Anatomy Atlas

Vermiform appendix

Appendix vermiformis
Also: Appendix
OrganHigh-yielddraftGI

Blind-ending tube arising from the cecum where the teniae coli converge. Acute appendicitis is the most common abdominal surgical emergency.

Core anatomy

Location

Right iliac fossa. Its base is on the posteromedial cecum about 2 cm below the ileocecal valve, where the three teniae coli converge (a surgical guide to finding it). The tip is variable (most often retrocecal, also pelvic, subcecal, pre- or post-ileal).

Parts
  • Base, body and tip; lumen rich in lymphoid tissue
  • Mesoappendix: a peritoneal fold from the terminal ileum mesentery, containing the appendicular artery
Relations

The base projects to McBurney point, one-third of the way from the right ASIS to the umbilicus. A retrocecal appendix lies against the psoas; a pelvic appendix against the obturator internus, bladder or rectum.

Arterial supply

Appendicular artery, a branch of the ileocolic artery (from the superior mesenteric artery).

Venous drainage

Appendicular vein → ileocolic vein → SMV → portal vein (portal pyelophlebitis and liver abscess are rare complications).

Innervation

Visceral afferents with sympathetic fibers to about T10, so early pain refers to the periumbilical region.

Mentioned in

Generated automatically from links in other entries.

Referred visceral painFront and back body outlines with numbered zones of referred pain. 1: the heart refers pain to the substernal region, left arm and jaw. 2: diaphragmatic irritation refers to the shoulder tip through C3–C5; on the left this is the Kehr sign of splenic rupture. 3: the stomach and duodenum (foregut) refer to the epigastrium. 4: the gallbladder refers to the right upper quadrant or epigastrium and to the right scapula. 5: the pancreas refers to the epigastrium and through to the back. 6: the small intestine and early appendicitis refer to the periumbilical region (midgut). 7: later appendicitis localizes to the right lower quadrant at McBurney point once the parietal peritoneum is inflamed. 8: the distal colon (hindgut) and bladder refer to the suprapubic region. 9: the kidney refers to the flank and costovertebral angle. 10: a ureteric stone causes pain from loin to groin.11223445678910Anterior · patient's right ←Posterior · patient's right →1Heart (angina, MI)Substernal, left arm, jaw (T1–T4)2DiaphragmShoulder tip (C3–C5, phrenic n.); left = Kehr sign3Stomach, duodenum (foregut)Epigastric4GallbladderRUQ or epigastric → right scapula5PancreasEpigastric, boring through to the back6Small intestine, early appendicitisPeriumbilical (midgut)7Appendicitis, laterRLQ (McBurney point) once parietal peritoneum is inflamed8Distal colon (hindgut), bladderSuprapubic9KidneyFlank, costovertebral angle10Ureter (stone)Loin to groin (testis or labium)

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Referred visceral pain. Visceral pain is poorly localized and felt in the dermatomes that share spinal segments with the organ's afferent fibers. Pain becomes sharp and localized once the parietal peritoneum is involved (appendicitis: periumbilical → RLQ). Zones are approximate and vary between people.
Original schematic, created for this atlas.
Cecum, terminal ileum and appendix with the ileocolic and appendicular arteries
The cecum and appendix with the appendicular artery in the mesoappendix.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 1073. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Acute appendicitis PANCE

Mechanism / lesion

Luminal obstruction (fecalith, lymphoid hyperplasia, rarely tumor) → distension, ischemia, bacterial invasion, and perforation if untreated.

Classic presentation

Periumbilical pain migrating to the RLQ, then anorexia, nausea/vomiting (usually after the pain begins), and low-grade fever. McBurney point tenderness, rebound and guarding. Signs by position: Rovsing, psoas (retrocecal), obturator (pelvic). Leukocytosis. Presentation can be atypical in children, older adults and pregnancy (the appendix is displaced upward).

Appendiceal neoplasms

Mechanism / lesion

Neuroendocrine (carcinoid) tumors are among the most common appendiceal tumors, often found incidentally after appendectomy; also mucinous neoplasms.

Classic presentation

Usually incidental. Mucinous tumors can cause pseudomyxoma peritonei.

High-yield PANCE pearls

  • Appendicitis sequence: periumbilical pain → RLQ, anorexia, then vomiting.
  • Signs: McBurney, Rovsing (LLQ pressure → RLQ pain), psoas (retrocecal), obturator (pelvic).
  • Imaging: CT in adults; ultrasound first in children and pregnancy (MRI if US non-diagnostic in pregnancy).
  • Alvarado score helps risk-stratify.

Imaging anatomy

X-ray

Rarely helpful; an appendicolith may be visible.

CT

CT with IV contrast is the most accurate test in adults: a dilated appendix (more than about 6 mm), wall thickening and enhancement, periappendiceal fat stranding, appendicolith, abscess or perforation. verify

MRI

Preferred in pregnancy when ultrasound is non-diagnostic (no radiation).

Ultrasound

First-line in children and pregnant patients (graded compression): a non-compressible, blind-ending tubular structure larger than about 6 mm in diameter, a target appearance in cross-section, periappendiceal fluid, and focal tenderness.

Key views & landmarks
  • Graded-compression ultrasound of the RLQ
  • CT abdomen/pelvis with IV contrast

Physical exam

Surface landmarks

McBurney point: one-third of the distance from the right ASIS to the umbilicus.

Palpation

Maximal tenderness at McBurney point; rebound tenderness and guarding with peritoneal involvement.

Rovsing sign

Technique

Press deeply in the left lower quadrant.

Positive test

Pain felt in the right lower quadrant.

Significance

Appendicitis (peritoneal irritation in the RLQ).

Psoas sign

Technique

Patient lies on the left side; the examiner passively extends the right hip (or the supine patient flexes the right hip against resistance).

Positive test

RLQ pain.

Significance

Inflamed appendix against the psoas, typical of a retrocecal appendix. Also positive with psoas abscess.

Obturator sign

Technique

With the patient supine, flex the right hip and knee to 90° and passively internally rotate the hip.

Positive test

Hypogastric or RLQ pain.

Significance

Inflammation adjacent to obturator internus, typical of a pelvic appendix.

Self-quiz

Q1.

A 21-year-old woman has 18 hours of pain that began around the umbilicus and moved to the right lower quadrant, with anorexia and one episode of vomiting. Pressing in the left lower quadrant causes pain in the right lower quadrant. What is this sign called?

Show answer

B

Rovsing sign (LLQ pressure producing RLQ pain) supports appendicitis. Murphy sign is for cholecystitis; psoas and obturator signs suggest retrocecal and pelvic positions respectively.

Q2.

A 24-year-old pregnant woman at 20 weeks has right-sided abdominal pain and suspected appendicitis. What is the first imaging test?

Show answer

B

In pregnancy (and children), ultrasound is first. If it's non-diagnostic, MRI is preferred over CT to avoid radiation.

Q3.

Why does early appendicitis cause periumbilical pain?

Show answer

B

Visceral afferents from the appendix (midgut) enter at about T10, the dermatome of the umbilicus, so early pain is referred there before the parietal peritoneum is involved.

Q4.

A surgeon has difficulty finding the appendix. Which feature reliably leads to its base?

Show answer

B

The three teniae coli converge at the base of the appendix on the cecum, a reliable intraoperative guide.

Q5.

A patient with appendicitis has right lower quadrant pain when the examiner passively extends the right hip. Where is the appendix most likely positioned?

Show answer

C

A positive psoas sign (pain on hip extension) suggests an inflamed retrocecal appendix lying against the psoas. A positive obturator sign (pain on internal rotation of the flexed hip) suggests a pelvic appendix against obturator internus.

Flashcards

See also