Craniovertebral (CV) Junction Anomalies
A variation in the anatomical structure at the craniovertebral junction can lead to compression of the spinal column, which, in turn, may cause damage to the spine.
These variations can come about:
- develop over time
- due to trauma, tumor or infection.
Disorders of this type are a result of the anatomical challenges posed by this unique location in the body, where the skull (cranio) meets the spine (vertebral), as well as the disproportion of head to body weight in the developing infant.
At birth, the brain is typically 25% of its adult size, although the bodyweight of the newborn is only about 5% of its adult weight. Importantly, about half of the postnatal growth of the brain volume occurs during the first year of life and attains about 75% of its adult size by the end of the second year.
The circumference of the head at birth is about 13–14 inches. It increases by 17% during the first 3 months of life, and by 25% at 6 months of age. Head circumference increases markedly during the first postnatal year due to the progressive and rapid growth of the brain as a whole.
The important relation of brain size and cranium size can be demonstrated on a percentage basis, which shows that:
- 70% of the adult brain weight is achieved at 18 months
- 80% at 3 years
- 90% at 5–8 years
- approximately 95% at the 10th year.
By contrast, genital organs develop very slowly during this period but, instead, reach their adult size during the second decade of life.
Infants and children are not miniature adults and their anatomy differs from the adult in a number of ways. The growth of a child is dependent upon the normal activity of growth centers and the protection of these centers are vital. Abnormalities of body stature and limb mobility might result from injury to these growth centers.
The brain and spinal cord are protected by bony structures: the skull and spinal column.
There are three main parts of the brain:
- cerebrum – controls higher brain functions
- cerebellum – controls balance, coordination, and fine muscle control
- brain stem – controls things we do without thinking, like our heartbeat, breathing, and swallowing.
The cerebrum has four lobes, each with different functions:
- Frontal lobe: executive function, decisions, personality, language, planning, movement
- Parietal lobe: intelligence, reasoning, sensation, reading
- Occipital lobe: vision
- Temporal lobe: language, behavior, hearing, vision, emotions, memory
Another vital point is the Foramen Magnum, a funnel-like opening to the spinal canal.
- The Spinal Cord starts at the brain stem and goes to the tail bone. It is about as wide as your little finger and extends the length of your back. Messages are carried from the spinal cord to and from the brain to the rest of the body
- Meninges are membranes that cover and protect the brain and spinal cord. There are three layers of meninges: Dura mater (closest to the bone), Arachnoid is loosely around the brain, Pia mater is closely attached to the brain and spinal cord surface
- Cerebrospinal Fluid (CSF) cushions the brain and spinal cord. It is a clear, water-like fluid, also called spinal fluid, found between the arachnoid and pia mater. The brain and spinal cord are bathed and cushioned by this spinal fluid, which flows and circulates around the brain and spine
If the cause of the CV malfunction is congenital, it is generally referred to by its location.
Malformations of Occiput
Occiput is another term for the skull. The basi occiput forms the lower portion and the upper portion is formed by the basisphenoid, separated from the basi occiput by the sphenooccipital synchondrosis.
Most occipital anomalies are associated with decreased skull base height and basilar invagination.
Occipital malformations cause a variety of visual disturbances and headaches. Early diagnosis may lead to treatment that reduces the risk of hemorrhages, visual field loss and other neurological deficits, and death.
Malformations of the Atlas (C1)
The C1 atlas is the uppermost cervical vertebra of the spine. It supports the head and — along with the C2 axis, the cervical vertebra just below it — allows the head to nod and rotate from side to side.
At birth, children have softer bones. That is true of the C1 atlas, as well. C1 ossification (solid, hard bone) begins in fetal life and continues to the third or fourth year of life.
Children’s heads are larger, with respect to their body size than adults. Due to this mismatch, young patients have increased chances of spine injuries throughout the cervical spine, but especially between the skull (occiput) and the upper cervical spine.
Malformations of the Axis (C2)
The axis (C2) cervical vertebra is the second vertebra of the spine. It is unique in that it contains the odontoid process (odontoid means “tooth” and that is what this bone looks like) that forms a pivot point on which the C1 atlas can rotate.
Injuries to the odontoid are common in motor vehicle accidents and falls. The C1 atlas and C2 axis form the atlantoaxial joint. The atlas (C1) rotates around the odontoid process of the axis (C2), allowing a person’s head to turn from side-to-side (rotate). This joint accounts for approximately 50% of the head’s ability to turn left and right.
The CV junction is a transition site between the mobile cranium and relatively rigid spinal column. It is also the site of the medullo spinal junction. CV anomalies are defects in development, not necessarily congenital and may not manifest at birth.
Similar to congenital disorders, the underlying cause leads to compression and instability of the spine, with the inherent threat of damage to the spine and surrounding tissues.