DOI:10.2214/AJR.05.0476
AJR 2006; 187:1611-1613
© American Roentgen Ray Society
99mTc Sestamibi Uptake by Acute Pulmonary Embolism
Conrad Wittram1,
Stephen E. Jones1 and
James A. Scott2
1 Division of Thoracic Radiology, Department of Radiology, FND 202,
Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114.
2 Division of Thoracic Radiology, Department of Nuclear Medicine, Massachusetts
General Hospital, Boston, MA.
Received March 17, 2005;
accepted after revision May 25, 2005.
Address correspondence to C. Wittram
(cwittram{at}partners.org).
Keywords: chest • CT angiography • embolism • nuclear medicine
Introduction
Technetium-99m sestamibi myocardial perfusion scintigraphy is widely used
for the diagnosis and assessment of prognosis of patients with suspected
coronary artery disease. During these investigations, coincidental disease,
which includes lung and breast cancer, was found in 1.7% of cases based on
inspection of the raw data projectional images
[1]. This report describes a
symptomatic woman in whom an extracardiac focus of 99mTc sestamibi
uptake was shown within the lung, which was subsequently identified as an
acute pulmonary embolism.
Case Report
A 37-year-old woman recently diagnosed with diabetes mellitus presented to
our emergency department with the chief complaints of dizziness and blurred
vision. Three days before admission she complained of chest tightness
associated with shortness of breath, especially while walking upstairs. Her
medical history was also significant for hypertension and obesity. Family and
social history were noncontributory. Review of systems was negative except for
chest pain and shortness of breath. She was taking no medications.
Physical examination was significant for a blood pressure of 167/97 mm Hq,
a respiration rate of 18 breaths per minute, and O2 saturation of
97% on room air. Other than some coarse crackles noted at the left lung base,
her examination was normal. Laboratory investigations showed a high serum
glucose level of 293 mg/dL, a high hemoglobin A1c of 12%, and a low
serum CO2 of 22.5 mmol/L. ECG findings were noncontributory and the
cardiac enzymes were normal. Urinalysis was 3+ for glucose and negative for
ketones. A head CT scan showed no acute process.
The patient was admitted to the hospital, the diabetes mellitus was
controlled with glyburide, and the hypertension was treated with lisinopril.
The patient's symptoms of chest tightness and associated dyspnea prompted an
adenosine 99mTc sestamibi scan (Figs.
1A,
1B, and
1C). The study was negative for
signs of cardiac ischemia, and the left ventricle function was normal.
However, an abnormal focus of increase in radiotracer uptake was seen in the
right lower lobe of the lung.
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Fig. 1A —Acute pulmonary embolism in 37-year-old woman. Axial
99mTc sestamibi scan shows abnormal radiopharmaceutical uptake
within right lower lung (arrow). Normal cardiac uptake is on right of
image.
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|
After informing the referring physician, a contrast-enhanced CT scan of the
chest was obtained to further evaluate this abnormality, whereupon filling
defects were seen in the right lateral and posterior basal segmental arteries
(Figs. 1D and
1E). The remainder of the chest
CT was normal. A retrospective fusion of 99mTc sestamibi and CT
images, using the Reveal-MVS CL/239 version 6.1 software (CTI/Mirada Solutions
Ltd.), showed that the right lower lobe abnormality coincided with the
location of the pulmonary embolism (Fig.
1F). Subsequent evaluation found no evidence for a hypercoagulable
condition, and there was no history of contraceptive use.
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Fig. 1D —Acute pulmonary embolism in 37-year-old woman. Axial
contrast-enhanced chest CT scan shows well-defined filling defect
(arrow) within right lower lobe pulmonary artery at level of
posterior and lateral basal segment bifurcation.
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Fig. 1F —Acute pulmonary embolism in 37-year-old woman. Technetium-99m
sestamibi and CT fusion image confirms that right lower lobe 99mTc
sestamibi abnormality overlies acute pulmonary emboli (arrow) in
posterior and lateral basal segmental arteries. On fusion image, abnormal
radiopharmaceutical uptake area on scintigram is larger than identified emboli
on CT. Explanation for this observation is that resolution of 99mTc
sestamibi perfusion scintigraphy is poor in comparison to that of CT.
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A repeat CT pulmonary angiogram 7 months later, for acute chest pain,
showed no acute pulmonary emboli. It also revealed clearing of the previously
noted filling defects within the right lower lobe arteries, indicating
resolution of the previous acute pulmonary embolism.
Discussion
Pulmonary embolism is a major public health problem, with an incidence of
approximately 1/1,000 per year in the adult population in the United States
[2]. The untreated mortality
rate of 26%-37% reduces to 8% with current therapies
[3]. Furthermore, it is
estimated that annually within the United States there are 45,000 recognized
cases and 90,000 unrecognized cases of pulmonary embolism
[4].
The pathology of acute embolism often involves the impaction of thrombus
within a pulmonary artery by pulsatile flow. The distention of an affected
artery can lead to focal vessel wall inflammation and necrosis with the
aggregation of leukocytes along the endothelial surface; these changes can
occur within the first few days of pulmonary thromboembolic disease. Why does
an acute pulmonary embolism take up 99mTc sestamibi? Although the
exact mechanisms for 99mTc sestamibi uptake are not yet clarified,
they are likely related to the radiopharmaceutical's chemical characteristics;
it is an isonitrile lipophilic complex with a positive charge and has a
biodistribution in a large part determined by negative transmembrane
potentials, particularly in the mitochondria
[5]. 99mTc sestamibi
is known to be taken up by inflammatory cells
[6]. We hypothesize that a
local influx of inflammatory cells, perhaps with heightened mitochondrial
activity, is the cause of the focal increase in 99mTc sestamibi
uptake at the embolic site. To our knowledge, this is the first case of
pulmonary thromboembolic disease identified on a 99mTc sestamibi
myocardial perfusion scan. The implications of this finding are obvious, as
patients with coronary artery disease and pulmonary thromboembolic disease
often experience similar symptoms.
In conclusion, a great number of patients undergo 99mTc
sestamibi cardiac perfusion scintigraphy for the investigation of suspected
coronary artery disease. The findings in this described case should prompt
increased surveillance of the lungs, and if an abnormality is found, CT
pulmonary angiography should be performed to exclude acute pulmonary
embolism.
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Introduction
Case Report
