Step 2 CK · Surgery

Acute Abdomen & Appendicitis

Name: Acute Abdomen & Appendicitis
Creator: Veli Bakalov, MD

Reading peritoneal signs, migrating pain, and knowing when the knife wins

Surgery·General Surgery·4 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Rebound, involuntary guarding, and rigidity mark peritoneal irritation; a rigid abdomen with hemodynamic instability goes to surgery rather than prolonged workup.
Get a β-hCG in every reproductive-age woman with abdominal pain and exclude ectopic pregnancy first.
Appendicitis: luminal obstruction (fecalith in adults, lymphoid hyperplasia in children) → periumbilical T10 visceral pain → anorexia → RLQ pain at McBurney point over 12–24 hours; perforation after 24–72 hours.
Signs: Rovsing (LLQ pressure → RLQ pain), psoas (right hip extension → retrocecal appendix), obturator (internal rotation of the flexed hip → pelvic appendix).
Imaging: CT abdomen/pelvis in adults (appendix >6 mm, fat stranding, appendicolith); ultrasound first in children and pregnancy; MRI next in pregnancy if ultrasound is inconclusive.
Uncomplicated appendicitis → laparoscopic appendectomy with perioperative antibiotics; antibiotics alone is an option, but ~40% eventually need appendectomy.
Walled-off appendiceal abscess in a stable patient → IV antibiotics plus percutaneous drainage, then interval appendectomy in 6–8 weeks; diffuse peritonitis → immediate surgery.
Pregnancy: appendicitis is the most common non-obstetric surgical emergency; the appendix is displaced upward; never delay appendectomy (perforation raises fetal loss).
Free air under the diaphragm = perforated viscus → emergent laparotomy; primary peritonitis (SBP, single organism) is treated with antibiotics, secondary (polymicrobial) needs source control.

Approach to the acute abdomen

Who goes to the OR now? Rebound tenderness, involuntary guarding, and rigidity signal peritoneal irritation and a possible surgical abdomen. A rigid, board-like abdomen with hemodynamic instability warrants urgent surgical evaluation rather than prolonged workup.

Visceral vs parietal pain. Early visceral pain from a distended hollow organ is dull, poorly localized, and midline; the appendix refers to the periumbilical (T10) dermatome. Once inflammation reaches the parietal peritoneum, pain becomes sharp and localized, and peritoneal signs appear.

Let the quadrant narrow it

Location	Key causes	Useful first test
RUQ	Cholecystitis, hepatitis	RUQ ultrasound, liver tests
Epigastric	Pancreatitis, peptic ulcer disease, MI	Lipase, ECG and troponin
RLQ	Appendicitis, ectopic pregnancy, ovarian torsion, Crohn disease, mesenteric adenitis	β-hCG; CT (adults) or ultrasound (children, pregnancy)
LLQ	Diverticulitis, ectopic pregnancy	β-hCG; CT
Diffuse	Obstruction, perforation, mesenteric ischemia	Upright chest film for free air; CT

Initial workup. Get a β-hCG in every woman of childbearing age, and exclude ectopic pregnancy in a reproductive-age woman with lower abdominal pain before anything else. Add a CBC, electrolytes, lipase, liver tests, and urinalysis. Early analgesia does not mask the diagnosis and should not be withheld.

Appendicitis: pathophysiology and presentation

Obstruction lights the fuse. Appendicitis begins with luminal obstruction: a fecalith in adults, post-viral lymphoid hyperplasia in children and teens. Distension raises intraluminal pressure, venous congestion leads to ischemia, bacteria invade the wall, and untreated disease perforates.

Luminal obstructionFecalith or lymphoid tissue.
DistensionRising intraluminal pressure.
IschemiaVenous congestion.
Bacterial invasionTransmural inflammation.
PerforationTypically after 24–72 hours.

Appendicitis cascade

Pain migrates to McBurney. The classic sequence is dull periumbilical (visceral) pain, then anorexia and nausea hours later, then pain migrating over 12–24 hours to the right lower quadrant at McBurney point (one-third of the way from the ASIS to the umbilicus), with low-grade fever and mild leukocytosis. Anorexia is nearly universal, and vomiting that precedes the pain argues against appendicitis.

Exam signs and diagnosis

Rovsing sign: LLQ palpation evokes RLQ pain.
Psoas sign: RLQ pain on passive extension of the right hip, pointing to a retrocecal appendix over the iliopsoas.
Obturator sign: pain on internal rotation of the flexed hip, pointing to a pelvic appendix.
Local peritonitis: guarding and rebound at McBurney point.

Imaging by patient. CT abdomen/pelvis is the adult test of choice: appendix diameter >6 mm, wall thickening, periappendiceal fat stranding, and an appendicolith. Ultrasound (an enlarged, noncompressible appendix) is first-line in children and pregnancy to avoid radiation; CT is reserved for inconclusive pediatric studies, while MRI is next in pregnancy. The Alvarado score (MANTRELS: Migration, Anorexia, Nausea/vomiting, RLQ Tenderness, Rebound, Elevated temperature, Leukocytosis, Shift to the left) aids the pretest probability.

Mimics. In women, appendicitis mimics ectopic pregnancy, ovarian torsion, a ruptured cyst, and pelvic inflammatory disease, so obtain β-hCG and a pelvic ultrasound. Mesenteric adenitis (post-viral, children) and cecal diverticulitis are other right-sided mimics.

Management and special situations

Managing appendicitis by scenario

Scenario	Management
Uncomplicated	Laparoscopic appendectomy with perioperative antibiotics (standard). Antibiotics alone is an option in selected patients, but roughly 40% eventually need appendectomy, so surgery stays the default answer.
Perforation with diffuse peritonitis	Rigid abdomen and sepsis: resuscitate, IV antibiotics, immediate appendectomy.
Walled-off abscess or phlegmon	Often a late, stable presentation: IV antibiotics plus percutaneous drainage, then interval appendectomy 6–8 weeks later.
Pregnancy	Ultrasound, then MRI without contrast (avoid CT); do not delay appendectomy.

Pregnancy. Appendicitis is the most common non-obstetric surgical emergency in pregnancy. The gravid uterus can displace the appendix upward, so pain may sit higher than expected. Do not delay appendectomy for the pregnancy: perforation sharply raises fetal loss.

The very young and the very old present late and perforate more often because their signs are atypical.

Peritonitis and the decision to operate

Peritonitis is peritoneal inflammation with rebound and rigidity, and it comes in two forms that are managed in opposite ways.

Primary vs secondary peritonitis

Feature	Primary (SBP)	Secondary
Setting	Cirrhotic ascites	Perforated viscus (ulcer, appendix, diverticulum)
Organisms	Single organism	Polymicrobial
Diagnosis	Paracentesis: ascitic neutrophils ≥250/mm³	Free air or perforation on imaging
Treatment	Third-generation cephalosporin; no surgery	Surgical source control plus broad-spectrum antibiotics

Free air demands the OR. Free air under the diaphragm on an upright film means a perforated viscus and emergent laparotomy.

Operate now, or watch closely. Operate emergently for diffuse peritonitis, free air, uncontrolled bleeding, bowel ischemia, or hemodynamic instability. Localized, stable pain without peritoneal signs can be observed with serial exams.

Elderly and immunosuppressed patients have blunted signs and progress silently; a benign-looking exam can hide catastrophe, so keep the threshold to image low.