Acute appendicitis and Meckel’s diverticulum
ACUTE APPENDICITIS: ANATOMY AND PATHOGENESIS
The vermiform appendix arises from the posteromedial caecum near the ileocaecal valve; its base is at the convergence of the taeniae coli. Positions include retrocaecal, pelvic, subcaecal, pre-ileal and post-ileal. The appendicular artery is usually an end artery from the ileocolic branch of the superior mesenteric artery. Obstruction by lymphoid hyperplasia or faecolith causes luminal distension, venous congestion, bacterial overgrowth, ischaemia and possible perforation.
CLINICAL FEATURES
Classical pain begins peri-umbilically (visceral afferents) then migrates to the right iliac fossa as parietal peritoneum becomes inflamed. Anorexia, nausea, low-grade fever and local tenderness are common. Signs include McBurney point tenderness, guarding, rebound, Rovsing sign, psoas sign (retrocaecal) and obturator sign (pelvic). Atypical positions, pregnancy, children and older adults may produce atypical presentations. Perforation may cause generalised peritonitis or a localised appendicular mass/abscess.
DIAGNOSIS AND DIFFERENTIAL
Diagnosis is clinical supported by FBC, CRP, urinalysis and pregnancy test where relevant. Ultrasound is useful in children and pregnancy; CT abdomen/pelvis is highly accurate in adults with uncertain diagnosis. Risk scores (Alvarado or AIR) support but do not replace assessment. Differential includes mesenteric adenitis, gastroenteritis, Meckel diverticulitis, Crohn disease, urinary infection/stone, ovarian torsion, ectopic pregnancy, pelvic inflammatory disease and right-sided colonic disease.
TREATMENT AND COMPLICATIONS
Resuscitate, provide analgesia, antiemetics and IV antibiotics when appendicitis is confirmed or strongly suspected. Laparoscopic appendicectomy is standard in many settings; open surgery is an alternative. Selected uncomplicated cases may be treated with antibiotics after shared decision-making, recognising recurrence and failure risk. Perforation/generalised peritonitis requires urgent source control and antibiotics. Appendicular abscess may be treated with antibiotics ± image-guided drainage, with interval surgery considered selectively. Histopathology is important because neoplasm can mimic appendicitis, especially in older adults. Complications include perforation, abscess, peritonitis, wound infection, ileus and stump appendicitis.
MECKEL’S DIVERTICULUM
Meckel’s diverticulum is a true congenital diverticulum on the antimesenteric border of the ileum, due to persistence of the vitelline duct. The 'rule of twos' is a memory aid only: about 2% prevalence, often within 2 feet of the ileocaecal valve, approximately 2 inches long, with possible ectopic gastric or pancreatic mucosa. It may cause painless lower GI bleeding (acid secretion ulcerates adjacent ileum), inflammation mimicking appendicitis, obstruction from a band/intussusception/volvulus, perforation or diverticulitis. Technetium-99m pertechnetate scan detects ectopic gastric mucosa, especially in children. Symptomatic Meckel’s is resected; incidental lesions are managed according to risk features and patient context.