The left minor fissure.

A left minor fissure (LMF) has been described anatomically as being present in 8%-18% of left lungs. Analogous to the right minor fissure (RMF), the LMF separates the anterior segment of the left upper lobe from the lingula. Two thousand consecutive normal radiographic examinations of the adult chest (posteroanterior, left lateral views with the subjects in the erect position) were reviewed prospectively. A definite LMF was identified in 32 of the subjects (1.6%). The fissure was dome-shaped (convex superior) on at least one projection in 26 (81%) of 32 subjects. The position of the LMF was usually more cephalad than that of the RMF (25 of 31 subjects, or 81%). The lateral end of the LMF was usually superior to the medial end (25 of 32; 78%) and rarely inferior to the medial end (three of 32; 9%). The LMF infrequently was horizontal (four of 32; 12%). In a number of additional patients whose control chest radiographs showed no evidence of an LMF, subsequent radiographs revealed an LMF outlined by active pulmonary or pleural disease.