Gross Anatomy: Anterior Abdominal Wall & Inguinal Region PDF 2024

Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 1 of 17 Dr. Mark Ireland SESSION LEARNING OBJECTIVES By the end of this session, the student should be able to accurately: 1. Describe the origins and attachments of the fascial layers of the anterior abdominal wa...

Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 1 of 17 Dr. Mark Ireland SESSION LEARNING OBJECTIVES By the end of this session, the student should be able to accurately: 1. Describe the origins and attachments of the fascial layers of the anterior abdominal wall. 2. Describe the muscles of the anterior abdominal wall including their attachments, innervation, and actions. 3. Describe the rectus sheath and its structural contribution to the anterior abdominal wall and inguinal region. 4. Describe the transversalis fascia and differentiate it from the other structures of the anterior abdominal wall including extraperitoneal connective tissue and peritoneum. 5. Describe the cutaneous nerves of the anterior abdominal wall and list their functions. 6. Describe the vasculature of the anterior abdominal wall including the arteries and regions supplied, and the veins and lymphatics and the regions drained. 7. Describe the formation, borders, and contents of the inguinal canal. 8. Describe the coverings of the spermatic cord and relate them to their fascial origin. 9. Apply anatomical knowledge to the clinical problem of indirect vs. direct inguinal hernias. Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 2 of 17 Dr. Mark Ireland SESSION OUTLINE I. Fascia A. Superficial - Camper’s/Scarpa’s B. Deep – Muscular and Transversalis II. Muscles of Anterior Abdominal Wall A. External Abdominal Oblique B. Internal Abdominal Oblique C. Transversus Abdominis D. Rectus Abdominis III. Rectus Sheath IV. Transversalis Fascia, Extraperitoneal Connective Tissue, Peritoneum V. Nerves of Anterior Abdominal Wall VI. Vasculature of Anterior Abdominal Wall VII. Inguinal Canal – Formation and Contents A. Floor B. Anterior Wall C. Posterior Wall VIII. Coverings of Spermatic Cord IX. Inguinal Hernia – Direct and Indirect Supplemental Reading Gray’s Anatomy for Students, 4th Ed. (2020) Drake, Vogl, & Mitchell (Elsevier) Chapter 4. Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 3 of 17 Dr. Mark Ireland I. FASCIA Fig 1 Superficial (Fig 1 Gray’s 4.24) →Camper’s fascia: superficial, fatty layer →Scarpa’s fascia: deep, membranous layer; well developed in lower anterior abdominal wall; attaches to the deep thigh fascia inferior to the inguinal ligament Deep →The fascia covering the superficial and deep surfaces of the individual anterior abdominal wall muscles; each muscle has its own deep fascia; several contribute to the coverings of the spermatic cord →Transversalis fascia: deep fascia covering the innermost surface of the deepest anterior wall muscle layer; derived posteriorly from the thoracolumbar fascia Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 4 of 17 Dr. Mark Ireland II. MUSCLES OF ANTERIOR ABDOMINAL WALL External Abdominal Oblique (Fig 2 Gray’s 4.27) Fig 2 Muscle Origin Insertion Innervation Action External slips from ribs V- iliac crest and anterior rami of compress Abdominal XII linea alba lower 6 thoracic abdominal Oblique through its spinal nn. T7-12 contents during aponeurosis, maximal lower extent of it expiration, aponeurosis coughing and forms the defecation, trunk inguinal ligament flexion and between ASIS rotation and pubic tubercle Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 5 of 17 Dr. Mark Ireland Internal Abdominal Oblique (Fig 3 Gray’s 4.30) Fig 3 Muscle Origin Insertion Innervation Action Internal thoracolumbar inferior border of anterior rami of compress Abdominal fascia, iliac crest, ribs IX-XII and lower 6 thoracic abdominal Oblique lateral 2/3 of the linea alba, spinal nn. T7-12 contents during inguinal ligament pubic crest and plus L1 maximal pectineal line expiration, through its coughing and aponeurosis defecation, trunk flexion and rotation →Its aponeurosis fuses with the aponeurosis of the transversus abdominis to form the conjoined (conjoint) tendon Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 6 of 17 Dr. Mark Ireland Transversus Abdominis (Fig 4 Gray’s 4.31) Fig 4 Muscle Origin Insertion Innervation Action Transversus thoracolumbar its aponeurosis anterior rami of compresses Abdominis fascia, iliac crest, attaches to linea lower 6 thoracic abdominal costal cartilages alba, pubic crest spinal nn. T7-12 contents during of lower few ribs and pectineal plus L1 maximal line expiration, coughing and defecation →Its aponeurosis fuses with the aponeurosis of the internal abdominal oblique to form the conjoined (conjoint) tendon Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 7 of 17 Dr. Mark Ireland Rectus Abdominis (Fig 5 Gray’s 4.32) Fig 5 Muscle Origin Insertion Innervation Action Rectus pubic crest, costal cartilages anterior rami of compress Abdominis pubic tubercle of ribs V-VII and lower 6 thoracic abdominal and pubic the xiphoid spinal nn. T7-12 contents during sympyhsis process maximal expiration, coughing and defecation, flex trunk Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 8 of 17 Dr. Mark Ireland III. RECTUS SHEATH (Fig 6 Gray’s 4.33) General description - dense connective tissue enclosing the rectus abdominis muscle; its anterior and posterior layers are formed by the aponeuroses of the external/internal abdominal oblique and transversus abdominis muscles; the aponeuroses meet at the lateral edge of the rectus abdominis (linea semilunaris) and fuse in the midline (linea alba) Rectus Sheath Above the Umbilicus (Fig 6) →the external abdominal oblique aponeurosis contributes to the anterior rectus sheath; the internal abdominal oblique contributes to the anterior and posterior rectus sheath; the aponeurosis of the transversus abdominis contributes to the posterior rectus sheath Rectus Sheath Below the Umbilicus (Fig 6) →At a point somewhere between the umbilicus and the pubic symphysis: the aponeuroses of the internal abdominal oblique and the transversus abdominis pass only to the anterior rectus sheath; inferior to this point (arcuate line) the posterior layer of the rectus sheath is absent and the rectus abdominis is in contact with the transversalis fascia Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 9 of 17 Dr. Mark Ireland IV. Transversalis Fascia, Extraperitoneal Connective Tissue, Peritoneum (Fig 7 Gray’s 4.34) →transversalis fascia is derived posteriorly from the Fig 7 thoracolumbar fascia; it lies just deep to the anterior abdominal wall muscular fascia →extraperitoneal connective tissue fills up the space between the transversalis fascia and the more deeply placed parietal peritoneum V. NERVES OF ANTERIOR ABDOMINAL WALL (Fig 8, 9 Gray’s 4.36, 4.37) Fig 8 General Description (Fig 8)- anterior (ventral) rami of spinal nerves T7-T11 (intercostal nn.) continue into the anterior abdominal wall as the thoracoabdominal nn.; the subcostal n. (T12) and the iliohypogastric and ilioinguinal nn. (L1) also enter the anterior abdominal wall Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 10 of 17 Dr. Mark Ireland Fig 9 Nerves of the anterior abdominal wall course inferiorly and medially within the neurovascular plane between the transversus abdominis and internal abdominal obliques mm. (Fig 9) and innervate all the muscles of the anterior abdomen →Dermatomal distribution: xiphoid process – T7 (some sources such as Grant’s Dissector say T6- don’t worry about the difference); umbilicus – T10; pubis – L1 via iliohypogastric n; the ilioinguinal n. enters the inguinal canal and supplies the anterior scrotum/labium majus and upper medial thigh VI. VASCULATURE OF ANTERIOR ABDOMINAL WALL (Fig 10 Gray’s 4.40) Arteries →Superior epigastric artery branches from the internal Fig 10 thoracic and descends within the posterior rectus sheath; anastomoses with the inferior epigastric a. →Inferior epigastric artery branches from the external iliac a. before the external iliac a. passes inferior to the inguinal ligament; courses superiorly and medially in the extraperitoneal connective tissue; penetrates the transversalis fascia inferior to the arcuate line; anastomses with the superior epigastric a. within the substance of the rectus abdominis m. → Deep and superficial circumflex iliac; superficial epigastric; intercostals Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 11 of 17 Dr. Mark Ireland Veins & Lymphatics →the lumbar and subcostal vv. drain into the azygos system; anteriorly, they anastomose with the superior and inferior epigastric vv. →thoracoepigastric vein (see Fig 11): a longitudinal vein running within the superficial fascia of the lateral part of the thorax and abdomen; drains into the SVC via the lateral thoracic v. and into the IVC via the superficial epigastric v.; tributaries near the umbilicus anastomose with the paraumbilical vv. and ultimately drain into the portal v.; with portal hypertension, blood flow through the portal v. can be impeded to such a degree that retrograde flow through the paraumbilical vv. and the thoracoepigastric Fig 11 tributaries enlarges their diameter to form the characteristic caput medusae →Lymphatics: superficial lymphatics of the anterior abdominal wall drain into the axillary and superficial inguinal nodes; lymphatics from abdominal wall muscles drain along the posterior intercostal and superior/inferior epigastric vv. to reach lumbar, parasternal and external iliac nodes VII. INGUINAL CANAL (Fig 12-16) Definition: an oblique passage through the fascial and muscular layers in the lower anterior abdominal wall; connects the scrotum/labium majus to the retroperitoneal region; transmits the ductus deferens in males and the round ligament of the uterus in females; lies parallel and superior to the inguinal ligament, extending from the deep to the superficial inguinal ring; the femoral vessels pass inferior to the inguinal ligament Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 12 of 17 Dr. Mark Ireland Boundaries or Walls of Inguinal Canal Fig 12 Floor of Inguinal Canal (Fig 12 Gray’s 4.29) laterally by inguinal ligament (inferior extent of ext. abd. oblique aponeurosis) medially by lacunar ligament (a posterior extension of inguinal ligament attaching to pectin pubis; pectineal ligament is an extension of lacunar ligament along the pectineal line of pelvis) Anterior Wall of Inguinal Canal (Fig 13, 14 Gray’s 4.44, 4.45) Fig 13 laterally, by aponeurosis of external abdominal oblique (Fig 13) plus internal oblique fibers originating from inguinal ligament which lie anterior to the contents of the inguinal canal (Fig 14) medially, by aponeurosis of external abdominal oblique→superficial inguinal ring (Fig 13) Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 13 of 17 Dr. Mark Ireland Fig 14 Posterior Wall of Inguinal Canal (Fig 14, 15 Gray’s 4.45, 4.46) medially, fibers of the internal abdominal oblique arch over the spermatic cord or round ligament to form the posterior wall of the inguinal canal (Fig 14); int. abd. oblique fibers also form the cremasteric muscle; remainder of medial posterior wall formed by aponeurosis of transversus abdominis which fuses with aponeurosis of int. abd. oblique to form the conjoint tendon (Fig 14, 15) Fig 15 Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 14 of 17 Dr. Mark Ireland laterally, the posterior wall is formed by the transversalis fascia (Fig 16 Gray’s 4.43); the transversalis fascia forms the deep inguinal ring Fig 16 Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 15 of 17 Dr. Mark Ireland VIII. COVERINGS OF THE SPERMATIC CORD (Fig 17 Gray’s 4.41) Fig 17 during embryonic development, as the testes and ductus deferens are “drawn” into the scrotum from their retroperitoneal origin, they pass through the inguinal canal; as they pass through the inguinal canal they acquire several fascial coverings derived from the structures forming the inguinal canal (also see Figure 18 below) Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 16 of 17 Dr. Mark Ireland Fig 18 internal spermatic fascia – evagination of the transversalis fascia ensheathing the ductus deferens, testis and blood vessels; the deep inguinal ring is formed at this site; the ring is located about midway between the pubic symphysis and ASIS; located lateral to the inferior epigastric vessels middle spermatic (cremasteric) fascia – derived from the fascia of the internal abdominal oblique m.; lower most fibers of the internal abdominal oblique m. continue onto the surface of the spermatic cord as the cremasteric m.; cremasteric m. is innervated by the genital branch of the genitofemoral n. and raises the testicle for temperature regulation; cremasteric relex elicited by stroking the upper, medial thigh confirms the integrity of L1-L2 spinal cord segments external spermatic fascia – outer most covering of the spermatic cord; derived from the fascia of the external abdominal oblique m. Inguinal (Hasselbach’s) Triangle – a potential weak area in the anterior abdominal wall bounded by the inguinal ligament, the inferior epigastric vessels and the lateral border of the rectus abdominis muscle IX. INGUINAL HERNIA General Description - a protrusion of abdominal contents (usually a loop of small intestine) protruding through a defect in the musculofascial walls of the inguinal canal; more frequent in males Gross Anatomy: Anterior Abdominal Wall & Inguinal Region Page 17 of 17 Dr. Mark Ireland Fig 19 Direct inguinal hernia (Fig 19 Gray’s 4.49): abdominal content protruding through the inguinal triangle; acquires the following coverings (from internal to external) – peritoneum, extraperitoneal connective tissue, transversalis fascia, conjoint tendon, external abdominal oblique aponeurosis and fascia; does not usually protrude through the superficial inguinal ring into the scrotum Fig 20 Indirect inguinal hernia (Fig 20 Gray’s 4.48): protrusion of abdominal content through the inguinal canal; always originates lateral to the inferior epigastric a.; acquires the coverings of the spermatic cord plus the peritonuem; emerges through the superficial inguinal ring and usually enters the scrotum; associated with a patent processus vaginalis