Unilateral Decreased Lung Perfusion

Unilaterally decreased lung perfusion can be seen in about 3% of patients referred for ventilation/perfusion scans.

Differential considerations for matched (absent or decreased ventilation) unilateral decreased perfusion to the lung:

• Pneumothorax:
• Pnuemonectomy:
• Massive pleural effusion:
• Endobronchial obstruction: For example mucous plug, foreign body, and broncholithiasis. Hypoperfusion is due to hypoxic vasoconstriction.
• Sweyer-James syndrome: Delayed wash-in with air trapping.

Differential considerations for mismatched (preserved ventilation) unilateral decreased perfusion to the lung:

• Centrally obstructing mass: Compressing the main pulmonary artery. Most common cause
• Radiation: Due to vascular and parenchymal damage. The case shown above is from a patient with prior radiation therapy. Ventilation is relatively preserved compared to perfusion.
• Pulmonary agenesis or stenosis:
• Pulmonary atresia (hypoplastic lung): Preserved ventilation to a small lung.
• Aortic dissection: Rare cause. Due to direct compression of the right pulmonary artery by intramural ascending aortic hemorrhage.
• Mediastinal fibrosis: Most commonly due to histoplasmosis. Can encase and obstruct the central pulmonary vessels
• Pulmonary embolism: About 2% of cases of unilateral decreased perfusion.

References

• Prato FS, Kurdyak R, Saibil EA, Rider WD, Aspin N. Physiological and radiographic assessment during the development of pulmonary radiation fibrosis. Radiology. 1977 Feb;122(2):389-97.
• Bergin CJ, Hauschildt JP, Brown MA, Channick RN, Fedullo PF. Identifying the cause of unilateral hypoperfusion in patients suspected to have chronic pulmonary thromboembolism: diagnostic accuracy of helical CT and conventional angiography. Radiology. 1999 Dec;213(3):743-9.
• Chow B, Wittram C, Lee VW. Unilateral absence of pulmonary perfusion mimicking pulmonary embolism. AJR Am J Roentgenol. 2001 Mar;176(3):712.
• Pickhardt PJ, Fischer KC. Unilateral hypoperfusion or absent perfusion on pulmonary scintigraphy: differential diagnosis. AJR Am J Roentgenol. 1998 Jul;171(1):145-50.
• White RI Jr, James AE Jr, Wagner HN Jr. The significance of unilateral absence of pulmonary artery perfusion by lung scanning. Am J Roentgenol Radium Ther Nucl Med. 1971 Mar;111(3):501-9.