Atlanto-occipital dislocation, orthopedic decapitation, or internal decapitation describes ligamentous separation of the spinal column from the skull base. It is possible for a human to survive such an injury; however, 70% of cases result in immediate
death
Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...
. It should not be confused with
atlanto-axial dislocation, which describes ligamentous separation between the first and second cervical
vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
.
Mechanism
The injury is a result of disruption of the stabilizing ligaments between the
occiput
The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cereb ...
, or posterior skull base, and the C1 vertebral body, otherwise known as the
atlas
An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth.
Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...
. The diagnosis is usually suspected by history and physical exam, but confirmed by imaging, typically by
CT due to its faster speed in the acute trauma setting, although
MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
can also help with assessment in equivocal cases. The treatment is initial stabilization with a cervical spine collar, and then surgical intervention in cases in which reversal of paralysis is possible. The most common mechanism of injury is high-speed motor vehicle accidents. The injury is more likely in children due to the large size of their heads relative to their bodies, and more horizontal orientation of the occipital condyles. It represents <1% of all cervical spine injuries.
Several subtypes of atlanto-occipital dislocation are known. Traynelis et al. differentiates anterior dislocation (type 1), vertical dislocation (type 2) and posterior dislocation (type 3) of the head relative to the spine. Other variants with lateral or rotatory displacement have been described, as well as mixed types. Common etiology for such injuries is sudden and severe deceleration leading to a
whiplash
Whiplash may refer to:
* The long flexible part of a whip
* Whiplash (medicine), a neck injury
** Whiplash Injury Protection System (WHIPS), in automobiles
Film and television
* ''Whiplash'' (1948 film), a US film noir about a boxer
* ''Whiplas ...
-like mechanism.
Diagnosis
The distances between the
dens and surrounding structures are also key features that can suggest the diagnosis, with the normal distance between the dens and basion (BDI) measuring less than 9 mm on CT, and the distance between the dens and atlas (ADI) measuring less than 3 mm on CT, although this can be increased in cases of
rheumatoid arthritis
Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are involv ...
due to
pannus
Pannus is an abnormal layer of fibrovascular tissue or granulation tissue. Common sites for pannus formation include over the cornea, over a joint surface (as seen in rheumatoid arthritis), or on a prosthetic heart valve. Pannus may grow in a t ...
formation.
Several indirect measurements on CT can be used to assess ligamentous integrity at the craniocervical junction. The Wackenheim line, a straight line extending along the posterior margin of the
clivus through the
dens, should not intersect the dens on plain film, with violation of this relationship raising concern for
basilar invagination. The
basion
The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblon ...
to
axion
An axion () is a hypothetical elementary particle postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics (QCD). If axions exist and have low mass within a specific range, they are of interes ...
interval, or BAI, is also used, which is determined by measuring the distance between an imaginary vertical line at the anterior skull base, or basion, at the
foramen magnum
The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblon ...
, and the axis of the cervical spine along its posterior margin, which should measure 12 mm, an assessment more reliable on
radiograph
Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical radiography ("diagnostic" and "therapeut ...
than CT. The distance between the atlas and the occipital condyles, the atlanto-occipital interval (AOI), should measure less than 4 mm, and is better assessed on
coronal images.
The Powers ratio was formerly used, which was the tip of the basion to the spinolaminar line, divided by the distance from the tip of the
opisthion to the midpoint of the posterior aspect of the anterior arch of C1. It is no longer recommended due to low sensitivity and difficulty identifying landmarks. It also will miss vertical or posterior displacement of the cervical spine.
Other measurements include occiput-atlas distance, angle between anterior arch of atlas and axis, vertical distance between posterior arch of atlas and spinous process of axis, vertical atlanto-dens interval, and joint space between C1 and C2.
Treatment
Treatment involves fixation of the cervical spine to the skull base, or occipitocervical fusion, using paramedian rods and transpedicular screws with cross-links for stabilization. The patient is subsequently unable to rotate their head in the horizontal plane. If there is obstructive
hydrocephalus
Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased intracranial pressure, pressure inside the skull. Older people may have headaches, double vision, poor ...
, a
pseudomeningocele can form, which is decompressed at the time of surgery.
Prognosis
The injury is immediately fatal in 70% of cases, with an additional 15% surviving to the emergency room but dying during the subsequent hospital stay. A basion-dental interval of 16 mm or greater is associated with mortality. In those with neurologic deficits, survival is unlikely.
Most deaths result from mechanical damage to the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...
and lower
brainstem
The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...
, ranging from localized
contusion
A bruise, also known as a contusion, is a type of hematoma of tissue, the most common cause being capillaries damaged by trauma, causing localized bleeding that extravasates into the surrounding interstitial tissues. Most bruises occur close ...
to
diffuse axonal injury
Diffuse axonal injury (DAI) is a brain injury in which scattered lesions occur over a widespread area in white matter tracts as well as grey matter. DAI is one of the most common and devastating types of traumatic brain injury and is a major cause ...
to complete transection. Vascular complications are also frequent, and may contribute significantly to delayed mortality. Combined dissections of the
vertebral
The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...
and
carotid arteries
In anatomy, the left and right common carotid arteries (carotids) (Entry "carotid"
in
cerebral ischemia
Brain ischemia is a condition in which there is insufficient bloodflow to the brain to meet metabolic demand. This leads to poor oxygen supply or cerebral hypoxia and thus leads to the death of brain tissue or cerebral infarction/ischemic stroke. ...
, whereas rupture of the vertebral artery/
PICA junction results in
subarachnoid hemorrhage
Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. Symptoms may include a severe headache of rapid onset, vomiting, decreased level of consci ...
compressing the brainstem. Hydrocephalus may also develop and cause a dangerous increase of
intracranial pressure
Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury (mmHg) and at rest, is normally 7–15 Millimeter of mercury, mmHg ...
. Further possible complications include damage to prevertebral structures (
pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...
, lower cranial nerves) and the
cerebellum
The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...
. Therefore, initial survivors of atlantooccipital dislocation may show severe and variable neurologic deficits, including reversible or irreversible
tetraplegia
Tetraplegia, also known as quadriplegia, is defined as the dysfunction or loss of motor and/or sensory function in the cervical area of the spinal cord. A loss of motor function can present as either weakness or paralysis leading to partial or t ...
, multiple
cranial nerve
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and ...
deficits, loss of consciousness, and recurrent
respiratory
The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...
and/or
cardiac arrest
Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possib ...
s. Children are more likely to survive with neurologic compromise than adults. Isolated cases of near-complete recovery after life-threatening symptoms are known.
In case of posterior displacement of the head, a concomitant fracture of the
atlas
An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth.
Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...
with backward migration of the posterior arch is associated with improved chance of survival, as this allows the spinal cord and
medulla
Medulla or Medullary may refer to:
Science
* Medulla oblongata, a part of the brain stem
* Renal medulla, a part of the kidney
* Adrenal medulla, a part of the adrenal gland
* Medulla of ovary, a stroma in the center of the ovary
* Medulla of t ...
to migrate backward without getting crushed.
Proximal cervical fractures associated with injury
The
Jefferson fracture can be associated with this injury, with the C1 ring, or atlas, being fractured in several places, allowing the spine to shift forward relative to the skull base. The
Hangman's fracture
Hangman's fracture is the colloquial name given to a fracture of both pedicles, or '' partes interarticulares'', of the ''axis vertebra'' ( C2).
Causes
The injury mainly occurs from falls, usually in elderly adults, and motor accidents mainly d ...
which is a fracture of the C2 vertebral body or
dens of the cervical spine upon which the skull base sits to allow the head to rotate, can also be associated with atlanto-occipital dislocation. Despite its eponym, the fracture is not usually associated with a hanging mechanism of injury.
In popular culture
In
Michael Connelly
Michael Joseph Connelly (born July 21, 1956) is an American author of detective novels and other crime fiction, notably those featuring LAPD Detective Hieronymus "Harry" Bosch and criminal defense attorney Mickey Haller.
Connelly is the bes ...
's 2020 thriller novel ''
Fair Warning,'' protagonist
Jack McEvoy
John "Jack" McEvoy is a literary character created by Michael Connelly in the 1996 novel '' The Poet'' and starring again in the sequel '' the Scarecrow'' thirteen years later. In the interim, McEvoy appeared in one Harry Bosch novel – 2 ...
investigates occurrences of atlanto-occipital dislocation. It is later learned that these deaths were at the hands of a
serial killer
A serial killer is typically a person who murders three or more persons,A
*
*
*
* with the murders taking place over more than a month and including a significant period of time between them. While most authorities set a threshold of three ...
, who manually twists the heads of his victims until their necks break and stages their deaths as accidents or suicides.
References
{{DEFAULTSORT:Internal Decapitation
Medical emergencies
Injuries of neck