Small Chest

Paula J. Woodward, MD

DIFFERENTIAL DIAGNOSIS

Common

Severe Oligohydramnios
- Renal Agenesis
- Autosomal Recessive Polycystic Kidney Disease, Severe
- Bilateral Multicystic Dysplastic Kidneys
- Posterior Urethral Valves, Complete
- Severe Intrauterine Growth Restriction (IUGR)

Less Common

Skeletal Dysplasias
- Thanatophoric Dysplasia (TD)
- Osteogenesis Imperfecta (OI)
- Achondroplasia
- Achondrogenesis
- Asphyxiating Thoracic Dysplasia (Jeune Syndrome)
- Short Rib-Polydactyly

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Is the chest truly small?
- Large heart or distended abdomen may create appearance of a small chest
Anything that causes severe oligohydramnios can result in a small chest and pulmonary hypoplasia
- Fetal compression causes decreased space for lung growth and restriction of breathing movements
- Efflux of lung fluid into amniotic space
  - Fetal lung fluid functions as a stent keeping developing air spaces distended
  - Vital for normal lung development
Many skeletal dysplasias have a small thoracic cavity
- Must look at multiple factors in order to make appropriate diagnosis
  - Which long bones are effected and how severely?
  - Is ossification normal or decreased?
  - Are there rib/long bone fractures or bowing?

Helpful Clues for Common Diagnoses

Renal Agenesis
- Absent kidneys and bladder
- Anhydramnios
Autosomal Recessive Polycystic Kidney Disease, Severe
- Large, echogenic kidneys
- Abdominal circumference often enlarged
- Amount of amniotic fluid varies according to severity of renal disease
Bilateral Multicystic Dysplastic Kidneys
- Non-functioning kidneys filled with multiple cysts of varying size
- Absent bladder
Posterior Urethral Valves, Complete
- Grossly distended bladder in male fetus
- Look for “keyhole” appearance of dilated posterior urethra
- May have associated hydronephrosis
Severe Intrauterine Growth Restriction (IUGR)
- Asymmetric IUGR: Abdomen and chest are small, with “sparing” of head growth
- Often associated with oligohydramnios
- Early onset asymmetric IUGR very concerning for triploidy

Helpful Clues for Less Common Diagnoses

Thanatophoric Dysplasia (TD)
- Divided into 2 subtypes based on morphologic findings
- Chest findings are similar in both types
  - Thorax is small and narrow with short horizontal ribs
  - Ossification is normal
  - No rib fractures
  - Pulmonary hypoplasia
- TD type I
  - “Telephone receiver” femur
  - All long bones severely affected (micromelia) with bowing
  - Platyspondyly
  - Prominent lumbar kyphosis
  - Trident-shaped hands (short fingers, appear same length; gap between 3rd and 4th fingers)
- TD type II
  - Kleeblattschädel (“cloverleaf”) skull
  - Femurs longer, less curved
  - Platyspondyly less marked
Osteogenesis Imperfecta (OI)
- Presence of fractures distinguishes OI from other skeletal dysplasias (except achondrogenesis type 1A)
- Multiple different types based on phenotype
  - Type II is most severe form and most likely to be diagnosed in utero
  - Type II is perinatal lethal
- Chest is small with “beaded” ribs (result of multiple rib fractures)
- Long bone shortening/angulation secondary to fractures
- Callus formation gives bones a “crumpled” appearance
- Decreased mineralization
  - Brain “too well seen”
  - Skull deformation from transducer pressure (“soft” bones)
Achondroplasia
- Most common heritable, non-lethal skeletal dysplasia
- Chest usually has mild “bell-shaped” appearance
- Much less severe than other dysplasias
- Early scans usually normal
- Rhizomelia (proximal limb shortening) noted after 22 weeks
- Normal ossification without fractures
- No bowing or angulation seen prenatally
- Progressive macrocephaly with frontal bossing
- Prominent thoracolumbar kyphosis
- Trident hands
Achondrogenesis
- Group of lethal disorders with severe micromelia, unossified spine, short trunk and disproportionately large head
- Chest findings vary with type
- Type 1A
  - Multiple rib fractures
  - Poorly ossified skull
- Type 1B
  - No rib fractures
  - Poorly ossified skull
- Type II
  - No rib fractures
  - Normal skull ossification
Asphyxiating Thoracic Dysplasia (Jeune Syndrome)
- Characterized by a severely constricted, long, narrow thorax
- Cystic kidneys
- Normal ossification
- Polydactyly in 15%
- Limbs shortened but may not be as profound as in other conditions
Short Rib-Polydactyly
- Characterized by severe micromelia, short horizontal ribs, polydactyly, visceral anomalies
- Visceral anomalies include cardiac, urogenital and central nervous system

Alternative Differential Approaches

Decreased ossification with beaded ribs
- Osteogenesis imperfecta
- Achondroplasia type Ia
Absent spine ossification
- Achondrogenesis (all types)
Small chest and polydactyly
- Short rib-polydactyly
- Asphyxiating thoracic dysplasia