Abdomen... PART ONE. Anterolateral abdominal muscles. Anterior abdominal wall. External oblique

Transcription

1 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. 185). 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 Fig. 5.1 Epigastric Umbilical Hypogastric or Suprapubic Regions of the abdomen. Midclavicular line Hypochondrial Lumbar Iliac Transpyloric plane Intertubercular plane 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. 242), 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. Anterolateral abdominal muscles The three muscle layers of the body wall (see p. 187) 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 as fleshy fibres into the anterior half of the outer lip of the iliac crest. Muscular fibres are replaced by an aponeurosis 229

2 Last s Anatomy..... Superior epigastric vessels Seventh costal cartilage Seventh intercostal nerve Tenth intercostal nerve Posterior layer of rectus sheath Tranversus abdominis Arcuate line Iliohypogastric nerve Inferior epigastric vessels Transversalis fascia Medial umbilical ligament Ilioinguinal nerve Lateral cutaneous nerves Rectus abdominis External oblique Cut edge of rectus sheath Tendinous intersection External oblique aponeurosis Skin over linea alba Spermatic cord Pyramidalis Fig. 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. 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. 230

3 ABDOMEN 5 Superficial ring Inguinal ligament Conjoint tendon Internal oblique Inguinal ligament Reflected part Intercrural fibres Cremaster muscle The posterior border of the muscle is free, and 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. 43). 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. From the medial end of the inguinal ligament the triangular lacunar ligament (of Gimbernat) extends horizontally backwards to the pectineal line on the pubis (see Fig. 3.1, p. 116). A fibrous band, the pectineal ligament (of Astley Cooper) extends further along the pectineal line. The crescentic free lateral edge of the lacunar ligament is the medial margin of the femoral ring (see p. 122). From the pubic tubercle, fibres may be traced upwards and medially, behind the spermatic cord, to interdigitate in the linea alba with those of the opposite side. This is the reflected part of the ligament (Fig. 5.3). Near the apex of the superficial inguinal ring are fibres running at right angles to those of the aponeurosis, the intercrural fibres, that prevent the crura from separating. Internal oblique Pubic tubercle Fig. 5.3 Left superficial inguinal ring, after removal of the external spermatic fascia which is continuous with the margins of the ring. Fleshy fibres of the muscle arise from the whole length of the lumbar fascia, from the intermediate area of the Pubic tubercle anterior two-thirds of the iliac crest and from the lateral two-thirds of the inguinal ligament. From the lumbar fascia the muscle fibres run upwards along the costal margin, to which they are attached, becoming aponeurotic at the tip of the ninth costal cartilage. Below the costal margin, the aponeurosis splits around the rectus muscle, the two layers rejoining at the linea alba. Halfway between the umbilicus and the pubic symphysis the posterior layer ends in a curved free margin, the arcuate line. Below this point, the aponeurosis passes wholly in front of the rectus muscle, to the linea alba (Fig. 5.6) (but see p. 232). The muscle fibres that arise from the inguinal ligament are continued into an aponeurosis that is attached to the crest of the pubic bone and, more laterally, to the pectineal line (Fig. 5.4). This aponeurosis is fused with a similar arrangement of the transversus aponeurosis to form the conjoint tendon. The internal oblique therefore has a free lower border, which arches over the spermatic cord: laterally the margin consists of muscle fibres in front of the cord; medially the margin consists of tendinous fibres behind the cord. Transversus abdominis Lacunar ligament Femoral ring Fig. 5.4 Left conjoint tendon and lacunar ligament. The lowest fibres of the internal oblique 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 in Figure 5.5. Note that the nearly vertical conjoint tendon lies at right angles to the nearly horizontal lacunar ligament. 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. 231

4 Last s Anatomy..... Aponeurosis Transversus abdominis Anterior superior iliac spine Inguinal ligament Pectineal ligament Lacunar ligament Conjoint tendon Pubic crest 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 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. Fig. 5.5 Left transversus abdominis, showing the lowest fibres arching medially to join the conjoint tendon. 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). 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 two muscles lie edge to edge in the lower part, but broaden out above, and are there 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. 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 posterior layer thus has a free lower margin concave downwards, the arcuate line or semicircular line (of Douglas). 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 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). 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 abdominis are each bilaminar, giving six layers in all; three form the anterior and three the posterior layers of the rectus sheath. These layers decussate across the midline. There may not be a well-defined arcuate line but a gradual diminution of aponeurotic fibres with increasing thickness of the transversalis fascia. The 232

5 ABDOMEN 5 Fig. 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, taking the external oblique aponeurosis to join the anterior layer and that of transversus to join the posterior layer; C below the arcuate line all three aponeuroses pass in front of the rectus muscle. See text for other possibilities. A B C External oblique External oblique Internal oblique Transversus Linea alba Rectus muscles lower thickened part of the transversalis fascia, between the iliac crest and pubis just above the inguinal ligament, is called the iliopubic tract. Contents. Apart from the rectus and pyramidalis muscles, the sheath contains the ends of the lower six thoracic nerves and their accompanying posterior intercostal vessels, and the superior and inferior epigastric arteries. The intercostal nerves (T7 11; see p. 189) pass from their intercostal spaces into the abdominal wall between the internal oblique and transversus muscles, and run round in this neurovascular plane to enter the sheath by piercing the posterior layer of the internal oblique aponeurosis. They then proceed behind the rectus muscle to about its midline (Fig. 5.2), where they pierce the muscle, supply it, and pass through the anterior layer of the sheath to become the anterior cutaneous nerves. In the sheath T7 runs upwards just below the costal margin, T8 transversely and the others obliquely downwards. Before they reach the sheath the nerves give off their lateral cutaneous branches, which pierce the internal and external oblique to reach the skin. The lowest thoracic nerve, T12 or subcostal, is described on page 289. The superior epigastric artery, a terminal branch of the internal thoracic (see p. 190), enters the sheath by passing between the sternal and highest costal fibres of the diaphragm. It supplies the rectus muscle and anastomoses within it with the inferior epigastric artery. This vessel leaves the external iliac at the inguinal ligament (Fig. 5.8), passes upwards behind the conjoint tendon, slips over the arcuate line and so enters the sheath. Veins accompany these arteries, draining to internal thoracic and external iliac veins respectively. 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 286; 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. 286) 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. 241). 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 233

6 Last s Anatomy..... 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. 411). 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 18. 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. 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 (ductus) 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 234

7 ABDOMEN 5 Fig. 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. Internal oblique Ilioinguinal nerve Transversus abdominis Internal spermatic fascia Ductus deferens Testicular artery Conjoint tendon External oblique aponeurosis Pampiniform venous plexus Internal spermatic fascia Cremasteric fascia External spermatic fascia Deep circumflex iliac artery Inguinal ligament Arcuate line Inferior epigastric artery Transversus abdominis Deep inguinal ring Iliacus Femoral nerve Psoas Femoral vein Pectineal ligament and pectineus Interfoveolar ligament Rectus abdominis Conjoint tendon Pubic branch Obturator nerve and vessels Pubic symphysis Fig. 5.8 Left inguinal region viewed from within the abdomen. The deep inguinal ring lies lateral to the inferior epigastric artery. The femoral ring lies medial to the external iliac (femoral) vein; the lacunar ligament which is at the medial border of the ring is here obscured by the conjoint tendon. 235

8 Last s Anatomy..... 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. 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 ductus 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. 122) 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. 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 ductus 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 ductus (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). Transversalis fascia External oblique aponeurosis Peritoneum Ductus deferens Fig. 5.9 Formation of the sheaths of the spermatic cord, testis and epididymis. Internal oblique muscle Transversus abdominis muscle Pubic bone Spermatic cord Tunica vaginalis External spermatic fascia Testis Epididymis Cremaster muscle and fascia Internal spermatic fascia 236

9 ABDOMEN 5 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 (ductus deferens) arises from the lower pole of the epididymis (see p. 239) 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. 331). 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. 315). 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 Fig Right testicular venogram. Venous catheter Testicular veins Pampiniform plexus in inguinal canal Pampiniform plexus in scrotum 237

10 Last s Anatomy..... 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 in the greater or 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 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 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. 311) and prostate (30%; see p. 309). 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. 25). 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, ductus 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 238

11 ABDOMEN 5 A Peritoneum Superficial epithelium Processus vaginalis Vasa efferentia (mesonephric tubules) Mesonephric duct Gubernaculum Ductus deferens Cremasteric fascia Internal spermatic fascia A septum Parietal tunica vaginalis Visceral tunica vaginalis External spermatic fascia Dartos muscle Skin B Peritoneum Fibrous cord Epididymis Degenerating gubernaculum Ductus deferens Lobule of testis Tunica albuginea Sinus of epididymis Epididymis Fig Mediastinum testis Testicular artery Deferent duct Artery of duct Transverse section of the left scrotum and testis. C Tunica vaginalis Epididymis Fig Stages of testicular descent: A in the fetus, the testis projects through the peritoneum into the coelomic cavity the ductus 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. 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. 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 ductus deferens The epididymis is a firm structure, attached behind the testis, with the ductus 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 ductus (vas) deferens, a direct continuation of the canal of the epididymis, provided with a thick wall of smooth muscle, passes up medially. It enters the spermatic cord, passes through the inguinal canal, across the side wall of the pelvis just under the peritoneum, and crosses the pelvic cavity. It pierces the prostate and opens by the ejaculatory duct into the prostatic urethra. Its pelvic course is described on page 311. Blood supply The epididymis is supplied by a branch of the testicular artery. This enters the upper pole and runs down to 239