Bell-Shaped Chest

Christopher M. Walker, MD

Stephen L. Done, MD

DIFFERENTIAL DIAGNOSIS

Common

Neonatal or Early Childhood Insult

Less Common

Down Syndrome
Muscular Disorders

Rare but Important

Rickets
Intrauterine Oligohydramnios
Skeletal Dysplasia
Giant Omphalocele

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Definition
- Narrow upper chest with outward bowing of lower chest
- Obliquely directed posterior ribs
Caused by disorders resulting in cerebral or muscular dysfunction
Clinical history key in diagnosis

Helpful Clues for Common Diagnoses

Neonatal or Early Childhood Insult
- Conditions leading to hypotonia
  - Sepsis, dehydration, infantile respiratory distress syndrome, spinal cord injury, and intracranial hemorrhage
- Transient occurrence secondary to traversing birth canal
- Paralytics for mechanical ventilation

Helpful Clues for Less Common Diagnoses

Down Syndrome
- Hypotonia and bell-shaped thorax ↓ in severity with age
- Thoracic skeletal manifestations
  - Bell-shaped chest in 80%
  - Multiple manubrial ossification centers in 80%
  - 11 rib pairs in 30%
  - 58% chance of Down syndrome with above 3 findings
- Gastrointestinal malformations
  - Duodenal atresia/web, tracheoesophageal fistula, omphalocele, Hirschsprung disease, and imperforate anus
- Cardiac malformations
  - Endocardial cushion defect, ventricular septal defect, atrial septal defect, tetralogy of Fallot, and patent ductus arteriosus
- Atlantoaxial instability in 14% of patients secondary to laxity of transverse ligaments
  - Diagnose with flexion/extension radiography
Muscular Disorders
- Spinal muscular atrophy
  - Progressive lower motor neuron degeneration
  - Multiple subtypes with varying ages of presentation
  - Autosomal recessive
  - Recurrent respiratory infections
  - Chest shape progressively ↑ in severity with most extreme example of bell-shaped thorax
- Muscular dystrophy
  - Primary muscle breakdown
  - Varying age of presentation and disease severity depending on type of muscular dystrophy
  - ± rapidly progressive scoliosis
- C-shaped scoliosis leads to respiratory insufficiency
  - Treat with long-segment fusion

Helpful Clues for Rare Diagnoses

Rickets
- Widened growth plates
- Osteomalacia
- Metaphyseal cupping and fraying
- Deformed costochondral junctions (rachitic rosary)
Intrauterine Oligohydramnios
- Long-term oligohydramnios leads to pulmonary hypoplasia with muscular hypotonia
- Causes
  - Renal abnormalities, urinary bladder obstruction, posterior urethral valves, or asymmetric growth retardation
- Fetal ultrasound
  - Amniotic fluid index (AFI) is defined by 4 largest AP fluid pockets in each quadrant
  - AFI ≤ 6 cm is diagnostic of oligohydramnios
Skeletal Dysplasia
- Abnormal skeletal development with muscular hypotonia
- Diagnosis important for prognosis and genetic counseling
- Skeletal survey useful in diagnosing and classifying skeletal dysplasias
- Important definitions
  - Rhizomelia implies proximal limb shortening (humerus and femur)
  - Mesomelia implies middle limb shortening (radius/ulna and tibia/fibula)
  - Acromelia implies distal limb shortening (hands and feet)
- Achondroplasia
  - Most common short-limbed dwarfism and nonlethal skeletal dysplasia
  - Autosomal dominant
  - Prenatal ultrasound demonstrates rhizomelic shortening
  - ↓ AP vertebral body diameter
  - ↓ interpediculate distance in lower lumbar spine
  - Tombstone-shaped iliac bones
  - Frontal bossing
  - Small foramen magnum
- Camptomelic dysplasia
  - Enlarged skull
  - ± 11 rib pairs
  - Late ossification of mid-thoracic pedicles
  - Hypoplastic scapulae
  - Bowed long bones
  - Tall and narrow iliac wings
- Jeune syndrome
  - Acromelic shortening
  - Short ribs with high clavicular position
  - Cone-shaped epiphyses of middle and distal phalanges
  - “Trident” acetabulum with 3 downward projecting spurs
  - Normal spine
  - ± ossified capital femoral epiphyses in infancy
- Cleidocranial dysplasia
  - Abnormal membrane bone development
  - Autosomal dominant
  - Absent or dysplastic clavicles
  - Widened pubic symphysis
  - Squared iliac wings
  - Wormian bones
  - Persistent metopic suture
- Thanatophoric dysplasia
  - In utero or early neonatal death
  - Sporadic disorder
  - Rhizomelic shortening
  - ± prenatal ultrasound demonstrates cloverleaf-shaped skull
  - Polyhydramnios
  - “Trident” acetabulum
  - Platyspondyly (a.k.a. flat vertebral bodies)
  - Short ribs
  - Telephone-receiver-shaped femurs
  - Metaphyseal flaring
Giant Omphalocele
- Herniated bowel and liver covered by peritoneal lining
- High association with cardiovascular abnormalities