A. Spinal cord hemisection (Brown-Sequard syndrome) [see Figure 8-2E] is caused by damage to the following structures:
1. The dorsal columns [gracile (leg) and cuneate (arm) fasciculi]. Damage results in ipsilateral loss of tactile discrimination and position and vibration sensation.
2. The lateral corticospinal tract. Damage results in ipsilateral spastic paresis with pyramidal signs below the lesion.
3. The lateral spinothalamic tract. Damage results in contralateral loss of pain and temperature sensation one segment below the lesion.
4. The hypothalamospinal tract at T-l and above. Damage results in ipsilateral Horner's syndrome (i.e., miosis, ptosis, hemianhidrosis, and apparent enoph-thalmos).
5. The ventral (anterior) horn. Damage results in ipsilateral flaccid paralysis of innervated muscles.
B. Ventral spinal artery occlusion (see Figure 8-2F) causes infarction of the anterior two-thirds of the spinal cord, but spares the dorsal columns and horns. It results in damage to the following structures:
1. The lateral corticospinal tracts. Damage results in bilateral spastic paresis with pyramidal signs below the lesion.
2. The lateral spinothalamic tracts. Damage results in bilateral loss of pain and temperature sensation below the lesion.
3. The hypothalamospinal tract at T-2 and above. Damage results in bilateral
4. The ventral (anterior) horns. Damage results in bilateral flaccid paralysis of the innervated muscles.
5. The corticospinal tracts to the sacral parasympathetic centers at S-2 to S-4.
Damage results in bilateral damage and loss of voluntary bladder and bowel control.
C. Subacute combined degeneration (vitamin B12 neuropathy) [see Figure 8-2G] is caused by pernicious (megaloblastic) anemia. It results from damage to the following sttuctures:
1. The dorsal columns (gracile and cuneate fasciculi). Damage results in bilateral loss of tactile discrimination and position and vibration sensation.
2. The lateral corticospinal tracts. Damage results in bilateral spastic paresis with pyramidal signs.
3. The spinocerebellar tracts. Damage results in bilateral arm and leg dystaxia.
D. Syringomyelia (see Figure 8-2H) is a central cavitation of the cervical cord of unknown etiology. It results in damage to the following structures:
1. The ventral white commissure. Damage to decussating lateral spinothalamic axons causes bilateral loss of pain and temperature sensation.
2. The ventral horns. LMN lesions result in flaccid paralysis of the intrinsic muscles of the hands.
E. Friedreich's ataxia has the same spinal cord pathology and symptoms as subacute combined degeneration.
F. Multiple sclerosis (see Figure 8-2B). Plaques primarily involve the white matter of the cervical segments of the spinal cord. The lesions are random and asymmetric.
IV. PERIPHERAL NERVOUS SYSTEM (PNS) LESIONS. An example of a PNS lesion is Guillain-Barre syndrome (acute idiopathic polyneuritis, or postinfectious polyneuritis). It primarily affects the motor fibers of the ventral roots and peripheral nerves, and it produces LMN symptoms (i.e., muscle weakness, ascending flaccid paralysis, and areflexia.) Guillain-Barre syndrome has the following features:
A. It is characterized by demyelination and edema.
B. Upper cervical root (C4) involvement and respiratory paralysis are common.
C. Caudal cranial nerve involvement with facial diplegia is present in 50% of cases.
D. Elevated protein levels may cause papilledema.
E. To a lesser degree, sensory fibers are affected, resulting in paresthesias.
F. The protein level in the cerebrospinal fluid is elevated, but without pleocytosis (albu-minocytologic dissociation).
V. INTERVERTEBRAL DISK HERNIATION is seen at the L-4 to L-5 or L-5 to S-l interspace in 90% of cases. It appears at the C-5 to C-6 or C-6 to C-7 interspace in 10% of cases.
A. Intervertebral disk herniation consists of prolapse, or herniation, of the nucleus pul-posus through the defective anulus fibrosus and into the vertebral canal.
B. The nucleus pulposus impinges on the spinal roots, resulting in spinal root symptoms (i.e., paresthesias, pain, sensory loss, hyporeflexia, and muscle weakness).
VI. CAUDA EQUINA SYNDROME (SPINAL ROOTS L3 TO CO) results usually from a nerve root tumor, an ependymoma, a dermoid tumor, or from a lipoma of the terminal cord. Is characterized by:
A. Severe radicular unilateral pain
B. Sensory distribution in unilateral saddle^shaped area
C. Unilateral muscle atrophy and absent quadriceps (L3) and ankle jerks (SI)
D. Incontinence and sexual functions are not marked
E. Onset gradual and unilateral
VII. CONUS MEDULLARIS SYNDROME (CORD SEGMENTS S3-C0) usually results from an intramedullary tumor, e.g. ependymoma. Is characterized by:
A. Pain usually bilateral and not severe
B. Sensory distribution in bilateral saddle^shaped area
C. Muscle changes not marked; quadriceps and ankle reflexes normal
D. Incontinence and sexual functions severly impaired
E. Onset sudden and bilateral
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