Thoracic Insufficiency Syndrome

Thoracic insufficiency syndrome is defined as the inability of the thorax to support normal respiration or lung growth. Malformation of the vertebra and rib cage can diminish thoracic volume and hinder the dynamic changes in volume necessary for respiration. These factors impair the growth and maturation of the underlying lung and lead to extrinsic restrictive lung disease. Depending on the severity of vertebral and/or rib malformations, affected patients may be symptomatic at birth or may not develop respiratory compromise until adolescence when body mass increases. In severe cases, diagnosis is made prenatally with ultrasound. Thoracic insufficiency syndrome can result from any abnormality in the normal development of the thoracic spine or rib cage. Jeune’s syndrome, or asphyxiating thoracic dystrophy, is a rare autosomal recessive disease characterized by a symmetrically hypoplastic rib cage resulting in a narrow chest and early respiratory insufficiency. Patients who survive childhood may develop renal, hepatic, pancreatic, or ocular complications. Spondylothoracic dysostosis, or Jarcho-Levin syndrome, is another autosomal recessive syndrome with heterogeneous costovertebral segmentation defects. Affected patients often have a shortened spine, kyphoscoliosis, meningomyelocele, and thoracic insufficiency. These hereditary spinal disorders have a mortality rate of 33%, largely due to respiratory compromise. Campbell et al. have described thoracic deformities with congenital scoliosis leading to thoracic insufficiency syndrome. Primary deformities include fusion of the ribs or absence of the ribs resulting in decreased hemithoracic volume and impaired growth of the underlying lung. Secondary deformities include rotation, curvature, or foreshortening of the vertebral column resulting in distortion of the rib cage. Diagnosis and monitoring of thoracic insufficiency syndrome is based on patient history, physical exam, pulmonary function tests, and imaging studies. The Cobb angle measured on anteroposterior and lateral chest radiographs can be followed to monitor the progression of kyphosis or scoliosis. The height of the thoracic spine and the ratio of the height of the concave hemithorax to the convex hemithorax can also be monitored, as this is a marker of the space available for the lung. However, these measurements may not accurately represent the amount of three dimensional distortion, and CT imaging is often necessary for further characterization. Three dimensional reconstructions can be used to determine lung volumes and aid in planning surgical intervention. Early surgical correction of the abnormal spinal curvature and thoracic volume is necessary in severe cases. Lung growth by alveolar multiplication may continue up to eight years of age, therefore intervention well before this age will maximize the lung’s growth potential. Expansion thoracoplasty and vertical expandable prosthetic titanium rib (VEPTR) placement in the constricted hemithorax increases the volume, corrects the kyphotic spine, and restores the growth potential of the lung.