Classically, this sign is associated with consolidation of the right upper lobe (Fig. 2) due to Klebsiella pneumoniae infection.7 Due to the tendency for Klebsiella to produce large volumes of inflammatory exudate, the involved lobe expands and exerts mass effect on the adjacent interlobar fissure.8 The normally straight minor fissure on the lateral view bulges convex posteroinferiorly due to rapid lobar expansion.3,7 Although previously reported in up to 30% of patients with Klebsiella pneumonia,8,9 the finding is identified less commonly today, most likely due to rapid prophylactic implementation of antibiotics.3 Other less common causes of the bulging fissure sign include Hemophilus influenzae, tuberculosis, pneumococcal pneumonia, large lung abscesses, and lung neoplasms.10