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Platybasia is a developmental or acquired abnormality of the skull base characterized by flattening of the skull base angle, often associated with Basilar invagination and Craniovertebral junction (CVJ) anomalies .

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Etiology

Clinical Features

Often asymptomatic if mild. In symptomatic cases:

• Occipital headache
• Bulbar symptoms: dysphagia, hoarseness, sleep apnea
• Quadriparesis or sensory disturbances (due to brainstem/spinal cord compression)

Associated conditions;

• Chiari I malformation
• Syringomyelia

Radiology

Measurement techniques:

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• Radiologically, platybasia refers to an increased skull base angle (nasion–sella–basion angle).
  • Normal skull base angle: 125°–143°
  • Platybasia: angle > 143° </aside>

![The Welcher basal angle is formed at the intersection of the nasion-tuberculum line and the tuberculum-basion line. Its average should always be less than 140. This angle is increased in platybasia. Wackenheim’s line is constructed by drawing a line along the clivus and extrapolating it inferiorly into the upper cervical spinal canal. This line should fall tangental to the posterior aspect of the tip of the odontoid process. The angle formed at the intersection of Wackenheim’s line with a line constructed along the posterior surface of the axis body and odontoid process (craniovertebral or clivus-canal angle) normally ranges between 150 and 180. Normally, the anterior arch of the atlas typically lies below Chamberlain’s line. The dens is 3.6 to 6.6 mm below the line.

Chen YF, Liu HM. Imaging of craniovertebral junction. Neuroimaging Clinics of North America. 2009;19(3):483-510. doi:10.1016/j.nic.2009.06.002](attachment:36e0a0ce-a5a9-40a5-b8ec-c30ab51b68d4:image.png)

The Welcher basal angle is formed at the intersection of the nasion-tuberculum line and the tuberculum-basion line. Its average should always be less than 140. This angle is increased in platybasia. Wackenheim’s line is constructed by drawing a line along the clivus and extrapolating it inferiorly into the upper cervical spinal canal. This line should fall tangental to the posterior aspect of the tip of the odontoid process. The angle formed at the intersection of Wackenheim’s line with a line constructed along the posterior surface of the axis body and odontoid process (craniovertebral or clivus-canal angle) normally ranges between 150 and 180. Normally, the anterior arch of the atlas typically lies below Chamberlain’s line. The dens is 3.6 to 6.6 mm below the line.

Chen YF, Liu HM. Imaging of craniovertebral junction. Neuroimaging Clinics of North America. 2009;19(3):483-510. doi:10.1016/j.nic.2009.06.002