The differential diagnosis of nodules in a perilymphatic distribution is limited :

• the most common cause is sarcoidosis (typically symmetrical and upper lobes)
• also common is lymphangitis carcinomatosis (often asymmetrical and lower lobe)
• silicosis
• coal workers' pneumoconiosis uncommonly give this appearance
• rare causes include amyloidosis and lymphocytic interstitial pneumonitis

In this case the diagnosis was sarcoidosis.