Acute appendicitisBMJ 2017; 357 doi: https://doi.org/10.1136/bmj.j1703 (Published 19 April 2017) Cite this as: BMJ 2017;357:j1703
All rapid responses
We feel that describing the role of ultrasound (US) imaging in the diagnosis of appendicitis as simply “safe in children” understates its potential importance. We accept that, excluding re-productive age women, CT has become the established as the imaging test of choice in adults for acute appendicitis. As you note, some enthusiasts have even advocated its routine use in suspected cases in the quest for lower negative appendicectomy rates at surgery. However, there is evidence that casts doubt on the ability of front-door CT in being able to achieve this goal. In any case, the susceptibility of children to ionising radiation renders this approach impractical in one of the largest population groups affected with this condition.
As a radiation free examination, US can be readily used to assess for appendicitis without the need for sedation, general anaesthesia or the administration of potentially allergenic contrast agents. It is superior to CT in evaluating the female urogenital tract in adolescent females in whom lower abdominal pain is a frequent diagnostic conundrum and transvaginal US is not usually performed. At the same time other mimics of acute appendicitis such as lymphoid hyperplasia and mesenteric adenitis have well recognized US appearances. Demonstration of specific complications such as perforation are, however, more accurately seen on CT or MRI.
In their series of 425 paediatric cases, Baldiserotto and Marchiori (2000) reported that US had a sensitivity and specificity for acute appendicitis of up to 98.5% and 98.2% respectively in their series of 425 paediatric cases with a negative predictive value of 98.7%. Despite similar results in other studies, some have suggested that while these figures are enviable they are not commonly achievable. However, while the sensitivity of US for appendicitis has been shown to vary with institutional and operator factors, its specificity remains high at between 95-98%, approaching that of CT. Furthermore, the diagnostic performance of US in this context is related to the prevalence of appendicitis in the population concerned. By current standard practice at many UK centres, in our experience, most patients undergoing US for appendicitis are of a low clinical suspicion while those in the aforementioned series mentioned had a relatively high disease prevalence, suggesting patient selection is important.
Many clinicans shy away from US in light of the frequently equivocal scan findings, feeling it adds no diagnostic value. A recent multi-center study in the UK reported that the appendix was not identified on US in 45% of cases eventually requiring appendicectomy. However, Blitman et al (2015) showed that despite 75% of cases in their cases having an inconclusive US, the negative predictive value increased from 89.7% to 99.6% when this was combined with a low Alvarado score. This has been validated in combination with other clinical scoring systems and serological markers. Combined with its high specificity we feel this puts US on the frontline as an imaging test in suspected appendicitis for children that require imaging. Its use in combination rather than in competition with CT and MRI for problem solving in cases with persistent diagnostic uncertainty has been shown to be both practical and cost-effective.
However, despite US many advantages its inter-operator variability and requirement for live acquisition in person are primarily what limit its wider use. In the UK these challenges can hopefully be met in tandem with drives to improve the provisioning of paediatric imaging services across the country. It is possible that with deepening operator and institutional ex-perience of its use, US may make its way as a more mainstream diagnostic tool for clinicians to reduce potentially unnecessary surgery and mitigate the risks associated with alternative imaging modalities.
1. Vadeboncoeur TF, Heister RR, Behling RR, Guss DA. Impact of helical computed tomography on the rate of negative appendicitis. Am J Emerg Med. 2006; 24(1):43-47
2. Strouse PJ. Paediatric Appendictis: An Argument for US. Radiology. 2010; 255(1):8-13
3. D’Souza N, D’Souza C, Grant D, Royston E et al. The value of ultrasonography in the diagnosis of appendicitis. Int J Surg. 2015; 13:165-169
4. Lofvenberg F, Salo M. Ultrasound for Appendicitis: Performance and Integration with Clinical Parameters. Biomed Res Int.2016 doi: 10.1155/2016/5697692
5. Wan MJ, Krahn M, Ungar WJ, Caku E et al. Acute Appendicitis in Young Children: Cost-effectiveness of US versus CT in Diagnosis – A Markov Decision Analytic Model. Radiology. 2009; 250(2):378-386
Competing interests: No competing interests