Dynamic Magnetic Resonance Imaging in Assessing Lung Function in Adolescent Idiopathic Scoliosis

Summary: There is restriction of total inspiratory and expiratory lung volumes in AIS patients. The neuromuscular function, however, is not affected as there is no difference in chest wall and diaphragmatic movement when compared with the controls. Six months after posterior spinal fusion, there is improvement of chest wall and diaphragmatic motions in AIS patients, associated with subjectively less breathing effort but no significant increase of lung volumes.

Introduction: Pulmonary function impairment in adolescent idiopathic scoliosis (AIS) might be related to restriction of the lung volume, poor chest wall expansibility or impaired diaphragmatic motion. Little is known about the exact mechanism and whether surgical operation can brought about any improvement.

Objectives: To measure the change in lung volume, chest wall and diaphragmatic motion in severe AIS patients before and after spinal fusion using breath-hold (BH) dynamic MRI. Comparison is also made with those with mild curve and normal controls.

Methods: 42 patients with severe right-sided thoracic scoliosis (Cobbs angle 40-98), 22 patients with mild scoliosis (Cobbs angle 10-30) and 12 healthy subjects, aged 11-18, females, were recruited into this study. BH-MR sequences were used to obtain coronal images of the whole chest during full inspiration and expiration. The following measurements were assessed: (1) inspiratory, expiratory and change in lung volume; (2) change in anteroposterior (AP) and transverse (TS) diameter of the chest wall (3) change in diaphragmatic heights. 21 patients with severe scoliosis also underwent repeated assessment 6 months after posterior spinal fusion.

Results: There was significant reduction of total inspiratory, expiratory lung volume and diaphragmatic heights in the scoliosis group (p<0 .05). There was however no significant difference in the change of lung volumes, AP or TS diameter chest wall as well diaphragmatic movements. After operation, volumes showed slight but insignificant increase. however, increase movement at carina level and increased The median breathing effort also reduced (p<0.05).

Conclusions: Impairment in lung function of AIS patients is predominantly due to the restriction of lung volume. There is improvement of chest wall and diaphragmatic motions six months after operation but lung volumes do not significantly increase.