|Year : 2017 | Volume
| Issue : 2 | Page : 49-54
Role of high resolution computed tomography of chest in posttransplant pulmonary infection
Shruti P Gandhi1, Vivek Kute2, Kajal N Patel1, Harsh Sutariya1, Vaidehi Pandya1
1 Department of Radiology and Imaging, G. R. Doshi and K. M. Mehta Institute of Kidney Diseases and Research Centre, Dr. H. L. Trivedi Institute of Transplantation Sciences, Ahmedabad, Gujarat, India
2 Department of Nephrology, G. R. Doshi and K. M. Mehta Institute of Kidney Diseases and Research Centre, Dr. H. L. Trivedi Institute of Transplantation Sciences, Ahmedabad, Gujarat, India
|Date of Web Publication||12-Sep-2017|
Shruti P Gandhi
13-Vrundavan Apartment, Plot No 7, Laxminarayan Society, Near Shantinagar Jain Temple, Usmanpura, Ahmedabad - 380 013, Gujarat
Source of Support: None, Conflict of Interest: None
Aim of This Study: This study aims to describe the utility of high-resolution computed tomography (HRCT) of chest in renal transplant recipients in patients with pulmonary infection. Materials and Methods: We retrospectively analyzed the findings of HRCT of chest in 48 postrenal transplant patients with documented pulmonary infection from September 2013 to August 2014. All patients underwent detailed investigations including specific pathological tests, chest X-ray, sputum analysis, bronchoalveolar lavage and pleural fluid analysis as and when required. HRCT was done in all patients on Somatom sensation 64 scan. The spectrum of causative organism and utility of HRCT was studied. Results: Out of 48 patients, the causative organism was confirmed by microbiology in 27 patients. These include 14 patients with Gram-negative bacteria, 5 patients with Gram-positive bacteria, 8 patients with fungal infection, and 3 patients with Mycobacterium tuberculosis infection confirmed on sputum analysis. The causative organism was confirmed to be cytomegalovirus-based on serological tests in 3 patients. Laboratory investigations could not identify the causative organism in 18 patients, 2 of them were treated with broad spectrum antibiotic, 13 patients with anti-tuberculous drugs, and 3 patients with antifungal therapy based on CT findings. Spectrum of HRCT findings was studied. Conclusion: We found bacterial infection is the most common in postrenal transplant patients followed by M. tuberculosis. Tree in bud appearance is common in M. tuberculosis infection. We found HRCT makes the road of early diagnosis of pulmonary infections smoother when coupled with clinical data.
Keywords: High resolution computed tomography, postrenal transplant, pulmonary infection
|How to cite this article:|
Gandhi SP, Kute V, Patel KN, Sutariya H, Pandya V. Role of high resolution computed tomography of chest in posttransplant pulmonary infection. Indian J Transplant 2017;11:49-54
|How to cite this URL:|
Gandhi SP, Kute V, Patel KN, Sutariya H, Pandya V. Role of high resolution computed tomography of chest in posttransplant pulmonary infection. Indian J Transplant [serial online] 2017 [cited 2019 Mar 20];11:49-54. Available from: http://www.ijtonline.in/text.asp?2017/11/2/49/214391
| Introduction|| |
Pulmonary infection has been implicated as the most common cause of the infection-related mortality in renal transplant recipients. Early and aggressive diagnostic approach is essential for appropriate therapy. Since cultures are time-consuming, imaging plays an important role in establishing the probable etiology of pneumonia. Plain chest X-ray is generally used as screening for patients with suspected pulmonary infection. However, it could not define the exact pattern of involvement or specific sign to narrow differential diagnosis. Computed tomography (CT) is more sensitive in detection of subtle parenchymal and mediastinal disease. When there is no contraindication to contrast injection, mediastinal structures can also be assessed. High-resolution CT (HRCT) findings are not always specific; there are several signs that are more common in certain types of pneumonia. The aim of this article is to describe the utility of HRCT in renal transplant recipients in patients with pulmonary infection.
| Materials and Methods|| |
We retrospectively analyzed the findings of HRCT of chest in 48 postrenal transplant patients with documented pulmonary infection from September 2013 to August 2014 after ethical committee approval. The time interval from transplantation to the onset of illness varied from 4 days to 5 years. All patients underwent detailed investigations including specific pathological tests, chest X-ray, sputum analysis, bronchoalveolar lavage and pleural fluid analysis as and when required. HRCT was done in all patients on Somatom sensation 64 scan. CT images obtained from lung apices to bases in single breath hold. Following CT parameters were used: 103 mAS, 120 kV, field-of-view 356 mm. The images were reviewed at 1.0, 5.0, and 15 mm slice thickness in lung window and 1.0 mm thickness in mediastinal window. Multiplanar reconstruction was also performed. The spectrum of causative organism and utility of HRCT was studied.
| Results|| |
The mean age of the patient is 39 years (range from 11 to 61 years). Male to female ratio is 41:7. Out of 48 patients, the causative organism was confirmed by microbiology in 27 patients. These include 14 patients with Gram-negative bacteria (7 had Klebsiella and 7 had Pseudomonas infection) 5 patients with Gram-positive bacteria (3 patients with Streptococcus pyognes and 2 patients with Staphylococcus aures) 8 patients with fungal infection (3 Candida albicans, 4 Aspergillus fumigates, and 1 Mucorales). Three patients with Mycobacterium tuberculosis infection were confirmed on sputum analysis. Out of 48, one patient had dual and one patient had triple organism. One patient had combined bacterial and fungal infection. The causative organism was confirmed to be cytomegalovirus (CMV) based on serological tests in 3 patients. Laboratory investigations could not identify causative organism in 18 patients, 2 of them were treated with broad spectrum antibiotic, 13 patients with anti-tuberculous drugs, and 3 patients with antifungal therapy based on CT findings.
Eleven of 48 patients died of which 7 deaths could be attributed directly to pulmonary infection (mortality rate 22.9%) out of 11 patients causative organism was bacterial in 3, M. tuberculosis in 2, fungal in 2, and CMV disease in 1. Laboratory test could not identify organism in 3 cases.
Spectrum of HRCT findings include one or more of following pattern: consolidation (35.4%), thick or thin walled cavity (33.3%), nodular opacities (25%), tree in bud appearances (25%), mediastinal lymphadenopathy (16.6%), consolidation with cavitation (12.5%), ground-glass opacity (6%), milliary mottling (6%), and pleural effusion (4%). [Table 1] shows HRCT findings in bacterial, fungal, and M. tuberculosis infection. We found tree in bud appearance is most common in Mycobacterium infection and not seen in fungal infection [Figure 1]. Consolidation is more common in bacterial infection and nodular opacities are more common in fungal infection followed by cavitation.
|Figure 1: A case of Mycobacterium tuberculosis infection showing normal chest radiograph (a) with tree in bud appearance on high resolution computed tomography in axial scans (b and c).|
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|Table 1: High-resolution computed tomography findings in Mycobacterium tuberculosis, bacterial and fungal infections|
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| Discussion|| |
Renal transplant patients are susceptible to variety of infection because of severely depressed cellular and humoral immunity. Lungs are one of the most frequent infection locations among patients receiving immunosuppressive treatment. The precise incidence of postrenal transplant infection is unknown because the definition may vary from clinically significant and microbiologically, serologically, or histologically proven episode to positive culture report without clinical manifestation. In this article, we discuss HRCT findings to facilitate more prompt and accurate diagnosis of post-transplant pulmonary infection.
M. tuberculosis responsible for app. 20% of pneumonia cases among kidney recipients. The patients undergoing long-term immunosuppression have increased risk of reactivation of disease they had before. They are also prone to initial infection. The radiological spectrum is wide; HRCT findings of M. tuberculosis includes air space consolidation of varying degree, cavitation, centrilobular nodules, and branching linear opacities (tree in bud appearance) that reflects endobronchial spread of infection, small, well-defined randomly distributed nodules that indicate milliary or hematogenous spread of infection, pleural effusion and/or lymph node enlargement with central necrosis. Jiang et al. found tree in bud appearance statically more often in tuberculosis than in other bacterial infection similar to our study. In patients treated with deeper immunosuppressive drugs the milliary nodule and enlarged lymph nodes are more common compared to consolidation. HRCT can also differentiate active versus inactive disease. Soft tissue infiltration, nodules, miiliary mottling [Figure 2], tree in bud appearance, consolidation, cavities [Figure 3]suggest a active disease while calcified nodules, bronchiectasis, and linear opacities suggest inactive disease. The mortality due to tuberculosis in renal transplant recipient was quoted as 10.5%–23% in one Indian study  and 20%–25% in Quinbi series.
|Figure 2: A case of Mycobacterium tuberculosis infection: Axial scan of high resolution computed tomography shows multiple tiny randomly distributed opacities in both lungs suggest milliary mottling. Air-space consolidation is seen in basal segment of left lower lobe.|
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|Figure 3: A case of Mycobacterium tuberculosis infection: Coronal section of high resolution computed tomography showing cavities with surrounding consolidation in left upper lobe.|
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Gram-negative bacteria that can cause pneumonia includes Klebsiella pneumonia, Enterobacter spp., Serrata marcrescens, Proteus sp. Escheria coli, Pseudomonas aeruginosa, and Haemophilus influenza. Incidence of Gram-negative bacterial pneumonia is 29% in our study which includes Klebsiella and Pseudomonas infection. Similar to pneumococcal pneumonia, Klebsiella organism generally responsible for lobar pneumonia. However, in case of Klebsiella; the infected lobe has bigger size results in bulging of interlobar fissure. Abscess, cavitation, and effusions are more common in Klebsiella pneumonia. We found cavitation in 43% of Klebsiella infection and bulging of interlobar fissure was found in 57% of Klebsiella infection [Figure 4]. Pseudomonas infection occurs mainly as a result of aspiration in upper airway or through blood stream. Infection changes have character of bronchopneumonia. Radiological imaging presents as complex nodules with lower lobe predilection. With the development of disease, the nodules conglomerate and form complex lung parenchyma with air bronchogram.
|Figure 4: A case of Klebsiella pneumonia: Sagittal image of high resolution computed tomography showing consolidation with bulging of interlobar fissure in left upper lobe.|
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S. aureus pneumonia generally multifocal and bilateral and show segmental and patchy consolidation (bronchopneumonia) initially; that later become confluent and homogenous. Volume loss, an early effusion, empyema, and cavitation are common. Air bronchogram is unusual. This type of pneumonia is the most common cause of pneumatocele formation [Figure 5].
|Figure 5: A case of Staphylococcus aureus pneumonia showing two thick-walled cavities in right lower lobe and consolidation with pneumatocele formation in left lower lobe.|
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Viral infection includes CMV pneumonia, flu virus pneumonia (influenza virus). With current prophylactic treatment, CMV pneumonia can occur in <1% of postrenal transplant patients. Common findings of HRCT are Centrilobular nodules, ground-glass opacities, and reticular pattern and tend to bilateral and symmetrical. Thickening of bronchial wall, tree in bud appearance, and alveolar congestion occurs rarely. According to Franquet et al. in immunocompromised patients the presence of centrilobular nodules <10 mm in diameter on HRCT is most suggestive of viral infection, most commonly, CMV. He found that nodules limited in size to <10 mm in diameter were seen in 83% of viral infection, 5% of bacterial infection, 14% of fungal infection, and 0% of Mycobacterium infection. The initial HRCT findings in immunocompromised patients with CMV pneumonia also seem to predict the patient's outcome. The prognosis is unfavorable if disease begins bilaterally as diffuse or patchy ground-glass opacity followed by progressive airspace consolidation. In addition, a change in the CT morphology of pulmonary lesions from nodular opacities toward diffuse ground-glass opacity seems to correlate with an unfavorable disease course. We found 33.3% mortality in CMV pneumonia in our study. Influenza virus is a common cause of upper airway infection among immunocompetent patients but may cause pneumonia in immunosuppressed patients. Etiology is rather mixed and it is difficult to define characteristic features of flu pneumonia. Common findings on HRCT include Ground glass opacities, Centrilobular nodules and tree in bud appearance.
Pneumocystis carinii pneumonia
Before the introduction of cotrimoxazole prophylaxis, about 5%–10% of renal transplant recipients observed to develop pneumonia due to Pneumocystis carinii. The frequency is higher in patients receiving cyclosporine. The period of greatest risk is between 1 and 6 months of transplantation. The classic CT finding is extensive ground glass attenuation. Increasingly recognized characteristic patterns of P. carinii pneumonia (PCP) include cystic lung disease, spontaneous pneumothorax, and an upper lobe distribution of parenchymal opacities. Although the radiographic findings in PCP are similar for AIDS and cystic lung disease has not been described in the non-AIDS immunosuppressed patients. The radiographic changes in patients with PCP generally follow the clinical course of disease and appropriate therapy usually leads to definite improvement in imaging within 10 days. However, imaging appearance often get worse during first 3 days of therapy due to inflammatory reaction related to dead and dying parasites.
Common organisms include Aspergillus, Candida, Mucormycosis, Crypotcoccus.
Aspergillus reported in significant proportion of renal transplant recipients in tropical countries. Aspergillus is isolated in approximately 9% of patients after kidney transplantation. Aspergillus in pulmonary area develops depending on immunological conditions of the patients. In patients with normal immunity, it can cause aspergilloma or allergic bronchopulmonary aspergillosis. Minor immunocompromised patients suffer from semi-invasive aspergillosis (chronic necrotizing). Invasive aspergillosis generally occurs in severely immunocompromised patients. A typical finding on HRCT includes the presence of a well-defined homogenous nodular opacity within a thin or thick walled cavity with an air crescent sign. Mycetoma may be seen to move in prone or decubitus position [Figure 6]. Atypical appearance includes irregular sponge-like opacity containing air spaces and filling preexisting cavity. Chronic necrotizing aspergillosis is typically associated with slowly progressive upper lobe abnormality. Imaging show upper lobe consolidation with progressive cavitation indistinguishable from TB [Figure 7]. Invasive aspergillosis is the most fatal, with a mortality rate reaching 75%. CT findings demonstrate solitary or multiple pulmonary nodules/masses. A halo of hemorrhage may be seen around the nodule due to invasion into pulmonary vessels and is seen as an area of ground-glass opacity. It is most characteristic sign of angioinvasive aspergillosis; this sign presents as first stage of disease in 96% of patients. CT angiography study may helpful to demonstrate direct vessel involvement at peripheral level. If recovery occurs, the central necrotic lung separates away from surrounding parenchyma forming an air crescent. This typically occurs 2–3 weeks after treatment. Cavitation may also occur. The presence of cavitation with in nodule is considered as a good prognostic sign. Escuissato et al. reviewed HRCT findings in 111 patients with documented pulmonary infection and found nodules 1 cm or more in diameter in 62% of patients with fungal infection, 19% of bacterial pneumonia, and 12% of viral pneumonia.
|Figure 6: Axial section of high resolution computed tomography showing nodular opacity with air crescent in left upper lobe (a) air crescent moves in prone position (b).|
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|Figure 7: A case of semi-invasive aspergillosis: Axial image of high resolution computed tomography showing consolidation with cavitation in both upper lobes.|
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The predominant HRCT findings consist of multiple nodules and focal areas of consolidation. HRCT findings resemble aspergillosis. The centrilobular nodules are more common in patients with aspergillosis while random nodules are more common in candidiasis. Candidiasis is more common in lower lung lobes.
It is a common fungal infection among renal transplant recipients in tropical areas. Pulmonary involvement is usually rare. The imaging manifestations include pulmonary nodules or masses, segmental or lobar consolidation, or reticulonodular opacities, the Later most commonly seen in AIDS patients. These are usually bilateral and asymmetric with measurements ranging from 5 mm to 5 cm. Distribution is predominantly peripheral and lower lobe.
The incidence of nocardiosis among renal transplant patients has been reported to be between 0.7% and 2.6% in previous studies. Arduino et al. reported three-fold decrease in incidence who were on cyclosporine compared to azathioprine/prednisolone. The CT presentation of nocardiosis is heterogeneous; the nodules, masses, and consolidations are the most common presentation which progress to cavitation in short amount of time.
| Summary: Role of Computed Tomography|| |
CT is more sensitive in detecting small foci of parenchymal cavitation, both in areas of confluent pneumonia and in areas of dense fibro calcified disease associated with distortion of underlying lung parenchyma. HRCT helpful in distinguishing parenchymal cavities from areas of cystic bronchiectasis occurring in association with lung fibrosis. CT reveals milliary disease or tree in bud appearance when chest radiograph is normal. It is more sensitive in detecting endobronchial spread of disease – a finding that indicates the presence of activity. CT serves as guide to determine best sites for node biopsy. Endotracheal or bronchial lesions are also identified on CT. CT also valuable in diagnosis of bronchopleural fistula.
The limitation of our study is retrospective nature and small number of patient is hence no statically significant conclusion can be derived.
| Conclusion|| |
We found bacterial infection is the commonest in postrenal transplant patients followed by M. tuberculosis. Tree in bud appearance is common in M. tuberculosis infection. HRCT makes the road of early diagnosis of pulmonary infections smoother, particularly when pathological and microbiological investigations are equivocal. HRCT can narrow the differential diagnosis when couples with clinical data.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]