hours and at weekends, further limiting its usefulness. Its first line investigative role is greater in paediatric populations, who typically have thinner musculature, less abdominal fat than adults and a greater need for radiation avoidance. Computed tomography In adolescent and patients, computed tomography has become the most accepted imaging strategy. In the USA, it is used in 86% of patients, with a sensitivity of 92.3%. This has led to a normal appendectomy rate of 6%. Uptake outside of North America is lower due to concerns over risk of radiation exposure in children and young adults, differing hospitals remuneration systems, unavailability outside of normal hours and absence of scanners in low resource hospitals. In one RCT comapring low-dose versus standard-dose CT in 891 patients, the normal appendectomy rate was 3.5% versus 3.1% respectively, although these advanced technology scanners are not in widescale use. For older patients at higher risk of malignancy, pre-operative CT is recommended to identify malignancy masquerading as (or, causing) appendicitis. Selective CT based on clinical risk scores is likely to target its use and justify radiation exposure (figure 3). Magnetic resonance imaging (MRI) MRI for patients with an acute abdomen may eliminate the risks associated with radiation use in young patients. However, little is know about the exact utility and accuracy in acute abdomen. For one, there are few units worldwide able to provide immediate access MRI at present. Second, MRI currently has no better accuracy than ultrasound in discriminating perforated appendicitis. Diagnostic strategies in young female patients In fertile female patients, the initial approach includes urinary pregnancy test to identify possible ectopic pregnancy and transvaginal ultrasound to identify ovarian pathology. In equivocal cases, a thorough clinical assessment (including pelvic examination) by on-call gynaecologists can differentiate alternative pathology and direct further investigations. Early laparoscopy has been suggested as a method to improve diagnosis in female patients with an equivocal diagnosis, having so far been assessed in single centre randomised trials. When compared to clinical
pain and shorter length of stay) but no difference in long-term outcomes compared to open surgery. Conflict of interest statement AB – no conflicts of interest KS – no conflicts of interest SDS – no conflicts of interest JA – no conflicts of interest FTD – no conflicts of interest Contribution by authors: AB and KS planned the review. Each author drafted a topic section outline. AB collated the sections and drafted the first version. AB, KS, SDS, JA, FTD performed rounds of revisions, edited the draft and approved the final manuscript. Table 1: Stratified disease approach to acute appendicitis. Disease state Underlying pathology Macroscopic appearances Microscopic appearances Clinical relevance Normal (figure 1A) Normal No visible changes Absence of any abnormality Consider causes Acute inflammation No visible changes Luminal neutrophils only with no mucosal abnormality May be cause of symptoms; consider other causes. Acute mucosal/ submucosal inflammation No visible changes Mucosal/ submucosal neutrophils and/or ulceration May be cause of symptoms; consider other causes Simple, (figure 1B) Suppurative/ phlegmonous Congestion, colour changes, increased diameter, exudate, pus. Transmural inflammation/ ulceration/ thrombosis, +/- extramural pus Likely cause of symptoms Complex (figure 1C) Gangrenous Friable appendix with purple, green or black colour changes Transmural inflammation with necrosis Impending perforation Perforated Visible perforation Perforation; not always visible in microscope Higher risk of post-operative complications Abscess (pelvic/ abdominal) Mass found during examination or abscess seen on imaging; abscess or found at surgery Transmural inflammation with pus +/- perforation Higher risk of post-operative complications pre-