Basics
Description
- 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
Pathophysiology
- 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.
Etiology
- 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.
Diagnosis
History
- Prenatal ultrasound showing a hypoplastic thorax
- Onset of clinical scoliosis
- Onset of respiratory symptoms:
- Relative exertional intolerance
- Ineffective cough resulting in recurrent respiratory infections
- Need for supplemental oxygen or noninvasive ventilatory support (bilevel positive airway pressure [BLPAP] or continuous positive airway pressure [CPAP])
- Progression of the spinal or chest wall deformity
- Signs and symptoms:
- Exertional limitation relative to age and gross motor capability
- Recurrent respiratory illnesses
- Balance problems
- Back pain
Physical Exam
- Comprehensive respiratory examination:
- Assessment of work of breathing including accessory muscle use and thoracoabdominal asynchrony
- Qualitative assessment of chest wall compliance and motion
- Symmetry of aeration during auscultation
- Thoracic circumference is usually found to be <75% of head circumference at birth.
- Thumb excursion test: The palms of each hand are loosely positioned posteriorly over each side of the chest with the thumbs aligned on either side of the spinal column, and relative excursion is assessed by the amount of lateral thumb movement.
- Assessment for rib hump by having the patient bend forward while standing upright.
- Measure of liver size to evaluate for hepatomegaly and possible cor pulmonale
Diagnostic Tests & Interpretation
Lab
- Serum bicarbonate as an indirect assessment for chronic hypoventilation
- Arterial blood gas if there is a concern for acute respiratory failure
- Liver function testing to assess for coincident liver failure
- Brain-type natriuretic peptide to help assess for progressive heart strain or failure
- Genetic testing as indicated based on suspected underlying condition
Imaging
- Standing anteroposterior and lateral radiographs to establish severity of scoliosis in the sagittal and coronal planes; bending films to establish the flexibility of the curve
- Chest CT scan with 5-mm cuts noncontrast with optimal pediatric settings to minimize radiation, with spinal and chest wall reconstruction to assess 3-dimensional anatomy
- MRI of spine and spinal cord to look for spinal cord abnormality
- Dynamic MRI to assess motion of chest wall, diaphragm, and abdomen
- Additional radiologic testing may be employed in certain cases (e.g., ventilation " “perfusion scan of the lungs to quantify right vs. left functional perfusion asymmetry)
- Echocardiogram to evaluate for cor pulmonale and pulmonary hypertension
Diagnostic Procedures/Other
- Pulmonary assessment: baseline and subsequent pulmonary function testing at each clinic visit
- Dynamic lung volumes and flows
- Forced vital capacity (FVC)
- Timed expiratory volume (forced expiratory volume in 0.5 or 1 second) and the ratio to FVC
- Forced expiratory flow between 25% and 75% of vital capacity (FEF25 " “75%)
- Static lung volume measurements
- Total lung capacity (TLC), functional residual capacity (FRC), residual volume (RV), and RV/TLC
- Maximal inspiratory (MIP) and maximal expiratory pressure (MEP) measurements
- Specialized measurements of respiratory system compliance (stiffness) and partitioned measurements of chest wall and lung compliance
- Pulse oximetry and end-tidal carbon dioxide measurement
- Overnight polysomnography to assess the degree of underlying respiratory insufficiency and need for supplemental oxygen or noninvasive ventilation
- Exercise testing adapted for the capabilities of the patient (6-minute walk test) can be used to assess for exertional limitation.
- If there is significant thoracospinal abnormality and certainly if there is other dysmorphology, a genetics assessment is very helpful to comprehensively assess for other comorbidities and help anticipate future problems.
Treatment
Additional Therapies
General Measures
- Bracing and halo-gravity traction can be used as a temporizing procedure and at best has been shown to control some forms of scoliosis or partially improve, but not correct, scoliosis.
- Physical and occupational therapy
Surgery/Other Procedures
- The goal of surgical treatment is to stabilize the chest and spine in order to support normal growth until skeletal maturity is attained, at which point procedures such as a spinal fusion can be considered.
- Vertical expandable prosthetic titanium rib (VEPTR) expansion thoracoplasty techniques enable 5 types of acute thoracic reconstructions to handle each of the subtypes of TIS.
- The procedure can be performed as early as 4 " “6 months of age to exploit the growth potential of the developing lungs and provide additional thoracic volume and compensatory lung growth.
- After implantation to stabilize the initial thoracospinal reconstruction, it can then be expanded about every 6 months commensurate with patient growth until skeletal maturity.
Ongoing Care
Follow-up Recommendations
- After TIS surgery, patients are followed with radiographs at regular intervals.
- Pulmonary follow-up should include careful assessment for respiratory insufficiency.
- Longitudinal measure of lung function and growth to demonstrate an improvement in respiratory status or lung function, or at the very least a decrease in the rate of decline, in the most severely affected patients
Prognosis
- Prognosis will vary depending on the underlying cause of TIS, severity of respiratory insufficiency, and the age of the patient at surgery.
- In infants and toddlers, however, there may be preservation of lung growth, but there has not been evidence to support regaining lung function that has been lost.
- The expectation in infancy would be for growth preservation and an increase in lung volume above the preoperative value as a percent of predicted. There does appear to be an inverse relationship between the age of the patient at the time of surgery and the level of positive impact of VEPTR insertion on lung function.
- In school-aged and older children, lung volume remains stable.
- For older patients near skeletal maturity, the focus is chest wall reconstruction, spinal stabilization, and stabilization in pulmonary function.
- Jeune syndrome is one of the more severe forms of TIS, with 60 " “70% mortality in early infancy from respiratory failure. However, after VEPTR insertion, there has been a 50% decrease in mortality.
- Of those patients with TIS due to an STD, 47% die in infancy from respiratory complications and pulmonary hypertension. VEPTR treatment of STD remains controversial.
- Improved quality of life following VEPTR insertion
Complications
- In the immediate postoperative period " ”wound infection, skin slough, and bleeding
- Implant-related complication such as device breakage or dislodgement is uncommon.
- Decreased chest wall compliance
- Neurologic complications are rare.
Additional Reading
- Campbell ‚ RM Jr. VEPTR: past experience and the future of VEPTR principles. Eur Spine J. 2013;22(Suppl 2):S106 " “S117. ‚ [View Abstract]
- Gadepalli ‚ SK, Hirschl ‚ RB, Tsai ‚ WC, et al. Vertical expandable prosthetic titanium rib device insertion: does it improve pulmonary function? J Pediatr Surg. 2011;46(1):77 " “80. ‚ [View Abstract]
- Mayer ‚ OH. Management of thoracic insufficiency syndrome. Curr Opin Pediatr. 2009;21(3):333. ‚ [View Abstract]
Codes
ICD09
- 756.9 Other and unspecified anomalies of musculoskeletal system
- 756.3 Other anomalies of ribs and sternum
- 756.4 Chondrodystrophy
- 756.89 Other specified anomalies of muscle, tendon, fascia, and connective tissue
- 756.55 Chondroectodermal dysplasia
ICD10
- Q76.8 Other congenital malformations of bony thorax
- Q76.6 Other congenital malformations of ribs
- Q77.2 Short rib syndrome
- Q79.8 Other congenital malformations of musculoskeletal system
- Q77.6 Chondroectodermal dysplasia
SNOMED
- 8649001 Congenital anomaly of thoracic cage (disorder)
- 70974002 Congenital absence of rib (disorder)
- 75049004 Jeune thoracic dystrophy (disorder)
- 51780007 Cerebro-costo-mandibular syndrome (disorder)
- 62501005 Chondroectodermal dysplasia (disorder)
- 61367005 Jarcho-Levin syndrome (disorder)