Some specific anomalies have a characteristic shape of the head.
Lemon sign: a concave deformity of the frontal bones at the level of the coronal suture, which may be associated with
- normal fetus (1-2% of normal fetuses)
- spina bifida (common)
- occipital cephalocele (rare)
- thanatophoric dysplasia (rare)
- long-term oligohydramnios
Cloverleaf skull (found in 14% of cases of thanatophoric dysplasia)
- thanatophoric dysplasia (most common)
- homozygous achondroplasia
- Apert’s syndrome
- Pfeiffer’s syndrome
- Carpenter’s syndrome
Strawberry head shape (often associated with fetal trisomy 18).