Structural and topical anatomy of the lower segments
The lower segments of the spinal cord have a complex topography that determines the clinical presentation in pathologies:
- Epiconus: encompasses segments L4–S2.
- Conus medullaris (conus medullaris): includes segments S3–Co.
- Cauda equina (cauda equina): a bundle of roots of the lumbar, sacral, and coccygeal segments running in the subarachnoid space.
The segmental level of the spinal cord is significantly higher than the level of the vertebral bodies, which is important to consider when assessing injuries.
Spinal circulation disorders
Acute ischemia in the basin of the anterior spinal artery leads to spinal cord infarction.
The clinical presentation is dominated by:
- Flaccid paraplegia and sphincter dysfunction (bladder and rectum).
- Pronounced impairment of pain and temperature sensitivity.
- Preservation of proprioceptive sensitivity due to the functioning of posterolateral vessels.
Compression syndromes and tumors
Space-occupying processes are classified in relation to the cord and meninges:
- Extradural tumors: grow rapidly and cause severe compression with spastic paresis.
- Intradural extramedullary tumors: often originate from the dorsal roots, causing radicular pain and ascending sensory disturbances.
- Intradural intramedullary tumors: are characterized by early pelvic disorders and dissociated sensory disturbances.
Radicular syndromes in degenerative diseases
Nerve root lesions are most commonly associated with osteochondrosis and disc herniations. In the intervertebral foramina, the roots undergo mechanical compression.
Clinical manifestations include:
- Intense pain and hypoesthesia in the area of the corresponding dermatome.
- Weakness in indicator muscles and decreased reflexes.
- Absence of autonomic disorders in the limbs, since sympathetic fibers join distally to the roots.
Briefly: answers to topical questions
What are the classical clinical signs of central paralysis?
Central spastic paresis syndrome includes a decrease in muscle strength and a spastic increase in muscle tone. There is a pathological increase in tendon reflexes, manifested by hyperreflexia, as well as the presence of pathological reflexes. Superficial reflexes are reduced or absent. Muscle atrophy is absent in the initial stage, and in later stages, a mild degree of hypotrophy due to disuse may develop.
What are the classical clinical signs of peripheral paralysis?
Disruption of the reflex arc in a peripheral motor neuron lesion leads to a characteristic complex of clinical signs. The main manifestations are a sharp decrease in muscle strength up to plegia, as well as pronounced muscle hypotonia or complete atonia. Hyporeflexia or complete areflexia of deep reflexes is observed. Pronounced muscle hypotrophy and atrophy develop in the affected muscles, accompanied by decreased excitability and trophic changes.
Which muscles act as indicators in L5 root compression?
For topical diagnosis of an L5 lumbar nerve root lesion, certain indicator muscles are identified whose innervation is predominantly associated with this segment. These include the extensor hallucis longus and extensor digitorum brevis. Damage to these muscle groups is important when assessing radicular syndromes.
What types of sensitivity are impaired in lesions of the posterior columns of the spinal cord?
Damage to the posterior columns of the spinal cord leads to isolated impairment and loss of proprioceptive deep sensitivity, including joint-position sense. Stereognosis, vibration, and discriminative sensitivity are also lost. The clinical consequence of this is the development of sensory ataxia, manifested by instability and swaying in the Romberg pose.
The epiconus (L4-S2) is responsible for the legs, the conus (S3-Co) for the pelvis and perineum, and the cauda equina gathers the roots below.
Class and exam questions
What is the difference between the manifestations of cauda equina and conus medullaris tumors?
A cauda equina tumor causes uneven progression, radicular pain in the sciatic nerve, and flaccid paresis. A conus medullaris tumor produces early pelvic disorders and sensory disturbances in the perineal region without leg paresis.
Why is deep sensitivity preserved during a stroke in the anterior spinal artery basin?
The dorsal parts of the spinal cord are supplied with blood from posterolateral vessels, so the proprioceptive pathways in the posterior columns do not undergo ischemia.
Why are there no autonomic disorders in the limbs during an isolated radicular syndrome?
Autonomic fibers join the peripheral nerves distal to the level of the nerve roots, so they remain intact during a radicular lesion.
What else to study on this topic
- Anatomic structure of the meninges and spaces of the spinal cord
- Differential diagnosis of intramedullary and extramedullary tumors
- Features of craniocervical junction tumors
- Pathogenesis of spondylarthrosis and uncovertebral arthrosis
- The role of indicator muscles in topical diagnosis
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