Case Author(s): John R. Leahy, M.D. and Jerold W. Wallis, M.D. , 6/21/99 . Rating: #D3, #Q3

Diagnosis: Idiopathic pulmonary fibrosis

Brief history:

Evaluation prior to lung transplantation in a patient with chronic shortness of breath.

Images:

Xenon ventilation and perfusion images

View main image(vq) in a separate image viewer

View second image(xr). PA and lateral chest radiograph

Full history/Diagnosis is available below

Diagnosis: Idiopathic pulmonary fibrosis

Full history:

53 year old with long standing history of pulmonary fibrosis is evaluated for lung transplantation.

Radiopharmaceutical:

11.4 mCi Xe-133 gas by inhalation and 4.2 mCi Tc-99m MAA i.v.

Findings:

The ventilation images show a uniform distribution of activity throughout both lungs. There is no retention of the tracer in either lung during the washout phase. The perfusion images show wedge shaped defects in the lung bases and in the lingula.

A comparison chest radiograph shows a pattern of reticular interstitial opacities in both lungs.

Discussion:

There are many potential causes of absent perfusion with preserved ventilation (V-P mismatches) on a ventilation-perfusion scan. Common causes include pulmonary embolism, carcinoma, and radiation therapy. Less common causes include air embolism, vasculitis, pulmonary artery stenosis, and fibrosing mediastinitis. Idiopathic pulmonary fibrosis (IPF), the etiology in this case, is one of the rarer causes.

Studies done to assess the mechanism by which IPF causes this scintigraphic appearance have shown that the perfusion defects correspond to areas of cystic air spaces in the periphery of the lung in IPF patients. Unlike emphysema, these cystic spaces in IPF are ventilated normally, and therefore do not produce ventilatory defects which correspond to the perfusion abnormalities. In this case, the patient was without acute symptoms, and the study was done as part of a lung transplant evaluation. Assesssment for pulmonary embolism superimposed on a patient with IPF would be more problematic. Chest CT could be obtained to correlate the defects to areas of cystic spaces. Alternatively, the patient could be evaluated with pulmonary angiography or spiral CT to look for pulmonary embolism (though little data on spiral CT is available in this disorder).

Reference:

Strickland NH. Cause of regional ventilation perfusion mismatching in patients with idiopathic pulmonary fibrosis. AJR 1993; 16: 719-725

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: vq038

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