Unilateral absence of the pulmonary veins: an unusual diagnosis with characteristic imaging findings.

BACKGROUND: Congenital unilateral absence of the pulmonary vein (UCAPV) is a rare entity with characteristic clinical and imaging findings. Despite its congenital nature, the radiographic findings and symptoms of UCAPV may not be recognized at birth and patients may present in childhood or early adulthood with findings that may mimic other diagnoses.

METHODS: The evolution of imaging findings in UCAPV is presented through two cases, one of which demonstrates the progression of findings over several years. The embryologic basis of this entity is reviewed and the clinical presentation and characteristic imaging findings including radiographs, nuclear scintigraphy, computed tomography, magnetic resonance imaging and cardiac catheterization are demonstrated.

RESULTS: Characteristically, normal at birth, radiographs demonstrate the gradual development of a small lung and ipsilateral pulmonary artery over time. In addition to unilateral absence of the pulmonary veins on CT or MRI, a mediastinal "soft tissue mass" reflecting the development of mediastinal collaterals is a common finding and should be recognized as secondary to the absent ipsilateral pulmonary veins rather than as a primary process causing occlusion of the pulmonary veins. Scintigraphy will show absent perfusion to the affected lung.

CONCLUSION: Awareness of the distinctive imaging findings in this unusual condition is critical to avoid misdiagnosis and to prevent the consequences of UCAPV which include pulmonary hypertension and extensive venous collaterals with or without hemoptysis, both of which may prevent definitive repair.