Synopsis
In this presentation, we will discuss the diagnostic accuracy of MR to diagnose appendicitis, both in the general population and in select cohorts. Additionally, we will discuss the evidence for various MR sequences (unenhanced, intravenous contrast-enhanced, and DWI) as well as the affect of radiologist expertise in abdominal MR on diagnostic accuracy. Finally, we will discuss how using MR in the emergency department setting impacts patient care, particularly their timely evaluation.Highlights
·
Though
CT is the most frequently used imaging test for diagnosing appendicitis in the
U.S., there are drawbacks including exposure to ionizing radiation and nephrotoxic
intravenous contrast material
·
MRI
to diagnose appendicitis has now been studied in the general population as well
as subgroups including pregnant patients and children; most studies have
yielded test characteristics mimicking CT
·
The
utility of using intravenous contrast enhancement versus unenhanced MR alone
has not been fully delineated
·
Throughput
metrics appear to be reasonable for patients undergoing MRI to evaluate for
appendicitis in the emergency department
Objective
To educate attendees on the current state of knowledge regarding the use
of MRI to diagnose appendicitis in the emergency department setting. In
particular, we will review the most current studies evaluating the diagnostic
accuracy of MRI to diagnose appendicitis. Further, we will discuss how efficacy
changes based on MRI sequence used, whether intravenous contrast is
administered, the experience/training level of the interpreting radiologist,
and patient characteristics (pediatrics, pregnant patients, etc.). Finally, we
will investigate the feasibility of incorporating MRI into the diagnostic
pathway for patients seen in the emergency department for abdominal pain
concerning for possible appendicitis.
Purpose
In the United States in 2011, over 11
million patients were seen in emergency departments (EDs) for abdominal pain.
Appendicitis was a frequent cause of such visits, and leads to approximately
250,000 appendectomies performed annually. While traditionally viewed as a
diagnosis made by history and physical exam alone, this method of diagnosing
appendicitis is incorrect up to 30% of the time because the presenting symptoms
for appendicitis and various other abdominal conditions overlap significantly. Children
under 5 years old are particularly difficult to diagnose appendicitis in, and
70% of them perforate their appendix before 48 hours. Indeed, a missed
diagnosis of appendicitis carries significant consequences including
appendiceal rupture, abscess formation, peritonitis, sepsis, and death. Data
from the pre-antibiotic era shows that the mortality of untreated appendicitis is
66%.
The accurate diagnosis of appendicitis,
or identification of alternative diagnoses, is critical to patient management. Physicians
must minimize both the number of missed cases of appendicitis as well as the
number of laparotomies performed in patients with a normal appendix (known as
the negative laparotomy rate [NLR]). Although a negative laparotomy rate of
10-20% was previously considerable acceptable, the diagnostic accuracy of
medical imaging has lowered this acceptability threshold. One study found that
the NLR decreased from 23% in 1990 to 1.7% in 2007 when pre-operative CT use to
confirm the diagnosis of appendicitis increased from 1% to 97.5% of patients.
Additionally, the use of CT allows for the diagnosis of other non-appendicitis
pathologies. Pooler et al. found that for adults referred to the ED for
evaluation of appendicitis, 23.6% were found to have appendicitis while another
31.6% had a significant alternative diagnosis, 41.1% of which required
hospitalization and 22% required a surgical intervention. Alternatively, the
use of ultrasound (US) has been studied and found to have accuracy approaching
that of CT. More recently, magnetic resonance imaging (MRI) has been evaluated
as a primary means of diagnosing appendicitis, and has been shown to have test
accuracy equivalent to CT. Additionally, some studies have reported that using
MR in the diagnostic algorithm for the evaluation of appendicitis was feasible
in the ED setting because images were able to be acquired rapidly and doing so did
not lead to significant increases in the ED length of stay for patients.
Methods
Our group has recently completed a meta-analysis of published studies in
2005-2015 that evaluate the diagnostic efficacy of MRI to diagnose acute appendicitis.
We will discuss the studies that we included in the analysis as well as how one
of the studies, which was determined to be an outlier, affected the summary
test characteristics. Additionally, we will discuss another meta-analysis which
evaluated a broader array of articles, including the pregnant and pediatric
populations. Finally, we will discuss studies that evaluated the impact of
using MR on throughput metrics for patients in the ED. These studies are of
particular interest to emergency physicians because access to MR and feasibility
of using MR in the diagnostic algorithm of patients seen for possible
appendicitis is frequently cited as a barrier to its use.
Results
There are a wide array of MR protocols currently in use or previously
reported for the detection of appendicitis. Most include unenhanced sequences
on 1-1.5T scanner platforms. Others include diffusion-weighted imaging or the
use of intravenous contrast-enhancement. Limitations of many of these studies
include the use of expert readers with extensive experience interpreting MR for
abdominal pathology, particularly appendicitis. Additionally, the prevalence of
appendicitis in the studied populations are generally much higher than what is
typically encountered in regular clinical practice. Our own prospectively gathered
data, however, do not have these limitations, yet still demonstrate similar
results. Additionally, retrospective analyses of throughput metrics suggests at
other centers suggest that MR can be done in a time efficient manner.
Discussion
There is a substantially increasing body of evidence to support the use
of MR to diagnose appendicitis in the ED setting. This is irrespective of age
or pregnancy status. More questions still exist with regard to the importance
of including intravenous contrast enhancement in MR appendicitis protocols and
how much training is optimal for radiologists to become “expert” in the
interpretation of such protocols. Further, the effectiveness of this technology
when translated to the community setting is still unknown. Finally, assessing
the barriers to the wide-spread adoption of this technological advance into routine
clinical practice has not been completed.
Conclusion
Using MR to diagnose appendicitis in the ED is gaining traction and is
supported by an increasing number of prospective studies. Future research
efforts will need to extend beyond basic diagnostic efficacy studies into evaluation
of the impact on clinical practice and patient-oriented outcomes.
Acknowledgements
I would like to thank my collaborators, particularly Drs. Scott Reeder, Perry Pickhardt, Jessica Robbins, Tim Ziemlewicz, and Doug Kitchin for their significant contributions to this work and the guidance they have provided to me as a non-radiologist.References
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