Ch. 26, 28, 29 Neurosurgery Flashcards
what are the six parts of the neurologic exam
- sensorium and behavior
- posture and gait
- postural reactions
- spinal reflexes, muscle mass, muscle tone
- cranial nerves
- cutaneous sensation
what is decerebrate rigidity
severe intracranial lesion can lead to decerebrate rigidity which is opisthotonus with rigid extension of the neck and all four limbs and is usually associated with midbrain or rostral cerebellar lesions
Lesions that result in decerebrate rigidity will always have a severe impact on mentation and the menace response
what is decerebellate rigidity
severe cerebellar lesions that have opisthotonus and extensor rigidity of the limbs but the hips are flexed!
may or may not affect mentation
what is pleurothotonus
deviation of the head and neck to one side and may be present with mid to rostral brainstem or cerebral lesions
what is the typical gait associated with general proprioceptive ataxia
elements of both incoordination typified by hypermetria and upper motor neuron spasticity/rigidity
why are paw placing (checking CP deficits) not totally reliable for checking conscious proprioception
- the patient may not be able to replace the paw because of a pure lower motor neuron disease - like it is too weak to replace the paw
- proprioceptive placing does not isolate the conscious proprioceptive pathway from other afferent sensory pathways- there could be a problem in a different sensory pathway and you would still get a CP deficit
what nerve mediates the patellar tendon reflex
the femoral nerve, which comes through spinal cord segments L4-L6
hyperreflexive - upper motor neuron disease
hypo or absent - occurs with a disease in the reflex arc so LMN or sensory
what nerve mediates the biceps tendon reflex
musculocutaneous nerve from C6-8
what nerve mediates the triceps reflex
radial nerve from C7-T2
where do the nerves for the thoracic limb reflex originate from?
C6-T2
dorsal thoracic, axillary, musculocutaneous, median, ulnar, radial nerves
Where do the nerves for the withdrawal reflex of the pelvic limb arise
all from the sciatic nerve from L6-S1
how does a positive crossed extensor reflex occur
normally, a patient in lateral recumbency will not have extension of the contralateral limb because of UMN inhibition
With lesions that are cranial to the spinal cord segments containing the LMN of the limb, however, the crossed extensor reflex may be shown
what nerve mediates the perineal reflex
pudendal nerve
what must be intact for the menace response to be present
requires a functional retina, optic nerve, optic tract, lateral geniculate nucleus of the thalamus (diencephalon) and optic radiation and occipital lobe of the cerebrum as well as the efferent pathway (facial neurons, nerves, muscles)
also requires a functional cerebellum
How does schiff sherrington syndrome occur
peracute T3-L3 spinal cord lesions produce the markedly increased extensor tone in the thoracic limbs because of disruption of ascending inhibitory axons from interneurons (border cells) located in the dorsolateral border of the ventral gray column of spinal cord segments L1-L4
These ascending interneurons normally have some inhibition on the LMN of the cervical intumescence
what do you see in spinal shock
lesions in T3-L3 which normally would show as UMN lesions in the hind limbs actually are flaccid and act like LMN lesions
usually accompanied by schiff sherrington posture
what are the parts of a lower motor neuron unit
alpha motor neuron (nerve cell in the ventral gray matter of spinal cord) ventral nerve root spinal nerve nerve plexus named nerves of the limb neuromuscular junction muscle
why is the spatial resolution of MRI generally superior to CT
MRI images are obtained with separate acquisitions whereas CT is reformatted from the transverse images
what is back projection
computer generated images of each slice of scanned CT anatomy are constructed to an image we can use - back projection
what is the hounsfield unit of water
0
what is the hounsfield unit of air
-1000
what is the hounsfield unit of fat
-100
what is the hounsfield unit of brain
30-40
what is the hounsfield unit of acute to subacute clotted blood
60 to 100
what is the hounsfield unit of mineral and bone
variable but 100 to >1000
what is the hounsfield unit of metal
variable but 100 to >3000 (includes iodine)
How will an MRI be weighted if the operator selects a short repetition time?
the differences between tissues that differ in T1 relaxation times will be accentuated and the image will be T1 weighted
How will an MRI be weighted with a long echo time?
It will be T2 weighted
How does gadolinium work as a contrast agent to increase the intensity on T1 weighted images
Gadolinum is paramagnetic and strengthens the field
It will shorten the relaxation times of neighboring hydrogen protons and then will make tissue appear hyperintense on T1 (T1 shows substance with short T1 recovery time)
what are the layers of the meninges? what is the leptomeninges? what is the pachymeninges?
pia mater
arachnoid mater
dura mater
Pia and arachnoid make up the leptomeninges
Arachnoid and dura make up the pachymeninges
What is the subarachnoid space
the space between the arachnoid and the pia mater and contains CSF
what is the subdural space
a potential space, this is between the dura and the arachnoid where blood vessels pass
what is the epidural space
a fat-filled space surrounding the dura in the vertebral column
*in the cranial cavity, the dura is already fused with the periosteum of the skull
what is the falx cerebri
this is the separation of the two cerebral hemispheres
what is the tentorium cerebelli
the separation between the cerebellum and cerebrum
what cells produce myelin
oligodendrocytes
What change in PaCO2 results in a 5% change in cerebral perfusion?
a 1 mmHg change in PaCO2 results in a 5% change in cerebral perfusion - perfusion is extremely sensitive to changes in the partial pressure of CO2
what is the normal intracranial pressure for dogs and cats
8-15 mmHg
what compensatory mechanisms will manage increased intracranial pressure
move CSF to the subarachnoid space
reduce CSF production
decrease cerebral blood flow
How much will a durotomy decrease intracranial pressure?
a durotomy will decrease ICP by 65%
a craniotomy alone decreases it by 15%
what are the components of the blood brain barrier
tight junctions between endothelial cells and foot processes of astrocytes
basal lamina
pericytes
perivascular miroglia
what antibiotics have good BBB penetration
third generation cephalosporins fluoroquinolones metronidazole sulfonamides chloramphenicol trimethoprim
what antibiotics have moderate penetration of BBB with a meningitis
tetracyclines (especially doxy and minocycline)
erythromycin
penicillins
rifampin
what antibiotics have poor BBB penetration
first and second generation cephalosporins
aminoglycosides
clindamycin
vancomycin
What are the Trp genes?
transient membrane potential monovalent cation channels
Trpm4 and Trpm5 are two genes that, if knocked out, will have less hemorrhage, reduced lesion volume and improved outcome
They play a role in the secondary injury changes with a contusion of the brain
what does increased intracellular calcium lead to?
- activates intracellular proteases such as calpains and caspase, which destroys the cytoskeleton and chromosomes and initiates cell death
- activates phospholipase A2 –> produces eicosanoids and initiates an inflammatory response
- binds intracellular phosphates, further depleting the cell of energy
what is the role of peptidase matrix metalloproteinase 9 in spinal cord injury?
may be an important early trigger to the inflammatory response
what is CIDS in relation to spinal cord injury
central nervous system injury-induced immunodepression
a syndrome of immunodeficiency that is associated with central nervous system injury
elevation of ACTH and catecholamines –> increased cortisol… is this why steroids are contraindicated in spinal injury patients
what is cytotoxic edema
cellular swelling that is secondary to intracellular increases in Na, Cl, and Ca that will increase the osmotic pressure and cause swelling
what is excitotoxicity
neuron and oligodendrocyte death from increased glutamate levels
which is more affected by vascular obstruction, white or gray matter?
gray matter is more severely affected
Hemorrhage affects spinal cord tissue in a similar way to contusion. What is a unique feature that also causes damage
iron and copper complexes will oxidize and hemoglobin is released into the parenchyma. the hemoglobin release produces free radicals
how can malformations of the CNS lead to dysfunction?
either by compression, like an obstructive hydrocephalus, or by disruption of normal patterns of central nervous system circuitry
what are some mechanisms by which metabolic/toxic diseases like hypoglycemia, hepatic encephalopathy, uremic encephalopathy may occur
- an interruption in the energy supply like hypoglycemia or thiamine deficiency
- imbalance of excitatory and inhibitory neurotransmitters (like hepatic encephalopathy)
- presence of neurotoxins like ammonia, urea, phosphates
- ionic imbalances (uremic encephalopathy)
- blood pressure changes (uremic encephalopathy)
what are the three most common neoplasms to metastasize to the CNS
hemangiosarcoma
melanoma
carcinomas
what is vasogenic edema
results from increased vascular permeability and causes accumulation of extracellular fluid, particularly within white matter tracts
commonly associated with contusion, inflammatory disease, vascular disease, and compressive diseases such as neoplasia
*corticosteroids are ususally effective with this type of edema
what is the etiology of Hansen type 1 degenerative disc
- nucleus undergoes progressive decrease in proteoglycan content with consequant dehydration and accumulation of mineral (aka chondroid degeneration)
- this degeneration leads to loss of its ability to withstand pressure equally and causes secondary degeneration and tearing in the annulus fibrosus
- annulus will tear and the nucleus will be expelled
- injury is some contusion and some compression
what is the etiology of Hansen type II disc degeneration
- nucleus is progressively dehydrated and replaced by fibrinoid tissue with a consequent increase in stress transfer to the annulus
- annulus undergoes wear and tear degeneration that leads to rupture of fibers over months to years –> nucleus will cause protrusions of the dorsal aspect of the annulus
- injury is compressive
what are the two main theories for why we cannot regrow axons?
- reactive astrocytes produce a large number of inhibitory molecules in the extracellular space, including chondroitin sulfate proteoglycan
- CNS myelin is known to contain several ligands that activate receptors (like the nogo receptor) to mediate growth cone collapse
what is syringomyelia
accumulation of CSF within the parenchyma of the spinal cord
