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High-Resolution MDCT of Pulmonary Septic Embolism: Evaluation of the Feeding Vessel Sign

¹ Department of Radiology, Vancouver General Hospital, Vancouver, BC, Canada.
² Department of Radiology, St. Vincents University Hospital, 855 W 12th Ave., Vancouver, BC, Canada V6K 1R4.

Received April 21, 2005; accepted after revision July 18, 2005.

 
Address correspondence to J. D. Dodd (jdodd{at}vanhosp.bc.ca).

Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
OBJECTIVE. The objective of this study was to use high-resolution MDCT to assess the relation of the pulmonary vasculature to septic emboli with particular attention to the feeding vessel sign.

MATERIALS AND METHODS. The MDCT scans of nine patients with septic emboli were retrospectively, blindly evaluated by two observers. A control group of 10 patients with documented pulmonary metastasis and pathologically proven carcinoma also were included. Transverse images, multiplanar reconstructions, and maximum intensity projections were used to analyze nodules and the pulmonary vasculature. The CT scans were obtained with 1- to 1.25-mm collimation on a 4-, 8-, or 16-MDCT scanner. The feeding vessel sign was defined as a vessel coursing directly into a nodule.

RESULTS. The patients with septic embolism had a total of 141 nodules and 52 wedge-shaped opacities. Transverse images showed that 52 (37%) of the nodules and 11 (22%) of the wedge-shaped opacities had a vessel that appeared to enter the nodule, but multiplanar reconstructions (without IV contrast enhancement) and maximum intensity projections (with IV contrast enhancement) showed the vessels passed around the nodules. Twenty-one (15%) of the spherical nodules and seven (13%) of the wedge-shaped opacities exhibited a central vessel entering the lesion in all imaging planes. All of these vessels were traced to the left atrium on transverse images, a finding consistent with pulmonary vein branches. Similar findings were seen in pulmonary metastatic lesions.

CONCLUSION. Although pulmonary septic emboli often appear to have a feeding vessel on conventional cross-sectional images, multiplanar reconstructions show that most of these vessels course around the nodule and that the others are pulmonary veins.

Keywords: bacterial infections/radiography • high-resolution CT • infectious diseases • pulmonary embolism/etiology

Introduction

Top Abstract Introduction Materials and Methods Results Discussion References

 
Septic emboli are seen most commonly in patients with infective endocarditis, patients with infected venous catheters or pacemaker leads, and patients with periodontal disease [1-3]. The CT appearance of septic emboli includes nodules and wedge-shaped subpleural opacities with or without cavitation and the feeding vessel sign [4-6]. The feeding vessel sign consists of a distinct vessel leading directly into the center of a nodule. This sign has been considered highly suggestive of septic embolism, the prevalence varying from 67-100% in various series [4-6].

The feeding vessel sign also occurs in pulmonary metastasis [7]. Murata et al. [7], in a careful stereomicroscopic CT-pathologic correlation of pulmonary vasculature to pulmonary metastasis, found that only 18% of nodules identified had a definitive pulmonary arterial branch entering the center of the nodule. In 58% of nodules, stereomicroscopic examination showed that the vessel did not enter the nodule but coursed along its border, being displaced by the nodule.

The advent of MDCT has allowed narrower collimation and faster acquisition during a single breath-hold with near isometric z-axis resolution [8, 9]. Despite the faster scanning time, MDCT image quality is equal to that of conventional high-resolution CT in cadaveric lungs [10]. We hypothesized that high-resolution MDCT may more clearly depict the relation between septic emboli and the pulmonary vasculature and that feeding vessels may be an uncommon finding on MDCT. The objective of this study was to use MDCT with particular attention to assessment of the feeding vessel sign to assess the relation of septic emboli to the pulmonary vasculature.

Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion References

 
The MDCT scans of nine patients (six men, three women; mean age 36 years; age range, 18-66 years) who had a diagnosis of septic emboli made at our institution between 2002 and 2005 were included in the study. A control group of 10 patients (six men, four women; mean age, 57 years; age range, 18-81 years) with documented pulmonary metastasis and pathologically proven carcinoma were also included in the analysis. Patients with pulmonary metastasis were chosen as a control group because the lesions commonly appear as spherical nodules with or without cavitation and have been described in association with the feeding vessel sign. The diagnosis of septic embolism was based on the presence of clinical and radiologic features consistent with septic emboli and microbiologic confirmation of sepsis. The study was approved by the hospital ethics committee.

Of the patients with septic emboli, four used IV drugs, two had undergone bone marrow transplantation (one for non-Hodgkin's lymphoma, one for acute lymphocytic leukemia), one was undergoing immunosuppressive therapy for systemic lupus erythematosus, one had osteomyelitis, and one had no identifiable risk factors for sepsis but had echocardiographic evidence of tricuspid valve vegetation consistent with infective endocarditis. Six patients had blood culture results positive for Staphylococcus aureus [6] or Streptococcus viridans [2]. Of the other three patients, the patient who had undergone bone marrow transplantation for non-Hodgkin's lymphoma had tricuspid valve vegetation identified at echocardiography, another patient had a central venous line catheter tip with culture results positive for Staphylococcus aureus, and the third had a liver abscess with culture results positive for Aspergillus organisms. The median interval between MDCT and positive culture results or echocardiography was 1 day (range, 1-7 days).

Of the control group of 10 patients with pathologically proven carcinoma and pulmonary metastasis, four had primary pulmonary carcinoma, two had colon carcinoma, one had giant cell tumor of the patella (with biopsy-proven lung metastasis), one had sarcoma, one had breast carcinoma, and one had renal cell carcinoma.

All patients underwent MDCT of the chest. Six patients underwent 4-MDCT (LightSpeed 4 scanner, GE Healthcare), eight underwent 8-MDCT (LightSpeed 8 scanner, GE Healthcare), and five underwent 16-MDCT (Somatom Sensation scanner, Siemens Medical Solutions). All examinations were performed from lung apex to lung base with 13.5-mm table speed per rotation, 0.5-second gantry rotation time, 120 kVp, and 360 mA. Contiguous slices were reconstructed at 1 or 1.25 mm. Lung parenchymal images were viewed with a high-spatial-frequency bone edge-enhancing algorithm on a PACS at a window width of 1,500 H and level of -700 H. Mediastinal images were viewed at a window width of 450 H and level of 50 H. Five patients (four with septic emboli and one with pulmonary metastasis) received a bolus dose of 90 mL of IV contrast medium at a flow rate of 3.5 mL/s.

View larger version (100K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —49-year-old male IV drug user with epidural abscess and positive culture results for Staphylococcus aureus. Blood cultures also were positive for Staphylococcus aureus. Transverse 1.25-mm contiguous MDCT images through left upper lobe show irregular nodule (curved arrow) with distinct central vessel (straight arrow) leading into its center.

View larger version (91K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —49-year-old male IV drug user with epidural abscess and positive culture results for Staphylococcus aureus. Blood cultures also were positive for Staphylococcus aureus. Transverse 1.25-mm contiguous MDCT images through left upper lobe show irregular nodule (curved arrow) with distinct central vessel (straight arrow) leading into its center.

View larger version (86K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C —49-year-old male IV drug user with epidural abscess and positive culture results for Staphylococcus aureus. Blood cultures also were positive for Staphylococcus aureus. Transverse 1.25-mm contiguous MDCT images through left upper lobe show irregular nodule (curved arrow) with distinct central vessel (straight arrow) leading into its center.

View larger version (68K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1D —49-year-old male IV drug user with epidural abscess and positive culture results for Staphylococcus aureus. Blood cultures also were positive for Staphylococcus aureus. Contiguous coronal 1.25-mm multiplanar reconstructions show vessel (arrow) passing around nodule, which was not appreciable on transverse images.

View larger version (67K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1E —49-year-old male IV drug user with epidural abscess and positive culture results for Staphylococcus aureus. Blood cultures also were positive for Staphylococcus aureus. Contiguous coronal 1.25-mm multiplanar reconstructions show vessel (arrow) passing around nodule, which was not appreciable on transverse images.

View larger version (67K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1F —49-year-old male IV drug user with epidural abscess and positive culture results for Staphylococcus aureus. Blood cultures also were positive for Staphylococcus aureus. Contiguous coronal 1.25-mm multiplanar reconstructions show vessel (arrow) passing around nodule, which was not appreciable on transverse images.

View larger version (58K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1G —49-year-old male IV drug user with epidural abscess and positive culture results for Staphylococcus aureus. Blood cultures also were positive for Staphylococcus aureus. Contiguous coronal 1.25-mm multiplanar reconstructions show vessel (arrow) passing around nodule, which was not appreciable on transverse images.

View larger version (95K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A —25-year-old female IV drug user admitted to hospital with shortness of breath. Blood cultures were positive for Staphylococcus aureus. Transverse 1.25-mm MDCT image through left lower lobe shows cavitating wedge-shaped opacity with distinct central vessel (arrow) leading into it.

View larger version (72K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B —25-year-old female IV drug user admitted to hospital with shortness of breath. Blood cultures were positive for Staphylococcus aureus. Contiguous coronal oblique 1.25-mm multiplanar reconstruction does not adequately depict precise relation of vessel relative to cavitating opacity (arrow).

View larger version (107K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C —25-year-old female IV drug user admitted to hospital with shortness of breath. Blood cultures were positive for Staphylococcus aureus. Oblique IV contrast-enhanced 20-mm maximum-intensity-projection (MIP) image shows vessels (arrows) passing around sides of cavitating nodule that were not identified on transverse images. MIP images confirmed vessel to be venous. Second, smaller more caudal nodule has several vessels (arrowheads) passing around it.

Top Abstract Introduction Materials and Methods Results Discussion References

Sixty-three percent of nodules and 78% of wedge-shaped opacities did not have a central vessel on all imaging planes. Fifty-two (37%) of the 141 nodules and 11 (22%) of the 52 wedge-shaped opacities exhibited a central feeding vessel on transverse images that was subsequently shown to pass around the nodule on multiplanar reconstructions and MIP images (Figs. 1A, 1B, 1C, 1D, 1E, 1F, 1G, 2A, 2B, and 2C). In all imaging planes, 21 (15%) of the spherical nodules and seven (13%) of the wedge-shaped opacities had a central feeding vessel entering the lesion. All of these vessels were traced to the left atrium, a finding consistent with pulmonary vein branches (Figs. 3A, 3B, 3C, 3D, 3E, 3F, 3G, and 3H).

View larger version (98K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A —Same patient as in Figures 2A, 2B, and 2C. Transverse 1.25-mm MDCT image through right lower lobe shows cavitating nodule (curved arrow) with distinct central vessel (straight arrow) leading into it.

View larger version (84K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B —Same patient as in Figures 2A, 2B, and 2C. Coronal oblique1.25-mm multiplanar reconstruction confirms presence of distinct central vessel (arrow) leading into opacity.

View larger version (94K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C —Same patient as in Figures 2A, 2B, and 2C. Selected transverse 1.25-mm MDCT images after IV administration of contrast bolus show vessel (arrow) filled with contrast material coursing superiorly and medially and inserting into left atrium, consistent with pulmonary vein. Curved arrow indicates nodule.

View larger version (90K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3D —Same patient as in Figures 2A, 2B, and 2C. Selected transverse 1.25-mm MDCT images after IV administration of contrast bolus show vessel (arrow) filled with contrast material coursing superiorly and medially and inserting into left atrium, consistent with pulmonary vein. Curved arrow indicates nodule.

View larger version (85K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3E —Same patient as in Figures 2A, 2B, and 2C. Selected transverse 1.25-mm MDCT images after IV administration of contrast bolus show vessel (arrow) filled with contrast material coursing superiorly and medially and inserting into left atrium, consistent with pulmonary vein. Curved arrow indicates nodule.

View larger version (86K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3F —Same patient as in Figures 2A, 2B, and 2C. Selected transverse 1.25-mm MDCT images after IV administration of contrast bolus show vessel (arrow) filled with contrast material coursing superiorly and medially and inserting into left atrium, consistent with pulmonary vein. Curved arrow indicates nodule.

View larger version (70K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3G —Same patient as in Figures 2A, 2B, and 2C. Coronal oblique 20-mm maximum-intensity-projection images confirm vessel (arrow) as venous.

View larger version (71K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3H —Same patient as in Figures 2A, 2B, and 2C. Coronal oblique 20-mm maximum-intensity-projection images confirm vessel (arrow) as venous.

Pleural abnormalities were seen in seven patients, four of these abnormalities being bilateral and three unilateral. Of the patients with bilateral changes, three had nonloculated effusions with no pleural thickening and one had minor diffuse bilateral pleural thickening without effusion, which appeared unrelated to any parenchymal lesions. One of the patients with unilateral changes had a right-sided loculated effusion with pleural thickening and enhancement consistent with empyema. One patient had minor, diffuse right-sided pleural thickening not directly abutting lung parenchymal lesions. The third patient had a simple left-sided pleural effusion. Two patients had pericardial effusions, which were associated with bilateral pleural effusions and increased septal lines suggestive of fluid overload.

Two patients had evidence of mediastinal lymphadenopathy, presumably reactive. In one patient, enlarged nodes were seen in the subcarinal region and in one lymphadenopathy involved the paraaortic, prevascular, and pretracheal regions.

The 10 patients in the control group had a total of 121 nodules and 11 wedge-shaped opacities. Thirteen nodules showed evidence of cavitation. Forty-six (38%) of the nodules and four (36%) of the wedge-shaped opacities showed a central vessel that on transverse images appeared to enter the lesion but was subsequently shown to pass around the lesion on multiplanar reconstructions and MIP images. In all imaging planes, 18 (15%) of the spherical nodules and two (18%) of the wedge-shaped opacities showed a central vessel entering the lesion. As with the septic emboli, all of these vessels were traced to the left atrium, a finding consistent with pulmonary vein branches.

Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
Septic emboli are seen most commonly in patients with infective endocarditis, patients with infected venous catheters or pacemaker leads, and in patients with periodontal disease [1-3]. CT is superior to chest radiography in showing the presence and extent of septic embolism [14]. The characteristic CT manifestations have been reported as consisting of well-defined, spherical nodules, wedge-shaped subpleural opacities, and the feeding vessel sign [4-6]. The feeding vessel sign was found in 100% of patients in one series and is considered a highly suggestive sign of septic emboli [4-6].

We counted 141 nodules and 52 wedge-shaped opacities, many of which initially appeared to have a feeding vessel sign on transverse images. Multiplanar reconstructions, however, showed that most of these vessels passed around the lesions. MIP images proved the optimal technique in assessment of the pulmonary vasculature in the periphery of the lung, particularly for larger lesions. Sonnet et al. [15] described the potential utility of MIP images obtained with 16-MDCT in the detection of direct vessel involvement in 10 patients in whom angioinvasive aspergillosis was clinically suspected. Although several of these patients had pulmonary lesions with MDCT features of occlusion of a central vessel, this finding was not exactly correlated with the vascular occlusion depicted on corresponding histopathologic images. A key finding in our study was that many nodules had a prominent central vessel in all imaging planes but were not arteries. These vessels were traced to the left atrium, a finding consistent with pulmonary veins. It is likely that many "feeding vessels" identified in previous studies of septic emboli were in fact pulmonary veins. Tracing these vessels to the heart in these studies may have been difficult, particularly in studies in which noncontiguous CT protocols were used.

In this study we assessed the MDCT appearance of septic emboli in nine patients, paying particular attention to the feeding vessel sign. The main appearance of septic emboli in our cohort was multiple nodules in various stages of cavitation. The prevalence of nodules was higher than in two previous evaluations of the CT findings of septic embolism. In a study by Kuhlman et al. [6], 83% of patients had nodules, whereas in a study by Huang et al. [5], 67% of patients had nodules. This discrepancy may be related to different patient populations or to differences in CT technique. In both previous studies investigators used a noncontiguous CT protocol. In the study by Kuhlman et al., 4- to 8-mm slices were used, whereas in the study by Huang et al. it was unclear what slice thickness was used. The combination of thick sections and noncontiguous CT images in these studies probably led to underestimation of the number of nodules. In a more recent study [4] of septic emboli in 10 patients, investigators used single-slice helical CT and found nodules in all patients.

Our findings are in keeping with those of previous radiologic-pathologic studies in which the relation between the pulmonary vasculature and pulmonary metastasis was assessed. Murata et al. [7] assessed the relation of the pulmonary vasculature to pulmonary metastasis in detail in a correlative CT-pathologic study of five human lungs. In that study, only 18% of nodules had a pulmonary arterial branch entering the center of the nodule. In 58% of nodules the vessels lay along the border of the nodule. In addition, the authors found that certain nodules in close apposition to each other may have had a vessel passing between the two lesions. Further growth would circumferentially engulf the vessel, giving the appearance of a vessel entering the center of a "single nodule." Our conclusion therefore is that septic emboli, like blood-borne metastasis, are supplied by small arteriolar branch vessels too small for detection with current CT technology.

There were several limitations to the study. It was retrospective with a small number of patients. We used clinical, microbiologic, and radiologic evidence to diagnose septic emboli without histologic confirmation. Therefore we were unable to correlate the CT findings with those in pathologic specimens. Not all patients with septic emboli received IV contrast medium, so MIP analysis was precluded in those cases. We do not believe this factor invalidates our findings, because the pulmonary vasculature was clearly depicted with contiguous thin-slice MDCT. Interpreting the multiplanar reconstructions and MIP images at the same time as the axial sections when a feeding vessel was identified may have created interpretation bias. This bias was difficult to avoid because most of the multiplanar reconstructions and MIP images were reconstructed by the observers in oblique planes directly in the plane of the nodule and associated apparent feeding vessel. These oblique reconstructions would have been difficult to obtain before evaluation of the transverse images.

In conclusion, septic embolism is characterized by the presence of multiple nodules in various stages of cavitation and pleura-based wedge-shaped opacities. Although many of these nodules appear to have a central vessel on cross-sectional images, multiplanar reconstructions and MIP images show that in most cases these vessels course around the nodule. The "feeding vessel" seen in the other cases represents a pulmonary vein.

References

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