Thrombotic and nonthrombotic pulmonary arterial embolism: spectrum of imaging findings

The rise in the incidence of pulmonary embolus after joint arthroplasty: is modern imaging to blame?

In recent years, there has been an apparent increase in the incidence of pulmonary embolus after joint arthroplasty at our institution. We hypothesized the use of sophisticated imaging modalities such as the multidetector computed tomography scan, with better sensitivity, resulted in an apparent increase in the incidence of pulmonary embolus. We studied all patients with pulmonary embolus after joint arthroplasty between 2000 and 2005. The incidence of pulmonary embolus increased from 0.21% (six of 2859) when VQ scan was the modality of choice to 0.98% (50 of 5095) during the time spiral computed tomography was used to 1.72% (89 of 5179) in recent years when multidetector computed tomography was used. Despite the apparent increase in pulmonary embolus, we observed no change in mortality during the study period. Surgeons should be aware of the challenges sophisticated imaging modalities in general and modern imaging introduce for pulmonary embolus in particular. Extremely sensitive imaging tests with unknown specificity have resulted in an increase in diagnosed pulmonary embolus. However, diagnosing pulmonary embolus generates implications for further treatment such as prolonged anticoagulation and/or inferior vena cava filter insertion with potential for catastrophic complications. The challenge is to distinguish which require treatment and which do not.

MDCT of acute thrombotic and nonthrombotic pulmonary emboli

Acute pulmonary embolism (PE) remains a common clinical challenge. MDCT pulmonary angiography has become the first line imaging study in the diagnosis of PE because of its speed, accuracy, low-interobserver variability, and ability to provide alternative diagnoses. This review article highlights the role of MDCT in the evaluation of acute thrombotic PE in the era of PIOPED 2. MDCT findings of acute PE and some potential pitfalls are covered as well as some of the controversies in imaging young and pregnant patients. MDCT findings of acute non-thrombotic PE are also covered. This latter group may be occult on the angiographic portion of the study but may declare themselves through secondary findings. Their findings and potential mimics are included so that the interpreting radiologist can make the most of a CT to rule out PE.

Chronic-Stage Deep Vein Thrombosis of the Lower Extremities

OBJECTIVE

To describe the computed tomographic (CT) findings of chronic deep vein thrombosis (DVT) and its evolution from acute DVT.

METHODS

Fifty-one consecutive patients with 52 legs confirmed as acute DVT by CT venography underwent follow-up computed tomography more than 2 months later. Follow-up CT findings were assessed retrospectively by consensus between 2 radiologists. The frequencies of CT findings were analyzed for affected venous segments: common iliac, external iliac, femoral, popliteal, and calf veins.

RESULTS

Twelve legs (23%) were completely normalized on follow-up computed tomography, but 40 legs (77%) showed abnormal findings as follows: luminal obliteration (n = 16), decreased caliber (n = 30), residual thrombi (n = 3), fibrotic bands (n = 28), ipsilateral muscle enlargement (n = 28), ipsilateral subcutaneous edema (n = 11), and superficial collateral vein development (n = 23). The external iliac vein (26/40, 65%) was the most commonly affected site followed in decreasing order by femoral (29/50, 58%), common iliac (9/18, 50%), popliteal (22/47, 47%), and calf veins (9/43, 21%). Trends were observed whereby luminal obliteration affected iliac veins and fibrotic bands affected femoropopliteal veins.

CONCLUSIONS

Luminal obliteration, decreased caliber, fibrotic bands, ipsilateral muscle enlargement, and superficial collateral vein development are common CT findings in chronic DVT of the lower extremity.

Pulmonary Embolism: Prognostic CT Findings

PURPOSE

To retrospectively determine whether three computed tomographic (CT) findings-ventricular septal bowing (VSB), ratio between the diameters of right ventricle (RV) and left ventricle (LV), and embolic burden-are associated with short-term death, defined as in-hospital death or death within 30 days of CT, whichever was longer, due to acute pulmonary embolism (PE).

MATERIALS AND METHODS

Institutional Review Board approval was obtained, and patient information was reviewed in compliance with HIPAA regulations. A total of 1193 patients with CT scans positive for PE from January 1, 1997, to December 31, 2002, who had given authorization for retrospective research were included. Scans were independently reviewed by two observers. CT findings were compared with risk of death by using univariate analysis (chi(2) statistic) and multivariate logistic regression. Interobserver variability (kappa statistic or intraclass correlation coefficient), sensitivity, and specificity of CT findings for predicting death were calculated. A third observer reviewed discrepant cases post hoc.

RESULTS

Fifty-four percent of patients were women and 46% were men (mean age, 63 years +/- 16). For observer 1, VSB was associated with death in univariate (odds ratio [OR], 1.98; P = .04) and multivariate modeling (OR, 1.97; P = .05). Interobserver variability was only fair (kappa = 0.54) for VSB, and observer 2 found no association with death (OR, 1.52; P = .22). For both observers, VSB had low sensitivity (21% and 18%) and high specificity (88% and 87%) for predicting death. Neither RV/LV diameter ratio nor embolic burden was associated with increased risk of death. For observer 3, VSB was associated with death in univariate (OR, 2.10; P = .05) and multivariate analyses (OR, 2.18; P = .05).

CONCLUSION

CT-depicted VSB is predictive of death due to PE, but with low sensitivity and high interobserver variability. RV/LV diameter ratio and embolic burden are not associated with short-term death due to PE.

CT of pregnancy-related complications

During pregnancy, the risk of radiation exposure to the fetus is increased so that more than the usual benefit is necessary to justify computed tomography (CT; or other radiation exposure) than in non-pregnant patients. In the setting of a life-threatening illness, CT may be indicated to assess for potentially fatal complications such as hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome. After delivery, patients rarely develop serious problems requiring radiologic evaluation. When indicated, however, CT may be invaluable in making the diagnosis or determining the severity of peri- and post-partum complications, including uterine perforation, hemorrhage, endometritis, thrombophlebitis, and abscess formation. At times, CT may be the first to uncover conditions, such as post-partum cardiomyopathy, and heart failure, which are usually diagnosed by other modalities but may explain the symptoms for which the study was ordered. In some centers, CT pulmonary angiography represents the standard of care to diagnose pulmonary thromboembolism. In this article, we illustrate the spectrum of peri-partum and post-partum complications on CT to familiarize the radiologist with the CT features of these potentially life-threatening pregnancy-related complications.

Virtual pulmonary arterioscopy in pulmonary embolic disease

16 slice multidetector CT provides virtual endoscopic views of the inside of arteries, or any other hollow structures. This is performed non-invasively using post-processing of three-dimensional isotropic image data sets, acquired during standard CT examinations. These virtual endoscopic views are simultaneously correlated with the standard multiplanar reconstructions, with the ability to navigate a virtual camera through the hollow structure under study. Normal and abnormal volume rendered images of the pulmonary arteries are presented in correlation with the multiplanar reformats. The abnormal images show the volume rendered appearances of acute and chronic pulmonary embolic disease. It is also postulated that this technique has a problem solving role in the differential diagnosis of chronic mural emboli from extravascular structures such as adjacent lymph nodes or bronchiolar impaction. This technique may also have a role in medical education, providing clinicians and medical students with interactive three-dimensional representations of disease processes.

Congenital and acquired pulmonary artery anomalies in the adult: radiologic overview

Various congenital and acquired anomalies may affect the pulmonary arteries in adult patients. Congenital anomalies (proximal interruption, anomalous origin of the left pulmonary artery [pulmonary artery sling], and idiopathic dilatation of the pulmonary trunk) are usually found incidentally at chest radiography or computed tomography (CT). Acquired anomalies include diffuse or focal enlargement of the arteries because of pulmonary hypertension, aneurysm, and intravascular pulmonary metastasis; decreased arterial diameter because of bronchial carcinoma, mediastinal fibrosis, and Takayasu arteritis; and intraluminal filling defects due to pulmonary thromboembolism and pulmonary artery sarcoma. An awareness of the radiologic manifestations of the disease entities and potential pulmonary artery complications secondary to infection or vasculitis may enable an early diagnosis. CT angiography is becoming the standard method for evaluating patients in whom the presence of pulmonary embolism is suspected. CT assessment of the extent of heart effects in patients with pulmonary hypertension and pulmonary embolism is particularly important because such effects largely determine the prognosis.

[Pulmonary artery sarcoma during postpartum: CT findings]

We report the case of a 28 year-old female, who gave birth seven weeks previously, presenting with a pulmonary artery leiomyosarcoma discovered on a thoracic CT performed for clinical suspicion of pulmonary embolism. This case presents two major points of interest: on the first hand, it is a particular context (young post-partum patient), with classic symptoms of routine pulmonary embolism. On the other hand, the exam clearly demonstrates tumor enhancement, which is characteristic but rarely described.

Thin-section CT of the secondary pulmonary lobule: anatomy and the image--the 2004 Fleischner lecture

The secondary pulmonary lobule is a fundamental unit of lung structure, and it reproduces the lung in miniature. Airways, pulmonary arteries, veins, lymphatics, and the lung interstitium are all represented at the level of the secondary lobule. Several of these components of the secondary lobule are normally visible on thin-section computed tomographic (CT) scans of the lung. The recognition of lung abnormalities relative to the structures of the secondary lobule is fundamental to the interpretation of thin-section CT scans. Pathologic alterations in secondary lobular anatomy visible on thin-section CT scans include interlobular septal thickening and diseases with peripheral lobular distribution, centrilobular abnormalities, and panlobular abnormalities. The differential diagnosis of lobular abnormalities is based on comparisons between lobular anatomy and lung pathology.

Massive pulmonary tumor microembolism from a hepatocellular carcinoma

A 48-year-old patient with known alcohol abuse and long-standing liver cirrhosis presented with spontaneous bacterial peritonitis and subsequent hepato-renal syndrome. Autopsy revealed a large hepatocellular carcinoma of the right liver lobe. Histologically, pulmonary arteries, arterioles, and capillaries were occluded by numerous tumor emboli. Small tumor emboli also covered the endocardium of the right ventricle. A review of the literature shows that macroscopic as well as microscopic pulmonary tumor embolism is often diagnosed in patients with a previously unknown malignancy. Moreover, pulmonary tumor embolism radiologically mimics pneumonia, tuberculosis, or interstitial lung disease. Therefore, an autopsy should be considered in cases of fulminant or massive pulmonary embolism to exclude tumor embolism even when the patients' history is insignificant as to this point, and in cases with known malignant tumors and respiratory symptoms to exclude tumor microembolism.

CT angiography of pulmonary embolism: diagnostic criteria and causes of misdiagnosis

Computed tomographic (CT) pulmonary angiography is becoming the standard of care at many institutions for the evaluation of patients with suspected pulmonary embolism. This pathologic condition, whether acute or chronic, causes both partial and complete intraluminal filling defects, which should have a sharp interface with intravascular contrast material. In acute pulmonary embolism that manifests as complete arterial occlusion, the affected artery may be enlarged. Partial filling defects due to acute pulmonary embolism are often centrally located, but when eccentrically located they form acute angles with the vessel wall. Chronic pulmonary embolism can manifest as complete occlusive disease in vessels that are smaller than adjacent patent vessels. Other CT pulmonary angiographic findings in chronic pulmonary embolism include evidence of recanalization, webs or flaps, and partial filling defects that form obtuse angles with the vessel wall. Factors that cause misdiagnosis of pulmonary embolism may be patient related, technical, anatomic, or pathologic. The radiologist needs to determine the quality of a CT pulmonary angiographic study and whether pulmonary embolism is present. If the quality of the study is poor, the radiologist should identify which pulmonary arteries have been rendered indeterminate and whether additional imaging is necessary.

Molecular magnetic resonance imaging of pulmonary emboli with a fibrin-specific contrast agent

RATIONALE AND OBJECTIVES

The detection of pulmonary embolism is still challenging due to the often nonspecific clinical findings. The aim of this study was to investigate the potential of molecular targeted magnetic resonance imaging (MRI) of pulmonary emboli using low-dose application of a fibrin-specific contrast agent (EP-2104R; Epix Pharmaceuticals, Cambridge, MA).

METHODS

Fresh clots from human blood were engineered ex vivo and delivered in the lungs of 11 swine. Subsequently, a T1-weighted breath-hold three-dimensional gradient-echo sequence was performed before as well as 5 minutes, 1 hour, and 2 hours after systemic administration of 7.5 (n = 5) or 4 (n = 5) micromol/kg EP-2104R. One swine that did not receive any contrast agent served as a control. MR images were analyzed by two investigators and contrast-to-noise ratio between the thrombus and the surrounding tissue (blood pool and lung parenchyma) was assessed. Localization of thrombi was compared with 16-row multislice computed tomography. Finally, the animals were killed and thrombi were removed for assessment of gadolinium concentration.

MAIN RESULTS

Before contrast media application, thrombi were not visible on MR images. At 1 and 2 hours after contrast media injection, pulmonary emboli were selectively visualized with high-signal intensity foci, independent of the dosage used. A high gadolinium concentration in thrombi was found after both dosages (83 +/- 41 microM for 4 micromol/kg and 130 +/- 57microM for 7.5 micromol/kg), resulting in a similar high contrast-to-noise ratio on MR images (between 11 and 13).

CONCLUSION

Systemic low-dose application of EP-2104R allows for selective molecular MRI of fresh pulmonary thromboembolism in a swine model.

Clinical Usefulness of Computed Tomography Study Without Contrast Injection in the Evaluation of Acute Pulmonary Embolism

OBJECTIVE

To evaluate the percentage of cases in which emboli can be detected in unenhanced scans and to identify the cases in which they appear hyperattenuating or hypoattenuating in comparison to the circulating blood.

METHOD

An angio-computed tomography (CT) scan was performed before and after contrast injection in 140 consecutive patients after clinical suspicion of pulmonary embolism. A radiologist analyzed the examination results thus obtained. The enhanced scan was analyzed first, and after detecting the thrombus, the unenhanced scan was evaluated.

RESULTS

Fifty-one examinations were positive for a pulmonary embolism; in 21 cases, it was possible to identify the embolus even in the unenhanced scans. In 10 cases, the clots were hyperattenuating in comparison to the circulating blood; in 5 cases, they were hypoattenuating; and in 6 cases, they were mixed hyper-hypoattenuating.

CONCLUSION

In a relatively high percentage of cases, particularly those of central thromboembolism, it is possible to identify and characterize the clots even in unenhanced scans.