B Segmental (radicular) cutaneous innervation of the anterior trunk wall (dermatomes)

Right half of the trunk and adjacent upper limb, anterior view. Every sensory nerve root (dorsal root) innervates a specific skin area with its fibers. These “dermatomes” (see p. 88), then, correspond to associated spinal cord segments. The dermatomes are arranged in bandlike patterns that encircle the chest wall and upper abdomen. Below the umbilicus, the dermatomes become angled slightly downward toward the median plane. A “segmental gap” exists between the C 4 and T 2 dermatomes because the phylogenetic outgrowth of the human upper limb has removed the sensory fibers of C 5–C 8 and T 1 from the trunk wall (after Mumenthaler).

C Peripheral sensory cutaneous innervation of the anterior trunk wall

Right half of the trunk and adjacent upper limb, anterior view. The color-coded map of the peripheral cutaneous nerve territories follows the branching pattern of the cutaneous nerves in the subcutaneous connective tissue. Besides the cutaneous branches of the intercostal nerves (anterior and lateral cutaneous branches), it is chiefly the supraclavicular nerves and the iliohypogastric and ilioinguinal nerves that supply the skin of the anterior trunk wall (after Mumenthaler).

E Criteria for dividing the abdomen into regions

a The abdomen is divided into four quadrants by two perpendicular lines that intersect at the umbilicus.

b Coordinate system composed of two vertical and two horizontal lines. They divide the abdomen into nine regions, each located in either the upper, middle, or lower abdomen. The two vertical lines represent the left and right midclavicular lines. The two horizontal lines pass through the lowest point of the tenth ribs or the summit of the two iliac crests (see p. 35).

F Projection of the abdominal organs onto the four quadrants of the anterior abdominal wall

a Organs of the anterior layer, b organs of the middle layer, c organs of the posterior layer.

The organs of the anterior layer abut the anterior abdominal wall. The organs of the middle layer are located in the posterior part of the abdominal cavity (some are partially retroperitoneal), and those of the posterior layer are located outside or behind the actual abdominal cavity (i. e., they are retroperitoneal).

A Neurovascular structures of the posterior trunk wall and nuchal region

Posterior view. The segmentally arranged neurovascular structures of the posterior trunk wall (posterior rami of the spinal nerves and posterior branches of the posterior intercostal and lumbar vessels) are demonstrated on the left side of the trunk (all muscle fasciae have been removed except for the superficial layer of the thoracolumbar fascia). On the right side, the trapezius muscle has been detached from its origins and reflected laterally to show the course of the transverse cervical artery in the deep scapular region (compare with B).

Note: On the posterior trunk wall, only the lateral nuchal region (lesser occipital nerve, see C) and the lower gluteal region (inferior clunial nerves) receive their sensory supply from anterior spinal nerve rami.

The latissimus dorsi muscle has been partially removed on the right side to demonstrate the upper costolumbar triangle (of Grynfeltt). The fibrous lumbar triangle (boundaries: twelfth rib, intrinsic back muscles, and internal oblique) is similar to the lower iliolumbar triangle (of Petit, bounded by the iliac crest, latissimus dorsi, and external oblique) in that it creates a site of predilection for rare, usually acquired lumbar hernias (Grynfeltt or Petit hernia, see also p. 223).

Right scapular region, posterior view. The trapezius, splenius capitis, deltoid, infraspinatus, and rhomboid major and minor muscles have been completely or partially removed on the right side. The deep scapular region is supplied by the transverse cervical artery, deep cervical artery (see C), suprascapular artery, circumflex scapular artery, and posterior circumflex humeral artery. All of these vessels arise directly or indirectly—via the thyrocervical trunk—from the subclavian artery (neither is visible here). The suprascapular, circumflex scapular, dorsal scapular, and thoracodorsal arteries form the “scapular arcade” (see p. 391). Medial to the mastoid process, the occipital artery appears below the tendon of insertion of the sternocleidomastoid muscle and runs upward with the sensory greater occipital nerve to the skin of the occiput. The greater occipital nerve pierces both the trapezius and semispinalis capitis muscles in the area of their firm tendinous attachments. It may become compressed at these sites, leading to occipital neuralgia.

C Suboccipital triangle (vertebral artery triangle)

Posterior view. The trapezius, sternocleidomastoid, splenius capitis, and semispinalis capitis muscles have been removed to display the suboccipital region on the right side. The suboccipital triangle is bounded by the suboccipital muscles (rectus capitis posterior major and the obliquus capitis superior and inferior). In the deep portion of the triangle, the vertebral artery runs through its groove in the atlas. The suboccipital nerve (C 1), which is purely motor, emerges above the posterior arch of the atlas to supply the short muscles of the head. The greater occipital nerve (C 2) and, at a lower level, the third occipital nerve (C 3) wind posteriorly as they pass the lower margin of the obliquus capitis inferior. The deep cervical artery, a branch of the costocervical trunk, runs between the semispinalis capitis and cervicis muscles.

A Neurovascular structures on the anterior side of the posterior trunk wall

Anterior view.

a Lumbar fossa on the right side after removal of the anterior and lateral trunk wall, the intra- and retroperitoneal organs, the peritoneum, and all the fasciae of the trunk wall. The inferior vena cava has been partially removed.

b Lumbar fossa with the lumbar plexus of the right side after removal of the superficial layer of the psoas major.

The lumbar plexus (see p. 536) is formed by the anterior rami of the T 12–L 4 nerves lateral to the lumbar spine and is partially covered by the psoas major muscle. The nerves run laterally and obliquely downward to the abdominal wall and thigh, except for the obturator nerve (see b), which runs through the lateral wall of the lesser pelvis and the obturator foramen (not visible here) to the medial part of the thigh.

Note: The sites of emergence of the lumbar and iliolumbar vessels are located below the psoas major muscle. They run almost horizontally across the quadratus lumborum and iliacus muscles. Medial to the psoas major (and covered by the inferior vena cava) is the lumbar sympathetic trunk.

D Preserving the intercostal vein, artery, and nerve during the insertion of a chest tube

A chest tube may be inserted to drain an abnormal fluid collection from the pleural space, such as a pleural effusion due to bronchial carcinoma. The best site for placing the chest tube can be determined by percussion or ultrasound examination. Generally, one optimum puncture site in the sitting patient is at the level of the seventh or eighth intercostal space on the posterior axillary line (see e and p. 34). The drain should always be introduced at the upper margin of a rib to avoid injuring the intercostal vein, artery, and nerve. For additional puncture sites, see textbooks on surgery.

a–d Steps in the placement of a chest tube (anterior view; after Henne-Bruns, Dürig, and Kremer):

a A skin incision is made under local anesthesia, and the drainage tube is introduced perpendicular to the chest wall.

b On reaching the ribs, the tube is angled 90° and advanced cephalad in the subcutaneous plane, parallel to the chest wall.

c On reaching the next higher intercostal space, the tube is passed through the intercostal muscles above the rib.

d The tube is then advanced into the pleural cavity.

e Longitudinal section through the chest wall at the level of the posterior axillary line, after placement of the chest tube in the presence of pleural effusion.

F Lymphatic drainage of the breast

The lymphatic vessels of the breast can be divided into a superficial, subcutaneous, and deep system. The deep system begins with lymphatic capillaries at the acinar level (see Cb and c) and is particularly important as a route for tumor metastasis. The main regional filtering stations are the axillary and parasternal lymph nodes, the approximately 30 to 60 axillary lymph nodes receiving most of the lymphatic drainage. They are the first nodes to be affected by metastasis (see G) and therefore have major oncological significance. The axillary lymph nodes are subdivided into levels (see p. 360):

• Level I: lower axillary group (lateral to the pectoralis minor):

– Pectoral axillary lymph nodes

– Subscapular axillary lymph nodes

– Lateral axillary lymph nodes

– Paramammary lymph nodes

• Level II: middle axillary group (at the level of the pectoralis minor):

– Interpectoral axillary lymph nodes

– Central axillary lymph nodes

• Level III: upper infraclavicular group (medial to the pectoralis minor):

– Apical axillary lymph nodes

The parasternal lymph nodes, which are distributed along the thoracic vessels, chiefly drain the medial portion of the breast. From there, tumor cells may spread across the midline to the opposite side. The survival rate in breast cancer patients correlates most strongly with the number of involved lymph nodes at the various axillary nodal levels. The parasternal lymph nodes are rarely important in this regard. According to Henne-Bruns, Dürig, and Kremer, the 5-year survival rate is approximately 65% with metastatic involvement of level I, 31% with involvement of level II, but approaches 0% in patients with level III involvement. This explains the key prognostic importance of a sentinel lymphadenectomy (removal of the sentinel lymph node). This technique is based on the assumption that every point in the integument drains via specific lymphatic pathways to a particular lymph node, rarely draining to more than one. Accordingly, the lymph node that is the first to receive lymph from the primary tumor will be the first node to contain tumor cells that have spread from the primary tumor by lymphogenous metastasis. The specific lymphatic drainage path, and thus the sentinel node, can be identified by scintigraphic mapping with radio-labeled colloids (^99mTC sulfur microcolloid), which has superseded the older technique of patent blue dye injection. The first lymph node to be visualized is the sentinel node. That node is selectively removed and histologically examined for the presence of tumor cells. If the sentinel node does not contain tumor cells, generally the rest of the axillary nodes will also be negative. This method is 98% accurate in predicting the level of axillary nodal involvement prior to surgery.

G Distribution of malignant tumors by quadrant in the female breast

The numbers indicate the average percentage location of malignant breast tumors.

A Location of the inguinal canal in the male

Right inguinal region, anterior view. Approximately 4 to 6 cm long, the inguinal canal passes obliquely forward, downward, and medially above the inguinal ligament to pierce the anterior abdominal wall. It begins internally at the deep inguinal ring (D and E) in the lateral inguinal fossa (see p. 214) and opens externally at the superficial inguinal ring, lateral to the pubic tubercle. With the superficial abdominal fascia removed, this “external opening” of the canal can be identified as a slitlike orifice in the aponeurosis of the external oblique muscle (external oblique aponeurosis). It is bounded by the medial crus superomedially and by the lateral crus inferolaterally. Both crura are interconnected by the intercrural fibers. The superficial inguinal ring is completed internally by arched fibers from the inguinal ligament (reflex ligament), forming a deep groove. The inguinal canal in the male provides a pathway for the descent of the testis during fetal life (see p. 226). Its contents in the male (after testicular descent) include the spermatic cord, and its contents in the female include the round ligament of the uterus.

B Sagittal section through the inguinal canal in the male

Medial view. Note the structures that form the walls of the inguinal canal above and below the spermatic cord and on the anterior and posterior sides (compare with C). The openings and wall structures of the inguinal canal bear an important relationship to the pathophysiology of hernias (after Schumpelick).

D Contribution of the oblique abdominal muscles to the structure of the male inguinal canal

Right inguinal region, anterior view.

a–c Progressive removal of the abdominal wall muscles.

E The inguinal canal, progressively opened to expose the spermatic cord

a Division of the external oblique aponeurosis reveals the internal oblique muscle, some of whose fibers are continued onto the spermatic cord as the cremaster muscle. The genital branch of the genitofemoral nerve runs with it below the cremasteric fascia (see p. 538). The ilioinguinal nerve runs through the inguinal canal on the spermatic cord. Its sensory fibers pass through the superficial inguinal ring to the skin over the pubic symphysis and are distributed to the lateral portion of the scrotum or labia majora and medial thigh.

b With the internal oblique muscle divided and the cremaster muscle split, the full course of the spermatic cord through the inguinal canal can be displayed. The spermatic cord appears at the deep inguinal ring, where the transversalis fascia is invaginated into the inguinal canal (and encloses the spermatic cord on its way to the testis as the internal spermatic fascia). It runs below the transversus abdominis along the posterior wall of the inguinal canal (transversalis fascia and peritoneum). The wall at the midportion of the canal is formed by the interfoveolar ligament and is reinforced medially by the reflected inguinal ligament. Medial to the interfoveolar ligament, deep to which run the epigastric vessels, and superior to the inguinal ligament is the medial inguinal fossa, a weak spot in the abdominal wall that is a common site for direct inguinal hernias (after Schumpelick; see also p. 215).

D Triangle of doom and triangle of pain

In two key regions in the preperitoneal space known respectively as the “triangle of pain” and the “triangle of doom,” it is important to avoid placing clips to secure mesh implants, particularly in laparoscopic hernia repairs (see p. 221). The iliopubic tract (the union of the transverse fascia and the inguinal ligament) defines the superior border of both triangles. The triangle of pain lies lateral to the testicular vessels, the triangle of doom medial to them. The triangle of pain contains both branches of the genitofemoral nerve, the femoral nerve, and the lateral femoral cutaneous nerve. Injury to these nerves can result in pain and dysesthesia. The testicular vessels and the major vessels of the leg (the external iliac vessels) course through the triangle of doom. Injury to these vessels can lead to poorly controllable bleeding.