I. What is craniocervical junctional area deformity? Craniocervical junction zone, also known as occipital foramen or atlanto-occipital zone, refers to the transition area between the skull and the cervical spine, specifically the occipital, atlanto-axial (first cervical) and pivotal (second cervical) areas around the occipital foramen. Craniocervical junction deformity is a congenital condition that refers to a congenital bony deformity occurring in the craniocervical junction region with involvement of neural structures. Due to the congenital bony deformity and the complex pathological changes that occur gradually later in life, patients often end up with atlanto-axial and pivotal dislocation, which leads to compression of the medulla oblongata and upper cervical medulla, manifesting symptoms of the disease mainly in the form of impaired motor and sensory functions of the extremities. Although the disease is rare clinically, severe cases can compress the medulla oblongata and cervical medulla and produce severe symptoms, and can often be accompanied by other congenital diseases in the spinal canal. What are the main deformities of the craniocervical junction area? Craniocervical junction malformation includes many types of congenital malformation, and the malformation can be single or multiple in the same body. They mainly include atlanto-occipital deformity, atlanto-axial dislocation, atlanto-occipital fusion, skull base depression, flattened skull base, cervical 2-3 incomplete segmentation (fusion), cerebellar subungual herniation deformity (Chiari malformation) and spinal cord cavity. Sometimes these deformities do not exist independently and are often associated with congenital deformities in adjacent areas, such as atlantoaxial arch deficiency and congenital atlanto-axial fusion, atlanto-occipital ossification (atlanto-occipital fusion), dentate hypoplasia or hypoplasia, and congenital cervical 2-3 subsegmental insufficiency. These disorders can be broadly classified as congenital craniocervical junctional anomalies, which share the same etiology, similar disease progression, and similar symptoms. However, their treatment may differ greatly due to the specific details. Third, what kind of symptoms occur before the disease needs to be suspected? Patients can have no obvious signs or symptoms until they develop neurological dysfunction. However, there are often some external features: short neck (short neck), low back hairline (patients may be noticed by the barber during haircut), oblique neck deformity (crooked neck), asymmetrical facial development, and limited neck movement (often overlooked because the patient grew up that way). Patients may present with soreness, numbness, sensory hypersensitivity in the occiput, neck and both upper extremities, and dissociative sensory deficits in the upper extremities, i.e., decreased pain and temperature sensation with normal tactile sensation (e.g., they can count money well, but are easily blistered by hot water cups without knowing the pain). Craniocervical junction malformation can also compress the vertebral artery and affect the blood supply to the brain, resulting in headache, dizziness, memory loss, syncope and seizures (convulsions). The presence of progressive muscle weakness in the extremities further indicates that the conus fasciculus, which conducts motor functions, has been compromised due to compression of the medulla oblongata and ventral aspect of the upper cervical medulla. In addition, craniocervical junction malformations may be associated with cervical ribs, occult spina bifida, nerve root or plexus distribution malformations, and may present with brachial pain, low back pain, and sciatica. Short neck deformity can be combined with scoliosis, high scaphoid and webbing deformity. How to confirm the diagnosis of craniocervical junction deformity? If a patient has the above symptoms and suspects this disease, he/she should go to the neurosurgery department promptly. First of all, the simplest examination is to go to the hospital to take x-ray films. The site and shape of congenital developmental deformity of the cervical spine can be found on conventional frontal and lateral X-ray films of the cervical spine, and oblique and dynamic lateral films (neutral, hyperextension and hyperflexion) can be taken to fully observe the extent of deformity and stability of the cervical spine. To further clarify the diagnosis, CT thin-section scans of the craniocervical junction with coronal, sagittal and triple reconstruction are feasible to determine the bony structures and the status of the spinal canal. For those with spinal cord symptoms combined with spinal canal stenosis, magnetic resonance imaging should be performed to clarify whether there is a submicrocephalic tonsillar herniation malformation and spinal cord cavitation. For suspected vertebral artery abnormalities, CTA (CT angiography) or MRA (magnetic resonance angiography) or DSA (digital subtraction angiography of the brain and spinal cord) should also be added. V. If the disease is diagnosed, how should it be treated? There are two trends in the natural regression of congenital craniocervical junctional area malformation: one is a persistent instability that eventually leads to clinical onset, and the other is to remain relatively stable and may be lifelong without onset. The latter does not require further treatment and should be kept on follow-up. However, care should be taken to avoid excessive activity of the cervical spine, prevent the occurrence of trauma, and slow down the process of cervical degeneration. For those with symptoms of local structural instability and neurological compression, surgical treatment is required, with options such as bone window decompression, atlantoaxial internal fixation or occipitocervical internal fixation with bone graft fusion depending on the situation. The purpose of surgery is to relieve the compression and promote the recovery of the involved nerve; bone graft fusion to rebuild the stability of the occipital neck. Removal of compression is the prerequisite for recovery of the involved nerve, and bone graft fusion is the key to ensure the surgical results. The treatment of craniocervical junction deformity is one of the difficulties in neurosurgery. Common deformities of bone structure in the junction region include: free dentition, dentition deficiency, atlantoaxial posterior arch deficiency, atlantoaxial posterior arch discontinuity, atlanto-occipital ossification, atlanto-lateral block asymmetry, C2-congenital fusion, as well as occipital condyles and and skull base developmental deformities. The presence of these deformities poses the following surgical challenges: (1) for atlantoaxial posterior arch defects or discontinuities, the use of the conventional posterior transpedicular screw fixation technique or the pedicle hook technique causes difficulties; (2) in cases of C2-3 fusion, the structural development of the cardinal spine is abnormal, and the use of the conventional cardinal transpedicular screw fixation often encounters difficulties; (3) for combined atlantooccipital ossification and atlanto-lateral block dysplasia, both posterior and anterior atlantoaxial nailing is difficult. (3) For combined atlanto-occipital ossification and atlanto-lateral block dysplasia, both posterior and anterior atlanto-axial nailing are difficult.