rectal instruments

ANATOMY OF RECTUM


By • Дек 26th, 2010 • Category: For surgery

The length of the rectum, together with the Perineal region (anal canal), is 15 to 16 cm. The length of the anal canal is 2.5—3 cm, that of the rectal ampula 9 cm, and of the rectosigmoid region 3 cm (Fig. 3).

In the pelvis the rectum has bends both in the sagit­tal (Figs 1 and 2) and frontal planes (Fig. 4). At ope­ration, after the rectum has been mobilized, these bends are straightened to increase its length by 5 to 6 cm. The proximal part of the rectum is invested with peritoneum forming a space known to surgeons as the pouch of Douglas. The distal part of the rectum (9—10 cm long) lies in the pelvic fatty tissue and is free from peritone­um, and it is essential that this should be taken into ac­count when removing tumors and electrocoagulating po­lyps. The rectal wall consists of three layers: mucous membrane, muscular layer, and fibrous membrane.

Fig. I. Sagittal section of the male pelvis. (From Sobbota's Ailas)

Fig. I. Sagittal section of the male pelvis. (From Sobbota’s Ailas)

The anal canal is covered with a multilayer flat epi­thelium. Here in the middle a circular groove referred to as Hilton’s while line can often be recognized. At the place where the anal canal becomes the rectal rnucosa covered with cylindrical epithelium, there is the pecti­nate line (linea pectinea). Figures 5 and 6 show columns of Morgagni disposed longitudinally on rectal mucosa and having their bases joined by folds known as semi-lunal valves (colimnae Morgagni). These valves are lo­cated along the pectinate line and form small pockets called sinuses or crypts of Morgagni. Infection of these crypts often leads to acute anorectal abscesses, anal fis­tulas, or anal fissures.

Lateral view of the male pelvic organs. (From Sobbota's Atlas)

Fig. 2. Lateral view of the male pelvic organs. (From Sobbota’s Atlas):

1. Left spermatic duct. 2. Left urether. 3. Rectovcsical space. 4. First coccygeal vertebra. 5. Rectal ampula. 6. Seminal vesicles

Within the anal canal, the muscular membrane of the rectum becomes thicker to form the internal anal sphinc­ter. Its role in anal continence is extremely small.

Anatomic divisions of the rectum

Fig. 3 Anatomic divisions of the rectum:

1. Promontory of the sacrum. 2. Mesocolon pelvinum. 3. Pelvic colon. 4. Peritoneal edge of the pouch of Douglas. 5. Pelvic part of the rectum. 6. Perineal part of the rectum

The external anal sphincter consists of three portions: subcutaneous, superficial, and deep (Figs 5, 6 and 7). They surround the rectum in the form of a cone, the sub­cutaneous portion being adjacent to the anal mucosa, and the deep portion spaced some 2 cm apart from the crypts of Morgagni. This permits the rectal wall to be safety dissected from within to a depth of one centime­ter.

Fig. 4. Curves of the rectum on frontal plane. (Schematic representation after Rauber)

Fig. 4. Curves of the rectum on frontal plane. (Schematic representation after Rauber)

The levator ani muscle is a flat muscle that forms the floor of the lesser pelvis (Figs 7, 8 and 9); this muscle, which is also referred to as the pelvic diaphragm, con­sists in fact of three parts: the iliococcygeal, pubococcygeal, and puboperineal muscles (Fig. 9).

Fasclocellular spaces of the pelvis. All these spaces ire liable to become filled with pus in acute anorectal abscesses. A distinction should be made between those fascial spaces situated inferior to the pelvic diaphragm and those situated superior to it.

Fig. 5. Longitudinal section of the terminal segment of rectum. (Schematic):

Fig. 5. Longitudinal section of the terminal segment of rectum. (Schematic):

1. Subcutaneous portion of the external sphincter. 2. Superficial portion of the ex­ternal sphincter. 3. Deep portion of the external sphincter. 4. Levator ani muscle. 5. Inner rectal plexus. 6. Internal sphincter

The subcutaneous fat of the perineum is frequently :he site of anorectal abcesses (in 50—55 per cent of ca­ses). The boundaries of perineal subcutaneous fat have :r.e form of a rhomb with its apex at the scrotal root, ::s lateral points at the ischial tuberosities and its pos­terior point at the coccygeal apex.

Vertical section of the distal rectum and anus

Fig. 6. Vertical section of the distal rectum and anus:

1. Columns of Morgagni. 2. Semilunal valves. 3. Subcutaneous portion of the external sphincter. 4. Superficial portion of the external sphincter. 5. Deep portion of the external sphincter. 6. Levator ani muscle

The ischiorectal space (fossa) lies on either side of :he rectum. As can be seen in Fig. 10 it is bounded inte­riorly and superiorly by the levator ani muscles, and laerally by the obturator muscle and the ischial tuberosi-ty. Abcesses are encountered in this space in 35—40 per cent of cases with acute anorectal abscesses.

External anal sphincter as viewed from below. (After Rauber)

Fig. 7. External anal sphincter as viewed from below. (After Rauber):

1. Superficial transverse muscle of the perineum. 2. Levator ani muscle. 3. Deep portion of the external sphincter. 4. Superficial portion of the external sphincter. 5. Subcutaneous portion of the external sphincter. 6. Coccyx

The pelvirectal space lies above the pelvic diaphragm between this muscle and the pelvic floor peritoneum. In this space run the urethers and all those ligaments of the rectum connecting it to the side wall of the pelvis (Fig. 11). In 7 to 8 per cent of cases with acute anorectal abs­cesses pus accumulations are encountered in this space.

Diaphragm of the pelvic floor as viewed from above. (From Sobbota's Atlas)

Fig. 8 Diaphragm of the pelvic floor as viewed from above. (From Sobbota’s Atlas):

1. Sacrum. 2. Coccygea! muscle. 3. Levator ani muscle. 4. Rectum. 5. Urethra. 6. Ten­dinous arch of the levator ani muscle. 7. Obturator internus muscle

The retrorectal space is situated posteriorly to the rectum between its posterior wall and the anterior sur­face of the sacrum, its upper boundary reaching the pro-montorium. Retrorectal abscesses are encountered in 2 per cent of cases with acute anorectal abscesses.

Blood supply to the rectum. The main arterial trunk of the rectum is the superior rectal artery, which is a continuation of the inferior mesenteric artery in the pel­vis.

 Levator ani muscle and coccygeal muscle

Fig. 9. Levator ani muscle and coccygeal muscle:

1. Coccyx. 2. Iliococcygeal muscle. 3. Pubococcygeal muscle. 4. Puborectal muscle. 5. Anus

The superior rectal artery descends with its accom­panying veins to the posterior surface of the rectum where it divides into the right and left branches (Fig. 12). These branches then turn to the lateral walls of the rectum where they break up into a profuse network of vessels.

Middle rectal arteries are small in caliber. They arise from the iliac artery and run medially and posteriorly along the pelvic diaphragm to branch off alongside the lateral walls of the rectum (Fig. 12).

Right ischiorectal space. (After Tillaux)

Fig. 10 Right ischiorectal space. (After Tillaux):

1. Coccyx. 2. Ischiorectal space. 3. Posterior edge of the gluteus maximus muscle. 4. Tuber ischiadicum (cut). 5. Inferior rectal artery. 6. Levator ani muscle. 7. Obturator internus muscle. 8. Pelviorectal space. 9. Peritoneum of the pouch of Douglas. 10. Rectum. 11. Anococcygeal ligament.

Inferior rectal arteries spring from the pudenda ar­tery (Fig. 10) and proceed medialward and forward to­ward the distal rectum, the anal canal and the external sphincter, traversing the ishiorectal space.

Frontal section of the pelvis showing the pelvirectal space. (After Bacon)

Fig. 11 Frontal section of the pelvis showing the pelvirectal space. (After Bacon):

1. Perineal rectum. 2. Levator ani muscle. 3. Right urether. 4. Common :::sc vessels. 5. Left urether. 6. Pelviorectal space. 7. Ischiorectal space. 8. External sphincter.

Rectal arteries

Fig. 12 Rectal arteries:

Superior rectal artery. 2. Middle rectal arterv. 3. Inferior rectal artery. 4. The pelvic diaphragm



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