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Caecum

Caecum

For medical students2 min readUpdated 2026-10-10

The caecum is a blind-ended pouch that forms the initial and widest part of the large intestine. It is typically located in the right iliac fossa and serves as the attachment site for the vermiform appendix.

LocationRight iliac fossa (*fossa iliaca dextra*)
Peritoneal relationIntraperitoneal (completely covered by peritoneum)
DimensionsLength 3–8 cm, width 4–7 cm
AppendixLength 2.5–15 cm, diameter 3–4 mm

Topography and External Structure

Anatomically, the caecum (caecum) is a distinct pouch-like expansion of the proximal large intestine. Its typical location is the right iliac fossa. In this region, it lies inferior to the ileocaecal junction, where chyme passes from the small intestine into the large bowel.

The dimensions of the organ vary individually within the following ranges:

Regarding its peritoneal relations, the caecum is completely invested by peritoneum (intraperitoneal). Despite this full peritoneal coverage, its mobility within the peritoneal cavity can vary significantly among individuals.

Vermiform Appendix

A crucial anatomical structure closely associated with the caecum is the vermiform appendix (appendix vermiformis). It originates from the posteromedial wall of the caecum.

Visually, the appendix is a narrow, worm-like tube whose dimensions show considerable inter-individual variability:

Internal Openings and Variations

The lumen of the vermiform appendix opens directly into the cavity of the caecum via the appendicular orifice (ostium appendicis vermiformis).

The position of the appendix within the peritoneal cavity is notoriously variable. The main anatomical positions relative to the caecum and surrounding structures include:

  1. Retrocaecal (behind the caecum).
  2. Pelvic (descending into the lesser pelvis).
  3. Medial (pointing toward the midline).
  4. Lateral (pointing outward toward the lateral abdominal wall).

Mnemonic

To remember the common positions of the appendix, use the mnemonic PRML: Pelvic, Retrocaecal, Medial, Lateral (or Retrocaecal, Pelvic, Medial, Lateral).

Frequently asked questions

What anatomical positions of the vermiform appendix are recognized in topographical anatomy?

Topographical anatomy distinguishes several positions of the vermiform appendix:

  • Pelvic (descending) position (descendens) — the appendix points inferiorly into the lesser pelvis.
  • Medial position (medialis) — runs parallel to the ileum toward the midline.
  • Lateral position (lateralis) — points laterally into the right paracolic gutter.
  • Anterior position (anterior) — lies on the anterior surface of the caecum.
  • Ascending (subhepatic) position (ascendens) — the tip points superiorly, frequently reaching the subhepatic region.
  • Retrocaecal position (retrocaecalis) — lies posterior to the caecum.
Which muscular bands (*taeniae coli*) converge at the base of the vermiform appendix?

All three longitudinal muscular bands (taeniae) of the caecum converge at the base of the appendix, merging to form a continuous outer longitudinal muscle layer around the appendix.

Which arteries supply blood to the caecum?

Blood supply to the caecum is derived from:

  • Ileocolic artery (a. ileocolica) — the primary source supplying the ileocaecal region.
  • Anterior caecal artery (a. caecalis anterior) — supplies the anterior surface of the caecum.
  • Posterior caecal artery (a. caecalis posterior) — supplies the posterior surface of the caecum.
Where does venous drainage from the caecum and appendix go?

Venous blood drains into the portal venous system via the superior mesenteric vein (v. mesenterica superior), which receives the ileocolic vein (v. ileocolica) alongside the appendicular vein (v. appendicularis).

Which lymph nodes serve as regional nodes for the caecum?

Regional lymph nodes for the caecum include:

  • Superior mesenteric lymph nodes (nodi lymphoidei mesenterici superiores)
  • Ileocolic lymph nodes (nodi ileocolici)
  • Precaecal nodes (nodi precaecales) — located along the anterior caecal artery
  • Retrocaecal nodes (nodi retrocaecales) — located around the posterior caecal artery

Additional nodes are found along the courses of the a. ileocolica and a. colica dextra.

How is the base of the appendix projected onto the anterior abdominal wall?

Standard surgical surface markings for the base of the appendix include:

  • McBurney's point — at the junction of the lateral and middle thirds of a line connecting the right anterior superior iliac spine to the umbilicus.
  • Lanz's point — at the junction of the right and middle thirds of the interspinous line (between both anterior superior iliac spines).
What are the sources of sympathetic and parasympathetic innervation of the caecum?

Innervation is provided by sympathetic, parasympathetic, and visceral sensory fibers.

Autonomic sources include:

  • Superior mesenteric plexus (plexus mesentericus superior) — the main source of innervation for the caecum and ileocaecal region.
  • Intermesenteric plexus (plexus intermesentericus) — connects the superior and inferior mesenteric plexuses.
  • Parasympathetic fibers — derived from the posterior vagal trunk (truncus vagalis posterior), branches of the vagus nerve (n. vagus).
Where is the caecum located?

It is located in the right iliac fossa, lying inferior to the ileocaecal junction.

What is the peritoneal covering of the caecum?

It is covered by peritoneum on all sides (intraperitoneal), though its mobility can vary.

From which wall of the caecum does the appendix arise?

The appendix arises from the posteromedial wall of the caecum.

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