

recent work assessing the ultrastructural anatomy of the rectogenital

septum, as described above, shows that this septum is formed within a local

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condensation of collagenous ﬁbers from the beginning of the fetal period as early as the 9

^th

week. In plastination studies, it has been found that the tissue components of the rectogenital septum in both sexes are not deriva- tives of any fascial structures demonstrable at any developmental stage that have undergone fusion either from the lateral pelvic wall or from the peri- toneal pouch. Instead, it is suggested that they result more from an anatomic separation between the rectum and the bladder and prostate in men and the rectum and the vagina in women, where longitudinal muscle bundles can be found both within the rectogenital septum extending to and inter- mingling with the anal sphincter musculature and terminating in the per- ineal body in both sexes. This is of clinical and operative signiﬁcance because this component of the levator ani complex (namely the rec- tourethralis muscle) is an important landmark in the anterior perineal dis- section of the rectum during abdominoperineal resection, where it tethers and angulates the rectum against the membranous urethra (vide supra, 78).

Conclusions

An improved understanding of rectal and anal canal anatomy has resulted from advances in coronal and sagittal modality imaging in vivo, as well as from ultrastructural whole-image work and fetal and adult plastination (112). This improvement in anatomical deﬁnition has re-highlighted the clinical importance of the IAS as a central component in the maintenance of continence and has shown the signiﬁcance of the rectogenital septum repair in low and mid rectocele (113).

References

1. deSouza NM, Puni R, Zbar A, Gilderdale DJ, Coutts GA, and Krausz T. MR imaging of the anal sphincter in multiparous females using an endoanal coil:

correlation with in vitro anatomy and appearances in fecal incontinence. AJR Am J Roentgenol. 1996;167:1465–71.

2. Gold DM, Bartram CI, Halligan S, Humphries KN, Kamm MA, and Kmiot WA. Three-dimensional endoanal sonography in assessing anal canal injury. Br J Surg. 1999;86:365–70.

3. Zbar AP and Kmiot WA. Anorectal investigation. In: Phillips RKS, editor. A companion to specialist surgical practice—Colorectal surgery. 1st ed. London:

W.B. Saunders Company Ltd; 1998. p. 1–32.

4. Williams AB, Cheetham MJ, Bartram CI, Halligan S, Kamm MA, Nicholls RJ, and Kmiot WA. Gender differences in the longitudinal pressure proﬁle of the anal canal related to anatomical structure as demonstrated by three- dimensional anal endosonography. Br J Surg. 2000;87:1674–9.

5. Zbar AP, Beer-Gabel M, Chiappa AC, and Aslam M. Fecal incontinence after minor anorectal surgery. Dis Colon Rectum. 2001;44:1610–23.

6. Kluth D and Lambrecht W. Current concepts in the embryology of anorectal malformations. Semin Pediatr Surg. 1997;6(4):180–6.

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7. Tourneux F. Sur le premiers developments du cloaque du tubercle genitale et de l’anus chez l’embryon moutons avec quelques remarques concernant le development des glandes prostatiques. J Anat Physiol. 1888;24:503–17.

8. Retterer E. Sur l’origin et de l’evolution de la region ano-genitale des mam- miﬁeres. J Anat Physiol. 1890;26:126–210.

9. Stephens FD. Embryology of the cloaca and embryogenesis of anorectal malformations. In: Stephens FD and Durham-Smith E, editors. Anorectal malformations in children: Update. New York: Alan R Liss Inc.; 1988. p. 177–209.

10. Van der Putte SCJ. Normal and abnormal development of the anorectum.

J Pediatr Surg. 1986;21(5):434–40.

11. Bill AH and Johnson RJ. Failure of migration of the rectal opening as the cause for most cases of imperforate anus. Surg Gynecol Obstet. 1958;106:643–51.

12. Ikebukuro K-I and Ohkawa H. 3-dimensional analysis of anorectal embryology. A new technique for microscopic study using computer graphics. Pediatr Surg Int. 1994;9:2–7.

13. Kluth D, Hiller M, and Lambrecht W. The principles of normal and abnormal hindgut development. J Pediatr Surg. 1995;30:1143–7.

14. Danforth CH. Developmental anomalies in a special strain of mice. Am J Anat.

1930;45:275–87.

15. Dunn LC, Gluecksohn-Schoenheimer S, and Bryson V. A new mutation in the mouse affecting spinal column and urogenital system. J Hered. 1940;31:343–8.

16. Gluecksohn-Schoenheimer S. The morphological manifestation of a dominant mutation in mice affecting tail and urogenital systems. Genetics. 1943;28:341–8.

17. Kluth D, Lambrecht W, Reich P, et al. SD-mice—an animal model for complex anorectal malformations. Eur J Pediatr Surg. 1991;1:183–8.

18. Hassink EA, Riev PN, and Severijnen RS. Are adults content or continent after repair for high anal atresia? Ann Surg. 1993;218:196–2000.

19. Gaston E. Physiological basis for preservation of fecal continence after resection of the rectum. JAMA. 1952;146:1486–9.

20. Hollinshead H. Anatomy for surgeons, Vol 2. Thorax, abdomen and Pelvis. 2nd ed. New York: Harper & Row; 1971. p. 708–9.

21. Duthie HL and Watts J. Contribution of the external anal sphincter to the pressure zone in the anal canal. Gut. 1965;6:64–8.

22. Ihre T. Studies on anal function in continent and incontinent patients. Scand J Gastroenterol. 1974;9 Suppl 25:1–64.

23. Frenckner B, von Euler B. Inﬂuence of pudendal block on the function of the anal sphincters. Gut. 1975;16:482–9.

24. Lund JN and Scholeﬁeld JH. Aetiology and treatment of anal ﬁssure. Br J Surg.

1996;83:1335–44.

25. Lewis WG, Williamson ME, Miller AS, Sagar PM, Holdsworth PJ, and Johnston D. Preservation of complete sphincteric proprioception in restorative proctocolectomy: the inhibitory reﬂex and ﬁne control of continence need not be impaired. Gut. 1995;36:902–6.

26. Tuckson W, Lavery I, Fazio VW, Oakley J, Church J, and Milsom J. Manomet- ric and functional comparison of ileal pouch anal anastomosis with and without anal manipulation. Am J Surg. 1991;161:90–6.

27. Abbasakoor MG, Nelson M, Beynon J, Patel B, and Carr ND. Anal endosonography in patients with anorectal symptoms after haemorrhoidectomy. Br J Surg. 1998;85:1522–4.

(11)

28. Zbar AP, Aslam M, and Allgar V. Faecal incontinence after internal sphincterotomy for anal ﬁssure. Tech Coloproctol. 2000;4:25–8.

29. Zbar AP, Aslam M, Gold DM, Gatzen C,Gosling A, and Kmiot WA.

Parameters of the rectoanal inhibitory reﬂex in patients with idiopathic fecal incontinence and chronic constipation. Dis Colon Rectum. 1998;41:200–

8.

30. Kaur G, Gardiner A, and Duthie GS. Rectoanal reﬂex parameters in incontinence and constipation. Dis Colon Rectum. 2002;45:928–33.

31. Zbar AP and Jonnalagadda R. Parameters of the rectoanal inhibitory reﬂex in different anorectal disorders. Dis Colon Rectum. 2003;46:557–8.

32. Sultan AH, Kamm MA, Hudsson CN, Nicholls JR, and Bartram CI.

Endosonography of the anal sphincters: normal anatomy and comparison with manometry. Clin Radiol. 1994;49:368–74.

33. Zbar AP, Kmiot WA, Aslam M, Williams A, Hider A, Audisio RA, Chiappa AC, and deSouza NM. Use of vector volume manometry and endoanal magnetic resonance imaging in the adult female for assessment of anal sphincter dysfunction. Dis Colon Rectum. 1999;42:1411–8.

34. Burnett SJD and Bartram CI. Endosonographic variations in the normal internal anal sphincter. Int J Colorectal Dis. 1991;6:2–4.

35. Vaizey CJ, Kamm MA, and Bartram CI. Primary degeneration of the internal anal sphincter as a cause of passive faecal incontinence. Lancet. 1997;

349:612–5.

36. Schafer A, Enck P, Furst G, Kahn T, Frieling T, and Lubke HJ. Anatomy of the anal sphincters: comparison of anal endosonography to magnetic resonance imaging. Dis Colon Rectum. 1994;37:777–81.

37. Sangwan YP and Coller JA. Internal anal sphincter: advances and insights. Dis Colon Rectum. 1998;41:1297–1311.

38. Zbar AP, Jayne DG, Mathur D, Ambrose NS, and Guillou PJ. The importance of the internal anal sphincter (IAS) in maintaining continence: anatomical, physiological and pharmacological considerations. Colorectal Dis. 2000;

2:193–202.

39. Zbar AP, Salazar R, Ramesh J, and Pescatori M. Conventional cutting versus internal anal sphincter-preserving seton for high trans-sphincteric ﬁstula: a prospective randomized manometric and clincal trial. Tech Coloproctol. In press 2003.

40. Zbar AP. Magnetic resonance imaging and the coloproctologist. Tech Colo- proctol. 2001;5:1–7.

41. Kmiot WA, Zbar AP, and deSouza NM. MRI in anorectal disease. In: Nicholls RJ and Dozois RR, editors. Surgery of the colon and rectum. New York:

Churchill Livingstone. p. 68–98.

42. Riolan J. Anatomia 162 (1577–1657). As quoted in Dalley AF. The riddle of the sphincters: the morphophysiology of the anorectal mechanisms reviewed. Am Surgeon. 1987;53:298–306.

43. Santorini GD. Septum decum tabulae edit et explicit. Parone: Mich. Gerardi.

1715;tabula 15.

44. von Holl M. Handbuch der anatomie des menchen von Bardeleben. 1897;7 book 2, section 7.

45. Milligan ETC and Morgan CN. Surgical anatomy of the anal canal with special reference to ano-rectal ﬁstulae. Lancet. 1934;2:150–6, 1213–7.

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46. Gorsch RV. Proctologic anatomy. 2nd ed. Baltimore (MD): Williams & Wilkins;

1955.

47. Courtney H. Anatomy of the pelvic diaphragm and anorectal musculature as related to sphincter preservation in anorectal surgery. Am J Surg.

1950;79:155–73.

48. Fowler R. Landmarks and legends of the anal canal. Aust N Z J Surg.

1957;27:1–8.

49. Wilson PM. Anchoring mechanisms of the anorectal region. S Afr Med J.

1967;41:1127–32, 1138–43.

50. Oh C and Kark AE. Anatomy of the external anal sphincter. Br J Surg.

1972;59:717–23.

51. Shaﬁk A. A new concept of the anatomy of the anal sphincter mechanism and the physiology of defecation. I. The external anal sphincter: a triple loop system. Invest Urol. 1975;13: 412–9.

52. Milligan ETC. The surgical anatomy and disorders of the perianal space. Proc R Soc Med. 1942;36:366–78.

53. Frudinger A, Bartram CI, and Kamm MA. Transvaginal versus anal endosonography for detecting damage to the anal sphincter. AJR Am J Roentgenol. 1997;168:1435–8.

54. Bollard RC, Gardiner A, Phillips K, and Duthie GS. Natural gaps in the female anal sphincter and the risk of postdelivery sphincter injury. Br J Surg. 1999;86 Suppl 1:50–1(A).

55. Fucini C, Elbetti C, and Messerini L. Anatomical pnae of seperation between the external anal sphincter and puborectalis muscle: clinical implications. Dis Colon Rectum. 1999;42:374–9.

56. Bogduk N. Issues in anatomy: the external anal sphincter revisited. Aust N Z J Surg. 1996;66:626–9.

57. Zbar AP and Beer-Gabel M. Gender differences in the longitudinal pressure proﬁle of the anal canal related to anatomical structure as demonstrated on three-dimensional anal endosonography. Br J Surg. 2001;88:1016.

58. Bartram CI and Frudinger A. Handbook of endoanal endosonography.

Petersﬁeld, UK: Wrightson Biomedical Publishing; 1997.

59. Zbar AP and deSouza NM. The anal sphincter. In: deSouza, editor. Endo- cavitary MRI of the pelvis. The Netherlands: Harwood Academic Publishers;

2001. p. 91–109.

60. Cruvelhier H. Traite d’anatomie descriptive. Paris: Labe; 1852.

61. Lawson JON. Pelvic anatomy. I. Pelvic ﬂoor muscles. Ann R Coll Surg Engl.

1974;54:244–52.

62. Shaﬁk A. A new concept of the anatomy of the anal sphincter mechanism and the physiology of defecation. III. The longitudinal anal muscle: anatomy and role in sphincter mechanism. Invest Urol. 1976;13:271–7.

63. Ayoub SF. The anterior ﬁbres of the levator ani muscle in man. J Anat.

1979;128:571–80.

64. Shaﬁk A. A new concept of the anatomy of the anal sphincter mechanism and the physiology of defecation. IV. Anatomy of the perianal spaces. Invest Urol.

1976;13:424–8.

65. Rudinger N. Topographisch chirurgische Anatomie des Menschen. Stuttgart:

JG Cotta;1878. p. 111–2.

66. Roux C. Contribution to the knowledge of the anal muscles in man. Arch Mikr Anat. 1881;19:721–3.

(13)

67. Parks AG. A note on the anatomy of the anal canal. Proc R Soc Med.

1954;47:997–8.

68. Wilde FR. The anal intermuscular septum. Br J Surg. 1949;36:279–85.

69. Lunniss PJ and Phillips RKS. Anatomy and function of the anal longitudinal muscle. Br J Surg. 1992;79:882–4.

70. Gerdes B, Kohler HH, Stinner B, Barth PJ, Celik I, and Rothmund M. The longitudinal muscle of the anal canal. Chirug. 1997;68:1281–5.

71. Hansen HH. Die Betendung des Musculus canalis ani für die Kontinenz und anorectale Erkrangungen. Langenbecks Arch Chir. 1976;341:23–7.

72. Treitz W. Uber Einen neuen Muskel am Doudenum des Menschen, uber elastische Sehnen, und einige andere anatomische Verhaltuisse. Viertal- Jahrschrift für die praktische Heilkunde. 1853;37:113–44.

73. Levy E. Anorectal musculature. Am J Surg. 1936;34:141–98.

74. Fine J and Wickhma Lawes CH. On the muscle ﬁbres of the anal submucosa, with special reference to the pectin band. Br J Surg. 1940;27:723–7.

75. Haas PA and Fox TA. The importance of the perianal connective tissue in the surgical anatomy and function of the anus. Dis Colon Rectum. 1977;20:303–13.

76. Morgan CN and Thompson HR. Surgical anatomy of the anal canal with special reference to the surgical importance of the internal sphincter and con- joint longitudinal muscle. Ann R Coll Surg Engl. 1956;19:88–114.

77. Goligher JC. Surgery of the anus, rectum and colon. 4th ed. London: Baillière Tindall; 1980. p. 7–20.

78. Brooks JD, Eggener SE, and Chao W-M. Anatomy of the rectourethralis muscle. Eur Urol. 2002;41:94–100.

79. Ellis GV. Demonstrations of anatomy. 8th ed. London: Smith Elder; 1878.

p. 420.

80. Goff BH. Histological study of the perivaginal fascia in nullipara. Surg Gynecol Obstet. 1931;52:32–42.

81. Ricci JV and Thom CH. The myth of a surgically useful fascia in vaginal plastic reconstructions. Q Rev Surg Obstet Gynecol. 1954;11:253–61.

82. Uhlenluth E, Wolfe WM, Smith EM, and Middleton EB. The rectovaginal septum. Surg Gynecol Obstet. 1948;86:148–63.

83. Uhlenluth E and Nolley GW. Vaginal fascia,a myth? Obstet Gynecol.

1957;10:349–58.

84. Milley PS and Nichols DH. A correlative investigation of the human rectovaginal septum. Anat Rec. 1969;163(3):443–51.

85. Nichols DH and Milley PS. Surgical signiﬁcance of the rectovaginal septum.

Am J Obstet Gynecol. 1970;15:215–20.

86. Fritsch H. The connective tissue sheath of uterus and vagina in the human female fetus. Ann Anat. 1992;174:261–4.

87. Fritsch H. Topography and subdivision of the pelvic connective tissue in human fetuses and in the adult. Surg Radiol Anat. 1994;16:259–65.

88. Fritsch H and Hotzinger H. Tomographical anatomy of the pelvis, visceral pelvic connective tissue and its compartments. Clin Anat. 1995;8:17–24.

89. Fröhlich B, Hötzinger H, and Fritsch H. Tomographical anatomy of the pelvis, pelvic ﬂoor, and related structures. Clin Anat. 1997;10:223–30.

90. Kocks J. Normale und Pathologische Lage und Gestalt des Uterus Sowie Deren Mechanik, Bonn: Cohen; 1880. p. 1–60.

91. Thompson P. On the arrangement of the fasciae of the pelvis and their relationship to the levator ani. J Anat Physiol. 1901;35:127–41.

(14)

92. Pernkopf E. Topograﬁsche Anatomie. Bd 2, 1. und 2. Hälfte. Berlin: Urban and Schwarzenberg; 1941. p. 191–7, 513–23.

93. Courtney H. Anatomy of the pelvic diaphragm and anorectal musculature as related to sphincter preservation in anorectal surgery. Am J Surg. 1959;

79:155–73.

94. Fritsch H, Bruch H-P, and Kühnel W. Development and topography of the perirectal spaces. Proceedings of the First European Congress of Clinical Anatomy; September 1991; Bruxelles.

95. Fritsch H, Fröhlich B. Development of the levator ani muscle in human fetuses.

Early Hum Dev. 1994;37:15–25.

96. Fritsch H. Klinische anatomie des kontinenzorgans. Zentralb Chir. 1996;

121:613–6.

97. Fritsch H, Kühnel W, and Stelzner F. Entwicklung und klinische anatomie der adventita recti; Bedeutung für die Radikaloperation eines Mastadrmkrebses.

Langenbecks Arch Chir. 1996;381:237–43.

98. Ludwikowski B, Hayward IO, and Fritsch H. Rectovaginal fascia: An important structure in pelvic visceral surgery? About its development, structure, and function. J Pediatr Surg. 2002;37:634–8.

99. DeLancey JO. Standing anatomy of the pelvic ﬂoor. J Pelv Surg. 1996;2:260–3.

100. DeLancey JOL. Structural anatomy of the posterior pelvic compartment as it relates to rectocele. Am J Obstet Gynecol. 1999;180:815–23.

101. Denonvilliers C.P-D.Anatomie du perinée. Bull Soc Anat, Paris. 1836;11:105–6.

102. Denonvilliers C. Propositions et observations d’anatomie, de physiologie et de pathologie. Theses 285, Paris; 1837. As cited in Wesson MB, 1922.

103. Wesson MB. The development and surgical importance of the rectourethralis muscle and Denonvilliers’ fascia. J Urol. 1922;8:339–59.

104. Dietrich H. Giovanni Domenico Santorini (1681–1737) Charles-Pierre Denonvilliers (1808–1872). First description of urosurgically relevant structures in the small pelvis. Eur Urol. 1997;32(1):124–7.

105. Van Ophoven A and Roth S. The anatomy and embryological origins of the fascia of Denonvilliers: a medico-historical debate. J Urol. 1997;157:3–9.

106. Young HH. The early diagnosis and radical cure of carcinoma of the prostate.

Being a study of 40 cases and a presentation of a radical operation which was carried out in 4 cases. Johns Hopkins Hosp Bull. 1905;16:315.

107. Cuneo B and Veau V. De la signiﬁcation morphologique des aponeuroses perivesicales. J Anat Physiol. 1899;35:235.

108. Smith GE. Studies in the anatomy of the pelvis, with special reference to the fasciae and visceral supports. Part 1. J Anat Physiol. 1908;42:198, 252.

109. Aigner F, Zbar AP, Ludwikowski B, Kreczy A, Kovacs P, and Fritsch H. The rectogenital septum: morphology, function and clinical relevance. Dis Colon Rectum. In press 2003.

110. Richardson AC. The rectovaginal septum revisited: its relationship to rectocele and its importance in rectocele repair. Clin Obstet Gynecol. 1993;36:976–83.

111. Richardson AC. The anatomic defects in rectocele and enterocele. J Pelv Surg.

1995;1:214–21.

112. von Hagens G, Tiedemann K, and Kriz W. The current potential of plastination. Anat Embryol (Berl). 1987;175:411–21.

113. Zbar AP, Lienemann A, Fritsch H, Beer-Gabel M, and Pescatori M. Rectocele:

pathogenesis and surgical management. Int J Colorectal Dis. 2003;18:369–84.