April Case of the Month Clinical History: A 32-year-old man, non-smoker, was referred to our centre from an outside hospital for pleurodesis for unresolving spontaneous right pneumothorax despite chest tube placement. Preoperative CT scan confirmed the pneumothorax with proper chest tube placement, significant right lung atelectasis, and unremarkable left lung parenchyma (see Figure 1). Preoperative blood work showed a borderline eosinophilia (value of 0.5 x 10^9/L; upper limit of normal in our lab is 0.45). Intraoperatively the patient was found to have a right apical bullae, and underwent uncomplicated bullectomy and pleurodesis.

Specimens sent to pathology were a wedge resection of lung (7g, 4.5 cm in greatest diameter) and fragments of parietal pleura. A single subpleural bullae was noted grossly, without other significant abnormalities. Low power microscopic examination confirmed the subpleural bullae, on a backdrop of relatively normal appearing underlying parenchyma with the exception of rare interstitial non-necrotizing granulomas (Figure 2; star = bullae; circles= granulomas). At higher power, the wall of the bullae was characterized by a reactive pleuritis with mesothelial hyperplasia, histiocytes and eosinophils, with underlying fibroinflammatory remodelling, indicating some degree of chronicity (Figure 3). The granulomas consisted of a peripheral rim of epithelioid histiocytes and eosinophils, surrounding a structure consisting of a thin walled ovoid ring with a central body reminiscent of a multinucleated giant cell; these central structures were 70 to 80 µm in greatest dimension, had occasional spine-like projections (Figures 4 and 5). The structures had no significant refringence to polarized light and PAS-D positive (Figure 6).

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