Apendisitis

01Pathophysiology

Appendicitis begins with obstruction of the appendiceal lumen. In adults, the most common cause is a fecalith (a hardened mass of stool). In children and young adults, lymphoid hyperplasia (often triggered by a viral infection) is the leading cause. In older adults, consider neoplasm (carcinoid tumor or cecal adenocarcinoma) as an obstructing lesion, which is why colonoscopy is often recommended after appendectomy in patients over 40.

Once the lumen is blocked, mucus continues to be secreted by the appendiceal mucosa but has no outlet. This causes progressive distension of the appendix and a rise in intraluminal pressure. As pressure increases, it exceeds capillary perfusion pressure, leading first to venous congestion and then to arterial compromise. The ischemic wall becomes a fertile environment for bacterial translocation, most commonly by Escherichia coli, Bacteroides fragilis, and Peptostreptococcus species.

This sequence directly explains the clinical progression the patient experiences. Early on, distension of the appendix stimulates visceral afferent fibers that travel alongside sympathetic nerves at the T10 dermatome level. Visceral pain is poorly localized, which is why the patient initially reports a dull, crampy periumbilical ache. As inflammation extends transmurally and reaches the parietal peritoneum, the pain localizes sharply to the RLQ because the parietal peritoneum is innervated by somatic nerves that can precisely identify the site of irritation. This visceral-to-somatic pain migration is the hallmark feature tested in exam vignettes.

If the appendix is not removed, ongoing ischemia leads to gangrenous appendicitis and eventual perforation. In younger patients, perforation tends to cause diffuse peritonitis because the omentum is underdeveloped and cannot wall off the infection. In older children and adults, the omentum may successfully contain the perforation, forming a periappendiceal abscess or phlegmon. This distinction determines whether the patient undergoes emergent surgery or a staged approach.

02Classification and Clinical Manifestation

The classic symptom timeline is highly testable. Pain characteristically begins in the periumbilical region, followed by anorexia (nearly universal and often the earliest associated symptom), then nausea and vomiting. Pain then migrates to the RLQ. The sequence "pain first, then vomiting" helps distinguish appendicitis from gastroenteritis, where vomiting typically precedes or accompanies the onset of pain.

Physical examination findings correlate with anatomical position. An anterior appendix produces maximal tenderness at McBurney's point (one-third the distance from the anterior superior iliac spine to the umbilicus). A retrocecal appendix (the most common anatomic variant, approximately 65% of cases) may present with flank pain or a positive psoas sign (pain on passive right hip extension) because the inflamed appendix lies against the psoas muscle. A pelvic appendix may produce suprapubic pain, diarrhea, or urinary frequency, and is best elicited by a positive obturator sign (pain on internal rotation of the flexed right hip). These atypical presentations are frequently tested to evaluate whether students can recognize appendicitis despite an unusual pain location.

03Diagnostic Workup

CT abdomen and pelvis with IV contrast is the best initial diagnostic study in adult patients and also serves as the most accurate test, with sensitivity and specificity both exceeding 95%. The cardinal CT finding is an appendiceal diameter greater than 6 mm with surrounding fat stranding. The presence of an appendicolith is highly suggestive but not required for diagnosis. Wall thickening, enhancement, and periappendiceal fluid further support the diagnosis. If a well-formed abscess is visualized, it changes the management pathway entirely.

In children and pregnant women, ultrasound is the best initial test because it avoids ionizing radiation. The hallmark finding is a non-compressible, blind-ended tubular structure exceeding 6 mm in diameter. If ultrasound is inconclusive in a pregnant patient, MRI without gadolinium is the next step. CT should be reserved only if MRI is unavailable and the clinical suspicion remains high.

Laboratory studies are supportive but never diagnostic in isolation. A normal white blood cell count does not rule out appendicitis, particularly in early disease. The combination of leukocytosis, elevated CRP, and clinical findings significantly strengthens the pretest probability. A urinalysis should be obtained in all patients to exclude urinary tract infection or nephrolithiasis, though keep in mind that a retrocecal or pelvic appendix lying near the ureter can cause mild sterile pyuria, which is a classic exam trap.

For women of reproductive age, a beta-hCG is mandatory before any imaging or surgical intervention to rule out ectopic pregnancy.

Clinical scoring systems such as the Alvarado score (also called the MANTRELS score) are sometimes referenced. This score assigns points for Migration of pain, Anorexia, Nausea/vomiting, Tenderness in the RLQ, Rebound pain, Elevated temperature, Leukocytosis, and Shift to the left. A score of 7 to 10 is considered high probability. While rarely the focus of a standalone question, understanding this framework helps in questions about which patients can safely go to imaging versus proceeding to surgery.

04Management and Treatment

The "next best step" for a patient presenting with classic appendicitis (migratory pain, RLQ tenderness, fever, leukocytosis) and a CT confirming the diagnosis is surgical consultation for appendectomy. Do not delay surgery for additional workup once the diagnosis is established.

Acute stabilization begins with making the patient NPO, establishing IV access, and starting IV fluid resuscitation with isotonic crystalloid (lactated Ringer's or normal saline). Preoperative antibiotics covering gram-negative and anaerobic organisms should be administered as soon as the decision for surgery is made. A single agent like cefoxitin 2 g IV provides adequate coverage for uncomplicated cases. Alternatively, a combination of ceftriaxone 2 g IV plus metronidazole 500 mg IV is commonly used. Antibiotics are given before incision and typically discontinued within 24 hours postoperatively if the appendix is found to be non-perforated intraoperatively.

For perforated appendicitis with peritonitis, the patient requires emergent surgical intervention regardless of the time of presentation. Broad-spectrum antibiotics such as piperacillin-tazobactam or a carbapenem are initiated and continued for 4 to 7 days postoperatively, guided by clinical response (resolution of fever, normalizing WBC, return of bowel function).

The most commonly tested management distinction involves the stable patient with a well-formed periappendiceal abscess. Attempting immediate surgery in this setting is associated with higher complication rates because inflamed, friable tissue planes make dissection hazardous. The preferred approach is percutaneous CT-guided drainage plus IV antibiotics to allow the acute inflammation to resolve, followed by interval appendectomy at 6 to 8 weeks. The interval procedure serves two purposes: preventing recurrent appendicitis and obtaining tissue to exclude an underlying cecal neoplasm, which is found in up to 10 to 15% of older adults presenting with appendiceal abscess.

In pregnant patients, appendicitis is the most common non-obstetric surgical emergency. Perforation risk rises with delayed diagnosis, and perforation carries significant risk of preterm labor and fetal loss. Surgery should not be delayed. Laparoscopic appendectomy is safe and preferred in the first and second trimesters. In the third trimester, laparoscopic or open approaches are both acceptable depending on uterine size and surgeon experience.

A growing body of evidence supports antibiotic-only treatment for select cases of uncomplicated appendicitis in adults. However, for exam purposes, appendectomy remains the standard of care unless the question stem explicitly describes a patient who refuses surgery or is not a surgical candidate.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common way students miss appendicitis questions is by failing to recognize atypical presentations. A retrocecal appendix produces flank or back pain rather than classic RLQ tenderness, and a pelvic appendix can mimic a urinary tract infection or gynecologic pathology. When a vignette describes an unusual pain location but includes the classic periumbilical-to-focal pain migration sequence, appendicitis should remain at the top of the differential regardless of where the pain ends up.

Another frequent trap involves the sequence of symptoms. In appendicitis, pain almost always appears before vomiting. In gastroenteritis, vomiting comes first or at the same time as the pain. Test-writers rely on this subtle distinction to separate students who understand the pathophysiology from those who are merely pattern-matching.

The stable patient with a periappendiceal abscess is among the most commonly tested management decisions. Students instinctively choose emergent surgery for any perforated appendicitis, but the correct answer for a stable patient with a well-formed abscess is percutaneous drainage plus antibiotics, followed by interval appendectomy weeks later. Conversely, if the patient shows signs of sepsis, peritonitis, or hemodynamic instability, the answer switches to emergent operative intervention regardless of whether an abscess is present.

Be alert for the pregnant patient with RLQ pain. The question is testing whether you will order a beta-hCG before committing to a surgical diagnosis, and whether you know that ultrasound, not CT, is the first imaging modality. Once appendicitis is confirmed in pregnancy, do not delay surgery.

Finally, remember that mild pyuria on urinalysis does not exclude appendicitis. An inflamed appendix lying against the ureter or bladder can cause sterile pyuria. If the vignette provides RLQ pain with migratory features, a mildly abnormal urinalysis, and imaging showing an inflamed appendix, the diagnosis is still appendicitis, not a urinary tract infection. The core competency being tested here is the ability to integrate clinical reasoning across overlapping findings rather than anchoring on a single lab result.