British Journal of Radiology (2005) 78, 783-786
© 2005 British Institute of Radiology
doi: 10.1259/bjr/84768811
Rhodococcus equi pneumonia in AIDS: high-resolution CT findings in five patients
E Marchiori, MD
1
N L Müller, MD, PhD
2
R G de Mendonça, MD
1
D Capone, MD
1
A S Souza, Jr, MD
3
D L Escuissato, MD
4
E L Gasparetto, MD
4 and
E M F P de Cerqueira, MD
5
Departments of Diagnostic Radiology, 1 University of Rio de Janeiro, Rio de Janeiro, Brazil, 2 University of British Columbia, 2329 West Mall Vancouver, BC Canada V6T 1Z4, 3 University of São José do Rio Preto, Brazil, 4 University of Paraná, Curitiba, Brazil and 5 University of Campinas, Brazil
Correspondence: Dr Edson Marchiori, Rua Thomaz Cameron, 438, Valparaíso. Petrópolis, RJ, 25685-120, Brazil
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Abstract
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The aim of this study was to describe the high-resolution CT scan findings in five patients with AIDS and pulmonary infection due to Rhodococcus equi. The study included five patients with AIDS and proven R. equi infection. The CT scans were reviewed by two observers. The patients included four men and one woman ranging from 39 years to 49 years in age (mean 42 years). The findings included areas of consolidation (n=5) with single (n=1) or multiple cavitation (n=4), ground-glass opacities (n=5), centrilobular nodules (n=3), small centrilobular nodular opacities (n=3) and "tree in bud" opacities (n=3). None of the patients had pleural effusion or lymph node enlargement. The most common high-resolution CT manifestations of R. equi infection consist of areas of consolidation with cavitation, ground-glass opacities, nodules and a tree-in-bud pattern.
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Introduction
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Rhodococcus equi (R. equi) is a gram-positive rod aerobic organism found predominantly in animals, manure and soil. The infection is rare in humans, being seen almost exclusively in patients with severe immunodeficiency. This opportunistic pathogen is usually associated with granulomata, and responds relatively well to the antimicrobial therapy [1]. Approximately 80% of infections occur in patients with acquired immunodeficiency syndrome (AIDS), usually in patients with CD4 lymphocyte counts less than 200 cells mm–3 [2, 3].
The most common clinical manifestations are cough, fever and constitutional symptoms. The radiological manifestations of R. equi pulmonary infection consist of single or multiple areas of consolidation with cavitation usually involving the upper lobes [2, 4–6]. The findings on conventional CT include dense pulmonary consolidations with or without cavitation, mediastinal lymphadenopathy and, occasionally, multiple bilateral pulmonary nodular opacities [6]. To our knowledge, the findings on high-resolution CT have not been previously described.
The aim of this study was to review the high-resolution CT scan findings in five patients with AIDS and R. equi infection.
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Patients and methods
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The study was retrospective and included five patients with R. equi infection who had high-resolution CT scans performed at one of three university hospitals in Rio de Janeiro (Clementino Fraga Filho University Hospital, Pedro Ernesto University Hospital and Antônio Pedro University Hospital) between 1996 and 2003.
The patients included four men and one woman ranging from 39 years to 49 years in age (mean age 42 years). All the patients had confirmed diagnosis of AIDS and CD4 lymphocyte counts lower than 50 cells per mm3. All patients had a 1 to 2 month history of cough and fever and presented with progressive shortness of breath and pleuritic chest pain. R. equi infection was confirmed by culture from bronchoalveolar lavage (n=4) or transthoracic needle aspiration (n=1); two patients also had positive blood cultures.
Four high-resolution CT scans were performed on a Siemens Somaton AR (Siemens Medical Solutions, Munich, Germany) scanner and one on a GE 9800 S (General Electric Medical Systems, Milwaukee, WI) scanner, using 1–2 mm collimation at 10 mm intervals through the chest. All images were reconstructed using an edge-enhancing (high-resolution) algorithm and photographed at lung (width 1000–1300 HU; level –500–700 HU) and mediastinal (width 200–600 HU; level 10–100 HU) window settings. No intravenous contrast was administered in any of the patients.
Two observers assessed the chest CT scans and reached a decision by consensus. The CT scans were assessed for the presence, extent and anatomical distribution of parenchymal abnormalities including air-space consolidation, areas of ground-glass attenuation, nodules, and centrilobular branching structures (tree-in-bud pattern). Ground-glass attenuation was defined as an area of hazy increased attenuation without obscuration of underlying vascular markings. Air-space consolidation was considered present when the opacities obscured the underlying vessels. Parenchymal nodules were subcategorized according to their diameters (smaller and larger than 10 mm) and distribution (centrilobular, peribronchovascular, subpleural, random). The presence of associated findings, such as pleural effusion and mediastinal lymphadenopathy was also assessed.
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Results
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The findings included areas of consolidation (n=5) with single (n=1) or multiple cavitation (n=4), ground-glass opacities (n=5), small centrilobular nodules (n=3), small centrilobular nodular opacities (n=3) and branching linear and nodular opacities ("tree-in-bud" pattern) (n=3) (Figures 1–3
). The predominant abnormality in all patients was unilateral (n=3) or bilateral (n=2) segmental consolidation with air bronchograms and with ill-defined borders. In four patients the consolidation involved the upper lobes and in one the lower lobe. Concomitant involvement of the middle lobe was seen in one patient. Four patients had multiple cavitations within the areas of consolidation and one had a single cavity. In one of the cases the consolidation simulated a mass. In one case there was a thin walled septated cavity in the right middle lobe.
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Figure 1. 39-year-old man with AIDS and Rhodococcus pneumonia (case 2). (a) High-resolution CT demonstrates consolidation with multiple areas of cavitation in the right upper lobe. Ground-glass opacities are seen adjacent to the consolidation. (b) A thin walled septated cavity is present in the right middle lobe.
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Figure 2. 42-year-old man with AIDS and Rhodococcus pneumonia (case 3). (a) High-resolution CT shows consolidation with areas of cavitation in the upper segment of the left lower lobe. Note adjacent centrilobular nodules (white curved arrows) and ground-glass opacities. (b) High-resolution CT demonstrates small centrilobular nodules and ground-glass opacities in the periphery of the consolidation (black arrow). Also note centrilobular nodules (white curved arrows) and "tree in bud" pattern (black curved arrows).
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Figure 3. 42-year-old woman with AIDS and Rhodococcus pneumonia (case 1). (a, b) High-resolution CT shows air-space consolidation and cavitation in the posterior segment of the right upper lobe. Areas of consolidation, centrilobular opacities, confluent centrilobular nodules and areas of ground-glass attenuation can be seen adjacent to the consolidation. Also noted are confluent centrilobular nodules and ground-glass opacities (curved black arrows) in the left lung.
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Ground-glass opacities were seen in all five patients, predominantly located adjacent to the areas of consolidation. One patient had patchy bilateral ground-glass opacities.
Small centrilobular nodular opacities and tree-in-bud opacities were seen in three patients, with a predominant distribution around the areas of consolidation. In one of these patients, the findings were bilateral and seen mainly in the lower lobes. Small centrilobular nodules were also observed in the periphery of the pulmonary consolidation in three patients. In one of them, nodules with similar characteristics were also seen at the lung bases.
None of the patients had pleural effusion or lymph node enlargement.
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Discussion
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R. equi is a rare cause of infection in humans, being seen mainly in patients with AIDS [2]. Wicky et al [6] reviewed the chest radiographs and conventional CT findings in nine patients with AIDS and R. equi lung infection. The predominant CT findings consisted of dense areas of consolidation with or without cavitation. CT confirmed the presence of cavitation and air-fluid levels seen on the radiographs, and also identified these findings in three patients in whom the cavitation was not apparent on the radiograph. Eight out of nine patients had mediastinal lymph node enlargement. Small centrilobular nodules and areas of bronchiolar filling, representing bronchogenic dissemination, were observed in one case. Multiple nodules measuring 5–20 mm in diameter, most of then with cavitation, were observed in two patients [6]. Similar to Wicky et al [6], the predominant findings seen in our study were segmental areas of consolidation with air bronchograms and multiple areas of cavitation. However, high-resolution CT is superior to conventional CT in demonstrating the presence of centrilobular nodules and branching opacities (tree-in-bud pattern). The presence of a tree-in-bud pattern on high-resolution CT is highly suggestive of infection [11, 12]. In the current study small centrilobular nodules and a tree-in-bud pattern were each seen in 60% of patients. The centrilobular nodules and tree-in-bud pattern presumably are secondary to endobronchial spread of the infection.
Air-space consolidations, ground-glass opacities, centrilobular nodules and tree-in-bud pattern, which were the main high-resolution CT findings in this study, are frequently seen in other pulmonary diseases affecting patients with AIDS [3, 6], making the differential diagnosis sometimes difficult. Pneumocystis carinii pneumonia usually presents with ground-glass opacities, but consolidation and centrilobular nodules may also be seen. Tuberculosis frequently demonstrates the pattern of large nodules, consolidation, centrilobular nodules and a tree-in-bud pattern. Patients with bacterial pneumonia show a high-resolution CT pattern similar to those observed in immunocompetent patients, consisting of areas of consolidation. In addition, in cases of invasive pulmonary aspergillosis, cavities and less commonly nodules and consolidation has been reported [3].
Muñoz et al [9] reported a case of an asymptomatic male patient with a single pulmonary nodule, which appeared during immunosuppressant therapy 3 months after heart transplantation. The nodule was seen on the chest radiography and confirmed by CT, which also guided fine needle puncture for diagnosis.
The typical histopathological finding of R. equi infection is a necrotizing cavity or a soft tissue mass composed of dense infiltration of histiocytes with copious eosinophilic granular cytoplasm (von Hansemann cells) [10]. Polymorphonuclear leukocytes are abundant in the microabscesses. The coccobacillus is readily seen on Gram stains.
The most common clinical manifestations are cough, which may be dry or productive, fever, dyspnoea, and pleuritic chest pain [1, 2, 6, 10]. The prognosis is poor, the mortality in AIDS patients being approximately 50% [8].
In summary, the most common findings on high resolution CT of patients with AIDS and Rhodococcus equi pulmonary infection include consolidation with single or multiple cavities, associated with surrounding ground-glass opacities, small centrilobular nodules or a tree-in-bud pattern. Moreover, this infection shares high-resolution CT findings with other pulmonary diseases seen in patients with AIDS.
Received for publication February 7, 2005.
Revision received March 4, 2005.
Accepted for publication March 21, 2005.
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References
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Abstract
Introduction
