Abses Apendiks

01Pathophysiology

Appendiceal abscess represents a contained complication of acute appendicitis. The process begins with luminal obstruction of the appendix, most commonly by a fecalith (appendicolith), though lymphoid hyperplasia, parasites, or rarely tumors can also serve as the inciting cause. Once the lumen is blocked, intraluminal pressure rises as mucus continues to be secreted. This elevated pressure compromises venous and then arterial blood flow to the appendiceal wall, resulting in ischemia, transmural necrosis, and eventual perforation.
In a subset of patients, particularly those who present late (beyond 48 to 72 hours of symptom onset), the body mounts a protective response. The greater omentum migrates to the site of perforation and, together with loops of terminal ileum and cecum, walls off the contaminated area. This containment prevents free spillage of enteric contents into the peritoneal cavity and blocks the development of generalized peritonitis. Within this walled-off zone, a phlegmon (an inflammatory mass without a drainable fluid component) may form first. If the infection progresses and liquefactive necrosis occurs within the phlegmon, a true abscess develops, defined as an organized collection of pus surrounded by a distinct wall of granulation tissue and fibrin.
The clinical consequence of this sequence is that the patient's symptoms evolve. Rather than the classic acute appendicitis timeline of periumbilical pain migrating to the RLQ within 12 to 24 hours, these patients present with prolonged symptoms over days, an often palpable RLQ mass, and systemic signs of ongoing infection such as persistent fever and elevated inflammatory markers. The localized nature of the peritoneal irritation (as opposed to diffuse peritonitis) is a direct result of the omental containment.

02Classification and Clinical Manifestation

Understanding the distinction between phlegmon and abscess is critical because management differs.

The exam will test whether you can distinguish a contained perforation (phlegmon or abscess, managed conservatively) from an uncontained perforation with diffuse peritonitis (managed with emergent surgery). The pivot point is the physical exam: localized RLQ findings with a mass favor containment, while diffuse peritoneal signs with hemodynamic compromise demand the operating room.

03Diagnostic Workup

CT abdomen and pelvis with IV contrast is both the best initial and most accurate test for appendiceal abscess. It serves a dual purpose: it confirms the diagnosis and it guides the treatment plan by determining whether the collection is a phlegmon or a drainable abscess, defining the abscess size, and identifying a safe percutaneous drainage route. The hallmark finding is a rim-enhancing hypodense fluid collection in the RLQ, often with surrounding inflammatory fat stranding. The presence of an appendicolith within or adjacent to the collection strongly supports the appendiceal origin.
Ultrasound is a reasonable alternative in pediatric patients and pregnant women. However, its sensitivity is lower than CT for characterizing the collection and planning intervention, so CT remains the standard for most adults.
Laboratory studies are supportive rather than diagnostic. A WBC > $\mathrm{15,000}\mathrm{/}\mu L15\{,\}000/\backslash mu\; L$ with a left shift and a CRP > 100 mg/L in a patient with several days of RLQ symptoms should raise suspicion for complicated appendicitis with abscess formation. Blood cultures should be drawn if the patient shows signs of systemic sepsis (fever, tachycardia, hypotension) before initiating antibiotics.

04Management and Treatment

Acute stabilization begins with IV fluid resuscitation, nothing by mouth, and initiation of broad-spectrum antibiotics targeting enteric gram-negative rods and anaerobes. The first-line regimen is piperacillin-tazobactam 3.375 g IV every 6 hours (or 4.5 g IV every 8 hours at some centers). An acceptable alternative is ceftriaxone 2 g IV once daily combined with metronidazole 500 mg IV every 8 hours. For patients with severe penicillin allergy, ertapenem 1 g IV once daily is a reasonable option. Antibiotic therapy typically runs 7 to 14 days total, with transition to oral agents (ciprofloxacin 500 mg PO twice daily plus metronidazole 500 mg PO three times daily, or amoxicillin-clavulanate 875/125 mg PO twice daily) once the patient has been afebrile for at least 48 hours with a downtrending WBC.
The central management decision and the one most frequently tested is whether to operate immediately or pursue nonoperative management. In a hemodynamically stable patient with a well-formed abscess on CT and localized peritoneal signs, the correct answer is percutaneous drainage plus IV antibiotics, not immediate appendectomy. Immediate surgery in this setting is associated with higher complication rates including bowel injury, enterocutaneous fistula, and the need for more extensive resection such as right hemicolectomy. The abscess cavity is drained under CT or ultrasound guidance, a pigtail catheter is left in place, and the catheter is removed once the daily output falls below 10 to 20 mL and imaging confirms resolution.
Interval appendectomy at 6 to 8 weeks after complete resolution is the standard recommendation. This serves two purposes: it prevents recurrent appendicitis (recurrence rate approximately 15 to 25% without appendectomy) and it allows histologic examination to exclude an underlying appendiceal neoplasm, which is found in up to 10 to 15% of cases in patients older than 40. A colonoscopy should be performed before the interval appendectomy in any patient 40 years or older to evaluate the cecum for malignancy.
Contraindications and exceptions: In patients with diffuse peritonitis, signs of septic shock, or failure to improve after 48 to 72 hours of drainage and antibiotics, the next step is operative intervention. Do not continue nonoperative management in a deteriorating patient.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common error on this topic is choosing immediate surgical appendectomy for a stable patient who presents with a well-formed appendiceal abscess. Test-writers construct vignettes of patients with several days of RLQ symptoms, fever, and a CT showing a 5 cm rim-enhancing collection, then offer "emergent laparoscopic appendectomy" as a tempting answer choice. The correct answer in this setting is percutaneous drainage plus IV antibiotics. Remember: operating into a "hot" abscess bed leads to worse outcomes.
The second common trap involves forgetting the interval appendectomy. A vignette may describe a patient who was treated successfully with drainage and antibiotics, now returns to clinic feeling well 6 weeks later, and asks about next steps. Students may select "reassurance and observation," but the correct answer is interval appendectomy, both to prevent recurrence and to rule out occult malignancy.
A third pitfall is confusing phlegmon with abscess. Both present similarly, but the management differs. A phlegmon has no drainable fluid and is treated with antibiotics alone. Attempting percutaneous drainage of a phlegmon is futile and potentially harmful.
Finally, watch for the patient over 40 years old with an appendiceal abscess. The vignette may subtly embed risk factors for malignancy (weight loss, anemia, change in bowel habits). The exam expects you to recognize that a colonoscopy before interval appendectomy is indicated in this age group. The core competency being tested across all these scenarios is your ability to correctly sequence the management of complicated appendicitis: stabilize, determine if the perforation is contained, choose the right nonoperative or operative pathway, and follow through with definitive care and cancer screening.