Combined isotope venography and lung scanning. A new diagnostic appraoch to thromboembolism

Clinical features and diagnosis of venous thrombosis

The clinical diagnosis of venous thrombosis is inaccurate because the clinical findings are both insensitive and nonspecific. The sensitivity of clinical diagnosis is low because many potentially dangerous venous thrombi are clinically silent. The specificity of clinical diagnosis is low because the symptoms or signs of venous thrombosis all can be caused by nonthrombotic disorders. For these reasons, a practical approach for the diagnosis of venous thrombosis is important. A current approach to the diagnosis of clinically suspected venous thrombosis favors the use of impedance plethysmography over Doppler ultrasonography as the main test for this disorder. This is because impedance plethysmography is precise and objective, whereas the interpretation of Doppler ultrasonography is subjective and requires considerable skill and experience to form reliable diagnoses. The use of serial impedance plethysmography has been evaluated recently in a prospective study. The rationale of repeated impedance plethysmography evaluation is based on the premise that calf vein thrombi are only clinically important when they extend into the proximal veins, at which point detection with impedance plethysmography is possible. Therefore, by performing repeated examinations with impedance plethysmography in patients with clinically suspected venous thrombosis, it is possible to identify patients with extending calf vein thrombosis who can be treated appropriately. Impedance plethysmography is performed immediately on referral; if it is positive in the absence of clinical conditions that are known to produce falsely positive results, the diagnosis of venous thrombosis is established, and the patient is treated accordingly. If the result of the initial impedance plethysmography evaluation is negative, anticoagulant therapy is withheld, and impedance plethysmography is repeated the following day, again on day 5 to 7 and on day 10 to 14. If impedance plethysmography becomes positive during this time, a diagnosis of venous thrombosis is made and anticoagulant therapy is commenced. Positive impedance plethysmography in the presence of conditions known to produce a false positive result (for example, congestive cardiac failure) should be confirmed by venography. If noninvasive tests for the diagnosis of venous thrombosis are not available, a clinical suspicion of venous thrombosis should be objectively confirmed or excluded by performing ascending venography.

Emergency radionuclide scans

Radionuclide diagnostic imaging is an important adjunct to the diagnosis and treatment of several conditions that present to the emergency department. The emergency physician should be able to properly apply these tests. A normal radionuclide perfusion lung scan can reliably rule out pulmonary embolism. The use of the radionuclide ventilation lung scan may help interpretation of a perfusion lung scan that is of intermediate probability for pulmonary embolism. A radionuclide venogram of the lower extremities is both sensitive and accurate for detecting the presence of deep venous thrombosis. A radionuclide testicular scan is invaluable in the workup of the acute scrotum, as long as the test is available in a timely manner and the diagnosis has not been established by another means. A multiple-gated acquisition cardiac scan can help make the diagnosis of cardiac contusion after other causes of cardiac instability have been corrected. The renal radionuclide scan is useful in the workup of obstructive uropathy, especially if intravenous pyelography is contraindicated. The hepatobiliary nuclear scan is able to help differentiate acute cholecystitis from other causes of right upper quadrant pain. Proper and timely use of these tests can prevent serious sequelae from a missed diagnosis, and in some cases eliminate the need for invasive tests, dangerous treatment, or even exploratory surgery when it is unwarranted.

Radionuclide venography as an outpatient screening test for deep venous thrombosis

This study evaluated the use of radionuclide venography (RNV) as a screening test for patients with signs and symptoms of deep venous thrombosis (DVT). Seventy patients underwent RNV; 27 of the 70 patients also had contrast venography. The incidence of DVT was 19% (13 of 70). RNV had an observed sensitivity of 93% and an observed specificity of 100%. Follow-up at one month revealed no evidence of thromboembolic disease in patients with a negative scan. RNV is an accurate, practical screening test for DVT.

Thrombophlebitis: diagnostic techniques

A review of the extensive literature on the diagnosis of deep vein thrombophlebitis (DVT) is presented. DVT affects approximately 10% of all patients with superficial thrombophlebitis. Many authors have shown that the clinical finding of DVT are unreliable. Although pulmonary emboli are relatively frequent in all patients with calf DVT, these emboli are generally not associated with clincial events. Venography is the "gold standard" of diagnostic tests, but it is too cumbersome to be practical as a screening procedure. Radioisotope-labeled fibrinogen is reasonable accurate in diagnosing calf DVT, but much less so in proximal lesions. The results of Doppler ultrasound and impedance plethysmography (IPG) agree with those of venography in 90% of the cases of proximal DVT.

Isotope phlebography in the study of lower extremity venous thrombosis

Isotope phlebography is performed using 99mTc as pertecnetate, macroaggregates of albumin (MAA) or microspheres of albumin (MISA). The isotope is injected at a dose of 6-10 mCi into the dorsal foot veins. The area studied begins at the knee and is followed successively by the groin, the iliac area and the region of the IVC. A pulmonary scan is performed when MAA or MISA are used. Our method has proven to be reliable in showing 1) thrombosis of the veins of the groin and iliac area, which appear as a 'non visualisation' of the venous tract, 2) delayed transit time of the isotope, 3) visualisation of the superficial circulation (changes and irrgularities). The association of istope phlebography with pulmonary scan is useful for evaluating the femoral-iliac and the vena caval system and for detecting the presence of pulmonary embolism.

Pulmonary embolism in respiratory failure

The occurrence of pulmonary emboli in 617 patients admitted to a respiratory intensive care unit was studied. Pulmonary emboli were found in 18 (27 percent) of 66 autopsies. Half of these pulmonary emboli were not diagnosed before death, despite persistent aggressive attempts to document pulmonary emboli. In this subpopulation of patients with respiratory failure, the usual clinical manifestations of pulmonary emboli (symptoms, signs, chest x-ray film, electrocardiogram, and changes in arterial blood gas levels) frequently are already present, due to the severe underlying pulmonary disease, and any superimposed manifestations of pulmonary emboli are often inapparent. In this group under study, the ventilation/perfusion lung scan correlated poorly with pulmonary angiographic results and with examinations at autopsy; the scan generally was inadequate to rule in or rule out pulmonary emboli. Again, this was due to the distortion of both ventilation and perfusion by the severe underlying pulmonary disease. Currently, pulmonary angiographic studies remain the only reliable technique to confirm or exclude pulmonary emboli in patients with respiratory failure.

Radioactive tracers in peripheral vascular disease

The use of radioactive tracers in the diagnostic and therapeutic evaluation of the patient with peripheral arterial or venous disease has proven to be clinically useful. Their application has provided a means by which the regional distribution of perfusion at the level of the microcirculation, at rest and under various stresses, can be assessed. Graft patency can be determined simply and repeatedly, and the relative perfusion of "ischemic" ulcers can be used to assess their healing potential. The presence of arteriovenous shunts can be verified, localized, and quantified. Venous thrombi can be detected, and the competence of the venous valvular system and muscle pump as well as the hemodynamics of the venous system can be quantified.

Vascular injuries in pelvic cancer surgery

Although pelvic cancer surgery is attended by many difficulties, vascular injuries are actually rare. New techniques of isotopic and ultrasound monitoring allow objective assessment of such patients with vascular injury. In venous problems, absolutely precise diagnosis is now possible and in both arterial and venous injury, extra-anatomic reconstructions can be done which return the vascular status of the patient to near normal.