Case Author(s): Stephen Schmitter, M.D. and Farrokh Dehdashti, M.D. , 12/13/00 . Rating: #D3, #Q4

Diagnosis: Pulmonary Sling

Brief history:

Three year-old boy with murmur on routine physical examination.

Images:

Technetium-99m M.A.A. perfusion images

View main image(vq) in a separate image viewer

View second image(vq). Xenon-133 ventilation images

View third image(xr). Frontal and lateral chest radiographs

View fourth image(ct). Axial post-contrast CT images of the thorax

Full history/Diagnosis is available below

Diagnosis: Pulmonary Sling

Full history:

Three year-old asymptomatic boy with murmur on routine physical examination.

Radiopharmaceutical:

13.4 mCi Xe-133 gas by inhalation and 1 mCi Tc-99m MAA i.v.

Findings:

The Xe-133 washin ventilation images show a uniform distribution of activity. There is no abnormal Xe-133 retention during the washout phase. The perfusion images show diffuse heterogeneity of pulmonary perfusion with markedly decreased perfusion of the left lung relative to the right.

Based on the distribution of Xe-133 during the early washin phase, the right lung contributes 46% and the left lung contributes 54% of total pulmonary ventilation. The right lung receives 76% and the left lung receives 24% of total pulmonary perfusion.

The chest radiograph demonstrated no infiltrate or effusion. A rounded density is present posterior to the trachea.

Computed tomography demonstrated pulmonary sling with an aberrant origin of the left pulmonary artery (PA)from the right main PA. The left PA passes posterior to the trachea and appears slightly compressed as it passes to the left. Significant narrowing of the artery is noted which is responsible for findings on the ventilation/perfusion lung scan.

Discussion:

Differential considerations in a patient with unilateral pulmonary hypoperfusion and relatively normal ventilation include pulmonary thromboembolic disease, pulmonary arterial hypoplasia, stenosis, and extrinsic compression by tumor, lymphadenopathy, and fibrosis.

A pulmonary sling (aberrant left pulmonary artery) is due to failure of development or resorption of the ventral portion of the sixth aortic arch, leaving the developing left pulmonary plexus to connect with the right sixth aortic arch. The sling originates from the right pulmonary artery, passes to the left between the trachea and esophagus to the left hilum.

References:

Mettler, FA, Guiberteau, MJ. Essentials of Nuclear Medicine Imaging. Philadelphia: WB Saunders, 1998.

Fraser, RG, Pare, JAP, Pare, FD, Fraser, RS and Genereux, GP. Diagnosis of Diseases of the Chest. Philadelphia: WB Saunders, 1988.

Followup:

The patient underwent pulmonary arteriography (not shown), which demonstrated only a small pressure gradient. Because the patient is currently asymptomatic, no intervention was undertaken, and he will be followed clinically.

ACR Codes and Keywords:

References and General Discussion of Ventilation Perfusion Scintigraphy (Anatomic field:Heart and Great Vessels, Category:Normal, Technique, Congenital Anomaly)

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Case number: vq046

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