Atlas assimilation is a partial or complete fusion of the I cervical vertebra and the occipital bone of the skull. Atlanta assimilation may not be accompanied by clinically significant disorders. In other cases, it leads to compression of the structures of the craniovertebral region (upper cervical spinal cord and medulla oblongata), limited mobility in the upper cervical spine and the development of instability of the segments of the lower cervical spine. Atlanta assimilation is diagnosed by X-ray examination of the cervical spine and craniovertebral junction, Echo-EG, REG, EEG, MRI and CT brain, MRI of the cervical spine are additionally performed. Atlanta assimilation is treated mainly by conservative methods. Surgical interventions are performed to decompress brain structures.
ICD 10
M43.2 Other vertebral column splices
General information
Along with the Kimerli anomaly and Chiari anomaly, Atlas assimilation in neurology and vertebrology refers to congenital anomalies of the spine. Atlanta assimilation occurs in about 1-2% of cases and is most often manifested at the age of 20 to 30 years. As a rule, the development of the spine occurs before the age of 20-22, and the cervical spine is ossified first. Normally, the articular processes of the I cervical vertebra (Atlanta) are adjacent to the condyles of the occipital bone. The assimilation of the atlas is characterized by a dense increment of the atlas to the occipital bone. Often, the assimilation of the atlas is combined with its underdevelopment and displaced position in relation to the II cervical vertebra, as well as with basilar impression — an upward displacement of the basilar part of the occipital bone, which leads to a decrease in the volume of the posterior cranial fossa and compression of anatomical structures located in it.
Causes
Atlas assimilation is a violation of the formation of craniovertebral structures during embryonic development. To some extent, such disorders are genetically determined. This is evidenced by the high frequency of Atlanta assimilation in families whose members have certain anomalies of the development of the central nervous system (meningocele, platybasia, hydromyelia, Chiari anomaly, etc.). Factors that cause disorders in the process of intrauterine development include:
- radioactive radiation
- severe diseases of the mother (diabetes mellitus, heart disease, heart failure, bronchial asthma, etc.)
- complicated course of pregnancy: toxicosis, nephropathy and infections suffered during pregnancy (measles, rubella, cytomegaly, chlamydia, etc.).
Pathogenesis
The development of pathological changes that accompany the assimilation of the Atlantean can occur in two ways. The first way is connected with the fact that the assimilation of the Atlas causes narrowing and disruption of the configuration of the foramen magnum, resulting in compression of the structures of the medulla oblongata and the upper segments of the cervical spinal cord.
The second pathogenetic mechanism is due to the fact that the assimilation of the Atlas leads to a reduction in the amplitude of movements in the upper cervical spine. Restriction of movements in the upper part due to compensatory mechanisms leads to the development of increased mobility in the lower part of the cervical segment of the spine. As a result of hypermobility, the load on the CIV-CV and CV-CVI intervertebral discs increases. Thus, their excessive wear may occur, leading to the formation of instability of the spine at this level.
Symptoms
Mild Atlanta assimilation is characterized by an asymptomatic course and may not make itself felt throughout the patient’s life. Clinically significant assimilation of Atlanta usually debuts after 20 years. Its manifestations depend on the degree of fusion of the atlas with the occipital bone and combination with other congenital anomalies.
Atlanta assimilation is manifested by headaches, which can have a paroxysmal character and be accompanied by vegetative reactions: increased sweating, tachycardia, fluctuations in blood pressure, a feeling of heat in the body or, conversely, chilliness. In case of violation of the outflow of cerebrospinal fluid, assimilation of the atlant is manifested by a feeling of pressure on the eyeballs, nausea and vomiting. Sleep disorders and neck pain are possible. Pain syndrome with localization of pain in the cervical spine often appears if the assimilation of the Atlas is accompanied by instability of the lower neck segments. The intensity of pain may increase after physical exertion. On examination, such patients show an increased tone of the neck muscles.
Atlas assimilation, which leads to compression of the upper segments of the spinal cord, is usually not accompanied by severe compression myelopathy with severe motor disorders. As a rule, it is manifested by mild dissociated sensitivity disorders in the area of the lower cervical dermatomes, for the detection of which a thorough neurological examination is necessary.
If the assimilation of the Atlas leads to compression of the structures of the medulla oblongata, then there are signs of damage to the cranial nerves coming out of it. Compression of IX-XII pairs is manifested by a violation of swallowing with choking during meals, dysarthria, hoarseness of voice, decreased taste sensations. The defeat of the VIII pair of cranial nerves (vestibular cochlear nerve) is accompanied by the development of hearing loss, dizziness and the appearance of nystagmus, the VII pair — neuritis of the facial nerve.
Diagnostics
Clinical manifestations accompanying various variants of Atlanta assimilation and neurological examination data allow the neurologist to suspect disorders localized in the cervical spine and craniovertebral region. To identify the assimilation of Atlanta, it is necessary to conduct:
- Radiography. X-ray of the cervical spine with occipital bone capture in straight and lateral projections allows you to visualize the place of fusion. Standard and functional radiographs often show signs of instability of the CIV-CV and CV-CVI, which is accompanied by the assimilation of the Atlas: a change in the height of the intervertebral discs, displacement of the vertebrae and violation of the parallelism of their articular surfaces.
- EFI. During the standard primary examination (EEG, Echo-EG and REG), only increased intracranial pressure is usually detected in patients with Atlanta assimilation.
- Tomography. In cases where the assimilation of the Atlas is accompanied by symptoms of damage to the medulla oblongata, it is necessary to exclude other cerebral pathology: brain tumors, syringomyelic cyst, abscess. For this purpose, CT or MRI of the brain is performed, which in the case of assimilation of the Atlas can reveal signs of hydrocephalus. MRI of the spine allows you to judge the degree of compression of the spinal cord.
Atlas assimilation requires differentiation from spinal osteochondrosis, amyotrophic lateral sclerosis, arachnoiditis, syringomyelia, multiple sclerosis, funicular myelosis.
Treatment
Atlanta assimilation in the presence of clinical manifestations requires symptomatic treatment. It can be carried out by joint efforts of neurologists, vertebrologists and orthopedists. Analgesics, nonsteroidal anti-inflammatory drugs (nimesulide, meloxicam, diclofenac), reflexotherapy are used to relieve pain syndrome. To lower intracranial pressure, patients are prescribed diuretics (acetazolamide, spironolactone, mannitol). In the treatment of spinal instability, wearing a trench collar, physical therapy and massage, electrophoresis, ultraphonophoresis are used. To relieve severe pain syndrome, paravertebral blockades can be performed.
Surgically, Atlanta assimilation is treated only in cases of significant compression of the spinal cord or medulla oblongata. Surgery may include dilation of the occipital foramen and decompression of the spinal cord by laminectomy. Anterior and posterior spinal fusion operations are used to stabilize the cervical spine.