Basilar invagination refers to the inward folding of the skull base bone tissue centered around the foramen magnum of the occipital bone, causing structures of the upper cervical spine such as the atlas, axis, and odontoid process to protrude into the cranial cavity. This results in a reduction of the posterior cranial fossa volume and shortening of the anteroposterior diameter of the foramen magnum, leading to symptoms. It is also known as basilar impression or basilar invagination. The main clinical manifestations fall into two categories: (1) symptoms directly caused by basilar invagination itself, and (2) secondary neurological damage. Most cases do not present symptoms until the ages of 20–30 or even middle age. The incidence of this condition shows no regional or gender differences. Surgical treatment is only recommended when there are clear symptoms of secondary neurological damage or increased intracranial pressure. However, surgery must be performed before the secondary neurological damage becomes severe to achieve a better prognosis.

bubble_chart Clinical Manifestations

1. Manifestations of basilar invagination itself: short and thick neck, head and neck deviation, low posterior hairline, limited neck movement, and facial asymmetry. 2. Manifestations of secondary nerve damage: (1) Symptoms of cervical nerve root irritation: occipital and neck pain, hypoesthesia, numbness and soreness in one or both upper limbs, etc. (2) Symptoms of cranial nerve involvement: hoarseness, dysphagia, slurred speech, etc. (3) Symptoms of upper cervical cord and medulla compression: limb weakness or paralysis, sensory disturbances, urinary retention, dysphagia, etc. (4) Cerebellar symptoms: nystagmus, unsteady gait, positive Romberg's sign, etc. (5) Vertebral artery blood supply disorders: sudden episodes of vertigo, visual disturbances, vomiting, and pseudobulbar palsy, etc. 3. Advanced stage presents with manifestations of increased intracranial pressure: headache, vomiting, bilateral papilledema.

1. Short neck, low posterior hairline, skull deviation, and asymmetrical facial auricles. 2. Secondary nerve damage manifests as occipital neck pain, hoarseness, limb weakness, urinary retention, ataxia, and episodic vertigo. 3. Increased intracranial pressure presents with headache, vomiting, and bilateral optic disc edema. 4. X-ray imaging of the occipital-cervical region (including tomograms) shows the odontoid process of the axis exceeding the Chamberlain line by 3mm, the McRae line by 9mm, and the digastric line by over 12mm. 5. Pneumoencephalography, myelography with iophendylate, and computed tomography aid in assessing compression in the ventricular system and the foramen magnum region.

bubble_chart Treatment Measures

1. For patients with clear diagnosis and obvious symptoms, surgical treatment should be performed as early as possible. However, during anesthesia and patient positioning, excessive head extension should be avoided to prevent cerebellar tonsillar herniation, which may aggravate medullary damage and lead to respiratory arrest or death. 2. Prevent infection. 3. Symptomatic treatment.

This disease is mostly a congenital malformation related to genetic factors, but the onset age is relatively late, usually between 20-30 years or even older. This is because the presence of this malformation causes chronic damage to the structures in the atlanto-occipital region, leading to the slow appearance and gradual worsening of neurological symptoms. Symptoms may suddenly worsen due to trauma. Therefore, asymptomatic individuals should take care to avoid trauma. Symptomatic patients should seek early consultation with a specialist in neurosurgery at a major hospital and undergo surgical treatment to avoid delaying the condition. Once neurological damage becomes irreversible, even with decompression and release surgery, the prognosis remains poor.

1. Cured: Neurological function is basically restored, able to care for oneself, with normal intracranial pressure. 2. Improved: Neurological symptoms have improved, condition is stable, able to care for oneself or still requires assistance. 3. Not cured: Neurological symptoms show no improvement, unable to care for oneself.