Morphological and functional reserves of the right middle lobe: Radiological analysis of changes after right lower lobectomy in healthy individuals

Objectives: Remaining lung tissue after pulmonary resection can expand without decline in structural complexity and compensate for functional loss, showing morphological and functional reserves. However, the distribution of these reserves is unknown. This study examined the heterogeneity of morphological and functional reserves of the remaining lung tissue. Methods: We retrospectively analyzed 53 donors who underwent right lower lobectomy for living-donor lobar lung transplantation. We examined morphometric changes in computed tomography images from 3 to 12 months after lobectomy. We assessed lung volume and structural complexity expressed as the fractal dimension. We also assessed effective lung volume (the volume of the lung with intermediate density) and volumetric fluctuation during respiration. Changes were compared between the right upper lobe, middle lobe, and left lung. Results: The expansion of lung tissue was greater in the middle lobe (130.9% +/- 19.7%) than in the upper lobe (109.7% +/- 9.2%; P < .001). The fractal dimension declined in the upper lobe (P < .001) but was maintained in the middle lobe (P = .39). The increase in effective lung volume was larger in the middle lobe (97.2 +/- 73.5 mL) than in the upper lobe (62.7 +/- 87.1 mL; P < .001), but not significantly different from that of the left lung (55.8 +/- 186.3 mL; P = .052). A similar pattern was seen in respiratory fluctuation. Conclusions: Morphological and functional changes in lung tissue remaining after pulmonary resection were heterogeneous. The right middle lobe demonstrated morphological and functional reserves after right lower lobectomy.