Case Author(s): Jeff Chesnut, D.O. and Tom R. Miller, M.D., Ph.D. , 4/30/99 . Rating: #D2, #Q5
Diagnosis: Physiologic right-to-left shunt.
Brief history:
56 year-old male who underwent partial colon resection for ischemic bowel two days previously. He became dyspneic and hypoxic with rapidly decreasing oxygen saturation, finally leading to intubation.
Images:
Images from a portable ventilation study are shown.
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View second image(vq).
Images from a portable pulmonary perfusion study are shown.
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Portable chest radiograph is shown.
Full history/Diagnosis is available below
Diagnosis: Physiologic right-to-left shunt.
Full history:
56 year-old male who underwent partial colon resection for ischemic bowel 2 days previously. He became dyspneic and hypoxic with rapidly decreasing oxygen saturation, finally leading to intubation.
Radiopharmaceutical:
Tc-99m DTPA aerosal by inhalation and Tc-99m MAA i.v.
Findings:
There is absent ventilation to the left lower lobe. While perfusion to the left lower lobe may be minimally decreased, the left lower lobe is much better perfused than ventilated.
Discussion:
The ventilation/perfusion scintigram is commonly ordered when a patient becomes dyspneic and/or hypoxic. While the study is ordered primarily to screen for possible pulmonary embolus, the nuclear medicine physician should always be alert to other possible causes of hypoxia. In the case of an acute endobronchial lesion, ventilation may be diminished or absent to a pulmonary segment while perfusion is preserved. This creates a physiologic right-to-left shunt resulting in low oxygen saturation in the systemic blood pool. Aggressive treatment may result in a dramatic improvement in the patient's condition.
Followup:
Bronchoscopy was performed and a large mucous plug in the bronchus to the left lower lobe was removed. The patient rapidly improved.
Major teaching point(s):
1. Nuclear medicine physicians should always be aware of etiologies that may explain hypoxia other in addition to pulmonary embolus.
2. A physiologic right-to-left shunt due to an acute obstructing endobronchial lesion may cause profound hypoxia and may be readily detected on V/Q scintigraphy.
ACR Codes and Keywords:
References and General Discussion of Ventilation Perfusion Scintigraphy (Anatomic field:Lung, Mediastinum, and Pleura, Category:Organ specific)
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Case number: vq035
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