The Spinal Cord and its Lesions

7/28/2019 The Spinal Cordand its Lesions

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Spinal CordAnatomy

(Return to Lesions Front Page)Below the brainstem is the elongated, segmented spinal cord and its associated dorsal andventral roots which merge to form spinal nerves. Some disorders are confined to the spinalcord while others may include its roots; injuries to these structures produce a number ofdistinctive syndromes. The features of spinal cord disorders reflect its anatomy andphysiology, i.e., ascending sensory tracts, descending motor systems, sensory afferent fibersand the nuclei receiving incoming sensory information, nuclei giving rise to exiting motorfibers, and the reflexes which result from the interaction of all these elements.

A. Anatomy:

1) Dorsal roots feed a variety of sensory fibers carrying information to synapse in the dorsalgray horn nuclei and form the ascending pathways, e.g., nucleus proprius and Clarke's

column; some fibers ascend without synapsing: ascending pathways include:

a) the posterior white column - conscious proprioception, discriminative touch and vibratorysense - fibers ascend uncrossed without synapsing.

b) the anterior and lateral spinothalamic tracts - after synapsing in the nuclei of the dorsalgray horn, pain, temperature and light touch fibers cross in the anterior white commissure toascend.

c) the posterior spinocerebellar tract - "unconscious" proprioception from the lower extremity,incoming fibers synapse in Clarke's column of the dorsal gray horn and ascend withoutcrossing; upper extremity fibers ascend uncrossed without synapsing, in the posterior whitecolumn, to finally synapse in the ipsilateral accessory cuneate nucleus of the medulla.

2) Ventral roots from all spinal cord segments carry fibers from anterior horn cells to controlvoluntary muscle. Ventral roots from thoracolumbar and sacral regions also carrypreganglionic autonomic fibers from cells of the intermediate gray for control of the viscera.

a) the lateral corticospinal tract (along with the lateral reticulospinal tract) helps control theanterior horn cells for skeletal muscle volitional motor activity.

b) the lateral vestibulospinal tract (along with the medial reticulospinal tract) helps control theanterior horn cells and are especially important in the reflex control of skeletal muscle.

c) descending autonomic fibers descend (mixed with the lateral corticospinal tract) for thecontrol of the preganglionic autonomics responsible for visceral functions.
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1) HEMISECTION OF THE SPINAL CORD (BROWN-SEQUARD SYNDROME)

Pure hemisection of the cord rarely occurs but it is among the best cases for illustrating thefeatures of spinal cord injury.

Briefly stated, symptoms include: spastic paralysis, loss of position sense, discriminative

touch and vibratory sense on the side of the lesion - this represents involvement of the lateralcorticospinal tract and the posterior white column on the side of the lesion. On the sideopposite the lesion there is a loss of pain and temperature due to involvement of the lateralspinothalamic tract. At times, it is possible to also demonstrate a bilateral sensory deficit andflaccid paralysis at the level of the lesion.

A Sample Case: A young woman complained of pain in her left breast and progressiveweakness of her left lower limb for a period of many months before finally visiting herphysician.

The neurologic evaluation revealed weakness in the left lower limb. This was associated withspasticity (increased tone), hyperreflexia (increased deep tendon reflexes) at the knee and

ankle, which also demonstrated clonus. On the left side there was loss of two-point touch,vibratory sense and proprioception at levels below the hip. The right side showed a loss ofpain and temperature sensation below dermatome T-7.

The patient was determined to have an extramedullary tumor expanding from the dorsal rootsat spinal cord levels T-5,6.

Explanation -

Ipsilateral paralysis below the lesion. Paralysis is the "Upper Motor Neuron" or spastictype; there is spasticity, slow (disuse) muscle atrophy, hypertonia, ankle clonus and a positiveBabinski sign. Superficial reflexes, e.g., the abdominal and cremasteric are lost. Spastic

paralysis is attributed to interruption of the lateral corticospinal tract and the accompanyinglateral reticulospinal tract. Loss of these upper motor neurons deprives the anterior horn cells,i.e., lower motor neurons, of the impulses which generate contraction of skeletal muscle,hence, weakness (paresis) or paralysis. Hypertonia and hyperreflexia appear to result fromloss of the inhibitory effects of these two descending motor pathways on the stretch reflexes,leaving them hyperexcitable to segmental muscle afferents .

It may be possible to also demonstrate a "Lower Motor Neuron Syndrome" or flaccid paralysisipsilaterally at the level of the lesion. If the anterior horn cells supplying the skeletal musclesare injured at the level of the lesion then these muscles are denervated. This paralysis is ofthe flaccid type; muscles undergo rapid atrophy due to loss of the trophic influence of thenerves as well as disuse. Tone and tendon reflexes are diminished since they are reflexresponses and the injured lower motor neurons are the "final common pathway" to the muscle

in the stretch reflex, hence, there is no reflex.

Loss of conscious proprioception, two-point discrimination and vibratorysense ipsilaterally is due to interruption of the posterior white columns (fasciculusgracilis/cuneatus). This is frequently accompanied by a Romberg sign. A normal individual,standing erect with heels together and eyes closed, sways only slightly. Stable posture isachieve by 1) a sense of position from the vestibular system, 2) awareness of the positionand status of muscles and joints by conscious proprioception and 3) visual input regardingour position. Closing the eyes has only slight effect on the normal individual's stance since thevestibular and conscious proprioception systems are sufficient. In a patient with an impairedposterior column conscious proprioception is diminished; when the eyes are closed loss ofboth systems renders the patient unstable and they are likely to sway or fall to the side.

Pain and temperature sensation is lost below the lesion, on the opposite sidebeginningabout one dermatomal segment below the level of the lesion. These sensations are carried by


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the lateral spinothalamic tract whose fibers originated on the sideopposite the lesion butwhich crossed in the anterior white commissure. Dorsal root afferents carrying pain andtemperature synapse in the dorsal gray; the second order neuron crosses in the anteriorwhite commissure along an ascending path for a distance of about one spinal segment.Because of the oblique ascent of the crossing fibers in the anterior white commissure, injuryof the spinothalamic tract is not likely to be carrying sensation from that level.

A careful sensory evaluation may reveal that at the dermatomal level of the lesion there is abilateral loss of pain and temperature sensation. Since the second order neurons from bothsides cross in the midline below the central canal, a hemisection of the cord may interrupt thecrossing fibers from both sides and produce this limited bilateral deficit.

The pain in the left breast was the result of the pressure of the tumor on the dorsal root.

2) TRANSECTION OF THE CORD

Transection most frequently results from trauma but it can be associated withvascular infarction or hemorrhage, compression, demyelinating orinflammatory lesions. Shearing or compressing the cord produces destructionof the gray and white matter. Pathologic changes are maximal at the level ofthe lesion but injury extends above and below the lesion for a segment or two.The final clinical outcome is a result of the irreversible structural damage andfunctional disorders created.

A Sample Case: A healthy man of 50 years of age was thrown from hishorse. He was immediately rendered quadriplegic (paralyzed in all fourextremities) and described a numb feeling from the neck on down. He neverlost consciousness.

The immediate neurologic exam revealed flaccid paralysis of all fourextremities and no deep tendon reflexes could be demonstrated. All sensationwas absent bilaterally from his arms on down. Some weeks after the accidentthe limbs showed signs of spastic paralysis with markedly increased deeptendon reflexes but there was no return of sensory function. Bowel andbladder control were lost.

X-ray examination showed severe fractures and displacement of the C5,6vertebrae.

Explanation -

"Spinal shock". As a result of a rapid and complete transection there iscomplete loss of voluntary movement and sensation from levels below thecord lesion and loss of all reflexes in the isolated cord segments. This iscalled "spinal shock" and its duration can vary, 1 to 6 weeks is common. Asthis phenomenon fades it may be replaced by heightened flexor reflex activityin which exaggerated deep tendon reflexes occur in response to noxious oreven trivial stimuli. A mass reflex may develop in which slight stimuli elicitsevere bilateral flexor spasms of the arms and legs accompanied byevacuation of the bowel and bladder, profuse sweating and even priapism (a

sustained reflexogenic erection). Reflex emptying of the bowel and bladdermay also begin at this time. Autonomic reflex activity is also heightened and


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so filling of the bladder or rectum may result in increased sweating, flushing ofthe face, piloerection, shivering, slowing of the pulse, elevation of bloodpressure, etc. After 6 -12 months many of the exaggerated reflex responseswane. The mechanisms underlying all of the phenomena of spinal shock arenot completely understood. In general, the initial loss of all reflexes is thought

to be due to the effect of the sudden withdrawal of all supraspinal influenceson the segments of the cord below the lesion. After a period of time thesegmental reflex arcs reappear and become supersensitive to segmentalsensory information, the effects of which easily spread to adjacent cord levels.The reflex responses are now operating without the usual controls impartedby the now absent descending pathways.

Spastic paralysis follows the period of spinal shock. At first only a positiveBabinski sign occurs; later the other signs appear, e.g., increased muscletone, heightened deep tendon reflexes, disuse (slow) atrophy of muscle, andloss of superficial (abdominal and cremasteric) reflexes below the level of the

lesion.

There is loss of all sensation bilaterally below the level of the lesion: lossof proprioception, vibratory sense, tactile discrimination, pain, temperature,light touch, and visceral sensibility. All sensory tracts are immediately severedand if the lesion is in fact complete there is no recovery.

Autonomic disturbances include bowel and bladder functions. Initially, thereis retention of urine and feces, which are no longer under voluntary control.Since ascending sensory pathways are interrupted there is no awareness ofbowel or bladder fullness. After several weeks hypertrophy of the smoothmuscle overcomes sphincter resistance so emptying occurs when eventuallythose organs become overfilled (overflow incontinence). Even if there was anawareness, the absence of the descending tracts would preclude volitionalcontrol. Eventually, the bowel and bladder empty on a segmental automaticbasis reflexly, when they become full. Cutaneous blood vessels in the areasbelow the lesion do not respond to hot or cold stimuli. Horner's syndrome(ptosis, miosis, anhydrosis) also is likely, due to the loss of the descendingautonomics which are scattered among the lateral corticospinal tract fibers inthe cord.

A careful sensory evaluation may reveal that at the dermatomal level of thelesion there is a bilateral loss of pain and temperature sensation. Since thesecond order neurons from both sides cross in the midline below the centralcanal, a hemisection of the cord may interrupt the crossing fibers from bothsides and produce this limited bilateral deficit.

3) SYRINGOMYELIA

Syringomyelia refers to a cavitation of the cord characteristically originating in the centralcanal. The condition is frequently of congenital origin, however, it may result from defects inthe vasculature, neoplasms, trauma, etc. Degeneration often occurs in the central canal of thecervical cord and progresses peripherally in an irregular fashion. Generally, the cavitation first

affects the crossing spinothalamic fibers in the anterior white commissure producingsegmental loss of pain and temperature sensation. As the cavitation extends it may involve


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varied structures depending on the direction of the expansion. It may expand to involve theanterior horn with segmental signs of lower motor neuron disease; if the intermediolateral cellcolumn is involved there may localized autonomic effects. When syrinx proceeds dorsally itmay affect the posterior white columns leading to loss of discriminatory touch andproprioception below the level of the cavity.

A Sample Case: A 30 year old man noticed a weakness of his right hand which wasprogressing and causing him problems serious enough to seek medical attention.

On examination he demonstrated bilateral weakness, atrophy, and fasciculations of theintrinsic muscles of his hands and shoulders. Upper motor neuron syndrome signs, i.e.,weakness, hypertonia, hyperreflexia, positive Babinski, were evident in both lowerextremities. Dermatomes C-2 through T-6 demonstrated bilateral loss of pain andtemperature sensation. There was bilateral impairment of position and vibratory sense belowthe hips.

MRI investigation showed a central cavitation at C-2 through T-7 which expandedsymmetrically in all directions. It involved the anterior white commissure (spinothalamic fibers)

and included portions of the posterior white columns, lateral white funiculus, and anterior grayhorns.

Explanation -

Weakness in the right hand was the major complaint but the neurologic exam demonstratedweakness, atrophy and fasciculation indicative of lower motor neuron disease, i.e., anteriorhorn cells, in both hands.

Though the patient had not noticed loss of pain sensation in his hands the loss couldbe demonstrated upon testing; apparently there was enough sparing of the crossing fibersof the spinothalamic tracts to make the effect less noticeable.

Though the patient did not complain of weakness of the lower extremity, there were uppermotor neuron syndrome symptoms, e.g., hyperreflexia and Babinski sign, indicating someinvolvement of the lateral white funiculus containing the lateral corticospinal and lateralreticulospinal tracts.

The unrecognized loss of vibratory sensation from the lower extremity indicates someimpact on the fasciculus gracilis.

4) VASCULAR DISEASES - ANTERIOR SPINAL ARTERY SYNDROME

The spinal cord is not as susceptible to vascular disorders as the brain but infarction andhemorrhage do occur. Damage from such lesions reflects the pattern of the blood supply

where a) posterior spinal arteries supply the dorsal part of the cord, 2) anterior spinal arteriessupply the anterior 2/3rds of cord, and 3) the arterial vasocorona in the pial plexus suppliesthe periphery of the anterolateral cord.

A Sample Case: A sudden bilateral weakness of the legs occurred in a young womancausing her to seek medical attention.

The neurologic exam revealed bilateral loss of pain and temperature sensation in the legswithout loss of discriminative touch or vibratory sense. At first the lower limb paralysis wasflaccid and areflexic but after several weeks spasticity, hyperreflexia, and Babinski signsappeared. After an initial period of incontinence bowel and bladder control was regained.

Explanation-


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Spinal shock - An infarction of the anterior spinal artery usually involves the gray and white

matter (less frequently only the gray) of the anterolateral cord. The suddenness of the lesionleads to "spinal shock" and hence the voluntary and involuntary paralyses and areflexia.

With recovery from spinal shock you might expect to see evidence of lower motor neuronsigns at the level of the lesion with upper motor neurons signs below. Recovery of bowel and

bladder function indicates some sparing of the descending autonomic fibers which are in thelateral white funiculus, perhaps due to vessels of the pial plexus.

The sensory signs, i.e, bilateral loss of pain and temperature sense, are indicative of injuryto the spinothalamic tracts in the lateral white funiculi with sparing of the posterior whitecolumnswhich are supplied by the posterior spinal arteries.

5) DEGENERATIVE DISEASES - POLIOMYELITIS

Such diseases include a spectrum of disorders in which lesions may be widely disseminatedor may more specifically affect certain tracts or cell groups. Examples include: poliomyelitis(viral) which attacks anterior horn cells; amyotrophic lateral sclerosis (etiology unknown) in

which anterior horn cells as well as the corticospinal tracts are involved; tabes dorsalis(syphilis due to a spirochete infection) where there is involvement of the posterior whitecolumns and the dorsal roots; posterolateral sclerosis (a nutritional deficiency diseaseassociated with pernicious anemia) involving the corticospinal tracts and posterior whitecolumns; Friedreich's ataxia (an hereditary disorder) shows degenerative changes of theposterior columns, spinocerebellar tracts, lateral white funiculus and cerebellum.

A Sample Case: In the days before the polio vaccine, a 9 year old boy developed fever,headache, malaise, stiff neck, and increasing weakness of the left arm. He was admitted tothe hospital where examination revealed nuchal rigidity, a flaccid paresis with musclefasciculation, hypotonia and hyporeflexia of the left upper extremity which was mostpronounced in the biceps and deltoid muscles. Clinical diagnosis was poliomyelitis withinvolvement limited to the anterior horn cells on the left side, principally in the C-5,6

segmentsof the cord.

Explanation -

Flu-like symptoms of increased temperature, muscle ache, headache, sore throat, etc., mayaccompany the initial phase of the viral infection. After subsiding, these initial signs may recuralong with the CNS symptoms. Stiffness of the neck on forward flexion (nuchal rigidity)indicates inflammation of the meninges. These preparalytic signs may resolve without furtherincident. However, muscle weakness may occur during the fever stage; the weakness may belimited to the spinal cord as in this case or also involve the brainstem. Lower motor neuronsigns, e.g., coarse fasciculations are seen as the muscles weaken; atrophy and hypotonia aredetectable within 3 weeks of onset due to the killing of anterior horn cells.

5) DEGENERATIVE DISEASES - AMYOTROPHIC LATERAL SCLEROSISA Sample Case: A 30 year old man noticed that he was having trouble buttoning his shirt andbegan to drop items from either hand during a period of several months.

A neurologic exam demonstrated weakness in all tests of motor strength in both of his hands.In addition, there was atrophy of the intrinsic muscles of the hand and fasciculations could beseen. There were hyperactive deep tendon reflexes upon testing of the biceps, patellar, andankle reflexes.

Explanation -

Typically, this disease first manifests itself as uselessness of the hand and awkwardness offine finger movements. Slight atrophy of the hand usually accompanies this clumsiness along


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with fasciculations in the hand and arm. These are all signs of irritation and death of anteriorhorn cells. Increasing spasticity and hyperreflexia of the arms and then the legs indicateinvolvement of the tracts of the lateral white funiculus, e.g., lateral corticospinal tract. In time,the symptoms of atrophy spread to include the muscles of the neck, tongue, pharynx, larynxand trunk. Usually control over the sphincters is maintained.

5) DEGENERATIVE DISEASES - SYPHILIS (TABES DORSALIS)

A Sample Case: A 60 year old female complained of "shooting" pains in the legs and

enlargement of the knee joints for about 2 years. Her physician said that she had severearthritis. The patient began to experience difficulty walking in the dark and urinaryincontinence and sought other medical advice.The neurologic exam demonstrated Argyll Robertson pupils and radiographs of the kneeswere consistent with arthritic "Charcot type" joints. The patellar and ankle reflexes wereabsent and there was loss of vibratory and position sense in the lower extremity. The patient's

ataxia was evident as she walked with a broad-based gait. She was very nervous whenasked to walk or stand with her eyes closed and demonstrated the Romberg sign.

Explanation -

Syphilis is caused by the spirochete Treponema pallidum which may invade the CNS 3 - 18

months after infection. Even when clinical symptoms are referable to only one part of thenervous system post-mortem examination reveals diffuse changes in both the brain andspinal cord. In its most severe form there is progressive mental and physical deterioration.The neurologic symptoms of tabes dorsalis usually develops 15 - 20 years after infection.

Ataxic gait and hyporeflexia are caused by purely sensory deficits due to irritation and

destruction of the sensory afferents in the lumbosacral dorsal roots, affecting the incomingheavily myelinated proprioceptive fibers (later seen as demyelination in the posterior whitecolumns). Dorsal root inflammation produces bouts of shooting pains, most common in thelegs but they "roam" over the body from the feet to the face. Other paresthesias are describedand are associated with impairment of pain, temperature and touch sensation; there is alsosensory impairment from the bowel and bladder (S-2,3) accounting for the incontinence.

"Charcot joints" is a neuropathic arthritis, a severe form of osteoarthritis. The arthritic kneejoints result from the relative insensitivity of the joints, due to destruction of the dorsal rootfibers, and the resultant repeated injury; remaining pain fibers however were still sufficient topermit painto occur. Charcot joints occur in less than 10 percent of tabes patients.

About 90 percent of the patients exhibit the Argyll Robertson pupils in which the pupils fail to

constrict in reactionto light but constrict during convergence when the focus moves from a farto a near object. The cause of this response is unknown but there are usually additional signsof ophthalmoplegia and optic atrophy.

5) DEGENERATIVE DISEASES - POSTEROLATERAL SCLEROSIS

A Sample Case: A 43 year old woman complained of increasing weakness of the legs anddifficulty walking which developed over a period of 9 months. She felt numbness and tingling(paresthesia) in her hands and feet.The neurologic exam revealed loss of position and vibratory sense in both lower extremities.The patient stood and walked clumsily on a wide base and demonstrated the Romberg sign.

There was paresis in the lower extremities, with hypertonia, hyperreflexia, and positiveBabinski signs. Obvious motor signs in the upper limb were not demonstrated.


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Lab studies indicated anemia and a blood smear showed large RBCs (macrocytes). Studiesof stomach contents showed a small volume of gastric secretions and a higher than normalpH. The Schilling test, measuring absorption of vitamin B12, showed a decrease.

Explanation -

Neurologic findings of faulty proprioception and paresthesia indicate involvement of theposterior white columns; motor findings indicating upper motor neuron disease implicate thecorticospinal tract.

The pathology is diffuse, usually symmetrical, and sometimes involves the legs before thearms. There is degeneration of myelin sheaths followed by death of the axons. Thesechanges are scattered irregularly and usually begin in the cervical and upper thoracicsegments and then spread up and down the cord.

Laboratory findings of megaloblastic anemia suggest the disease of pernicious anemia. Thisis usually caused by an atrophic gastric mucosa which fails to secrete intrinsic factor resultingin failure to absorb sufficient quantities of vitamin B12 as required for effective erythropoiesis.

B12 is also an important co-factor in synthesis of fatty acids, important building blocks of cellmembranes and hence myelin; this may be the basis of the neurologic findings.

5) DEGENERATIVE DISEASES - FRIEDREICH'S ATAXIA

A Sample Case:A 15 year old boy was referred to a neurologist when he complained of

difficulty in running and developed a staggering gait, poor articulation in speech andclumsiness in the hands during an 8 month period. These symptoms were recalled to be likethat of his uncle who became similarly disabled in his early 20's and confined to a wheelchairbefore finally becoming bedridden.The physical examination revealed an unsteady, broad-based stance and sudden lurching

when walking which was accompanied by a "slapping" sound made by the feet. Loss ofvibratory and position sense was observed bilaterally in all extremities. There was a tremor ofthe upper extremity as the patient reached for objects. Speech was slurred, slow and with anuneven pattern. Hyporeflexia was present but there was only a slight indication of muscleatrophy though there were bilateral Babinski signs.

Explanation -

The findings of the exam indicate an ataxia of the sensory as well as cerebellar type; thereare also indications of corticospinal tract disease. The broad-based, unsteady stance and gaitare consistent with posterior white column disease as well as cerebellar disease. Slapping ofthe feet, to auditorily supplement sensory feedback, is consistent with patients deprived ofconscious proprioception. Decreased or abolished tendon reflexes is usual with sensory

deprivation due to degeneration of the dorsal roots, as occurs with posterior white columndegeneration. Intention tremor and slurred speech is characteristic of patients with cerebellardisease.

Positive Babinski signs indicate involvement of the corticospinal tracts. In this disorder thereis usually a foot deformity called pes cavus in which there is hypertonia resulting in a highplantar arch with retraction of the toes at the metatarsal-phalangeal joints.

Pathologic examination of the cord in Friedreich's ataxia indicate a small cord withdegeneration in the posterior white columns, corticospinal and posterior spinocerebellartracts. The motor cortex and cerebellum also show loss of cells. This is a hereditaryprogressive ataxia. About half the cases appear before the age of 10 and within 5 years of

onset walking is no longer possible. There are two patterns of inheritance, one dominant theother recessive. Males are somewhat more susceptible.


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5) DEGENERATIVE DISEASES - INFANTILE MUSCULAR ATROPHY (WERDNIG-HOFFMAN'S DISEASE)

A Sample Case:

A woman with two prior pregnancies reported that the fetal movements of her third baby were

less vigorous than previous fetuses. At birth the baby was weak and limp, the cry and suckingmovements feeble, and respiratory movements ineffective. The baby died at 6 months.

Neurologic examination showed the baby was hypotonic and weak. Muscle fasciculationswerepresent but not visible, except for those of the tongue, because of the covering adipose

tissue. Tendon reflexes were absent but normal sensory responses to pain, temperature, andtouch were present.

Explanation -

The anterior horn cells in the spinal cord and major motor nuclei of the brainstem aredegenerative, dying, and reduced in number. Other systems of neurons are not affected.

This is a form of infantile, hereditary, progressive, non-myopathic muscular atrophy due todeath of the anterior horn cells. An adult form of this hereditary muscular atrophy, whichsimulates muscular dystrophy but is due to death of anterior horn cells, is the Kugelberg-Welander syndrome.

The Spinal Cord and its Lesions

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