Acute Appendicitis

Overview

Acute appendicitis is the commonest surgical emergency, with a lifetime risk of approximately 6%. It can occur at any age but is most frequent in the second and third decades of life. Early diagnosis and timely surgery are the cornerstones of management, as delayed treatment significantly increases the risk of perforation and its attendant complications.

Anatomy

The appendix is a blind-ending diverticulum arising from the posteromedial wall of the caecum, approximately 2 cm below the ileocaecal valve. Its external surface landmark is McBurney's point — the junction of the lateral third and medial two-thirds of a line drawn from the umbilicus to the right anterior superior iliac spine. This is classically the point of maximal tenderness in appendicitis.

The position of the appendix is variable. Approximately 65% of appendices lie in a retrocaecal (behind the caecum) position, which can make the clinical picture atypical, as the appendix is partially shielded from the anterior abdominal wall. Other positions include pelvic (pointing towards the pelvis), para-colic, and pre- or post-ileal. The position heavily influences the pattern of pain and signs on examination.

Pathology

Appendicitis occurs when the appendix lumen becomes obstructed. Common causes of obstruction include:

• Faecolith (hardened stool — the commonest cause in adults)
• Foreign body
• Hyperplasia of lymphoid follicles in the appendix wall (common in children following viral illness)
• Fibrous stricture from a previous episode of inflammation
• Filarial worms (a rare cause in endemic regions)
• Carcinoid tumour at or near the base of the appendix
• Extrinsic compression from a proximal caecal obstructing tumour

Appendicitis occurs less frequently at the extremes of age for two reasons:

1. In young children, the appendix opening is wide-mouthed and drains freely, making obstruction less likely.
2. In elderly patients, the appendix tends to be obliterated and fibrosed, again making obstruction less likely — though when it does occur in the elderly, perforation is more common due to delayed presentation.

Once the lumen is obstructed, the appendix behaves like a closed loop: bacteria multiply rapidly within the static contents, invade the bowel wall, and cause progressive inflammation. Pressure within the lumen rises, causing ischaemia through thrombosis of the end arteries of the appendicular branch of the ileocolic artery. This leads to gangrene and ultimately perforation. This process can occur anywhere between 12 hours and 3 to 4 days from the onset of symptoms.

Occasionally, obstruction occurs without bacterial colonisation, leading to a sterile mucocele — a fluid-filled dilatation of the appendix lumen. Rarely, appendicitis arises from direct haematogenous or lymphatic seeding (streptococcal appendicitis), which is more likely to resolve spontaneously than obstruction-driven appendicitis.

Clinical Features

Symptoms

The classical presentation follows a well-recognised sequence:

1. Peri-umbilical colicky pain — the initial visceral pain, which arises because the appendix is supplied by T10 autonomic afferents that refer pain to the umbilical region.
2. Migration to the right iliac fossa (RIF) — as inflammation spreads to the parietal peritoneum overlying the appendix, the pain localises to the RIF. This shift typically occurs within 4–6 hours and is a highly specific feature of appendicitis.
3. Anorexia — invariably present. A patient who remains hungry is less likely to have appendicitis.
4. Nausea and vomiting — nausea is common; significant vomiting is less prominent than in other causes of an acute abdomen. Vomiting, when present, characteristically follows the onset of pain (in gastroenteritis, vomiting typically precedes pain).
5. Low-grade fever — typically 37.5–38.5°C at presentation. Higher temperatures suggest perforation or abscess formation.
6. Constipation — more common than diarrhoea, though pelvic appendicitis can irritate the rectum and cause loose stool or increased frequency.

If the appendix is pelvic in position, it may irritate the bladder and produce urinary frequency and suprapubic discomfort, mimicking a urinary tract infection.

Signs

• Pyrexia and tachycardia — reflect the systemic inflammatory response.
• Furred tongue, foetor oris, and flushed appearance — indicate systemic toxaemia and dehydration.
• Peritonism — the patient lies still (movement worsens pain), coughing exacerbates pain, and there is localised tenderness, guarding (involuntary muscle contraction), and rebound tenderness at McBurney's point. Generalised peritonism suggests perforation.
• Rovsing's sign — pressure applied to the left iliac fossa (LIF) produces pain more prominently in the right iliac fossa than in the LIF. This occurs because compressing the left colon displaces bowel gas towards the caecum, distending it and aggravating the inflamed appendix.
• Psoas sign — passive extension of the right hip (with the patient in the left lateral position) causes RIF pain. This occurs when a retrocaecal appendix lies adjacent to the iliopsoas muscle, which becomes inflamed. A positive psoas sign suggests a retrocaecal appendix.
• Rectal examination — tenderness on the right side of the rectal wall is classically described, particularly with a pelvic appendix. However, rectal examination should be performed thoughtfully in younger patients.
• Polymorphonuclear leucocytosis — an elevated white cell count with a neutrophil predominance supports the diagnosis.

Atypical Presentations

• The infant with diarrhoea and vomiting — appendicitis can mimic gastroenteritis in young children.
• The schoolboy with vague abdominal pain who refuses his favourite food — anorexia is a key clue.
• The confused and shocked elderly patient who is not in significant pain — perforation with generalised peritonitis may present with minimal localising signs in the elderly.

The Alvarado Score (MANTRELS)

The Alvarado score (also known as the MANTRELS score) is a validated clinical scoring system used to risk-stratify patients with suspected appendicitis and guide the decision to operate or observe. Each component scores 1 or 2 points (total 10):

Interpretation: Score 1–4 = low risk (discharge with advice); score 5–6 = equivocal (observe and repeat); score 7–10 = high risk (likely appendicitis — consider theatre). Note that the score is a guide, not a substitute for senior clinical assessment.

Investigations

Bedside

• Urine dipstick — sterile pyuria and microscopic haematuria may occur when an inflamed appendix lies adjacent to the ureter or bladder. A positive dipstick does not exclude appendicitis. In women of reproductive age, always perform a urinary beta-hCG to exclude ectopic pregnancy.

Bloods

• Full blood count (FBC) — polymorphonuclear leucocytosis (raised WBC with neutrophilia) is a key feature, though a normal white cell count does not exclude appendicitis, particularly in early disease.
• C-reactive protein (CRP) — CRP is elevated in most cases and is more discriminating than WBC alone. A normal CRP in the first 12 hours of symptoms does not exclude appendicitis, as CRP rises more slowly than WBC.
• Serum amylase — useful to exclude pancreatitis in cases of diagnostic uncertainty.
• Group and save — routine pre-operatively.

Imaging

• Ultrasound (USS) — first-line imaging, particularly in women of reproductive age to exclude gynaecological pathology, and in children to avoid radiation. Sensitivity varies (70–90%) and is highly operator-dependent. A non-visualised appendix on ultrasound does not exclude appendicitis.
• CT abdomen and pelvis — the most sensitive imaging modality (sensitivity >94%, specificity >95%). It is particularly useful in adults when the diagnosis is uncertain, in elderly patients, and when an appendix mass or perforation is suspected. The significant radiation dose must be considered, particularly in younger patients and women of childbearing age; USS or MRI are preferred where possible in these groups.
• MRI — increasingly used in pregnancy and in children when USS is non-diagnostic, as it avoids ionising radiation.

Complications

• Perforation and peritonitis — occurs in approximately 20–30% of cases overall, and significantly more in young children and elderly patients who present late. Generalised peritonitis carries significant mortality.
• Appendix mass — the inflamed appendix becomes wrapped by adjacent omentum and small bowel, forming a palpable RIF mass. This represents a contained inflammatory response rather than free perforation.
• Appendix abscess — a collection of pus forms within the omental wrap or in the pelvis.
• Stump appendicitis — a rare but important complication in which residual appendix tissue left at the base following appendicectomy becomes inflamed. It can occur months to years after surgery and requires further surgical excision.
• Infertility in women — peritonitis secondary to a perforated appendix can lead to pelvic inflammatory disease and tubal damage, which is a cause of subsequent infertility.

Differential Diagnosis

Intra-Abdominal

• Non-specific mesenteric adenitis — common in young children, often following an upper respiratory tract infection. Mesenteric lymph nodes become enlarged and inflamed, mimicking appendicitis. The diagnosis is often made when a normal appendix is found at operation.
• Meckel's diverticulitis — inflammation of a Meckel's diverticulum (a remnant of the vitello-intestinal duct, present in 2% of the population, located within 60 cm of the ileocaecal valve) can mimic appendicitis exactly. It should be sought if the appendix is found to be normal at laparoscopy.
• Acute Crohn's disease — can present with RIF pain and tenderness, particularly in young adults. Terminal ileitis at laparoscopy or laparotomy should raise the diagnosis.
• Bowel obstruction — presents with colicky pain and vomiting, but is characterised by noisy, hyperactive bowel sounds (initially) and a distended bowel visible on plain abdominal X-ray.
• Acute gastroenteritis — diarrhoea and vomiting with more diffuse, less severe tenderness. Importantly, in gastroenteritis, vomiting typically precedes any abdominal pain, whereas in appendicitis, pain comes first.
• Perforated peptic ulcer — sudden onset of pain which may track down the right paracolic gutter to the RIF, mimicking appendicitis. Usually preceded by epigastric pain and has free air under the diaphragm on erect CXR.
• Acute cholecystitis — classically right upper quadrant (foregut) pain, but a distended, inflamed gallbladder may descend to the RIF in some patients.
• Pancreatitis — central epigastric pain radiating to the back, with a raised serum amylase or lipase.
• Acute diverticulitis — tends to occur in an older age group; sigmoid diverticulitis typically causes left iliac fossa (LIF) pain, but a redundant sigmoid or a caecal diverticulum can cause RIF pain.
• Caecal carcinoma — can present with RIF pain, particularly if there is an associated pericolorectal abscess. Always consider in older patients.

Gynaecological

• Ovarian pathology — ovarian cyst accidents (torsion or rupture) and haemorrhagic follicle rupture (Mittelschmerz) can present acutely with RIF or bilateral lower abdominal pain. USS of the pelvis is essential in women.
• Acute salpingitis (pelvic inflammatory disease) — more diffuse bilateral lower abdominal pain, often with vaginal discharge, cervical excitation, and bilateral adnexal tenderness.
• Ectopic pregnancy — a critical diagnosis not to miss. Every woman of reproductive age presenting with abdominal pain must be regarded as potentially pregnant until proved otherwise. An ectopic pregnancy can rupture catastrophically. Always check urinary or serum beta-hCG.

Urological

• Testicular torsion — peri-umbilical pain and vomiting are the early features; the key is to examine the genitalia in all male patients presenting with abdominal pain to exclude torsion and maldescent. A missed torsion can result in loss of the testis.
• Renal colic and acute pyelonephritis — always test the urine for blood and leucocytes. The patient with ureteric colic is typically restless and unable to find a comfortable position, with loin-to-groin pain. However, a retrocaecal appendix may lie adjacent to the ureter, causing microscopic haematuria or pyuria and confusing the picture.

Respiratory

• Basal pneumonia and pleurisy — referred lower abdominal pain from thoracic pathology is well described, particularly in children. A chest X-ray should be obtained if there is any respiratory history.

Other

• Herpes zoster (shingles) affecting the 11th and 12th thoracic dermatomes can cause right-sided abdominal pain before the rash appears.

Management

Initial Resuscitation

• Make the patient nil by mouth (NBM).
• Establish intravenous access and commence IV fluid resuscitation.
• Administer adequate analgesia — contrary to older teaching, appropriate analgesia does not mask signs and should not be withheld.
• Regular observations and early review by a senior surgeon.

Antibiotics

Perioperative prophylactic antibiotics are given to reduce post-operative wound infection. A common regimen is metronidazole 500 mg IV plus a cephalosporin (e.g., co-amoxiclav or cefuroxime). In cases of confirmed perforation, therapeutic antibiotics are continued for 3–5 days post-operatively. Antibiotic-only management of uncomplicated appendicitis has been evaluated in trials (e.g., APPAC trial) but appendicectomy remains the standard of care in the UK.

Appendicectomy

The definitive treatment for acute appendicitis is appendicectomy — surgical removal of the appendix. This may be performed:

• Laparoscopically — now the preferred approach at most centres. Advantages include a shorter hospital stay, reduced post-operative pain, lower wound infection rate, and diagnostic benefit (the pelvis can be inspected to exclude gynaecological pathology).
• Open (Lanz or gridiron incision) — via a transverse incision centred over McBurney's point. Still performed when laparoscopy is contraindicated, in resource-limited settings, or when perforation with dense adhesions makes laparoscopic dissection hazardous.

Special Circumstances

The moribund patient with advanced peritonitis — appendicectomy may not be the first priority. Initial resuscitation with IV fluids, nasogastric aspiration, broad-spectrum antibiotics, and cardiovascular support takes precedence. Theatre must be organised urgently once the patient is sufficiently stabilised.

Resolving appendicitis — if the attack appears to be resolving, an elective appendicectomy can be planned, typically within 6–8 weeks, to prevent recurrence.

Appendix mass without peritonitis — managed conservatively. The patient is kept nil by mouth on a fluid diet, with bed rest and close monitoring. Metronidazole is given. The outline of the mass is marked on the skin at presentation to monitor progress. Approximately 80% resolve with this approach. If the mass expands or the patient deteriorates, operative intervention is required. After resolution, an interval appendicectomy is planned at approximately 3 months to prevent recurrence and exclude an underlying caecal tumour.

Appendicitis in pregnancy — carries a higher maternal and foetal mortality due to diagnostic confusion with obstetric symptoms and reluctance to operate. The gravid uterus displaces the appendix upward and laterally, so pain may be more lateral and higher than expected. During the first trimester, there is a significant risk of miscarriage associated with surgery. Early senior obstetric and surgical collaboration is essential.