Clinical Cases - Deep Back & Spinal Cord
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A 25-year-old man is brought into the ER with a high fever, lethargy, and a stiff neck. After taking a history and performing a physical exam, you strongly suspect meningitis. In order to find the causative agent, you order a lumbar puncture. Laboratory analysis confirms your suspicion by showing bacterial growth in the cerebrospinal fluid (CSF). You administer the appropriate therapy and the patient recovers without any complications.
Questions to consider:
- Where along the vertebral column is a needle inserted for a lumbar puncture? Which landmark can you use to find this level?
The spinal cord usually ends at the inferior border of L1 or the superior border of L2. Therefore, inserting the needle between L3 and L4 or L4 and L5 is relatively safe. This level corresponds to the lumbar cistern. The line connecting the top of the two iliac crests, the supracrestal line, passes through the spinous process of the L4 vertebra .
- During a lumbar puncture, the syringe needle is inserted in the midline and within the median plane. Why? What structures, ligaments and others, does the needle traverse before entering the lumbar cistern?
At the level of the lumbar cistern the nerve roots are suspended in CSF and therefore float away from the pressure of the needle. However, as the nerve roots exiting the vertebral canal at this level approach their fixed dural sleeves laterally, they are unable to move freely. Hence it is necessary to remain in the median plane in order to avoid damage to the nerve roots. The needle must pass through the following body layers in order to reach the lumbar cistern : skin, fat, supraspinous ligament, interspinous ligament, between or through the ligamenta flava, epidural fat and veins, dura, subdural space, and arachnoid.
- What position is the patient placed in during this procedure? Justify this anatomically.
The patient is asked to flex his or her back as much as possible during a lumbar puncture, either sitting up or lying on their side in the fetal position . This increases the space between the spinous processes.
- Following the procedure, the patient complains of a severe headache. What is the cause of this complication of lumbar punctures?
The dura mater has a rich supply of pain receptors that respond to stretch and tension. It is believed that the decrease in CSF volume, however small, following a lumbar puncture causes the brain to sag a bit. This stretches the dura, which in turn causes severe headaches. In order to avoid this, the patient is asked to lay down with the head at a slightly lower level than the body (i.e. no pillow).
- Other than obtaining CSF samples, in what other situations are lumbar punctures performed?
A lumbar puncture may also be used for injecting anesthetic agents, as in a spinal block, or injecting of radiological contrast agents.
You are called to evaluate a newborn infant in the labor and delivery room. On physical exam you note that the infant has normal vital signs and appearance with the following exception - you note that the patient has a bulging cyst-like structure approximately 4 cm in diameter protruding from his back . You also note that he has limited movement of the lower extremities and that both feet are plantarflexed and inverted at the ankle.
Questions to consider:
- What are neural tube defects and how often do they occur?Neural tube defects occur on the order of one in every 1000 births, and the incidence varies with regard to geography, ethnicity, and other factors. Most involve an anomaly of the neural arch in which the vertebral column is split in the midline. This anomaly can be associated with a variety of structural involvements which can include the meninges, spinal cord, and can vary according to the site at which closure of the tube fails to occur - cephalic or caudal.
- What types of anatomical structures can be involved with a case of spina bifida?In spina bifida occulta the laminae of one or more vertebrae, typically in the lumbar region, fail to fuse. Usually this defect is covered by skin and frequently is diagnosed by the presence of a tuft of hair over the site of the defect . Spina bifida cystica occurs as a result of the failure of closure of one or more vertebral arches, and frequently this condition allows the herniation of meninges and/or spinal cord.
- How do the various types of neural tube disorders vary in their presentation?The types of neural tube defects vary according to the structures involved: those involving the spinal cord and meninges are known as myelomeningoceles. Involvement of just vertebral arch formation with an outward bulging of the meninges and a normal spinal cord is known as a meningocele . An encephalocele is limited to involvement of the posterior cranium with herniation of brain contents through the opening. Anencephaly is failure of the cranial portion of the neural tube to close, with associated cranial vault malformation.
- What is the cause of spina bifida?The most common cause of spina bifida is failure of neural tube closure at around 4 weeks gestation during embryological development. What causes neural tube defects is generally not known, but there is a larger recurrence risk in families, suggesting a genetic component.
- What other complications are associated with this condition?Depending on the extent of involvement, the patient could develop partial or full paralysis, hydrocephalus, lack of sphincter control, or contractures. These conditions are more likely to occur in a more extensive case such as a myelomeningocele .
- What simple prophylactic therapy can be undertaken prenatally to prevent such defects?Prenatal ingestion of folic acid supplements and continued supplementation during the early pregnancy period has been shown to decrease the incidence of neural tube defects.
Moore's Clinical Anatomy pp. 433 - 495.
Woodburne & Burkel pp. 73-76, 335-356.
Paramedics respond to a report of an 82 year old man unconscious after a fall. They find the patient on the floor in his house in cardiac arrest. His wife said that he fell approximately 18 inches from a lift assist device. The paramedics revive the patient to a normal sinus rhythm using ACLS protocols (Advanced Cardiac Life Support) but the patient remains profoundly unconscious. They fully immobilize his spine and transport him emergently to the hospital.
X-ray, CT, and MRI image studies at the hospital show C1 and C2 fractures with spinal cord injury, resulting in quadriplegia. T2-T4 spinous processes and several left ribs are also fractured. The patient never regains consciousness and dies the next day.
Questions to consider:
- What is the function of the dens of C2, and why are fractures in this region so dangerous?The dens, also called the odontoid process, is the portion of the C2 (the "axis") about which the C1 and the head rotate. Because the dens extends superiorly into the ring of C1, it is subjected to shear forces and fracture from C1 in neck injuries. The dens can then impact the spinal cord, injuring or severing it. In this case, although the patient's spinal cord was not severed, impact from the dens caused a spinal cord hematoma resulting in quadriplegia.
- What is spinal immobilization, and why is it used?You'll learn about spinal immobilization later should you choose a specialty that treats trauma; for now, what's important is that any vertebral fracture has the potential to injure the spinal cord. Spinal immobilization is like splinting the spine to prevent uncontrolled movement of potentially fractured vertebrae - see the picture for an example of an immobilized patient. Vertebral fracture can cause spinal cord injury; spinal cord injury can cause paralysis or death (the more cephalic the injury, the higher the morbidity.)
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