Definition
- Flattening of the skull base and is usually asymptomatic unless associated with other anomalies.
Pathology
- The skull base angle is formed by a line joining the nasion with the centre of the pituitary fossa and a line joining the anterior border of the foramen magnum with the centre of the pituitary fossa.
- Basilar kyphosis is present if it is less than 125°.
- Normal clival angle (top) measured by the NTB angle of Welcker joining the nasion (N), tuberculum (T) and basion (B).
The angle should be < 130°.
- Platybasia (middle) is marked by an increased NTB angle. This raises the basion and forces the foramen magnum plane (dotted line) to tilt upwards. (skull base angle>145°)
- The same upward tilt of this plane also occurs with a short clivus (lower)
Associated with
- basilar invagination
- Achondroplasia
- Down’s syndrome
- Chiari malformations
- Craniocleidodysostosis
- Craniofacial anomalies
- Osteogenesis imperfecta
- Paget’s disease
- Osteomalacia
- Rickets
- Fibrous dysplasia
- Hypoparathyroidism
Clinical features
- Platybasia without basilar impression is asymptomatic
- Indentation of the anterior medulla by the dens, however, produces brainstem dysfunction and lower cranial neuropathies more frequently than “pure” cerebellar ectopia without an anterior compression vector.
- Brainstem dysfunction
- Neurogenic dysphagia
- Nasal or hoarse voice
- due to paresis of the palatal levator and vocal cords
- Sleep apnea
- intermittent or progressive spastic quadriparesis.
- Cerebellar ectopia
- Gait discoodination
- Chiari 1 associated pressure difference
- Tussive Headaches