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Chapter 42: Neurosurgery

Electromyography (EMG) and nerve conduction studies (NCS) are useful for assessing the function of

A. Peripheral nerves

B. Bilateral carotid arteries

C. Intracranial liquids

D. Spinal nerves

Answer: A

Electromyography and nerve conduction studies (EMG/NCS) are useful for assessing the function of peripheral nerves. EMG records muscle activity in response to a proximal stimulation of the motor nerve. NCS record the velocity and amplitude of the nerve action potential. EMG/NCS typically is performed approximately 3 to 4 weeks after an acute injury, as nerves distal to the injury continue to transmit electrical impulses normally until degeneration of the distal nerve progresses. (See Schwartz 10th ed., p. 1712.)

The lesion that can cause mass effect and rapidly kill the patient is

A. Inferior fossa lesions

B. Posterior fossa lesions

C. Progressive obtundation

D. Bradycardial lesions

Answer: B

The posterior fossa (brain stem and cerebellum) requires special consideration because the volume of the posterior fossa within the cranial vault is small. Posterior fossa lesions such as tumors, hemorrhage, or stroke can cause mass effect that can rapidly kill the patient in two ways. Occlusion of the fourth ventricle can lead to acute obstructive hydrocephalus, raised intracranial pressure (ICP), herniation, and eventually death. This mass effect can also lead directly to brain stem compression (Fig. 42-1). Symptoms of brain stem compression include hypertension, agitation, and progressive obtundation, followed rapidly by brain death. A patient exhibiting any of these symptoms needs an emergent neurosurgical evaluation for possible ventriculostomy or suboccipital craniectomy (removal of the bone covering the cerebellum). This situation is especially critical, as expeditious decompression can lead to significant functional recovery. (See Schwartz 10th ed., Figure 42-5, pp. 1714–1715.)


Fig. 42-1. Maturing cerebellar stroke seen as a hypodense area in the right cerebellar hemisphere (arrowhead) on head computed tomography (CT) in a patient with rapidly progressing obtundation 2 days after the initial onset of symptoms. Swelling of the infarcted tissue causes posterior fossa mass effect. The fourth ventricle is obliterated and not visible, and the brain stem is being compressed.

According to the Glasgow Coma Scale (GCS), a patient with a head injury score of 5 is classified as

A. Mild

B. Moderate

C. Severe


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