Chapter 5. Abdomen

Part one. Anterior abdominal wall

The skin and subcutaneous tissues of the anterior abdominal wall have been dealt with as part of the body wall (see p. 179).

For clinical purposes, such as the description of sites of pain, swellings, and incisions, the abdomen is divided into regions that are defined by lines on the surface of the anterior abdominal wall. Usually nine regions are delineated by two vertical and two horizontal lines (Fig. 5.1). The vertical line on each side corresponds to the midclavicular line; when extended downwards it reaches the midinguinal point, which is midway between the pubic symphysis and the anterior superior iliac spine. The lower transverse line is drawn between the tubercles of the iliac crests (intertubercular plane) and the upper transverse line is in the transpyloric plane (see p. 233), midway between the jugular notch and the top of the pubic symphysis. (Some clinicians use the subcostal plane which is a little lower—level with the lowest part of the costal margin). Using these four lines, three central regions are defined from above downwards: epigastric, umbilical and hypogastric (or suprapubic). Similarly there are three lateral regions on each side: hypochondrial, lumbar and iliac.

Figure 5.1 Regions of the abdomen.

Anterolateral abdominal muscles

The three muscle layers of the body wall (see p. 181) are separate in the flanks, where they are known as the external oblique, internal oblique and transversus abdominis muscles. The layers have fused ventrally to form the rectus abdominis muscle.

External oblique

The muscle arises by eight digitations, one from each of the lower eight ribs just lateral to their anterior extremities. The lower four slips interdigitate with the costal fibres of latissimus dorsi and the upper four with digitations of serratus anterior. From its fleshy origin the muscle fans out to a very wide insertion, much of which is aponeurotic. The muscle has a free posterior border which extends from the twelfth rib to its insertion by fleshy fibres into the anterior half of the outer lip of the iliac crest. Muscular fibres are replaced by an aponeurosis below a line joining the anterior superior iliac spine to the umbilicus, and medial to a vertical line drawn from the tip of the ninth costal cartilage (Fig. 5.2). The limit of the fleshy fibres is visible in an athlete as a graceful curve. The aponeurotic fibres, directed obliquely downwards and forwards, interdigitate with each other across the front of the rectus abdominis along the whole length of the linea alba. (This description is adequate for all

practical purposes although detailed studies of cadaveric material have revealed that the aponeurotic fibres are in superficial and deep layers, the fibres in the superficial layer running obliquely upwards and those in the deep layer at right angles downwards. The fibres continue across the midline after decussation, the fibres from the deep layer passing to the superficial layer on the contralateral side of the abdominal wall and vice versa.) The free horizontal upper border of this aponeurosis extends from the fifth rib to the xiphisternum. It is the only structure in the anterior sheath of the rectus muscle above the costal margin.

Figure 5.2 Anterolateral abdominal muscles. The right rectus abdominis and pyramidalis have been removed to show the posterior wall of the rectus sheath, the arcuate line and the ends of the intercostal nerves.

The free posterior border of the muscle forms the anterior boundary of the lumbar triangle (of Petit) that is floored in by the internal oblique and bounded behind by the anterior border of latissimus dorsi and below by the iliac crest. The triangle may be the site of a rare lumbar hernia (see Fig. 2.4, p. 40).

The lower border, lying between the anterior superior iliac spine and the pubic tubercle, forms the inguinal ligament (of Poupart). Its edge is rolled inwards to form a gutter; the lateral part of this gutter gives origin to part of the internal oblique and transversus abdominis muscles. The fascia lata of the thigh is attached to the inguinal ligament and when the thigh is extended the fascia lata pulls the inguinal ligament downwards into a gentle convexity.

Just above and lateral to the pubic tubercle is an oblique, triangular gap, the superficial inguinal ring, in the aponeurosis (Fig. 5.3). The base of the gap is the pubic crest, and the margins are the crura of the ring.

arise from the inguinal ligament and arch medially to reach the conjoint tendon, forming as they do so the roof of the inguinal canal. They cover up the similar fibres of transversus abdominis, shown i n Figure 5.5. Note that the nearly vertical conjoint tendon lies at right angles to the nearly horizontal lacunar ligament. Only the upper part of the cremaster muscle is depicted.

Transversus abdominis

The muscle arises in continuity from the lateral third of the inguinal ligament, the anterior two-thirds of the inner lip of the iliac crest, the lumbar fascia, the twelfth rib, and from the inner aspects of the lower six costal cartilages where it interdigitates with the diaphragm. The muscle fibres become aponeurotic and pass behind the rectus to fuse with the internal oblique aponeurosis in the linea alba. Below the arcuate line the aponeurosis passes wholly in front of the rectus muscle. (As in the case of external oblique, detailed cadaveric studies have shown that the aponeurotic fibres of transverse abdominis that contribute to the rectus sheath are in two layers at right angles to each other.) In the upper part of the abdomen the outer margin of the aponeurosis is more medial, and muscular fibres lie behind the lateral part of rectus abdominis. The lower fibres of the aponeurosis curve downwards and medially with those of the internal oblique as the conjoint tendon, to insert on the pubic crest and the pectineal line (Fig. 5.5).

Figure 5.5 Left transversus abdominis, showing the lowest fibres arching medially to join the conjoint tendon.

Rectus abdominis and pyramidalis

Rectus abdominis arises by two heads: a medial from in front of the pubic symphysis and a lateral from the upper border of the pubic crest. The lower parts of the two muscles are narrower and lie edge to edge. The upper parts are broader and are separated from each other by the linea alba (Fig. 5.2). They are inserted on to the front of the fifth to seventh costal cartilages. Typically three tendinous intersections are found in the muscle, one at the umbilicus, one at the xiphisternum, and one between these two; one or two incomplete intersections are sometimes found below the umbilicus. The tendinous intersections blend inseparably with the anterior layer of the rectus sheath. They occupy only the superficial part of the rectus and do not penetrate to the posterior surface of the muscle, which is thus not connected to the posterior layer of the sheath. The contracting rectus abdominis can be seen as bulgings between the tendinous intersections in an individual who is not too

fat.

The small triangular pyramidalis muscle arises from the body of the pubis and the symphysis between rectus abdominis and its sheath. It converges with its fellow into the linea alba 4 cm or so above its origin.

Between the two recti all the aponeuroses that form the rectus sheath fuse to form the linea alba, a strong midline fibrous structure which is firmly attached to the xiphoid process above and the pubic symphysis below (Fig. 5.2). Above the symphysis it is very narrow, for here the two recti are in contact with one another behind it. From just below the umbilicus to the xiphisternum it broadens out between the recti. Here the fibres form a tough felted membrane. The umbilicus is a defect in the linea alba through which fetal umbilical vessels pass.

Rectus sheath

The aponeurosis of the internal oblique splits into anterior and posterior layers to enclose the rectus muscle (Fig. 5.6B). The external oblique aponeurosis fuses with the anterior layer to form the anterior layer of the sheath, and the transversus aponeurosis fuses with the posterior layer to form the posterior layer of the sheath. From halfway between the umbilicus and the pubic symphysis all three aponeuroses pass in front of the muscle (Fig. 5.6C). The aponeuroses of internal oblique and transversus fuse completely but that of the external oblique fuses only to the most medial part of the sheath. The posterior layer of the sheath has a free lower margin concave downwards, the arcuate line or semicircular line (of Douglas). Superiorly the posterior layer of the sheath is attached to the costal margin (seventh, eighth and ninth costal cartilages). Above the costal margin the anterior layer of the sheath consists only of the external oblique aponeurosis (Fig. 5.6A).

Figure 5.6 Formation of the rectus sheath as seen in horizontal sections: A above the costal margin —only the external oblique and its aponeurosis exist here; B between the umbilicus and the costal margin—the aponeurosis of the internal oblique splits around the rectus; the external oblique aponeurosis joins the anterior layer and that of transversus joins the posterior layer; C below the arcuate line—all three aponeuroses pass in front of the rectus muscle. See text for other possibilities.

The splitting of the internal oblique aponeurosis along the lateral border of the rectus muscle forms a relatively shallow groove, the semilunar line. It curves up from the pubic tubercle to the costal margin at the tip of the ninth costal cartilage in the transpyloric plane.

Detailed studies indicate that the aponeuroses of external oblique, internal oblique and transversus

A pedicled flap of the upper part of the rectus muscle based on the superior epigastric artery—or a free flap of the lower part with anastomosis of the divided inferior epigastric artery to the internal thoracic artery—is used in reconstructive breast surgery.

Blood supplies

Apart from the intercostal and epigastric vessels mentioned above, the anterolateral abdominal muscles also receive a blood supply from the lumbar and deep circumflex iliac arteries. The lumbar arteries are described on page 276; they end among the flat anterolateral muscles and do not reach the rectus sheath.

The deep circumflex iliac artery arises from the external iliac (see p. 276) behind the inguinal ligament (Fig. 5.8), and runs laterally towards the anterior superior iliac spine in a sheath formed by the transversalis and iliac fasciae where they meet. It continues along the inner lip of the iliac crest, pierces the transversus muscle to reach the neurovascular plane and anastomose with branches of the iliolumbar and superior gluteal arteries. At the anterior superior iliac spine it gives off an ascending branch which may be at risk in a gridiron incision (see p. 232).

Lymph drainage

The superficial tissues of the anterolateral abdominal wall drain in quadrants: to the pectoral group of axillary nodes above the umbilicus on each side, and to superficial inguinal nodes below that level. The deeper parts of the wall drain into vessels in the extraperitoneal tissues. Above the umbilicus these pierce the diaphragm to reach mediastinal nodes, and below it they run to the external iliac and para-aortic nodes.

Nerve supplies

The rectus muscle and external oblique are both supplied by the lower intercostal and subcostal nerves (T7–T12), and the internal oblique and transversus by those same nerves but with the addition of the iliohypogastric and ilioinguinal nerves (L1). The lowest fibres of the internal oblique and transversus that continue medially as the conjoint tendon receive the L1 innervation, which thus helps to maintain the integrity of the inguinal canal (see below). Pyramidalis is supplied by the subcostal nerve (T12).

Actions of abdominal muscles

The muscles of the anterior abdominal wall have four main roles: (1) to move the trunk, (2) to depress the ribs (expiration), (3) to compress the abdomen (evacuation, expiration, heavy lifting), and

(4) to support the viscera (intestines only). The abdominal wall, moving to and fro with breathing, conforms to the volume of the abdominal contents. Its shape is determined by the tonus of its own muscles. The subumbilical pull of healthy flank muscles keeps its lower part flat by holding back the lower recti.

Moving the trunk. As the muscles are attached to the thoracic cage and the bony pelvis their action is to approximate the two. They are flexors of the vertebral column in its lumbar and lower thoracic parts. Rectus abdominis is the most powerful flexor. The oblique muscles are also lateral flexors and rotators of the trunk.

Depressing the ribs. The recti and obliques approximate the ribs to the pelvic girdle. If erector spinae prevents thoracolumbar flexion this provides a powerful expiratory force (e.g. coughing, blowing the trumpet). Added to this is the abdominal compression (aided by transversus) that elevates the diaphragm to increase the expiratory effort.

Compressing the abdomen. While flexion of the vertebral column is prevented by the erector spinae muscles, the oblique muscles compress the abdominal cavity; in this they are aided strongly by transversus abdominis, which has no flexing action on the spine. The recti play little part in compression. If the diaphragm is relaxed, it is forced up, as in expiration. At the same time levator ani helps to hold the pelvic effluents closed. The reverse occurs in evacuation of the pelvic effluents. Here the diaphragm contracts to resist upward displacement, but it is a far weaker muscle than the abdominal wall, and in forceful compression it is prevented from rising by holding the breath, i.e. by closure of the glottis, and perhaps of the mouth and nostrils (see p. 395).

Supporting and protecting viscera. If the anterior abdominal wall is incised or removed, only the intestines spill out. The upper abdominal viscera, such as the liver, spleen and kidneys, do not require the support of the wall. Reflex contraction in response to a blow helps to protect all viscera.

Tests. Rectus abdominis can be tested by lying flat on the back and raising the head (without using the arms). There are no specific tests for the other flat muscles. The abdominal reflex and Beevor's sign have been referred to on page 17.

Inguinal canal

The inguinal canal is an oblique intermuscular slit about 4 cm long lying above the medial half of the inguinal ligament. It commences at the deep inguinal ring, ends at the superficial inguinal ring, and transmits the spermatic cord and ilioinguinal nerve in the male and the round ligament of the uterus and ilioinguinal nerve in the female. Its anterior wall is formed by the external oblique aponeurosis (Fig. 5.2), assisted laterally by the internal oblique muscle (Fig. 5.7). Its floor is the inrolled lower edge of the inguinal ligament, reinforced medially by the lacunar ligament (Fig. 5.4). Its roof is formed by the lower edges of the internal oblique and transversus muscles, which arch over from in front of the cord laterally to behind the cord medially, where their conjoined aponeuroses, constituting the conjoint tendon, are inserted into the pubic crest and the pectineal line of the pubic bone. The posterior wall of the canal is formed by the strong conjoint tendon medially and the weak transversalis fascia throughout.

Figure 5.7 Right inguinal canal after division of the external oblique aponeurosis and fasciae. The ilioinguinal nerve has been displaced downwards with the lower flap of the aponeurosis.

The integrity of the inguinal canal depends upon the strength of the anterior wall in the lateral part and of the posterior wall in the medial part, provided the abdominal muscles are of good tone and their aponeuroses unyielding. The deep and superficial inguinal rings lie at opposite ends of the inguinal canal and the intervening part of the canal is pressed flat when the aponeuroses are under tension and the intra-abdominal pressure raised. The conjoint tendon lies posterior to the superficial inguinal ring and helps to reinforce this area. Laterally the transversalis fascia in the posterior wall is strengthened by the presence in front of it of tendinous, and sometimes muscular, fibres derived from the transversus abdominis muscle. These fibres constitute the interfoveolar ligament (Fig. 5.8). They arch down from the lower border of transversus around the vas to the inguinal ligament, and constitute the functional medial edge of the deep ring.

The deep inguinal ring lies about 1.25 cm above the midpoint of the inguinal ligament and is an opening in the transversalis fascia. From the margins of this opening the transversalis fascia is projected along the canal, like a sleeve, the internal spermatic fascia, around the structures that pass through the ring. These are the vas deferens and its artery, the testicular artery and the accompanying veins (usually double at this level, Fig. 5.10), the obliterated remains of the processus vaginalis, the genital branch of the genitofemoral nerve, autonomic nerves and lymphatics. These structures constitute the spermatic cord; in the female they are replaced by the obliterated processus vaginalis, the round ligament and lymphatics from the uterus. The ilioinguinal nerve, although a content of the inguinal canal, does not enter the canal through the deep ring, but by piercing the internal oblique muscle, i.e. it slips into the canal from the side, not from the back. The nerve lies in front of the cord and leaves the canal through the superficial ring to supply skin of the inguinal region, upper part of the thigh, anterior third of the scrotum (or labium majus) and root of the penis.

Figure 5.10 Right testicular venogram.

Structures deep to the posterior wall

Crossing the posterior wall at the medial edge of the deep inguinal ring is the inferior epigastric artery. Lateral to the artery the vas deferens in the male and the round ligament of the uterus in the female enter the canal by hooking around the interfoveolar ligament. At the deep ring the inferior epigastric artery gives off the cremasteric branch to supply that muscle and the coverings of the cord. The area bounded laterally by the inferior epigastric artery, medially by the lateral border of the rectus muscle, and below by the inguinal ligament is the inguinal triangle (of Hesselbach). By definition a hernial sac passing lateral to the artery (i.e. through the deep ring) is an indirect hernia, one passing medial to the artery (through the inguinal triangle) is a direct hernia; the latter stretches out the conjoint tendon over itself and is therefore seldom large. As an inguinal hernia emerges through the superficial inguinal ring it lies above and medial to the pubic tubercle, while the neck of a femoral hernia (see p. 118) is below and lateral to the pubic tubercle.

Spermatic cord

The spermatic cord has three coverings and six (groups of) constituents.

Of the three coverings of the spermatic cord (Fig. 5.9), the internal spermatic fascia is derived from the transversalis fascia at the deep inguinal ring. As the cord passes through the ring into the inguinal canal, it picks up a second covering, the cremaster muscle and cremasteric fascia. This loosely arranged layer consists of striated muscle bundles united by areolar tissue. The muscle arises laterally from the inguinal ligament, the internal oblique and transversus abdominis muscles. The fibres spiral down the cord (the longest reaching as far as the tunica vaginalis of the testis) and loop back to become attached to the pubic tubercle. The third covering, the external spermatic fascia, is acquired from the external oblique aponeurosis as the cord passes between the crura of the superficial ring.

Figure 5.9 Schematic diagram illustrating the formation of the sheaths of the spermatic cord and the layers of the scrotal wall.

The cremaster muscle can elevate the testis towards or even into the inguinal canal; although the fibres are skeletal the action is reflex rather than voluntary. This cremasteric reflex is particularly active in the infant and child and must be borne in mind when examining the scrotum in the young, to avoid an erroneous diagnosis of undescended testis.

The constituents of the cord consist of:

•The vas deferens, which usually lies in the lower and posterior part of the cord.

•Arteries, the largest of which is the testicular artery (see below), with the artery to the vas (from the superior or inferior vesical), and the cremasteric artery (from the inferior epigastric, Fig. 5.8) to the coverings.

•Veins—the pampiniform plexus (see below).

•Lymphatics, essentially those from the testis draining to para-aortic nodes, but including some from the coverings which drain to external iliac nodes.

•Nerves, in particular the genital branch of the genitofemoral nerve which supplies the cremaster muscle. Other nerves are sympathetic twigs which accompany the arteries.

•The processus vaginalis, the obliterated remains of the peritoneal connection with the tunica vaginalis of the testis. When patent it forms the sac of an indirect inguinal hernia.

Testis

The testis (Fig. 5.12) is an oval organ possessing a thick covering of fibrous tissue, the tunica albuginea. The epididymis is attached to its posterolateral surface; this is an important point to remember when trying to distinguish between swellings of these two structures. The vas deferens arises from the lower pole of the epididymis (see p. 231) and runs up medial to it behind the testis. The front and sides of the testis lie free in a serous space formed by the overlying tunica vaginalis, a remnant of the fetal processus vaginalis. This serous membrane covers also the anterolateral part of the epididymis and lines a slit-like space, the sinus of the epididymis, which lies between testis and epididymis. Testis, epididymis and tunica vaginalis lie in the scrotum surrounded by thin membranes, adherent to each other, that are downward prolongations of the coverings of the spermatic cord (Fig. 5.9). Right and left sides are separated by the median scrotal septum (see p. 321). Average testicular dimensions are 5 cm (length), 2.5 cm (breadth), 3 cm (anteroposterior diameter). The appendix testis is a minute sessile cyst attached to the upper pole of the testis within the tunica vaginalis. It is a

remnant of the paramesonephric duct (see p. 304).

Figure 5.12 Transverse section of the left scrotum and testis—viewed from above.

Blood supply

The testicular artery, from the aorta, runs in the spermatic cord, gives off a branch to the epididymis, and reaches the back of the testis, where it divides into medial and lateral branches. These do not penetrate the mediastinum testis (see below), but sweep around horizontally within the tunica albuginea. Branches from these vessels penetrate the substance of the organ. In the region of the epididymis there is an anastomosis between the testicular, cremasteric and ductal arteries; but if the main artery is divided, the smaller vessels may not completely sustain the testis and atrophy may occur, though ischaemic necrosis is unlikely. Venules reach the mediastinum, from which several veins pass upwards in the spermatic cord as a mass of intercommunicating veins, the pampiniform plexus (Fig. 5.10), which surround the testicular artery. In the inguinal canal the plexus separates out into about four veins which join to form two that leave the deep inguinal ring, becoming single on psoas major on the posterior abdominal wall. The left vein invariably joins the left renal vein at a right angle and the right drains directly into the inferior vena cava at an acute angle. The testicular veins usually have valves. Varicocele (varicosities of the pampiniform and cremasteric veins) occurs much more frequently on the left side than the right.

Lymph drainage

Lymphatics from the testis run back with the testicular artery to para-aortic nodes lying alongside the aorta at the level of origin of the testicular arteries (L2 vertebra), i.e. just above the umbilicus. The testicular lymph therefore does not drain to inguinal nodes, although the overlying scrotal skin does.

Nerve supply

The testis is supplied by sympathetic nerves. Most of the connector cells lie in T10 segment of the cord. Passing mainly in the lesser splanchnic nerve to the coeliac ganglia the efferent fibres synapse there. Postganglionic grey fibres reach the testis along the testicular artery. Sensory fibres share the same sympathetic pathway. They run up along the testicular artery and through the coeliac plexus and lesser splanchnic nerve and its white ramus to cell bodies in the posterior root ganglion of T10 spinal nerve.

Structure

The upper pole of the epididymis is attached high up on the posterolateral surface of the testis. Here there is a fibrous mass, the mediastinum testis, from which septa radiate to reach the tunica albuginea. The septa divide the testis into some 200–300 lobules, each of which contains 1–4 highly convoluted seminiferous tubules. The cut surface of the organ bulges with protruding tubules. The seminiferous tubules open into the rete testis, which is a network of intercommunicating channels lying in the mediastinum testis. From the rete 12–20 vasa efferentia enter the commencement of the canal of the epididymis, thus attaching the head of the epididymis to the testis.

The seminiferous tubules have several layers of cells. The outermost layer consists of spermatogonia, which divide to produce the primary spermatocytes. These divide to form secondary spermatocytes. They have a very short life and divide almost immediately to form spermatids. These do not divide but undergo a metamorphosis into spermatozoa. The whole process of producing spermatozoa from spermatogonia is termed spermatogenesis.

Among the developing germ cells are the supporting or sustentacular cells (of Sertoli). The Sertoli cells secrete an androgen binding protein (ABP) which keeps a high concentration of testosterone in the germ cell environment.

Scattered among the cells of the connective tissue between the tubules (outside them) are the interstitial cells (of Leydig). Larger than fibroblasts, they constitute the endocrine portion of the testis and secrete testosterone.

Apart from spermatozoa, the testis makes only a small contribution to semen (seminal fluid); most of it (60%) comes from the seminal vesicles (see p. 301) and prostate (30%; see p. 299).

Development and descent of the testis

The testis develops from the gonadal ridge, formed by proliferation of the coelomic epithelium and a condensation of underlying mesoderm, on the medial side of the mesonephros (see p. 23). Primordial germ cells from the yolk sac migrate to the gonadal ridge and become incorporated in the developing gonad. At first the testis and mesonephros are situated on the posterior abdominal wall, attached by the urogenital mesentery. As the testis enlarges its cranial end degenerates and the remaining organ lies at a more caudal location. Most of the mesonephros atrophies. Derivatives of the remaining mesonephric tubules include the vasa efferentia of the testis and the paradidymis (a small collection of tubules above the epididymis at the lower end of the spermatic cord). In the male, the mesonephric duct forms the canal of the epididymis, vas deferens, ejaculatory duct and the appendix of the epididymis (a small appendage on the head of the epididymis).

A condensation of mesodermal cells, the gubernaculum, connects the lower pole of the testis to the region of the anterior abdominal wall that later forms the scrotum (Fig. 5.11). It traverses the site of the future inguinal canal, which is formed around it by the developing muscles of the abdominal wall. A sac of peritoneum, the processus vaginalis, protrudes down the inguinal canal anterosuperior to the gubernaculum. By the seventh month of fetal life the testis is in the deep inguinal ring and thereafter it progresses rapidly through the inguinal canal into the scrotum before birth. As the testis descends it is accompanied by the processus vaginalis. The testis projects into the distal part of the processus, which forms the tunica vaginalis. The rest of this peritoneal sac usually gets obliterated. Persistence

of the whole, or proximal part, of the sac maintaining its connection with the peritoneal cavity constitutes a hernial sac, a clinical hernia occurring when intra-abdominal contents enter the sac. Persistence of an intervening segment of the processus may lead to the development of a hydrocele of the cord. Accumulation of serous fluid between the layers of the tunica vaginalis forms the much more common hydrocele of the testis.

Figure 5.11 Stages of testicular descent: A in the fetus, the testis projects through the peritoneum into the coelomic cavity—the vas deferens (mesonephric duct) runs downwards; B in the neonate, the testis has reached the scrotum together with the tube-like prolongation of the peritoneal cavity, the processus vaginalis; C the end result, with the testis partly surrounded by the tunica vaginalis derived from the processus, and the rest of the processus reduced to a fibrous cord.

Sometimes the testis is not fully descended at birth, but enters the scrotum during the first few months thereafter. Failure to descend may result in cryptorchid testis, where it remains in the abdomen, or descent may be arrested anywhere from the deep inguinal ring downwards. Undescended testes are peculiarly liable to malignant disease; spermatogenesis is defective or absent but androgenic activity is not. They must be distinguished from retracted testes, where the cremaster muscle draws them back into the canal, especially in the young under the influence of cold examining hands!

Epididymis and vas deferens

The epididymis is a firm structure, attached behind the testis, with the vas deferens to its medial side. It consists of a single highly coiled tube packed together by fibrous tissue. It has a large head at its upper end, connected by a body to a pointed tail at its lower end. The head is connected to the upper pole of the testis by the vasa efferentia and the tail to the lower pole by loose connective tissue. The body is partly separated from the testis by a recess which is open laterally, the sinus of the epididymis (Fig. 5.12). The lateral surface of the epididymis is covered by the tunica vaginalis, which also lines the sinus.

From the tail the vas deferens, a direct continuation of the canal of the epididymis, provided with a

The simplest abdominal incision is the midline incision, above or below the umbilicus (or both, skirting the umbilicus) and passing through skin and subcutaneous tissues, the linea alba, transversalis fascia, extraperitoneal fat and peritoneum. No major vessels or nerves are involved, but a few small vessels may cross the midline of the peritoneum. In the lower abdomen the linea alba is very narrow and the two rectus muscles lie very close together; here poor suture technique predisposes to incisional hernias. In the suprapubic region the bladder must not be damaged.

For laparoscopic surgery, the incision for insertion of a needle to induce pneumoperitoneum was usually made in the midline, just above or below the umbilicus, and the instrument was first directed down towards the pelvic cavity to avoid damaging the aorta. Increasingly now the pneumoperitoneum is created by trocat and cannula insertion through an umbilical port, which is also used for camera insertion. Other ports for instruments lateral to the rectus sheath must not be made too low, to avoid the inferior epigastric vessels (see Fig. 4.1, p. 180); transillumination from within the peritoneal cavity helps to avoid them. The development of multifunctional instruments has enabled some minimally invasive procedures (such as appendicectomy and cholecystectomy) to be performed entirely via an umbilical port. Laparoscopic extraperitoneal inguinal and femoral hernia repair utilises pre-peritoneal balloon inflation to create the required surgical space. Sites below the umbilicus or at the lateral border of the rectus sheath are used for the insertion of a trocar and cannula for the drainage of peritoneal fluid (paracentesis) or a peritoneal dialysis catheter. A suprapubic catheter to drain a distended bladder is usually introduced through the midline.

In a paramedian incision, the anterior wall of the rectus sheath is incised vertically 2 cm from the midline and the rectus muscle retracted laterally so that the posterior wall of the sheath can be incised. The tendinous intersections in the rectus muscle at and above the umbilicus have to be dissected off the anterior wall of the sheath; they may contain vessels. Above the umbilicus on the right the falciform ligament may have to be divided. In a rectus split incision, through a vertical incision 3 cm from the midline the rectus is split instead of being retracted. The small part of the muscle medial to the split will be denervated and devascularized but this usually does not cause problems. The lack of a posterior wall of the sheath below a point midway between the umbilicus and pubic symphysis implies that sound healing depends on proper closure of the sheath's anterior wall.

The right subcostal (Kocher's) incision is made 3 cm parallel to and below the right costal margin, from the midline to beyond the lateral border of the rectus sheath. The incision is often made more horizontal than parallel to the subcostal margin. The anterior layer of the sheath (with the external oblique) and the rectus muscle are divided in the line of the skin incision, with ligation of the superior epigastric vessels and/or their branches. The posterior layer of the sheath is then incised, continuing laterally into the internal oblique and transversus and through to the peritoneum. The seventh intercostal nerve follows the costal margin upwards and is usually above the incision line, but the eighth or ninth nerve may have to be cut, with little effect on the rectus muscle. Cutting more than two nerves (paralysing more of the rectus) should be avoided.

The double Kocher or curved rooftop incision, combining subcostal incisions on both sides, gives a very wide exposure of the upper abdomen.

The gridiron (McBurney's) incision is a right lower oblique muscle-splitting incision, long used for appendicectomy. The skin incision runs downwards and medially through the junction of the outer and

middle thirds of a line drawn from the anterior superior iliac spine to the umbilicus. The external oblique muscle and its aponeurosis are divided in the line of their fibres and then the internal oblique and transversus are split transversely (in the line of their own fibres). The two muscles are close and may be split together. The transversus becomes aponeurotic at this level and some fibres may pass to the transversalis fascia. The peritoneum can then be incised. The iliohypogastric and ilioinguinal nerves may be seen between the internal oblique and transversus and must not be damaged, to avoid weakening the protective effect that the muscles exert upon the inguinal canal. Extending the incision laterally may cut the deep circumflex iliac artery's ascending branch, which runs upwards above the anterior superior iliac spine between the internal oblique and transversus.

For cosmetic reasons the gridiron incision is often replaced by a more transverse muscle-splitting incision in a skin crease starting above and medial to the anterior superior iliac spine and extending nearly to the lateral border of the rectus sheath.

T he oblique muscle-cutting incision (Rutherford Morison's) is similar to the gridiron but after incising the external oblique in the line of its fibres the internal oblique and transversus are cut in the same line (not in the line of their own fibres).

Transverse muscle-cutting incisions can be made at or about the level of the umbilicus, cutting the rectus sheaths and the obliques and transversus muscles. The rectus muscle is retracted medially or divided. Lower intercostal nerves run obliquely through the abdominal wall, but more than one is not likely to be cut by this incision.

The lower abdominal transverse incision (Pfannenstiel's) is commonly used for approach to the pelvic organs. A skin crease incision is made above the pubic symphysis, just below the hairline, as far as the lateral borders of the rectus sheaths. The anterior layers of the rectus sheaths are divided in the line of the skin incision and flaps dissected off the muscles both upwards and downwards, with the pyramidalis muscles included in the lower flap. The rectus muscles which at this level lie close together are separated to expose transversalis fascia which is incised with the peritoneum, care being taken to avoid the bladder. Transverse division of the rectus muscles gives wider exposure, and the incisions can be extended laterally into the flat muscles.

A lumbar incision is used for extraperitoneal approach to the kidney and upper ureter. The incision extends below the twelfth rib from the lateral border of erector spinae towards the anterior superior iliac spine. Latissimus dorsi and external oblique are incised and their cut edges retracted so that the internal oblique and transversus merging with the lumbar fascia can also be incised. The subcostal nerve deep to internal oblique should be preserved but the vessels can be ligated. The transversalis fascia and extraperitoneal fat in the posterior part of the incision are separated to expose the renal fascia. The peritoneal cavity is not entered. Proper identification of the twelfth rib is essential to avoid entering the pleural cavity, which extends below its medial part (see p. 213).