The medial bronchopulmonary segment of the middle lobe of the right lung is supplied by the medial segmental bronchus branch of the right middle lobe bronchus.
Unlike the lateral bronchopulmonary segment at the same level, its inferior surface largely rests on the diaphragm anteriorly and the medial basal bronchopulmonary segment of the inferior lobe posteriorly. Its lateral surface adjoins the lateral bronchopulmonary segment of the middle lobe. Its medial surface contributes to the mediastinal surface of the lung in the region of the cardiac impression. Its superior surface apposes the inferior surface of the anterior bronchopulmonary segment of the superior lobe. The horizontal fissure can extend between the two segments.
The surface markings of the segment present anteriorly between fourth costal cartilage medially and superiorly to the level of the diaphragm inferiorly. The lateral limit of the segment is approximately half way across the right lung field.
Lymph nodes are particularly densely packed around the right middle lobar bronchus which distributes to this segment. Consequently, any cause of pronounced hilar lymphadenopathy can cause collapse of the segment and the middle lobe.