Pathology of the Lung in Sarcoidosis: A Review

Sarcoidosis is a multisystem disease of unknown etiology, often affecting the respiratory tract. The diagnosis depends on a compatible clinical and radiological presentation, the finding of nonnecrotizing epithelioid granulomas by biopsy, and exclusion of other possible causes of granulomas. The granulomas are distributed in a lymphangitic pattern in lung; interstitial pneumonitis is sparse and can be the only finding in early stages. Up to 40% of granulomas show small central foci of necrosis. Granulomatous vasculitis can be found in 42% to 69% of cases and likely is due to intrusion of perivascular granulomas on vessel walls. Chronic sarcoidosis can lead to honeycomb lung; the fibrosis is often nodular and distributed along bronchovascular structures and preferentially involves the upper and middle lobes. Giant cells of sarcoidosis show Schaumann bodies, asteroid bodies, and calcium oxalates in 48% to 88%, 2% to 9%, and more than 66% of cases, respectively, in lung wedges. The inclusions are likely due to histiocytic catabolism. Diagnosis of sarcoidosis is usually made by transbronchial biopsy but cytological methods, such as endobronchial ultrasound-guided transbronchial needle aspiration, when combined with biopsy, produce an optimal diagnostic yield. In needle aspiration biopsies, use of cell blocks enhances diagnostic yield. Necrotizing sarcoid granulomatosis, characterized by variable necrosis, sarcoid-like granulomas, and granulomatous vasculitis, is currently considered a variant of sarcoidosis, likely corresponding to "nodular sarcoidosis." Only 3% to 5% of patients with sarcoidosis undergo lung transplantation. Recurrence of sarcoidosis in the allograft ranges from 47% to 67% but usually has no significant impact on short-term outcome.