Thoracic Insufficiency Syndrome
- Thoracic insufficiency syndrome (TIS) is the inability of the thorax to support normal respiration or lung growth.
- Patients are skeletally immature with varied anatomic deformities that often include the following:
- Flail chest syndrome: rib absence due to a congenital malformation or chest wall tumor resection, rib instability in cerebrocostomandibular syndrome, and others
- Constrictive chest wall syndrome, including rib fusion and scoliosis: VACTERL association, chest wall scarring from radiation treatment, windswept deformity of the chest from progressive scoliosis, and others
- Hypoplastic thorax syndrome including Jeune syndrome, Ellis–van Creveld syndrome, Jarcho-Levin syndrome, or spondylothoracic dysplasia (STD)
- Scoliosis (without rib anomaly) or neuromuscular scoliosis
- The recognizable anatomic abnormalities often occur before respiratory insufficiency, with patients compensating for low lung volumes and poor respiratory mechanics by increasing their respiratory rate.
- Subsequently decreased activity and chronic respiratory insufficiency
- The thorax is the respiratory pump, requiring adequate diaphragm (abdominal) and chest wall movement. Limitation in resting lung volume (functional residual capacity [FRC]) and/or the ability of the rib cage to expand during respiration can significantly alter respiratory function and cause TIS.
- The window of rapid lung growth and alveolar development is during the first 3 years of life.
- Although alveolar development is felt to continue up until 5 or 8 years of age, recent evidence suggests that it can occur through childhood and adolescence.
- Without concurrent thoracic growth, however, the lung cannot grow normally.
- Growth of the thoracic pump is also necessary so that the respiratory system can continue to meet a patient’s metabolic demands.
- Thoracic spinal height (TSH) directly contributes to thoracic volume and lung volume.
- At birth, the TSH is 13 cm normally, then during the first 5 years of life, thoracic spinal growth is 1.4 cm/year, 0.6 cm/year from 5 to 10 years, and 1.2 cm/year from 10 to 18 years of age.
- A thoracic length of 22 cm at skeletal maturity, the normal TSH of a 10-year-old, appears to be the minimum height necessary for normal respiration.
- Complex scoliosis with spinal rotation and lordosis into the convex hemithorax, the “windswept” deformity of the thorax, can further restrict lung volume.
- In neuromuscular disorders, unilateral caudal rotation of the ribs, the “collapsing parasol deformity,” typically occurs on the convex side of the scoliosis and may also severely narrow the thorax, worsen thoracic mechanics, and further increase work of breathing.
- The etiologies of TIS can be grouped into unilateral or bilateral volume depletion deformities (VDDs) of the thorax that reduce the volume available for the lungs in certain subsets of patients with rare syndromes. This causes primary TIS or deformity of the chest from scoliosis.
- Type I: absent ribs and scoliosis
- Type II: fused ribs and scoliosis
- Type III: hypoplastic thorax
- Type IIIa: foreshortening (Jarcho-Levin)
- Type IIIb: narrowed (Jeune)
- In addition, progressive congenital scoliosis without rib anomalies can result in TIS from a variant of type II VDD of the thorax.
- Type IIIb VDD of the thorax can also develop in neurogenic scoliosis, as in spinal muscular atrophy with marked intercostal muscle weakness.
- Spinal deformity, such as lumbar kyphosis in spina bifida, collapses the torso into the pelvis, raising abdominal pressure blocking diaphragm excursion, and causing secondary TIS.
Commonly Associated Conditions
- Congenital renal abnormalities can occur in 25–30% of congenital scoliosis.
- Cervical spine abnormalities, causing stenosis and proximal instability
- Spinal cord abnormalities, including spinal cord syrinx and tethered cord, which are especially prevalent in meningomyelocele
- Jeune syndrome
- Congenital renal abnormalities
- Hepatic fibrosis
- Cervical spinal stenosis in 60% of cases
- Retinal dystrophy
- Ellis–van Creveld syndrome: tracheomalacia
- STD: congenital diaphragmatic hernia
- Cerebrocostomandibular syndrome, Pierre Robin sequence: micrognathia
- Severe tracheal compression and narrowing can occur in advanced scoliosis or severe anteroposterior narrowing.
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