Conventional-dose CT versus 2-mSv CT for right colonic diverticulitis as an alternate diagnosis of appendicitis: secondary analysis of large pragmatic randomized trial data
Hae Young Kim, Seungjae Lee, Dong Hwan Kim, Yousun Ko, Ji Hoon Park, Ara Ko, Seok Min Jeong, Sung Bin Park, Kyoung Ho Lee and for the LOCAT Group
American Journal of Radiology, November 2021. https://www.ajronline.org/doi/10.2214/AJR.21.25584
The adoption of lower dose CT in routine practice in young adults has been slow, partly due to concern regarding missing alternative diagnoses, such as right colonic diverticulitis (RCD), and other more subtle abnormalities.
The purpose of this paper was to retrospectively compare diagnostic performance of 2mSv low dose CT (LD-CT) to conventional dose CT (CD-CT) for the diagnosis of right sided diverticulitis in a relatively young cohort (ages 15-44) with suspected appendicitis.
The original randomized control trial was performed in Korea and involved 3074 patients with suspected appendicitis (1). These patients underwent random assignment for Low dose or conventional dose CT. The imaging findings were compared and it was concluded that the low dose CT was non-inferior for diagnosis of appendicitis. Of note, 37% of the original cases were positive for appendicitis.
This retrospective analysis reviewed all of the previously seen right colonic diverticulitis cases seen in the original trial. End points for the diagnosis of right colonic diverticulitis between the different scan dosage were statistically analysed with different end points. In addition, all of the previously seen right colonic diverticulitis cases were re-reviewed by 4 radiologists (2 consultants and 2 trainees). The radiologists were blinded to the cases with additional alternative pathology cases, totaling 200 LD-CT and 200 CD-CT cases. A proforma was used and review only commented on if right colonic diverticulitis was present, indeterminate or absent.
Results demonstrated that interobserver group differences were minute at 95% confidence intervals. Both Gwet and Kappa coefficients were used to assess interobserver differences. Gwet coeffient was preferable to Kappa in this cohort as the prevalence of diverticulitis was high and this statistic is less vulnerable to disease prevalence compared to other common statistics. Gwet coefficient (2) were high and comparable between the low dose and conventional dose groups.
The paper concluded that 2msv CT is comparable to conventional-dose CT for the diagnosis of right colonic diverticulitis.
There were a number of limitations with this paper which were highlighted by the authors. The patient demographic were Korean patients with a high prevalence of right sided diverticulitis, which is presumably related to diet (7% of the 3074 cases). Although less prevalent in western societies, this study and the randomized control trial still highlight that reduced CT dosage is accurate for alternative diagnoses to appendicitis in an acute setting.
Although blinded there was potential bias for the 4 retrospective reporters. They each read an article on reporting diverticulitis before undertaking the study and there was a high proportion of positive studies with over 50% of the retrospective image reviews having right sided diverticulitis. Gwet coefficients were used to help eliminate this high bias.
Another very important limitation is that the median (IQR) dose received by the individual patients were more than double the target dose in both groups with 4.1 (3.7–4.5) mGy versus a target of 2mSv in the low dose group and 14.4 (12.9–16.2) versus a target of 7mSv in the conventional dose group. This clearly has implications for services considering adopting this technique.
In conclusion although there were several limitations this paper indicates that lower dose CT has comparable accuracy to conventional dose CT in the assessment of patients with right sided abdominal symptoms and a primary diagnosis is acute appendicitis. While a 2mSv dose was not actually achievable in a majority of patients in the trial setting this paper adds further support to the routine use of lower dose CT in younger patients with suspected appendicitis.
References:
- The LOCAT Group, Hyuk Jung Kim, Byeong Geon Jeon, Chong Kun Hong et al. Low-dose CT for the diagnosis of appendicitis in adolescents and young adults (LOCAT): a pragmatic, multicentre, randomised controlled non-inferiority trial. The Lancet Gastroenterology & Hepatology Volume 2, Issue 11, November 2017, Pages 793-804
- Charles Zaiontz. 2020. Gwets AC1 and AC2. Real statistics. Viewed 04/12/2021. https://www.real-statistics.com/reliability/interrater-reliability/gwets-ac2/
Dr William Hogg is a 4th year Radiology Registrar on the Leeds Radiology Training Scheme, England. He completed his undergraduate medical degree at Leeds Medical School in 2016, during this time he undertook a Radiology elective in Brisbane, Australia where he was involved with a Neuroradiology mechanical thrombectomy project. He stayed locally in Yorkshire for his foundation training and subsequent Radiology post within the Leeds Radiology Academy. After obtaining his FRCR qualification Dr Hogg has started subspecialty GI Radiology training. He is involved in a Crohn’s disease MRI/ultrasound research project which is exploring his interest in intestinal ultrasound and luminal GI work.
Comments may be sent to: william.hogg@nhs.net