Craniovertebral junction pathology

Definition

Craniovertebral junction pathology, or craniovertebral anomalies, are abnormalities in the anatomical location and structure of the structures of the contact area between the skull and the spine. They often have no clinical manifestations. In clinically significant cases, they manifest syndromes of intracranial hypertension, vertebral artery lesions, compression of the root, spinal cord, or trunk, and respiratory disorders in young children. Craniovertebral anomalies are diagnosed by craniography, MRI, or CT of the craniovertebral region. Neurologist supervision is required, and neurosurgical treatment is indicated.

General information

The craniovertebral junction includes the skull base formed by the occipital bone and the first two cervical vertebrae (atlas and axis). It is the junction area between the fixed cranium and the mobile spine. Violations of the correct anatomical structure and position of the bony formations underlying craniovertebral anomalies (CVA) often affect the structures of the brain and spinal cord located in this area, which entails the appearance of the corresponding neurological symptoms. The latter is quite variable, associated mainly with compression of the upper cervical segments of the spinal cord and spinal roots, brainstem, cerebellum, IX-XII cranial nerves, vertebral arteries, and impaired circulation of cerebrospinal fluid. Craniovertebral anomalies of mild severity are subclinical, but their detection is important in clinical neurology, especially when it comes to manual therapy.

Causes of craniovertebral anomalies

Congenital anomalies of the craniovertebral junction arise as a result of disruption of embryogenesis when the fetus is exposed to variable negative factors. The latter include increased radioactive background, intrauterine infections, intoxication in dysmetabolic diseases, and occupational hazards or addictions (drug addiction, smoking, alcoholism) of the pregnant woman. 

Acquired craniovertebral anomalies can form as a result of cervical spinal trauma or brain injury, including birth trauma to the newborn. In addition, trauma often serves as a trigger that provokes clinical manifestations of a previously asymptomatic anomaly. Craniovertebral deformities may be due to osteoporosis, which can be caused by rickets, hyperparathyroidism, deforming osteitis, and osteomalacia. 

Signs of craniovertebral anomalies

The clinical presentation of craniovertebral junction anomalies varies, ranging from subclinical to severe neurologic disorders. It is conditioned by the type and degree of bony defects present. Visual signs characterizing craniovertebral anomalies include low hair growth on the occiput, shortened neck, restricted head mobility, increased cervical lordosis, torticollis, and altered head posture. The clinic’s manifestation depends on the severity of the anomaly. Severe deformities usually occur in early childhood; moderate and mild deformities are possible at any age but are usually delayed.

Clinical symptoms include vertebral artery syndrome and chronic cerebral ischemia, syncope, hydrocephalus, intracranial hypertension, and, in severe cases, the syndrome of occipital occlusion of the cerebellar trunk and amygdala. In young children, craniovertebral anomalies can cause sleep apnea syndrome, stridor, and other respiratory disorders.

Types of craniovertebral anomalies

Proatlas is a rudimentary bony element in the occipital bone. It is a congenital pathology associated with a disorder of reduction of the connective tissue bundle formed on the ventral side of the vertebrae during ontogenesis. In the absence of fusion of the rudimentary element with the surrounding bone structures, it is said about a free proatlas. When it fuses with the anterior edge of the foramen occipitalis, the term “third condyle” is used. The term “perioccipital process” is used when it fuses with the posterior edge.

Hypoplasia and aplasia of the posterior arch of the atlas. In the first case, there are no clinical manifestations; the malformation is diagnosed radiologically. The anomaly occurs in 5-9% of the population. In the second case, compression of the distal part of the trunk and the upper parts of the spinal cord occurs in childhood or puberty. Rapid aggravation of symptoms is characteristic. The incidence of the malformation is 0.5-1%.

Assimilation of the atlas – fusion of the 1st cervical vertebra and occipital bone. It can be complete or incomplete, uni- or bilateral. The frequency of the anomaly does not exceed 2%. Atlas assimilation manifests clinically after the age of 20 years with headaches with vegetative symptoms. There may be liquor-hypertension syndrome, mild dissociated sensory disturbances, and disorders of the function of the lower cranial nerves.

According to various data, dental anomalies are found in 0.5-9% of the population. They include hypo- and aplasia and hypertrophy of the process, which occurs without clinical manifestations. Neurologic symptomatology occurs when the dentition is not fused with the axis but forms a separate dentition. In such conditions, there is chronic atlanto-axial subluxation and possible compression of the proximal spinal cord.

Platybasia is a flattening of the base of the skull. Clinically, platybasia is manifested only in the III degree of flattening, accompanied by a significant reduction in the size of the posterior cranial fossa, resulting in intracranial hypertension, compression of the cerebellum, and IX-XII pairs of cranial nerves.

The basilar impression is a depression of the skull base into the skull cavity. It occurs at a frequency of 1-2% in the population. In basilar impressions, symptoms due to the reduction of the posterior cranial fossa are combined with signs of compression of the spinal roots of the first cervical segments. Compression myelopathy with central tetraparesis may occur in these segments. 

Kimmerle’s anomaly is associated with the presence of an additional atlantal arch that restricts the vertebral artery. It can be complete or incomplete, unilateral or bilateral. Clinically significant in only a quarter of carriers of the malformation, it is manifested by vertebral artery syndrome, syncope, TIA, and, in severe cases, ischemic stroke.

Chiari anomaly is a congenital malformation in which part of the posterior cranial fossa structures prolapse into the occipital foramen. 80% of patients have syringomyelia. There are four types of Chiari anomaly, which differ in age of onset and clinical symptoms.

Klippel-Feil syndrome is a rare congenital anomaly (incidence 0.2-0.8%) in the form of a reduction in the number of cervical vertebrae and/or their fusion. It may be hereditary or sporadic. Klippel-Feil syndrome is often combined with other malformations (spinal splitting, polydactyly, wolf’s mouth, dental anomalies, congenital heart defects, etc.) and characterized by muscle weakness arising in early childhood with the outcome in paresis. In some cases, congenital hydrocephalus and oligophrenia are observed.

Diagnosis of craniovertebral anomalies

In addition to clinical examination, skull, and cervical spine radiography are important in the diagnosis. To visualize the soft tissue structures of the craniovertebral junction, an MRI of the brain and an MRI of the spine in the cervical spine are prescribed. The study is performed in T1 and T2 modes, in sagittal and axial projections. If indicated, an MRI of cerebral vessels is performed. If an MRI examination is not possible, and for more accurate visualization of bony formations in the craniovertebral zone, a CT of the spine and the brain is performed.

The presence of vertebral artery syndrome is an indication for vascular studies—rheoencephalography with functional tests and ultrasound of extracranial vessels. Genetic counseling and genealogical analysis are performed to identify hereditary pathology.

Treatment of craniovertebral anomalies

Patients with craniovertebral junction anomalies should take several precautions to avoid provoking or aggravating the clinical manifestations of the anomaly. Sharp head tilts and turns, headstands, tumbling, traumatic sports, and forced exertion are not desirable. A neurologist observes subclinical forms of craniovertebral anomalies and basic therapy for moderate manifestations. Traditionally, nootropic, neurotrophic, and vasoactive pharmaceuticals form the basis of basic treatment, although their efficacy in craniovertebral anomalies has not been proven.

In case of severe clinical manifestations, the possibility of neurosurgical correction of the malformation is considered. The indications for surgical treatment are symptoms of compression of the trunk, cerebellum, or spinal cord and cerebral circulation disorders. In basilar impression and Chiari anomaly, craniovertebral decompression is performed; in Kimmerle’s anomaly, resection of the atlantal arch; in atlas-assimilation, laminectomy for spinal cord decompression and spondylotic stabilization.

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