A 52-year-old man presented with two weeks of dyspnea and a productive cough. A high-resolution computed tomography (HRCT) scan of the chest showed a left lower lobe cyst with an air-fluid level and adjacent infiltrate (Figure ). He was treated with levofloxacin, which resolved the symptoms. Six months later he began to experience fatigue, dyspnea and a productive cough. A chest radiograph showed complete opacification of the cyst in the left lower lobe. He was treated empirically with azithromycin and levofloxacin, without improvement. A bronchoscopy with bronchoalveolar lavage was unrevealing. Routine bacterial, acid-fast bacilli (AFB), and fungal stains and cultures were negative. After four weeks, the patient continued to have a productive cough and fatigue, worsening dyspnea, weight loss and fevers. He was admitted to the hospital for resection of a presumed non-resolving lung abscess.
Figure 1 HRCT appearance of left lower lobe cyst, MAC-associated pneumonitis, and subsequent resolution. (a) Left lower lobe cyst with air-fluid level and adjacent infiltrate at initial presentation. (b) Bilateral, diffuse miliary nodular pattern six months later. (more ...)
His past medical history was unremarkable. He did not take any immunosuppressive medications and had no exposure to hot tubs. Physical examination revealed mild hypoxemia and coarse rales over the left lower lung field. White blood cell count was 12,400/mm3. HIV serology was negative, as was a tuberculin skin test. Blood and urine cultures were negative. A pre-operative HRCT showed a new diffuse pattern of miliary nodules throughout both lung fields (Figure ). No ground glass opacities were seen. Because of the central location of the lesion a left lower lobectomy was performed. Examination of the resected lobe revealed a cyst filled with thick yellow fluid that was AFB positive on a smear. Cultures from the cyst fluid eventually grew MAC; bacterial and fungal cultures were negative.
The patient was initially placed on a four-drug anti-tuberculosis regimen. After identification of MAC in the culture, his antibiotic regimen was changed to azithromycin, ethambutol, and rifampin. His respiratory symptoms resolved over the ensuing three months, with disappearance of the miliary nodules on chest HRCT (Figure ).
Histologic examination of the resected lung lobe revealed a bronchogenic cyst. The lung parenchyma surrounding the cyst was replaced by well-formed granulomas that were AFB negative (Figure ). The granulomas consisted of central CD68+ macrophages surrounded by a mantle of CD5+ T-lymphocytes, with some T-lymphocytes infiltrating the granulomas (Figure ). CD4+ T-cells constituted the main lymphocytic component of the granulomas and were closely associated with the CD68+ macrophages in the central core (Figure ). CD8+ T-cells were essentially restricted to the periphery, and there was a paucity of CD20+ B-cells in the perigranulomatous areas (Figure ). The central core of the granulomas and the surrounding tissue showed strong reactivity for tumor necrosis factor-α (TNF-α) (Figure ).
Figure 2 Immunohistochemical staining for macrophages (CD68) and T-lymphocyte subsets (CD5, CD4, and CD8) in lung tissue biopsy. (a) Lung tissue with well-formed granulomas, hematoxylin and eosin stain, 200× magnification. (b) Anti-CD68 (brown) and anti-CD5 (more ...)
Figure 3 Immunohistochemical staining for tumor necrosis factor-α in lung tissue biopsy. (a) Anti-tumor necrosis factor-α immunostaining (brown), 200× magnification. (b) Isotype control antibody immunostaining (negative control) for anti-tumor (more ...)