Gross Anatomy of Sigmoid Colon Rectum and Appendix BDS II 2024 (1)

SIGMOID COLON

• Definition and Location

  • Continuation of the descending colon.

  • Hangs down into the pelvis forming a loop.

  • Extends from the pelvic brim to the third piece of the sacrum, transitioning into the rectum.

  • Length: 25 to 40 cm.

  • Entirely retroperitoneal and mobile.

  • Suspended from the posterior abdominal wall by a fan-shaped mesentery known as sigmoid mesocolon.

ANTERIOR RELATIONS

• Uterus

• Urinary bladder (in males)

• Fornix

• Left gonadal vessels

• Upper part of vagina (in females)

• Pubic bone

• Psoas major

POSTERIOR RELATIONS

• Upper roots of sacral plexus

• Terminal part of ileum

• Bladder

• Sacrum

• Seminal vesicle (in males)

• External iliac vessels

• Prostate (in males)

• Left piriformis

• Urethra (in females)

• Rectum

BLOOD SUPPLY

• Arteries

  • Supplied by 1 to 4 sigmoid arteries, branches of the inferior mesenteric artery.

• Veins

  • Correspond to arteries, draining into portal venous system tributaries.

NERVE SUPPLY

• Sympathetic Nerves

  • Originates from lumbar sympathetic trunk via lumbar splanchnic nerves (L1-L2) and inferior hypogastric plexus from the inferior mesenteric plexus.

• Parasympathetic Nerves

  • Supplied by pelvic splanchnic nerves S2-S4.

LYMPHATIC DRAINAGE

• Accompanies sigmoid vessels to inferior mesenteric nodes and regional sigmoid nodes.

RECTUM

• Definition

  • Continuation of the sigmoid colon.

  • The lower end of the sigmoid mesocolon indicates the rectosigmoid junction.

• Transition

  • Lower part narrows through the pelvic diaphragm to form the anal canal.

APPENDIX

• Definition and Location

  • A narrow, elongated diverticulum of the caecum located in the right iliac fossa.

  • Opens postero-medially, about 2.5 cm below the ileocaecal orifice.

  • Length ranges from 0.5 cm to 25 cm (average 9 cm), diameter approximately 5 mm.

  • Typically longer in children and may atrophy in middle age.

EMBRYOLOGY AND POSITION

• Develops as a narrowed apex of the caecum, with the anterolateral wall of the caecum growing more rapidly, resulting in the appendix's final postero-medial position.

• Position Variations

  • Retrocaecal (64%)

  • Retrocolic

  • Pelvic (32%)

  • Postileal (0.5%)

  • Paracaecal/precaecal (1.5%)

  • Subcaecal (2.0%)

  • Preileal (1%)

  • Promontoric position.

BLOOD SUPPLY

• Arterial Supply

  • Appendicular artery, a lower branch of the ileocolic artery, enters mesoappendix.

• Venous Drainage

  • Corresponding appendicular vein drains into ileocolic and superior mesenteric vein to the portal vein.

NERVE SUPPLY

• Sympathetic Nerve Supply

  • Via lesser splanchnic nerves (T10-T11) with postganglionic fibers from superior mesenteric plexus.

• Parasympathetic Nerve Supply

  • From the right and left vagus nerves.

LYMPHATIC DRAINAGE

• Accompanies appendicular vessels to appendicular nodes and ileocolic nodes, connecting to regional superior mesenteric nodes.

McBURNEY’S POINT

• Used for surgical incision location.

• Draw a line from the umbilicus to the right anterior superior iliac spine (R ASIS).

• Divide the line into thirds; the point that lies two-thirds from the umbilicus to the R ASIS corresponds to the base of the appendix.

CLINICAL IMPLICATIONS

• Acute Appendicitis

  • Pain begins as vague discomfort in the periumbilical region, referred pain from T10 dermatome (visceral pain).

  • Pain shifts to the right iliac fossa due to the involvement of the parietal peritoneum as inflammation progresses (somatic pain).

CONCLUSION

• Understanding the anatomy, blood supply, nerve supply, and clinical relevance of the sigmoid colon and appendix is crucial for diagnosis and treatment of gastrointestinal conditions.