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Evidence-Based Imaging
I. Title
Imaging evaluation of sinusitis: Impact on Health Outcome
II. Authors
Yoshimi Anzai, MD
Department of Radiology
University of Washington
Williams Neighbor, MD
Department of Family Medicine
University of Washington
KEY POINTS
Issues
1. Acute sinusitis A: How can we identify patients with acute sinusitis who will benefit
from antibiotic treatment?
B: How accurate are imaging studies for diagnosis of acute
bacterial sinusitis?
Special case: Pediatric acute sinusitis
Special case: Cost-Effectiveness Analysis in acute sinusitis
2. Chronic sinusitis A: How can we diagnose chronic sinusitis?
IV. Key Points
- Acute bacterial sinusitis is over-diagnosed clinically and antibiotics are overprescribed, leading to antibiotics resistant infections. We need to differentiate
patients with acute bacterial sinusitis who may benefit from antibiotic treatment
from those with an uncomplicated upper respiratory viral infection (STRONG
EVIDENCE).
- Although a CT scan is frequently performed to assist diagnosis of sinusitis, no
adequate data exists on the sensitivity and specificity of sinus CT for diagnosis of
acute bacterial sinusitis. (LIMITED EVIDENCE).
- The diagnosis of chronic sinusitis is based on clinical grounds. No gold
standard exists to confirm clinical diagnosis. CT findings for chronic sinusitis
often do not correlate with patients' clinical symptoms. (LIMITED EVIDENCE).
- CT influences surgeons' decision regarding which patients will undergo sinus
surgery, in addition to providing anatomic information to guide endoscopic sinus
surgery (LIMITED EVIDENCE).
X. Discussion of Issues
Acute Sinusitis
Issue 1: How can we identify patients with acute sinusitis who benefit from
antibiotic treatment?
Summary
How to determine which sinusitis patients should receive antibiotic treatment and
how to distinguish those patients from ones with uncomplicated upper respiratory
tract infection are questions that have been studied in detail in the clinical
literature. The majority of the literature supports using clinical guidelines to
select patients with acute bacterial sinusitis and recommends the first-line
antibiotic treatment (amoxicillin) for patients with severe symptoms and illness
longer than 7 days. Imaging studies are not routinely recommended for initial
diagnosis of acute sinusitis (Limited Evidence). Evidence of imaging accuracy
for diagnosis of acute sinusitis is extremely limited.
Issue 2: How accurate are imaging studies for the diagnosis of acute bacterial
sinusitis?
Summary
There is no single report from the U.S. concerning testing sensitivity or specificity
of CT compared with a sinus puncture and culture of aspirate, which is the gold
standard of acute bacterial sinusitis. Only one report measured PPV compared
with the gold standard of sinus aspiration. Sinus radiography has been reported
to have moderate sensitivity. Sinus CT is reported to be more sensitive than
sinus radiography, but little is known about its specificity (Insufficient Evidence).
Special Cases: Pediatric Sinusitis
Imaging diagnosis of acute sinusitis in children is challenging. The
paranasal sinuses are in the process of development and mucosal thickening or
fluid collection is physiologically seen in such developing sinuses. Once sinuses
are well developed and pneumatized, then diagnosis with sinus CT or
radiography is similar to what is observed in an adult population.
A clinical practice guideline regarding the diagnosis, evaluation, and
treatment of children with acute bacterial sinusitis recommends that the diagnosis
of acute bacterial sinusitis be based on clinical criteria in children six years or
younger who present with upper respiratory symptoms that are either persistent
or severe. Although controversial, imaging studies may be necessary to confirm
a diagnosis of acute bacterial sinusitis in children older than six years. CT scans
of the paranasal sinuses should be reserved for children who present with
complications of acute bacterial sinusitis or who have very persistent or recurrent
infections and are not responsive to medical management (Moderate Evidence).
There are only 5 controlled randomized trials and 8 case series on
antibiotic therapy for acute bacterial sinusitis in children. A placebo-controlled
randomized trial by Garbutt et al revealed that no significant difference in the
clinical improvement of children treated with antibiotics compared with those with
a placebo. However, children with complications or suspected complications of
acute bacterial sinusitis should be treated promptly and aggressively with
antibiotics and, when appropriate, drainage.
Special Cases: Cost-effectiveness Analysis (CEA) in acute sinusitis
A few studies have rigorously addressed the cost effectiveness of
diagnosis and treatment for acute sinusitis. Balk et al reported on strategies for
diagnosing and treating suspected acute bacterial sinusitis. They created a
Markov model to examine four strategies for acute sinusitis: 1) no antibiotic
treatment; 2) empirical antibiotic treatment; 3) clinical criteria-guided treatment;
and 4) radiography-guided treatment. The model simulated a 14-day course of
illness and included sinusitis prevalence and symptom severity. They concluded
that the use of clinical criteria guided treatment was cost-effective in most cases.
The empirical use of antibiotics was cost-effective with higher prevalence. Sinus
radiography-guided treatment was never cost-effective for initial treatment.
A meta analysis by the AHRQ also reported that treatment of
uncomplicated sinusitis with amoxicillin or folate inhibitors based on clinical
criteria is the most cost-effective strategy. Fagnan et al also stated that sinus
radiography and CT generally were not cost effective in making an initial
diagnosis. Most of the literature suggests that sinus radiography is not
recommended for the diagnosis of routine cases. The role of sinus radiograph is
limited based on the literatures, which is in part due to the limited sensitivity or
specificity but also to the added cost for diagnosis of this highly prevalent
disease. A practice guide based on consensus of Canadian and American
experts in infectious diseases, microbiology, otolaryngology and family medicine
states that radiography is not warranted when the likelihood of acute sinusitis is
high or low but is useful when the diagnosis is in doubt (Limited Evidence).
The limitations of these CEAs are the unrealistic assumption that patients
receive the first line antibiotic, amoxicillin, which is inexpensive. Increasing
numbers of physicians, however, prescribe more expensive broad-spectrum
antibiotics, in part due to prevalent amoxicillin resistant infections in the
community. Moreover, the model used in the CEA by Balk did not account for
downstream societal cost of increasing antibiotic resistant infection. If a
diagnosis of acute sinusitis is made by a definitive test, such as CT, it may
potentially reduce necessity of antibiotic treatment.
Chronic Sinusitis
Issue 1: How Can We Diagnose Chronic Sinusitis?
Summary
A diagnosis of chronic sinusitis is usually based on clinical history and physical
examination. It is not a pathological diagnosis and, thus, patients' symptoms
drive medical care. Sinus CT may show mucosal thickening in various degrees,
from minimal mucosal thickening to severe opacification of the paranasal
sinuses. Mucosal thickening on CT is non-specific and could be subtle, since
many patients have been treated with antibiotics or anti-inflammatory medication
prior to CT. Occasionally, bone thickening or sclerosis of the affected sinus is
seen, suggestive of chronic periosteal inflammation.
Issue 2: What is the role of imaging in chronic sinusitis? Does imaging change
treatment decision-making?
Summary
The roles of sinus CT for chronic sinusitis patients are to support clinical
diagnosis, to evaluate the extent of disease, and to provide detailed anatomy to
assist treatment planning. The literature suggests that sinus CT findings do not
always correlate with patients' clinical symptoms. Whether patients with a normal
CT but with persistent clinical symptoms should undergo surgery remains
controversial. There is not enough evidence that sinus CT predicts clinical
outcomes or whether sinus CT affects treatment decisions. Evidence for the cost
effectiveness analysis of diagnosis and treatment of chronic sinusitis is lacking
(Insufficient Evidence).
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