Vulnerable spinal segments
These are cord segments which receive blood supply predominantly from one source, and would suffer vascular insufficiency if the source is occluded. The upper thoracic (T1-T2) and first lumbar spinal segments are among the most vulnerable regions. The intercostal arteries do not interconnect with other arteries, in the same way as the arteries of the cervical and lumbar regions do. Thus occlusion of one intercostal artery in a vulnerable region can result in spinal cord infarction.
Spread of malignancy to the central nervous system
There are free venous connections between the external segmental veins and the internal vertebral venous plexus which is devoid of valves. Therefore, malignancies for example of the prostate, the breast and the thyroid may freely spread haematogenously, to the vertebral column, and central nervous system, including the brain.
Localization of spinal cord lesions
Can be done in two ways:
A) Testing for impairment or loss of cutaneous sensation . Cutaneous areas supplied by adjacent spinal nerve overlap. For example, the upper half of the area supplied by T6 is also supplied by T5, while the lower half of this area is also supplied by T7.
b) Reflex contraction of muscles . The segments involved in the more commonly tested stretch or tendon reflexes are as follows:
Biceps reflex, C5 and C6;
Triceps reflex, C6 through C8;
Quadriceps reflex, L2 through L4;
Gastrocnemius reflex, S1 and S2.
Insertion of a needle into the subarachnoid space in the lumbar region. Commonly done to obtain a sample of cerebrospinal fluid, for diagnosis of meningitis. There is little danger that the spinal puncture needle will damage the cord if it is inserted between the arches of the third and fourth lumbar vertebrae. It may also be done to introduce drugs, dyes, air etc.
The needle traverses the following structures
Skin and subcutaneous tissue
Supraspinuous and interspinuous ligaments
Dura and arachnoid matter
Only a small amount of CFS should be withdrawn to avoid creating negative pressure in the lumbar region which may cause herniation of cerebellum and medulla down foramen magnum.
In anterior spinal artery (ASA) syndrome, occlusion of the ASA, affects ventral horns and tracts in the ventral and lateral columns. These include corticospinal and spinothalamic tracts. Its features include:
Bilateral lower motor neuron deficits
Bilateral upper motor neuron deficits
Cauda equina Syndrome (CES)
This results from compression of the cauda equina. It presents with:
Low back pain
Bilateral lower limb pain with motor and sensory deficits
Perineal sensory and motor deficit
Genitourinary dysfunction with overflow incontinence or retention