Case Author(s): Michael Quinn, M.D. and Keith Fischer, M.D. , 09/05/97 . Rating: #D2, #Q4

Diagnosis: Physiologic shunt (Perfused but non-ventilated lung.)

Brief history:

18 yo. male with SOB and hypoxia


Tc-99mDTPA aerosol ventilation images (Antrior, posterior, lpo, rpo)

View main image(vq) in a separate image viewer

View second image(vq). Tc99mMAA perfusion images (Ant, Post, LPO, LLat, RPO, RLat)

View third image(xr). Chest radiograph

Full history/Diagnosis is available below

Diagnosis: Physiologic shunt (Perfused but non-ventilated lung.)

Full history:

18 year old male involved in MVA 2 days prior to this study. During his hospital admission he developed shortness of breath and was found to be hypoxic. The referring service was concerned about possible pulmonary embolism.


Tc99mDTPA aerosol for ventilation, Tc99mMAA for perfusion


On ventilation images, there is decreased activity at the left lung base. The chest radiograph is remarkable for an area of retrocardiac consolidation corresponding to the region of decreased ventilation. The perfusion images demonstrate relative increased perfusion to the entire left lower lobe.


This study is an excellent example of a physiologic shunt causing clinical symptoms. Such shunts result when non-ventilated regions of lung continue to remain perfused secondary to failure of the usual reflex vasoconstriction associated with hypoventilation. In this patient, the decreased left lung base ventilation was thought to be secondary to an obstructing mucous plug. The lung distal to this obstruction continued to receive blood flow, causing non-oxygenated blood to enter the systemic circulation and resulting in hypoxia. There was no evidence for pulmonary embolism. When this patient was rolled onto his right side, this decreased the size of the shunt and the patients hypoxia immediately and drastically improved. Treatment consisted of relieving the bronchial obstruction.

Differential Diagnosis List

Mucous plug, endobronchial lesion, extrinsic bronchial compression.

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: vq024

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