By Mary Cheffers, MD
Appendicitis is one of the most common etiologies for patients who present to the Emergency Department with abdominal pain. It has historically been a disease of clinical diagnosis, but with the rise of ultrasound, CT, and MRI as possible helpful diagnostic imaging modalities, it is rare that we will diagnose this on clinical exam alone. However, the decision to image remains an important question that relies heavily on the clinical exam, especially with rising concerns regarding radiation and the responsible use of resources.
In the end, although you may have high certainty to suspect appendicitis based on exam, a suspicious exam does not outperform a negative CT or MRI.
Estimates claim that the prevalence of appendicitis in patients under age 60 who present with acute (<1 week) RLQ abdominal pain approaches 12%, with children contributing significantly to this high number. Over age 60, estimates are around 4%.
Often we cannot understand our surgeon’s reticence to take RLQ pain to the operating room without diagnostic imaging. However, if we look at this history, we may understand. Prior to 1995, the negative appendectomy rate was approximately 45% in young women, and between 15-35 in all comers. This has improved over time, decreasing from approximately 13% in 1996 to 3% in 2006, likely due to improved diagnostic imaging.
Here are two quick tables with recent estimates of performance of the three diagnostic modalities gathered from radiology literature:
|Test||LR (+)||LR (-)||Post-test prob (high prevalence)|
Ultrasound in children has a reported sensitivity of 77% and specificity of 97% in high-volume centers when the appendix is visualized. Ultrasound is less sensitive and specific in adults, and ultrasonographers are less likely to visualize the appendix in obese persons and in those with a lower Alvarado score.
|Test||Sensitivity||Specificity||PPV w/contrast*||NPV w/contrast*|
In terms of the clinical exam, best performers include the presence of RLQ pain, RLQ rigidity on exam, and history of migration of pain. Interestingly, the psoas sign is very specific but horrifically insensitive. The absence of anorexia, nausea, or vomiting were not helpful in lowering the probability of appendicitis, but absence of RLQ pain and the existence on history of past episodes of similar pain were helpful in significantly lowering the probability of appendicitis.
Overall, the Alvarado score has been the best tool for surgeons to combine various elements of the clinical exam help estimate probability of appendicitis. Surgeons may bring a patient to the operating room without imaging if the score is over 8.
In summary, we often will be in the position where we are considering appendicitis and need to make a decision about the type of imaging to perform.
Things to keep in mind are the pre-test likelihood of appendicitis (which relies heavily on age and demographic) and the presence of the constellation of symptoms summarized in the MANTRELS mnemonic.
For instance, choosing a RLQ US as the initial diagnostic test of choice in older persons has much less utility than in children given the lower prevalence and thus high rate of false negatives or positives. This consideration should be balanced with the reality of radiation exposure, gender, body habitus, and the likelihood of other diagnoses.
Acute appendicitis: meta-analysis of diagnostic performance of CT and graded compression US related to prevalence of disease. van Randen A1, Bipat S, Zwinderman AH, Ubbink DT, Stoker J, Boermeester MA. Radiology. 2008 Oct;249(1):97-106. doi: 10.1148/radiol.2483071652. Epub 2008 Aug 5.
Diagnostic performance of contrast-enhanced MR for acute appendicitis and alternative causes of abdominal pain in children. Koning JL1, Naheedy JH, Kruk PG. Pediatr Radiol. 2014 Aug;44(8):948-55. doi: 10.1007/s00247-014-2952-x. Epub 2014 Mar 29.
Negative appendicectomy and perforation rates in patients undergoing laparoscopic surgery for suspected appendicitis. Güller U1, Rosella L, McCall J, Brügger LE, Candinas D. Br J Surg. 2011 Apr;98(4):589-95. doi: 10.1002/bjs.7395. Epub 2011 Jan 24.
Equivocal Pediatric Appendicitis: Unenhanced MR Imaging Protocol for Nonsedated Children-A Clinical Effectiveness Study. Dillman JR1, Gadepalli S1, Sroufe NS1, Davenport MS1, Smith EA1, Chong ST1, Mazza MB1, Strouse PJ1. Radiology. 2015 Oct 9:150941. [Epub ahead of print]
Performance of ultrasound in the diagnosis of appendicitis in children in a multicenter cohort. Mittal MK1, Dayan PS, Macias CG, Bachur RG, Bennett J, Dudley NC, Bajaj L, Sinclair K, Stevenson MD, Kharbanda AB; Pediatric Emergency Medicine Collaborative Research Committee of the American Academy of Pediatrics. Acad Emerg Med. 2013 Jul;20(7):697-702. doi: 10.1111/acem.12161.