Answer: Amyloidosis

Histology: At low power, aside from some emphysematous changes, this lung looks fairly normal. However, closer inspection of the small arterioles within the pulmonary parenchyma reveals hyalinization, with loss of the normal smooth muscle of the media. Congo red stain demonstrates that this material is amyloid.

Discussion: BOOP would feature branching plugs of granulation tissue in small airways with extension into adjacent alveoli. Constrictive bronchiolitis would feature concentric narrowing of and potential obliteration of small airways.

Amyloidosis of the lung may come in several forms. It may be tracheobronchial or parenchymal. Parenchymal amyloidosis includes nodular forms which are often subpleural and asymptomatic, and interstitial amyloidosis which is frequently part of a systemic disease and bodes a poor prognosis. Either form can be associated with vascular amyloid. Pulmonary vascular amyloid correlates with the patient having cardiac amyloidosis.