Clinical Presentation of Adenocarcinoma of the Appendix

Histologic Subtypes & Their Typical Presentations

1. Colonic (nonmucinous) adenocarcinoma
2. Mucinous adenocarcinoma (cystadenocarcinoma) — approximately twice as common

1. Acute Appendicitis (Most Common Presentation)

• Acute right lower quadrant (RLQ) pain — sudden onset, localized to McBurney's point
• Rebound tenderness on palpation of the RLQ
• Guarding and rigidity
• Fever (low-grade to moderate)
• Nausea and vomiting
• Anorexia
• Leukocytosis (neutrophilic, elevated WBC)

"Nonmucin-producing tumors of the appendix typically manifest with a clinical picture indistinguishable from that of acute appendicitis, with acute RLQ pain and tenderness with or without leukocytosis." — Sleisenger & Fordtran's Gastrointestinal and Liver Disease

2. Incidental Discovery (Common in Mucinous Type)

• Found during operative procedure for an unrelated cause
• Detected on imaging studies (CT scan showing a cystic RLQ mass)
• Noted on pathologic examination of an appendectomy specimen removed for presumed appendicitis

3. Abdominal Mass & Increasing Abdominal Girth

• Palpable abdominal or RLQ mass — from mucin-filled, dilated appendix (mucocele)
• Progressive abdominal distension / increasing girth — due to accumulation of intraperitoneal mucin
• Vague, chronic, or intermittent abdominal pain (less acute than appendicitis)
• Weight loss
• Nausea and vomiting

4. Pseudomyxoma Peritonei (Advanced/Disseminated Disease)

• Massive ascites (jelly-belly appearance — tenacious, semisolid mucin filling the abdomen)
• Progressive abdominal distension
• Abdominal discomfort/pain
• Early satiety, nausea, bowel habit changes
• In women: may mimic ovarian cancer or present as an adnexal mass (PMP can coat ovaries)
• New hernia formation or umbilical hernia — due to raised intra-abdominal pressure

"More commonly, these lesions are found incidentally on imaging studies as a cystic RLQ mass or in a patient with increasing abdominal girth secondary to pseudomyxoma peritonei." — Sleisenger & Fordtran's

5. Imaging Clues (CT Scan)

• Appendix diameter >15 mm on CT
• Soft tissue mass adjacent to or involving the appendix
• Low-attenuation, round, well-encapsulated cystic mass in the RLQ
• Wall irregularity and soft tissue thickening (suggests neoplasm)
• Ascites, peritoneal nodules, or scalloping of liver surface

6. Late / Systemic Presentation

• Ascites (from peritoneal dissemination)
• Weight loss and cachexia
• Bowel obstruction — from peritoneal involvement or direct tumor extension
• Signs of synchronous GI neoplasms — approximately 33% of patients have synchronous or metachronous neoplasms, often from the GI tract (colorectal cancer most common)

Summary Table

Key Clinical Points

• Adenocarcinomas have a propensity for early perforation, though this does not clearly worsen prognosis.
• Because the presentation mimics appendicitis, the diagnosis is often made intraoperatively or on pathologic specimen.
• Any appendix with diameter >15 mm on CT or atypical imaging should raise suspicion for underlying malignancy.
• Patients are at significant risk for synchronous/metachronous GI neoplasms (~33–50%), so colonoscopy is recommended.