Chest Wall Deformities: Thoracic Insufficiency Syndrome

Nicholas L. Friedman DO, FAAP, and Oscar Henry Mayer, MD

Introduction

•Thoracic insufficiency syndrome (TIS) is the inability of the thorax to support normal respiration or lung growth.

•TIS is a broad categorization of chest wall and spinal deformities, all of which require a novel approach for both assessment and treatment.

•Progressive worsening of the chest wall and spine deformity can lead to respiratory insufficiency, as patients are not able to compensate fully for abnormal respiratory mechanics and restrictive respiratory disease by increasing their respiratory rate.

Etiology

•In TIS, there is a 3-dimensional deformity of the thorax that reduces the volume available for the lungs.

•These volume depletion deformities can be categorized as unilateral or bilateral and classified in 1 of the 4 categories discussed in the Differential Diagnosis section.

Pathophysiology

•The thorax includes the spine, ribs, and sternum and functions by increasing its cross-sectional area during inspiration.

•Thoracic expansion in inspiration occurs through both contraction of the diaphragm and upward and outward chest wall motion.

•Limitation of the thorax to fully expand during inspiration and/or limitation in the resting lung volume (functional residual capacity) may cause progressive loss of lung volume and an inability to support normal respiration.

•Alveolar development and lung growth primarily occur in the first 2–3 years of life; however, they occur throughout childhood and adolescence.

•Symmetrical growth of the thoracic cage must occur simultaneously to allow for normal lung growth.

•Caudal displacement of the ribs, as is seen in neuromuscular disease, can cause a narrow superior thorax and broad inferior thorax, shaped like a Christmas tree. This is known as the “collapsing parasol deformity,” and it restricts lung volumes and worsens respiratory mechanics.

Differential Diagnosis

Type I: Absent Ribs and Presence of Scoliosis

•Congenital rib absence

•Iatrogenic after chest wall resection (complication or deliberate alteration)

Type II: Fused Ribs and Scoliosis

•VATER (vertebral defects, imperforate anus, tracheoesophageal fistula, radial and renal dysplasia) and/or VACTERL (vertebral, anal, cardiac, tracheal, esophageal, renal, and limb) associations

•Chest wall scarring secondary to radiation treatment

Type IIIa: Thoracic Foreshortening

•Jarcho-Levin syndrome (spondylothoracic dysplasia or spondylocostal dysostosis)

•Severe thoracic kyphosis

•Early spine fusion

Type IIIb: Thoracic Narrowing

•Jeune syndrome (asphyxiating thoracic dystrophy)

•Ellis–van Creveld syndrome

Type IV: Congenital and Neuromuscular Scoliosis

•Congenital or infantile scoliosis

•Spinal muscular atrophy

•Spina bifida

•Spinal cord neoplasms

•Static encephalopathy

Diagnostic Considerations

History

•Hypoplastic thorax at prenatal ultrasonography

•Early onset of clinical scoliosis (<3 years of age)

•Truncal upright instability, with abnormal chest wall contour

•Chest wall deformity (rib hump and shoulder asymmetry)

•Exertional intolerance due to an inadequate ability to maintain minute ventilation

Physical Examination

•The physical examination in patients with suspected TIS should include comprehensive musculoskeletal and respiratory evaluations.

Musculoskeletal Evaluation