AJR 2003; 181:317-319
© American Roentgen Ray Society
Value of CT in Assessing Probable Severe Acute Respiratory Syndrome
T. N. Anuradha Rao1,
Narinder Paul1,
Taebong Chung1,
Tony Mazzulli2,
Sharon Walmsley3,
Colm E. Boylan1,
Yves Provost1,
Stephen J. Herman1,
Gordon L. Weisbrod1 and
Heidi C. Roberts1,4
1 Department of Medical Imaging, University Health Network and Mount Sinai
Hospital, Toronto, ON M5G 2C4 Canada.
2 Department of Microbiology, Mount Sinai Hospital, Toronto, ON M5G 2C4
Canada.
3 Department of Internal Medicine, Mount Sinai Hospital, Toronto, ON M5G 2C4
Canada.
4 Department of Medical Imaging, Toronto General Hospital, Rm. ES 1-401c, 200
Elizabeth St., Toronto, ON M5G 2C4, Canada.
Received May 13, 2003;
accepted after revision May 22, 2003.
Address correspondence to H. C. Roberts.
Introduction
Severe acute respiratory syndrome (SARS) is an acute medical condition
recently recognized in Asia, North America, and Europe. Although the specific
cause remains uncertain, current evidence points toward the role of a
Coronavirus organism [1]. The
incubation period is between 1 and 11 days
[2]. Because no specific test
is currently available, the diagnosis relies on the combination of clinical
symptoms found in most patients, such as fever, nonproductive cough or
dyspnea, malaise, myalgia, headache, and frequently lymphopenia or elevated
lactate dehydrogenase levels. A patient is considered suspect because of
contact with an individual believed to have SARS or travel to a region where
transmission of the disease has been documented
[3]. Typically, radiographic
features of pneumonia or respiratory distress syndrome support the diagnosis
[2,
4,
5]. However, in the early
course of the disease, findings on chest radiographs may be normal
[2].
We report a case of probable SARS in a health care professional who had
repeated normal chest radiographs in the presence of progressive symptoms. The
diagnosis was finally confirmed when pulmonary abnormalities were found on
chest CT. These abnormalities significantly showed improvement on the
follow-up CT performed during the course of her treatment. Chest radiography
was never interpreted as positive.
Case Report
A previously healthy health care professional who had worked in the SARS
unit for 2 weeks presented initially with a headache on April 14 (day 1). The
34-year-old woman reportedly had taken full precautions, wearing gloves, a
gown, eye protection, and N95 mask, at all times when caring for SARS
patients.
Her headache persisted and increased in severity on day 2, when she was
also noted to have fever (38°C), sinus "stuffiness," and a
mild cough. Consequently, she was transferred to the infection control unit,
where a chest radiograph in two views was obtained (Figs.
1A and
1B), the findings of which were
normal. On admission, her physical examination revealed a temperature of
38.4°C and an oxygen saturation level of 98% on room air. Her vital signs
and findings of neurologic, chest, cardiovascular, abdominal, and skin
examinations were normal. Findings of her blood workup were normal with no
evidence of lymphopenia or elevated lactate dehydrogenase levels (WBC, 5.42
[3.5 neutrophils; 1.46, lymphocytes]; platelet count, 193; hemoglobin level,
125; levels of electrolytes, blood urea nitrogen, creatinine,
aminotransferases, and alkaline phosphatase, all normal; lactate dehydrogenase
level, 87 U/L; creatine kinase level, 56 U/L).
From day 2 to day 6, she had persistent fever, headache, increasing
nonproductive cough, shortness of breath on exertion, and oxygen desaturation
levels of 88–90% on room air. She also developed increasing diffuse body
myalgia, nausea, vomiting, and decreased appetite. Subsequent portable chest
radiography performed on day 4 and day 6
(Fig. 1C) failed to show any
abnormal findings. Blood and urine cultures and nasal swabs were negative for
any pathogen. Given the discrepancy of clinical and radiographic findings
(i.e., the increasing clinical suspicion with normal chest radiographs), we
performed unenhanced multidetector CT on day 6 (LightSpeed, General Electric
Medical Systems, Milwaukee, WI) with 5-mm overlapping slices, 120 kV, and 180
mAs. CT showed focal centrilobular nodules with mild interlobular septal
thickening, predominantly located in the right lower lobe and, to a lesser
extent, in the right middle lobe and the left lower lobe (Figs.
1D and
1E). No cavitation was seen
within these nodules, and there was no associated pleural effusion or
lymphadenopathy.
View larger version (95K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1D. —34-year-old female health care professional with probable severe
acute respiratory syndrome. Unenhanced multidetector CT scans of chest (lung
window settings) obtained on day 6 show focal centrilobular ground-glass
opacities and mild interlobular septal thickening in both lower lobes
(D and E) and right middle lobe (D).
|
|
View larger version (92K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1E. —34-year-old female health care professional with probable severe
acute respiratory syndrome. Unenhanced multidetector CT scans of chest (lung
window settings) obtained on day 6 show focal centrilobular ground-glass
opacities and mild interlobular septal thickening in both lower lobes
(D and E) and right middle lobe (D).
|
|
On the basis of the CT results, our patient was diagnosed with probable
SARS, and treatment with ribavirin, prednisone, and levofloxacin was started.
Her symptoms persisted from day 6 to day 12. Levofloxacin was discontinued on
day 7. On day 14, she became afebrile, and her dyspnea improved during the
next few days. Results of repeated portable radiographs on days 8, 10, 12, and
14 were all negative. Repeated CT (Figs.
1F and
1G) on day 15 showed almost
complete resolution of the previously seen nodules. Ribavirin and prednisone
were continued to complete a 10-day treatment course.
View larger version (100K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1F. —34-year-old female health care professional with probable severe
acute respiratory syndrome. Repeated unenhanced helical CT scans of chest
obtained on day 15 show almost complete resolution of focal ground-glass
opacities seen on day 6 in D and E.
|
|
View larger version (89K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1G. —34-year-old female health care professional with probable severe
acute respiratory syndrome. Repeated unenhanced helical CT scans of chest
obtained on day 15 show almost complete resolution of focal ground-glass
opacities seen on day 6 in D and E.
|
|
Discussion
This case report emphasizes that chest radiographs may be falsely negative
until late in the SARS disease course or, as in our patient, remain normal
throughout. Our patient had consistently negative radiographs over a disease
course of 15 days, during which abnormalities could be found on her chest CT.
Negative chest radiographs at initial presentation have been described in the
recent literature on SARS [2],
all of which however became positive during the later course of the disease.
In another article, findings on chest radiographs were reported to show
opacities in all nine patients at initial presentation
[4].
The reason for the consistently negative radiographs in our patient might
be twofold. The patient had centrilobular ground-glass opacities, which may
not have been of sufficient density to be seen on radiographs. Moreover, the
basal and retrocardiac location of these faint opacities initially within the
lungs may have been difficult to see because these may have been obscured by
the overlying diaphragm on the frontal view and by the mediastinal structures
on the lateral view. The chest radiographs, including the radiograph
(Fig. 1C) that was obtained
just a few hours before the diagnostic CT scan, were never positive in our
patient in the entire duration of illness. The institution of treatment, in
particular antiviral and steroid therapy, immediately after the positive CT
may have prevented further progression of disease into denser coalescing
nodules and consolidation, which may have been visible on chest radiography
[2,
4]. Also, the initial viral
infection load may have been low in our patient.
Interestingly, the pattern of abnormality seen on CT reflects the presumed
mode of infection. The mode of transmission in SARS is thought to be
inhalation of infected droplets. Consequently, the areas involved, at least
initially, would be the peribronchiolar regions in the dependent lung
parenchyma, which were the predominantly involved areas seen on CT in our
patient (Figs. 1D and
1E).
Although chest radiography remained falsely negative during the entire
course of SARS in this patient, we do not know the exact onset of
abnormalities seen on CT. The diagnostic scans were obtained 6 days after the
onset of symptoms. Consequently, although CT clearly is more sensitive than
radiography, more data are needed to assess the utility of a negative CT scan
to exclude SARS. A low-dose chest CT may be an option in patients being
evaluated for SARS, especially in young patients, in whom radiation dose is
more of a concern.
In conclusion, chest radiographs could be normal in a patient with SARS
even after the onset and progression of the typical clinical symptoms. CT has
a higher sensitivity than chest radiography with abnormalities in the lungs
being identified earlier. Thus, CT may be used as an initial investigative
tool in patients with high clinical suspicion for SARS, such as health care
workers or close contacts presenting with typical symptoms. An early positive
CT may allow institution of appropriate treatment, which may prevent disease
progression.
References
- Ksiazek TG, Erdman D, Goldsmith CS, et al. A novel Coronavirus
associated with severe acute respiratory syndrome. N Engl J Med Web
site. Available at:
www.nejm.org.
Accessed May 2, 2003
- Tsang KW, Ho PL, Ooi GC, et al. A cluster of cases of severe acute
respiratory syndrome in Hong Kong. N Engl J Med Web site. Available
at:
www.nejm.org.
Accessed May 1, 2003
- World Health Organization Web site. Available at:
www.who.int/csr/sarscountry.
Accessed April 2, 2003
- Poutanen SM, Low DE, Henry B, et al. Identification of severe acute
respiratory syndrome in Canada. N Engl J Med Web site. Available at:
www.nejm.org.
Accessed May 1, 2003
- Nicolaou S, Al-Nakshabandi NA, Müller NL. SARS: imaging of
severe acute respiratory syndrome. AJR2003; 180:1247
–1249[Free Full Text]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
|
|
 
N. S. Paul, H. Roberts, J. Butany, T. Chung, W. Gold, S. Mehta, E. Konen, A. Rao, Y. Provost, H. H. Hong, et al.
Radiologic Pattern of Disease in Patients with Severe Acute Respiratory Syndrome: The Toronto Experience
RadioGraphics,
March 1, 2004;
24(2):
553 - 563.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
N. S. Paul, T. Chung, E. Konen, H. C. Roberts, T. N. A. Rao, W. L. Gold, S. Mehta, G. A. Tomlinson, C. E. Boylan, H. Grossman, et al.
Prognostic Significance of the Radiographic Pattern of Disease in Patients with Severe Acute Respiratory Syndrome
Am. J. Roentgenol.,
February 1, 2004;
182(2):
493 - 498.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Introduction
Case Report
