Applied Radiology

Case summary:

A 67-year-old woman presents to the emergency room complaining of shortness of breath, chest pain, and a cold, painful left arm two weeks after undergoing a right total hip replacement. She had no previous history of cardiothoracic disease. On physical examination, the patient was tachycardic at a rate of 110 and tachypneic at a rate of 30. The woman's left arm was cold to the touch and her pulses were decreased on the left side compared to the right. Initial po2 on room air was 41%. Chest x-ray and ECG on admission were within normal limits.

Diagnosis:

Paradoxical embolism.

There was strong clinical concern for a pulmonary embolism, as well as an arterial embolism, and the patient was sent for a pulmonary arteriogram. Initially, it was difficult to pass the catheter tip into the pulmonary artery, as the catheter tip preferentially entered the left pulmonary vein (figure 1). Contrast was injected into the right atrium and a communication between the right and left atrium (patent foramen ovale) was demonstrated (figure 2). The patient had no documented history of atrial septal defect. Pulmonary arterial pressures measured 42/20 mm Hg. Pulmonary arteriogram revealed multiple pulmonary emboli within the left upper and lower lobes (figure 3).

Using the right femoral artery approach, subselective catheterization of the left brachial artery was performed. Arteriogram demonstrated complete occlusion of the left brachial artery with a clot extending into the forearm (figure 4). The ulnar artery filled at the wrist. Urokinase therapy was not started due to the patient's recent postoperative status. An inferior vena cava filter was placed, and the patient was placed on heparin and subsequent coumadin therapy. Anticoagulation therapy resulted in complete resolution of her pulmonary and left upper extremity symptoms.

Discussion:

Paradoxical embolism, first described in 1877 by Connheim,1 refers to the passage of venous thrombus into the systemic circulation through a right-to-left shunt. Several conditions must be met in order to make the diagnosis of paradoxical embolism, including the presence of venous thrombus; an abnormal communication between the right and left circulation; a favorable pressure gradient to promote a right-to-left shunt; and clinical, angiographic, or pathologic evidence for systemic embolism.2 A "proved" case of paradoxical embolism is defined as one in which a venous thrombus is found trapped in an intracardiac defect during echocardiography or at autopsy.3 Prior to 1980, very few "proved" cases were documented in living patients. In the early 1980s, however, non-

invasve maneuvers performed during echocardiography became useful for defining a patent foramen ovale in patients with suspected paradoxical embolism.4-6 This led to an increase in the number of "proved" cases, although proving the diagnosis of paradoxical embolism during a patient's life remains a diagnostic challenge. A "presumptive" diagnosis during life can be made when the aforementioned conditions are met and when there is a favorable temporal relationship between pulmonary and systemic emboli.

The diagnosis of paradoxical embolus should be considered in any postoperative patient who has an unexpected arterial embolism.7 Risk factors are identical to those for pulmonary embolus. In order for a venous thrombus to cross a patent foramen ovale, a right-to-left pressure gradient must exist. Elevation of right atrial pressure may be secondary to a chronic condition such as chronic obstructive lung disease with cor pulmonale, tricuspid valve disease, or primary pulmonary hypertension.7 More commonly though, elevated right atrial pressures are secondary to an acute process such as substantial pulmonary embolism with acute right ventricular and atrial hypertension.7 The valsalva maneuver also has been shown to cause a sudden rise in right sided pressures.

A presumptive diagnosis of paradoxical embolism was made in this patient based on the temporal relationship between her pulmonary and systemic emboli without an evident cardiac or systemic source for the arterial embolus.7 Although this entity is uncommon, it should be included in the differential diagnosis of arterial embolism of which there is no obvious source.

References

1. Connheim J: Thrombose and embolie. VorIesung uber allgemeine pathologie, Vol. 1, p.134. Berlin, Hirschwald, 1877.

2. Johnson BI: Paradoxical embolism. J Clin Pathol 4:316, 1951.

3. Loscalzo J: Paradoxical embolism: Clinical presentation, diagnostic strategies, and thera-

peutic options. Am Heart J 112(1):141-145,

1986.

4. Higgins JR, Strunk BL, Shiller NB: Diagnosis of paradoxical embolism with contrast echocardiography. Am Heart J 107:375, 1984.

5. Cheng TO: Echocardiogram and paradoxical embolism. Ann Intern Med 95:515, 1981.

6. Rodgers DM, Singh S, Meister SG: Contrast echocardiographic documentation of paradoxical embolism. Am Heart J 107:1270, 1984.

7. Sperber SJ, Horowitz D: Paradoxical embolism after surgery. Hosp Pract 21(4):159-162, 1986.