Prevalence and Significance of Asymptomatic Venous Thromboembolic Disease Found on Oncologic Staging CT

Carmel G. Cronin; Derek G. Lohan; Maccon Keane; Clare Roche; Joseph M. Murphy

Disclosures

Am J Roentgenol. 2007;189(1):162-170. 

In This Article

Materials and Methods

Twelve examinations were initially excluded because of a known or suspected history of DVT in the prior 12 months. The remaining 435 consecutive staging CT examinations of the thorax, abdomen, and pelvis performed between January 2006 and March 2006 were retrospectively reviewed for the presence of venous thromboembolic disease (198 men, 237 women; age range, 20-79 years; mean age, 55 years). The staging CT examinations were performed for initial staging or restaging. One staging CT examination obtained during the study period was analyzed per patient.

These examinations were performed after patients received an IV injection of 150 mL of nonionic contrast medium (240 mg I/mL) administered at a rate of 2-2.5 mL/s. All examinations were performed on a Somatom scanner (Siemens Medical Solutions). CT of the thorax (collimation, 8 mm) was performed 30 seconds after contrast injection. CT of the abdomen and pelvis from the diaphragm to the pubic symphysis (collimation, 8 mm) was performed 90 seconds after the start of contrast medium infusion for CT of the thorax.

Disease type, stage, concomitant surgery or chemoradiation therapy regimes, and anticoagulation status were recorded. Cancer stages were divided into two broad groups: early stage disease (stages I and II) and late or advanced stage (stages III and IV). Because this study was retrospective, institutional review board approval was not required.

Statistical Analysis

SPSS software (version 14, SPSS) was used for statistical analysis. Logistic regression was used to determine the odds ratio (OR) and the statistical association between venous thromboembolism (DVT or PE) and patient age, patient sex, patient category (inpatient or outpatient), disease stage (early or advanced stage), current treatment (receiving or not), and disease type (hematologic, solid organ, or breast). We determined the relative risk (RR) of a thromboembolic event (DVT or PE) in inpatients, those on treatment, and those with advanced stage disease. A p value of 0.05 was considered to indicate a statistically significant difference.

Image Interpretation

CT scans were independently reviewed by a radiologist and a trainee radiologist. Acquired images were reviewed on a PACS workstation at a window width of 400 H and a window level of 40 H. The reviewers were free to use any window and level settings. Multiplanar reformation images were available on the same workstation. Based on standard diagnostic criteria for diagnosing DVT and PE, filling defects were required to be present on at least two consecutive slices.[15]

Exclusion criteria included a known recent (prior 12 months) history of DVT or PE (as determined by radiology records), or a clinical suspicion of DVT or PE at the time of staging scan (as determined by radiology records). We also retrospectively reviewed the medical records of the 25 patients with positive imaging findings for either DVT or PE and 25 randomly chosen patients with negative imaging findings for DVT or PE to assess whether any relevant evidence to suggest a history of DVT and PE had been omitted from the radiology records. Other exclusion criteria included reduced image quality because of excess patient motion, insufficient opacification of the femoral and iliac vessels, and metallic artifacts (caused by metal from hip prostheses), which reduce the diagnostic quality of the scan.

Each reviewer recorded confounding variables including lung masses, consolidation, effusions, abdominal masses, and retroperitoneal nodes compressing the abdominopelvic venous system. The location, size, and number of emboli were recorded for each patient. The presence of an embolus and all disagreements were resolved by a consensus panel of three radiologists and one trainee radiologist. There were no discrepancies with regard to the presence of thromboembolism.

Follow-Up

The radiology reports and clinical notes of the patients with a positive CT examination as judged by the consensus panel were reviewed and followed for 6 months. Follow-up is ongoing.

Diagnostic Criteria for DVT and PE

The CT criteria for diagnosing PE and IVC, iliofemoral, and iliac DVT using indirect CT venography were similar. A thrombus was defined as a low-attenuating partial or complete intraluminal filling defect surrounded by a high-attenuating ring of enhanced blood and seen on at least two consecutive transverse images. If only one transverse image showed a filling defect, a thrombus was not diagnosed.[16,17] Ancillary signs of PE, such as infarct or pleural effusions, were not included or used for the PE diagnosis. In our assessment for iliofemoral DVT, a mean venous attenuation (in Hounsfield units) of greater than 90 H was required. This level of contrast is the recommended degree of venous enhancement on CT venography as determined by Bruce et al.[18] and Ghaye et al.[19]

CT can be used to determine whether centrally located thrombi are present within the jugular veins, the brachiocephalic veins, and the superior vena cava and whether an extrinsic process is causing obstruction of the venous channels. However, delayed imaging at 2-3 minutes after contrast injection is required to evaluate these central veins. To our knowledge, no large series has looked at the diagnostic accuracy of this technique in the diagnosis of upper extremity venous thrombosis as other series have in lower extremity venous thrombosis, as outlined previously. Delayed imaging was not performed in our series and therefore precludes assessment for upper limb DVT.

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