Carlos Ballario and Ma. Eugenia Ferri
No review on spinal cord pathology would be valid if there were no clear concepts about its anatomy, systematization and vascularization. It is for this reason that we will briefly review them.
We call the spinal cord the part of the neuraxis that occupies the spinal canal. It takes the form of a long cylindrical stem, somewhat flattened from front to back, which extends from the occipitoatloid joint, where it continues upwards with the bulb, to the lower border of the first lumbar vertebra.
It presents two fusiform thickenings in its path, the upper one corresponds to the exit of the nerve roots destined for the upper limbs (Brachial Plexus) between the third cervical and the second dorsal vertebra, and the lower one to the exit of the roots for the limbs lower (lumbosacral plexus) between the ninth and twelfth dorsal vertebra.
31 pairs of nerves originate from the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, and 5 sacral. The medulla is further divided into overlapping transverse segments known as metamers and centered by the spinal pairs that "metamerically" innervate the body; they are named according to the vertebrae through which each pair comes out. (fig. 1)
A cross section of the medulla allows to see in the center the gray matter, which takes the shape of an H, whose horizontal branch constitutes the gray commissure, crossed in its middle part by the canal of the ependyma and whose vertical branches have the shape of two half moons.
The anterior parts of these vertical branches constitute the anterior antlers and the posterior parts, the posterior antlers. The anterior horns contain the bodies of the peripheral motor neurons, whose cylinders emerge from them and form the anterior roots. Between the anterior and posterior horns there is a small portion of gray matter called the intermediate lateral column, made up of fibers that belong to the sympathetic nervous system.
The posterior horn reaches the extensions of the ganglion cells that form the posterior roots.
The medullary gray matter is totally surrounded by white matter; the latter is divided into two lateral and symmetrical halves by the medioventral and mediodorsal sulci.
Each half of the white matter is divided by the anterior and posterior roots into three cords: anterior, lateral and posterior; the first two are usually considered together as a lateral intermediate chord. These cords are made up of myelinated nerve fibers of two kinds:
Long: relate the medulla to other portions of the neuraxis
Short: join medullary segments to each other
This is how the spinal cords are systematized in a series of bundles or fascicles that have a specific function. (Fig. 2)
Regarding the vascularization of the cord, the cervical region receives irrigation from the anterior spinal artery, a branch of the vertebral arteries, while the dorsal region is fed by radicular branches of the intercostal arteries. At the lumbar level, at the level of D12-L2, the Aorta gives rise to the Adamkiewicz artery, from which arises the anterior medial spinal artery that supplies two thirds of the lumbar thickening. Finally, from the Hypogastric or Obturator arteries, the Ascending Sacra artery that supplies the sacral medulla and the cauda equina.
Complete spinal cord transection
Complete injuries interrupt the entire tracts, altering motor and sensory functions below the level of injury. All sensory modalities (touch, position, vibration, temperature and pain) are abolished and depending on the height of the spinal cord involvement (cervical or dorsal) the patient will present tetraplegia (loss of motor function of the 4 limbs) or paraplegia (loss of the motor function of the lower limbs), which at the beginning will be flaccid and areflexic, constituting the so-called “Spinal Shock”.
Later, spasticity, hyperreflexia, bilateral Babinski's sign, and loss of abdominal cutaneous reflexes will develop. In all cases, bladder and rectal sphincter dysfunction will appear, initially atonic and later spastic. There is sexual dysfunction, anhidrosis, trophic changes of the skin, disorders in thermal control, and vasomotor instability below the injury.
Etiology : the most common are vertebro-spinal trauma, multiple sclerosis, post-infectious myelitis, medullary vascular disorders.
Hemisection of the spinal cord (Brown Sequard syndrome)
It is characterized by:
Loss of thermal and pain sensitivity contralateral to hemisection
Loss of proprioceptive function on the same side and below the injury
Paralysis or spastic paresis ipsilateral to the injury due to interruption of the corticospinal tract
At the level of the lesion, there are segmental sensory and lower motor neuron signs due to damage to the dorsal and ventral roots.
Etiology : traumatic or extramedullary tumor lesions.
Central spinal cord injuries
The spinothalamic fibers that carry thermal and painful sensations and that are decused in the anterior commissure are those that are affected first. This produces thermo-anesthesia and suspended analgesia in the patient, with unilateral or bilateral distribution and with preservation of tactile and proprioceptive sensitivity (dissociated anesthesia). When the process extends centrally, the motor neurons of the anterior horns are compromised, with consequent segmental paresis, atrophy, and areflexia.
Etiology : when the picture is acute it is due to trauma or hematomyelia. If it is of gradual and chronic development, it is observed in cases of syringomyelia and intramedullary tumors.
Posterior Cord Cord Syndrome
Damage to the posterior columns produces disturbances in positional and vibrational sensitivity. As a consequence of the interruption of proprioceptive information, the patient presents an ataxic gait.
The so-called Lhermitte's sign may appear, which consists of the appearance of a sensation of electric discharge that spreads along the spine and lower limbs when flexing the neck.
Etiology : tabes dorsalis (neurosyphilis), demyelinating lesions, extramedullary tumors (primary or metastasis).
Anterior horn syndromes
They present clinically with muscle weakness, atrophy, and twitching in the muscles of the extremities and trunk. Muscle tone is decreased and tendon reflexes are diminished or absent. Sensitivity is normal. The most common causes are: spinal muscular atrophies, polio.
When there is also involvement of the corticospinal tracts and the nuclei of the cranial nerves, the aforementioned lower motor neuron signs are added to the upper motor neuron signs.
Thus, the patient will present weakness of the muscles innervated by the affected cranial nerves and of the 4 limbs, fasciculations, hyperreflexia and Babinski's sign. Sensitivity is normal and there is no sphincter involvement. The most common cause is Amytrophic Lateral Sclerosis.
Complete anamnesis : that allows to collect a detailed history, in terms of time of evolution, sequence in the appearance of symptoms, personal history of the patient, habits, family history.
Complete general and neurological physical examination : investigating in detail cranial nerves, mobility and strength, superficial and deep sensitivity, cutaneous-abdominal, osteotendinous and plantar reflexes. Look for the sign of Lhermitte.
Radiology : useful in vertebral medullary trauma to determine the presence of vertebral fractures, with or without displacement.
Electromyography : of choice in case of suspected motor neuron disease.
Nuclear Magnetic Resonance : it is the method that gives direct information about the spinal cord. Provides descriptive information on ligament injuries, canal involvement, bone fragments, traumatic disc hernias, epidural hematomas, and subluxations. It allows direct examination of the spinal cord and detects the presence of transection, hematomyelia, contusion, edema, ischemia, and subarachnoid space problems.