Platybasia

Platybasia is a congenital or acquired skull base anomaly, where the angle between the clivus (a part of the skull base) and the body of the sphenoid bone is abnormally flattened or increased. This condition can result in the skull base becoming more horizontal than usual, which can affect the alignment of the craniovertebral junction and may compress or distort important neural structures such as the brainstem and upper spinal cord.

### Key Features of Platybasia:

1. Anatomy and Definition:

1. Normally, the angle between the clivus and the sphenoid bone is about 125 to 143 degrees.
2. In platybasia, this angle is greater than 143 degrees, making the base of the skull appear flatter.
3. It can occur in isolation or be associated with other craniovertebral junction abnormalities like basilar invagination (where the tip of the odontoid process moves upwards towards the skull base).

2. Types of Platybasia:

1. Congenital Platybasia: Present at birth and often associated with other congenital anomalies such as Chiari malformations, atlanto-occipital assimilation, or Klippel-Feil syndrome.
2. Acquired Platybasia: Can occur later in life due to conditions like Paget’s disease, osteomalacia, or trauma that affect bone structure and integrity.

3. Causes:

1. Congenital:
   1. May be associated with genetic syndromes or developmental anomalies of the craniovertebral junction.
   2. Frequently seen alongside other malformations such as Chiari malformation, where the brainstem and cerebellum may herniate into the spinal canal.
2. Acquired:
   1. Paget's disease of bone: A chronic condition that disrupts the normal recycling process of bone tissue, leading to weakened bones.
   2. Osteomalacia: A condition characterized by softening of the bones due to defective bone mineralization, often from vitamin D deficiency.
   3. Trauma: Severe head or neck injuries may cause damage to the skull base, leading to platybasia.

4. Symptoms:

1. Neck pain: Common in patients with platybasia, especially if there is compression of the neural structures.
2. Headaches: Frequently occipital (back of the head), especially if associated with compression or deformity of the craniovertebral junction.
3. Neurological symptoms: Occur when there is compression of the brainstem or spinal cord, leading to:
   1. Dizziness or vertigo.
   2. Visual disturbances.
   3. Difficulty swallowing (dysphagia).
   4. Gait disturbances or ataxia (lack of coordination).
   5. Muscle weakness or numbness, particularly in the limbs.
4. Respiratory and cardiovascular problems: In severe cases, compression of the brainstem can cause breathing difficulties or affect heart rate and blood pressure.

5. Diagnosis:

1. Imaging:
   1. X-rays: Can measure the basal angle of the skull and detect platybasia.
   2. CT scan: Provides a detailed view of the bones of the skull base and helps in identifying the extent of the deformity and any associated conditions like basilar invagination.
   3. MRI: Useful for evaluating the soft tissues and detecting compression of the brainstem or spinal cord.
2. Chamberlain or McGregor lines: Special radiographic lines used to evaluate the position of the odontoid process in relation to the skull base, helping to identify basilar invagination, which often coexists with platybasia.

6. Treatment:

1. Conservative Management:
   1. Observation: In cases where platybasia does not cause symptoms or neurological complications, regular monitoring and imaging may be sufficient.
   2. Pain management: Medications, including non-steroidal anti-inflammatory drugs (NSAIDs), may be prescribed to manage neck pain or headaches.
   3. Physical therapy: Can help improve neck stability and mobility, but should be approached cautiously in cases of instability.
2. Surgical Intervention:
   1. Surgery is generally required if there is significant compression of the brainstem or spinal cord.
   2. Craniovertebral decompression: Surgical removal of bone or soft tissue to relieve pressure on neural structures.
   3. Fusion surgery: Occipitocervical fusion may be necessary to stabilize the craniovertebral junction, particularly in cases where instability or severe misalignment exists.
   4. Reduction of basilar invagination: If basilar invagination accompanies platybasia, surgery may aim to reduce the upward displacement of the odontoid process.

7. Prognosis:

1. The prognosis for patients with platybasia depends on the severity of the condition and whether it is associated with other abnormalities.
2. Patients with mild platybasia who do not have significant neurological symptoms may have a good outcome with conservative management.
3. In cases where there is brainstem or spinal cord compression, early diagnosis and surgical intervention can significantly improve symptoms and prevent further neurological damage.

### Complications: - Basilar Invagination: Often seen with platybasia, this can cause severe neurological deficits due to compression of the brainstem or upper spinal cord. - Chiari Malformation: The downward displacement of the cerebellum can exacerbate symptoms, leading to balance issues, dizziness, and headaches. - Neurological deterioration: If left untreated, severe cases of platybasia with associated brainstem or spinal cord compression can lead to permanent neurological damage, respiratory failure, or even death.

Platybasia, particularly when symptomatic, is a serious condition that requires careful assessment and management to prevent long-term complications, especially when associated with other craniovertebral junction anomalies.

Flattening of the skull base. Originally assessed on plain X-rays (which are subject to error due to skull rotation or difficulty identifying landmarks), now more commonly evaluated on CT or MRI. May or may not be associated with BI, and may occur in association with craniofacial abnormalities, Chiari Malformation Type 1.5, Paget’s disease…

Platybasia: flattening of the skull base.

Pathology

Aetiology

congenital achondroplasia

May or may not be associated with basilar invagination (BI), and may occur in association with craniofacial abnormalities, Chiari malformation, Paget’s disease…

Down syndrome

craniocleidodysostosis craniofacial anomalies osteogenesis imperfecta

osteomalacia rickets trauma fibrous dysplasia hypoparathyroidism

see Platybasia diagnosis