Case Author(s): Stephanie P.F. Yen, M.D. and Jerold Wallis, M.D. , 2/13/98 . Rating: #D3, #Q4

Diagnosis: Right-to-left Shunt Secondary to RUL Pulmonary Arteriovenous Malformation

Brief history:

67-year-old female who presents with shortness of breath, congestive heart failure, and new onset atrial fibrillation.


Ventilation-perfusion scintigraphy, 1/98, with ventilation images at the left, and perfusion images at the right. Carefully examine the RPO and LPO perfusion images.

View main image(vq) in a separate image viewer

View second image(vq). Ventilation-perfusion scintigraphy, 8/92

View third image(xr). Portable chest, 1/26/98 (top) and PA chest, 8/10/92 (bottom), filmed to emphasize RUL findings

Full history/Diagnosis is available below

Diagnosis: Right-to-left Shunt Secondary to RUL Pulmonary Arteriovenous Malformation

Full history:

68-year-old woman who presents with progressive dyspnea, congestive heart failure, and new onset atrial fibrillation. The patient's peripheral arterial oxygenation was reported to be in the 40 mmHG range.


13.4 mCi Xe-133 gas by inhalation and 4.3 mCi Tc-99m MAA intravenously


The ventilation-perfusion pulmonary scintigraphy dated 1/26/98 demonstrates a subtle small ventilation defect in the right apex, with a matched small perfusion defect in the right apex (best seen on the RPO and right lateral images). These findings are more apparent on the prior ventilation-perfusion scintigraphy of 8/10/92, and correspond to an ill-defined opacity in the right upper lobe on the comparison portable chest radiograph of 1/26/98. A similar opacity was noted on the chest radiograph of 8/10/92. Both the ventilation-perfusion scintigraphies were interpreted as low likelihood ratio for pulmonary embolism.

In addition to the small matched right apical ventilation-perfusion defect, the perfusion studies also demonstrate activity in the kidneys. No activity is identified in the thyroid, salivary glands, or in the stomach. These findings are most indicative of a right-to-left shunt.


While the emphasis on ventilation-perfusion scintigraphy is to evaluate for ventilatory-perfusion mismatches, it is equally important to be aware of extrapulmonary activity. The presence of extrapulmonary activity on perfusion scintigraphy indicates the presence of free Tc-99m pertechnetate or an intra- or extracardiac right-to-left shunt. In a right-to-left shunt, radiopharmaceutical will accumulate in systemic capillary beds, such as the kidneys, brain, and spleen. In contrast, free Tc-99m pertechnate will accumulate most prominently in the stomach, thyroid, salivary glands, and kidneys. An image of the head is often helpful to distinguish between a right-to-left shunt and free Tc-99m pertechnetate, as intracerebral activity is present with a right-to-left shunt whereas localization of activity to the scalp and cerebral sinuses is suggestive of free Tc-99m pertechnetate.

The diagnosis of a right-to-left shunt is important, as this may be the explanantion for the patient's respiratory symptoms that prompted the initial investigation for pulmonary thromboembolic disease. Further investigation to determine whether a right-to-left shunt is intracardiac or extracardiac (such as due to a pulmonary arteriovenous malformation or right-to-left shunting from severe endstage liver disease), usually will include a transthoracic echocardiogram with bubble study as was done in this case. The findings on the ventilation-perfusion scintigraphy in conjunction with the chronic ill-defined right upper lobe opacity and the results of the bubble study strongly suggest the presence of an intrapulmonary right-to-left shunt, which was confirmed on pulmonary arteriography.


The patient subsequently underwent a transthoracic echocardiogram which demonstrated evidence of an extracardiac right-to-left shunt by bubble study. A pulmonary arteriogram was then performed, which revealed a right upper lobe pulmonary arteriovenous malformation (see followup image below). No other pulmonary arteriovenous malformations were identified. Moderate to severe pulmonary arterial hypertension was also noted, with pulmonary arterial pressure measurements of 63 mmHg systolic, 22 mmHG diastolic, and 45 mmHG mean.

On the following day, the patient underwent successful coil embolization of the right upper lobe arteriovenous malformation. Selective right pulmonary arteriogram following coil embolization demonstrated no residual flow within the arteriovenous malformation. The right upper lobe arteriovenous malformation was felt to be an incidental finding in this patient who does not have a history of Osler-Weber-Rendu.

View followup image(an). Selected images from selective right pulmonary arteriogram (left), and following coil embolization of RUL arteriovenous malformation (right).

Major teaching point(s):

This case emphasizes the importance of evaluating for extrapulmonary activity on perfusion scintigraphy.

A matched ventilation-perfusion defect with a corresponding radiographic parenchymal opacity, as illustrated in this case, is nonspecific. The most common differential diagnosis is pneumonia/infection. Less likely considerations would include chronic mucous plugging and pulmonary infarct. In this case, the chronicity of the right upper lobe opacity in addition to the chronicity of the ventilation-perfusion findings would make the likelihood of pulmonary embolism low.

Differential Diagnosis List

The presence of extrapulmonary activity on perfusion scintigraphy typically indicates the presence of a right-to-left shunt or free Tc-99m pertechnetate. Less commonly, it may be due to recent administration of tracer from another nuclear medicine study.

ACR Codes and Keywords:

References and General Discussion of Ventilation Perfusion Scintigraphy (Anatomic field:Lung, Mediastinum, and Pleura, Category:Normal, Technique, Congenital Anomaly)

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Case number: vq026

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