Mycobacterium Avium Complex

Mycobacterium Avium Complex

Jud W. Gurney, MD, FACR

Axial CECT shows clustered nodules in the right upper lobe image and the superior segment of the left lower lobe image.

Axial CECT shows a cavity image, feeding bronchus image, and clustered nodules image. MAC was cultured, and the findings were identical to those of Mycobacterium tuberculosis.


Abbreviations and Synonyms

  • Mycobacterium avium intracellulare complex (MAC), nontuberculous mycobacteria (NTM), atypical mycobacteria, chronic obstructive lung disease (COPD)


  • NTM pulmonary infection, most commonly caused by MAC

    • Other NTM: M. kansasii, M. xenopi, M. fortuitum, M. scrofulaceum, M. gordonae, M. abscessus, and M. chelonae

  • 5 types of disease

    • Classic infection that mimics Mycobacterium tuberculosis (MTb)

    • Bronchiectasis & nodules (Lady Windermere syndrome)

    • Disseminated disease in immunosuppressed patients

    • Hypersensitivity pneumonia (“hot tub” lung)

    • Consolidative pattern associated with achalasia and other esophageal motility disorders


CT Findings

  • Classic infection, 2 patterns, MTb or nodule(s)

    • Indistinguishable from M. tuberculosis

      • Upper lobe predominance, apical posterior segments (anterior segment less common)

      • Thin-walled cavities (thick-walled cavities are less common) hallmark of infection, associated with airspace opacities, masses, and nodules

      • Mean diameter of cavity is 2.5 cm

      • Bronchogenic spread with 5-15 mm peripheral centrilobular nodules in dependent lung

      • Bronchial wall thickening → bronchiectasis

      • Feeding bronchus: Patent bronchus running into cavitary lesion

      • Lymphadenopathy and effusions, uncommon

    • Nodule(s)

      • Solitary or multiple nodules; solitary nodules mimic bronchogenic carcinoma, range in size from 1 to 5 cm in diameter

      • Nodules of similar size often cluster together

    • Associated findings from underlying predisposing factors such as emphysema and pulmonary fibrosis

  • Bronchiectasis & nodules (Lady Windermere syndrome)

    • Bronchiectasis, cylindrical, distributed mainly in ventral lung, primarily right middle lobe (RML) and lingula

      • 33% of patients with bronchiectasis and nodules will have NTM infection

      • > 5 lobes with bronchiectasis highly associated with NTM

    • Centrilobular nodules

      • 85% < 5 mm diameter

      • 80% within same lobe as bronchiectasis

    • Bilateral multifocal bronchiolitis manifested by

      • Mosaic pattern of perfusion or hyperinflation with airway narrowing

      • Tree-in-bud pattern: Branching centrilobular nodules that occur within lobes affected with bronchiectasis but also scattered throughout uninvolved lung

    • Consolidation, lobular

    • Cavitation, mediastinal adenopathy, atelectasis rare

  • Disseminated disease in immunosuppressed patients

    • Wide range of abnormalities

      • Often normal or subtle pulmonary findings such as a few scattered centrilobular nodules

      • Aggressive cavitary disease also possible

      • Generalized lymphadenopathy or hepatosplenomegaly common

      • Lymphadenopathy may have low-density necrotic centers

  • Hypersensitivity pneumonia (“hot tub” lung)

    • Indistinguishable from other causes of subacute hypersensitivity pneumonitis

      • Diffuse centrilobular micronodules (85%) usually involving > 40% of lung

      • Centrilobular nodules either solid (50%) or ground-glass (50%)

      • Ground-glass opacities (75%), mosaic attenuation, and air-trapping at expiratory scanning (100%)

  • Achalasia and esophageal motility disorders

    • Pattern of aspiration pneumonia

      • Large bilateral dependent areas of consolidation

      • Pleural effusions (20%)

      • Cavitary disease (15%)

Radiographic Findings

  • Radiography

    • Classic infection

      • Should suspect in any patient with unexplained upper lung zone opacities

      • Tubular tram-track opacities suggest underlying bronchiectasis

      • Apical pleural thickening (50%) often striking; associated with cavitary disease even though cavities may not be radiographically apparent

      • Progression slow (average of 6 years to demonstrate progression)

    • Bronchiectasis & nodules (Lady Windermere syndrome)

      • Should suspect in patients (especially elderly females) with tubular or ill-defined opacities in RML or lingula

      • Often hyperinflated (but not from emphysema)

    • Disseminated disease in immunosuppressed patients

      • Normal radiograph with positive sputum cultures, common (20%)

      • Abnormal radiographs varied and nonspecific: Small scattered alveolar and nodular opacities, miliary nodules, & mass-like lesions

      • Cavitation more common in non-AIDS immunosuppressed patients

      • Hilar or mediastinal lymphadenopathy common and may be only finding

    • Hypersensitivity pneumonia

      • Normal radiograph (20%)

      • Nonspecific diffuse interstitial or nodular ground-glass opacities

    • Achalasia and esophageal motility disorder

      • Dilated esophagus, absent stomach bubble

      • Dependent airspace opacities


Post-Primary Tuberculosis

Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Mycobacterium Avium Complex

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