Imaging Utilization Affects Negative Appendectomy Rates in Appendicitis: An ACS-NSQIP Study

From the 2018 HVPAA National Conference

Joshua Tseng (Cedars-Sinai Medical Center), Tara Cohen (Cedars-Sinai Medical Center), Nicolas Melo (Cedars-Sinai Medical Center), Rodrigo Alban (Cedars-Sinai Medical Center)

Background

The rate of negative appendectomies (NA) – pathologically normal appendices in patients who undergo surgery for suspected appendicitis – ranged from 15-25% in the US. However, studies show that negative appendectomies are also associated with considerable cost, elongated hospitalizations, and morbidity.

Objectives

To assess current utilization rates of imaging studies in appendicitis, the effect of imaging studies on the negative appendectomy rate, the added value of additional imaging, and predictors of negative appendectomies.

Methods

Using the 2016 ACS-NSQIP database, we identified patients who underwent appendectomies for appendicitis.  Patients were divided into two cohorts – positive and negative appendectomies – for comparison. Variables including patient demographics, comorbidities, preoperative labs, imaging study results, pathology reports, hospital course, and postoperative outcomes were obtained.  Imaging results were classified as “consistent”, “not consistent”, and “indeterminate” as defined by the ACS-NSQIP database.  Patients with and without appendicitis on pathology were compared.  Multivariate analysis was used to identify predictors of negative appendectomies.

Results

11,841 patients underwent appendectomies, with a NAR of 4.5%. Utilization rates of US, CT and MRI were 14.9%, 86.1%, and 1.1%. NAR’s of US, CT, and MRI were 9.7%, 2.5%, and 7.1%, and 19.2% for patients without imaging. An ultrasound consistent with appendicitis has a NAR of 4.8%; adding a CT decreases it to 0.6%. On MVA, predictors of NA include females, smoking, no imaging, and ultrasounds. Factors with lower odds of NA include leukocytosis, sepsis, and CTs.

Conclusion

The negative appendectomy rate in the 2016 ACS-NSQIP population is 4.5%. CTs are the most frequently used imaging modality and have lower negative appendectomy rates than ultrasound and MRI.  Predictors of negative appendectomies include female gender, smoking history, and use of an ultrasound.  The lack of CT, any imaging study, leukocytosis, or SIRS/sepsis is also a predictor of negative appendectomy.  Obtaining a CT in addition to an ultrasound is associated with a lower rate of negative appendectomy.

Implications for the Patient

Compared to US or MRI, CT scans are associated with lower rates of negative appendectomy in patients with suspected appendicitis.  This finding should be further explored with a cost-benefit analysis between multiple imaging modalities versus negative appendectomies.