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Radiographic and CT Findings of Nontuberculous Mycobacterial Pulmonary Infection Caused by Mycobacterium abscessus

¹ Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-Dong, Kangnam-Ku, Seoul 135-710, Korea.
² Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea.

Received October 25, 2002; accepted after revision February 14, 2003.

 
Address correspondence to K. S. Lee.

Supported in part by grant R11-2002-103 from Korea Science and Engineering Foundation.

Abstract

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OBJECTIVE. The purpose of our study was to describe the radiographic and CT findings in patients with pulmonary infections caused by Mycobacterium abscessus, one of the more common rapidly growing nontuberculous mycobacteria that cause lung disease.

CONCLUSION. The main radiologic and CT manifestations of M. abscessus lung infection are bilateral small nodular opacities, bronchiectasis, and cavity formation.

Introduction

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The frequency of nontuberculous mycobacterial lung disease is increasing [1]. The disease is typically caused by slow-growing species such as Mycobacterium avium-intracellulara complex and Mycobacterium kansasii [1]. Most of the previously described CT findings of nontuberculous mycobacterial lung disease have been caused by M. avium-intracellulara complex [2]. However, in the United States, more than 80% of the relatively infrequent cases of nontuberculous mycobacterial lung disease attributable to rapidly growing mycobacterial species are caused by Mycobacterium abscessus [3]. M. abscessus has been known to cause localized infections of the skin and subcutaneous tissue [1], outbreaks of postsurgical wound infections [4], and posttransplantation-disseminated infections in patients with cystic fibrosis [1].

To our knowledge, the CT findings of M. abscessus lung infection have not been previously described. The purpose of our study was to review the radiographic and CT findings in patients with M. abscessus lung infection.

Materials and Methods

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Patient Selection
We reviewed all cases of patients who had culture specimens with positive results for M. abscessus obtained between January 1997 and September 2002 at a tertiary referral center for pulmonary disease and identified 12 patients (11 women, one man; all nonsmokers) who fulfilled the 1997 American Thoracic Society criteria [1] for diagnosis of the disease. The median age of patients at the time of diagnosis was 49 years (range, 22–73 years).

All 12 patients had three or more sputum specimens with positive smears for acid-fast bacilli and positive cultures for M. abscessus. Transbronchial lung biopsy via fiberoptic bronchoscopy performed in six patients revealed either granulomatous inflammation and caseous necrosis or positive culture results for M. abscessus. None of the 12 patients was immunocompromised. Although 11 of 12 patients had supposedly been treated for tuberculosis, detailed histories about how the diagnosis of pulmonary tuberculosis had been reached were not available. The patients had no other preexisting lung diseases.

All 12 patients had radiographs, and 10 patients had chest CT scans available. The interval between isolation of the M. abscessus bacteria and the initial radiographic and CT examinations ranged from 0 to 120 days (mean, 13.1 days) and from 0 to 230 days (mean, 52.4 days), respectively. All patients had follow-up radiographs, with the intervals between the initial and the final follow-up examinations ranging from 4 to 34 months (mean, 14.2 months). In four patients, specific treatment (amikacin, cefoxitin, and clarithromycin) for M. abscessus was given during the follow-up periods.

Imaging Technique
Posteroanterior chest radiographs were obtained with a computed radiography system (FCR 9501, Fuji, Tokyo, Japan). Unenhanced CT scans were obtained with either a HiSpeed Advantage (three patients) or a LightSpeed Advantage Q/xi scanner (seven patients) (both, General Electric Medical Systems, Milwaukee, WI). All CT data were reconstructed using a bone algorithm. On the HiSpeed Advantage scanner, we used a thin-section CT technique (1-mm collimation, 120 kVp, 170 mA, 10-mm intervals). On the LightSpeed Advantage Q/xi multidetector CT scanner, we obtained volumetric scan data (2.5-mm collimation, 120 kVp, 70 mA, pitch of 6, reconstructed with 2.5-mm thickness) through the thorax.

Review of Radiographs and CT Scans
Initial and follow-up radiographs and CT scans were reviewed jointly by three chest radiologists who were aware that all patients had proven nontuberculous mycobacterial pulmonary infections; the final decision on the findings was reached by consensus. On the radiographs, the observers assessed the presence of reticulonodular opacities, nodules, cavitation, consolidation, and volume decrease. For the purpose of analysis, we divided each lung into three zones, and each zone was assessed separately. Lesions were considered to be in the upper zone of the lung if cephalad to the aortic arch, in the lower zone if caudad to the inferior pulmonary vein, and in the middle zone if seen between the two other zones. The overall extent of each pattern was estimated by calculating the involved zones of the 72 lung zones in 12 patients (six zones in each patient). The chest radiographic findings were classified as showing either upper lobe cavitary disease (i.e., classic pulmonary nontuberculous mycobacterial infection) [5] or nodular bronchiectatic disease [1]. A combination of cavities, consolidation, volume decrease, and pleural thickening in the upper lobes was considered upper lobe cavitary disease, regardless of whether reticulonodular opacities were present [4]. Bilateral nodular or reticulonodular changes that were predominantly seen in the middle and lower lung zones without visible cavities or marked volume decrease of the lobes or the lungs were considered nodular bronchiectatic disease.

The CT scans available for 10 patients were evaluated with regard to the presence or absence of well-defined nodules, branching centrilobular nodules (i.e., the tree-in-bud pattern), consolidation, cavity formation, volume loss, and bronchiectasis. When present, the morphology of bronchiectasis was recorded as being cylindrical, varicose, or cystic [6]. The extent of of overall involvement and of the involvement of each pattern was estimated by calculating the involved lobes of the 60 lung lobes in 10 patients (six lobes in each patient; each lingular segment was considered a lobe). The presence or absence of mediastinal adenopathy and pleural effusion or thickening was also recorded.

On follow-up radiographs, we evaluated the changes in overall extent and each pattern of abnormalities over time in each patient.

Results

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The most common radiographic finding was the presence of reticulonodular opacities (40% or 29/72 lung zones), which were seen in 11 (92%) of the 12 patients (Fig. 1A, 1B, 1C). The opacities were bilateral in six patients and unilateral in five and showed no zonal predominance. Cavitary lesions (10% or 7/72 lung zones) and lobar volume decrease (11% or 8/72 lung zones) were seen in five patients (42%) (Fig. 2A, 2B). Cavities were unilateral in four patients and bilateral in one and were seen most commonly in the upper lung zone. Lobar volume loss was unilateral in three patients and bilateral in two; volume loss mainly involved the upper lung zone. Consolidation (11% or 8/72 zones) was also most commonly found in the upper lung zone and was seen in four patients (33%). Consolidation was unilateral in three patients and bilateral in one.

View larger version (151K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —Pulmonary Mycobacterium abscessus infection in 64-year-old woman. Posteroanterior chest radiograph shows reticulonodular opacities throughout both lungs.

View larger version (104K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —Pulmonary Mycobacterium abscessus infection in 64-year-old woman. Axial thin-section CT scan (2.5-mm collimation, 70 mA, 120 kVp) obtained at level of main bronchi shows nodules (arrow) smaller than 10 mm in diameter in both lungs.

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C. —Pulmonary Mycobacterium abscessus infection in 64-year-old woman. CT scan obtained at level of distal bronchus intermedius shows small centrilobular nodules (arrow) with tree-in-bud appearance suggesting bronchiolitis and multiple nodules smaller than 10 mm in diameter.

View larger version (143K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —Pulmonary Mycobacterium abscessus infection in 37-year-old woman. Posteroanterior chest radiograph shows large cavity in right upper lung zone surrounded by air-space consolidation inferiorly and apical pleural thickening superiorly. Also note reticulonodular opacities in left upper lung zone and volume loss in upper zones of both lungs.

View larger version (100K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —Pulmonary Mycobacterium abscessus infection in 37-year-old woman. Axial thin-section CT scan (2.5-mm collimation, 70 mA, 120 kVp) obtained at level of right upper lobar bronchus shows large cavity surrounded by consolidation in right upper lobe. Also note retracted left upper lobe with parenchymal bands, ground-glass opacity, and consolidation.

Overall, the nodular bronchiectatic form of nontuberculous mycobacterial lung infection (Fig. 1A, 1B, 1C) was observed in seven patients, and the upper lobe cavitary form of infection (Fig. 2A, 2B) was seen in five. The seven patients with nodular bronchiectatic disease had reticulonodular opacities as an isolated finding on radiographs. The five patients with upper lobe cavitary disease included four patients with a combination of a lung cavity, volume loss, and consolidation and one patient with a lung cavity, volume loss, and reticulonodular opacities.

Radiographic abnormalities were patchy in distribution in all patients except one in whom diffuse reticulonodular opacities were present throughout both lungs. Lymph node enlargement was not seen on the radiographs of any patients.

On CT, the most common findings were branching nodular opacities (i.e., the tree-inbud pattern) and bronchiectasis, each finding being seen in nine (90%) of the 10 patients for whom CT scans were available (Fig. 1A, 1B, 1C). Branching nodular opacities (53% or 32/60 lobes) were unilateral in three patients and bilateral in six and showed no lobar predominance. Bronchiectasis (43% or 26/60 lobes) was unilateral in five patients and bilateral in four and showed no lobar predominance. Bronchiectasis was mainly cylindrical in 16 lobes, cystic in eight, and varicose in two. Well-defined nodules smaller than 1 cm in diameter (35% or 21/60 lobes) (Fig. 1A, 1B, 1C) were identified in seven patients; the nodules were distributed bilaterally in six patients and unilaterally in one without lobar predilection. Cavities (17% or 10/60 lobes) were seen in four patients (Fig. 2A, 2B). The cavities were unilateral in three patients and bilateral in one and mainly involved the upper lobes. Other CT findings included air-space consolidation (13% or 8/60 lobes) seen in four patients, lobar volume loss (13% or 8/60 lobes) in three patients, pleural thickening in three patients, and mediastinal lymphadenopathy in two patients.

On follow-up radiographs, the overall extent of parenchymal lesions decreased in four patients (Fig. 3A, 3B), remained unchanged in seven, and increased in one. The extent of reticulonodular opacities remained unchanged in seven of the 11 patients in whom opacities were seen, decreased in three, and increased in one. Both the number and size of cavities in the five patients in whom cavities were seen decreased in three patients and showed no change in two. Volume decrease remained unchanged in four of the five patients in whom this condition was seen and improved in one. The extent of consolidation decreased in two of the four patients in whom consolidation occurred and remained unchanged in two. In four patients who received specific antibiotic therapy, interval changes were diverse: in one patient, an interval increase in the extent of reticulonodular opacity was observed; in two, the disease was stationary; and in one, an interval decrease in the extent of both the consolidation and the cavity was noted.

View larger version (161K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —Pulmonary Mycobacterium abscessus infection in 44-year-old woman. Posteroanterior chest radiograph shows reticulonodular lesions (arrows) in right upper and middle lung zones and left upper lung zone.

View larger version (153K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —Pulmonary Mycobacterium abscessus infection in 44-year-old woman. Follow-up radiograph obtained 1 month after specific antibiotic treatment with amikacin, cefoxitin, and clarithromycin shows lung lesions are nearly completely resolved.

Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
The clinical and radiologic findings of pulmonary infection with slow-growing mycobacteria such as M. avium-intracellulara complex and M. kansasii are well known [1]. Limited information is available, however, on the manifestations of rapidly growing mycobacteria [2, 3, 7]. Griffith et al. [3] described the clinical features of 154 patients who had rapidly growing nontuberculous mycobacterial infection, 82% of whom had M. abscessus infection. In their study, patients were predominantly women (65%) and nonsmokers (66%). Among study participants, 70% had no underlying disease; 18% had previously treated or coexistent mycobacterial disease; and 12% had specific underlying diseases, including achalasia. These demographic characteristics are similar to those of the patients in our study, most of whom were immunocompetent women with no chronic underlying lung disease.

Griffith et al. [3] found the most frequent radiologic pattern to be reticulonodular lesions. The disease frequently was bilateral (77%) and involved the upper lobes (88%). Multilobar involvement was also common. Cavitation was seen in 16% of patients. In our study, we also found reticulonodular opacities (92% or 11/12 patients) to be the most common pattern of abnormality on radiographs. However, we saw cavitary lesions more frequently (42% or 5/12 patients) than Griffith and colleagues saw in their study (16% of patients).

To our knowledge, the CT findings of M. abscessus lung infection have not been previously described. The predominant abnormalities seen in our study were branching nodular opacities (tree-in-bud pattern) and bronchiectasis, each being seen in nine (90%) of 10 patients with CT scans. These findings were most commonly bilateral and showed no lobar predominance. Other common findings included well-defined nodules smaller than 1 cm in diameter, which we found in seven of the patients; consolidation, which we found in five; and cavities, which we found in four.

CT findings of the lung abnormalities caused by M. avium-intracellulara complex infection have been reported to be limited to the right middle lobe or the lingular division [5], but we found that abnormalities of bronchiectasis, bronchiolitis, and nodules in patients with M. abscessus lung infection commonly showed no predilection for these anatomic locations. Upper and lower lobes were as frequently involved as were middle lobes or the lingular division. Therefore, our CT findings for M. abscessus were similar to those described for Mycobacterium chelonae lung infection [2], another rapidly growing mycobacterium. In the study by Hazelton et al. [2] of 14 patients with M. chelonae lung infection, common CT findings such as bronchiectasis, nodules, and consolidation were widely distributed in both lungs.

In our study, cavitary lesions were seen in five (42%) of 12 patients on radiography and four (40%) of 10 patients on CT. Because most patients (11/12) had a history of Mycobacterium tuberculosis infection, we are not certain whether cavities were caused by previous tuberculous infection or M. abscessus infection itself. However, because tuberculous infection is a predisposing condition for nontuberculous mycobacterial infection, a distinction as to the cause of the cavitary lesions may not be important.

In our study, the radiographic findings of reticulonodular lesions with bilateral and multilobar distribution coincided with the CT findings of widespread branching nodular opacities or tree-in-bud appearance, bronchiectasis, and small nodules. Cavitary and consolidative lesions seen on radiographs in volume-decreased upper lobes corresponded to the cavities, consolidations, and parenchymal bands in retracted lobes seen on CT scans. In addition, our radiologic findings showed interval improvement in some patients but no change or interval progression in others. Some patients showed mixed interval changes; patterns in some patients showed improvement, whereas patterns in others showed progression. Although we believe that these diverse interval changes represent the chronic and persistent nature of the infection, we cannot explain the mechanism of spontaneous interval decrease in the extent of disease over time in some patients.

We did not encounter a patient with pulmonary infection involving multiple organisms, but the possibility that a patient could have such an infection should be kept in mind [3, 8]. In the study by Griffith et al. [3], 8% of the patients with rapidly growing mycobacterial lung disease had coexisting M. avium-intracellulara complex infection. Some patients with M. avium-intracellulara complex lung disease also had M. abscessus isolated in their sputum cultures some time during the course of their disease [8]. Therefore, deciding which of the two mycobacteria is the most important pathogen to treat may be difficult.

The treatment of M. abscessus is complex [7, 9]. M. abscessus is generally susceptible only in vitro to parenteral antibiotics such as amikacin, cefoxitin, and imipenem and to the newer oral macrolides such as clarithromycin [10], making surgical resection of localized disease the only effective long-term therapy for patients infected with the organism [3, 7]. Although both M. chelonae and M. abscessus belong to M. chelonae group, M. chelonae tends to be more resistant than M. abscessus to antimicrobial drugs [10].

We observed no imaging features that allowed distinction of M. abscessus lung infection from M. chelonae infection [2] in our study. In addition, imaging findings of M. abscessus were similar to those of M. avium-intracellulara complex lung infection except that in patients with M. avium lung infection, most nodular bronchiectasis was either isolated to or most severe in the middle lobes or the lingula [5]. As in previous descriptions of rapidly growing M. chelonae and M. abscessus lung infections [2, 3], we found that the distribution of nodular bronchiectasis was rather more extensive and showed no zonal predominance.

In conclusion, bilateral multilobar bronchiectasis and bronchiolitis or upper lobe cavities combined with consolidations in volume-decreased upper lobes are the predominant radiographic and CT findings in patients with M. abscessus lung infection. These patterns of parenchymal abnormalities on both chest radiographs and CT scans are similar to the patterns of lung infection seen with other rapidly growing mycobacteria—M. chelonae or M. avium-intracellulara complex. However, the lung involvement seen in patients with M. abscessus lung infection is more extensive than that seen in patients with M. avium-intracellulara complex infection.

Acknowledgments
 
We thank Nestor L. Müller for helping us to revise this manuscript.

References

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1. American Thoracic Society. Diagnosis and treatment of disease caused by nontuberculous mycobacteria. Am J Respir Crit Care Med 1997;156[suppl 2 pt 2]:S1 –S25
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3. Griffith DE, Girard WM, Wallace RJ. Clinical features of pulmonary disease caused by rapidly growing mycobacteria: an analysis of 154 patients. Am Rev Respir Dis1993; 147:1271 –1278[Medline]
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6. Webb WR, Müller NL, Naidich DP. High-resolution CT of the lung, 3rd ed. Philadelphia: Lippincott Williams & Wilkins, 2001: 467–546
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