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62 Cards in this Set
- Front
- Back
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Hydrocephalus
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“Water on the brain”
Dilation of the ventricles caused by obstruction within the ventricular system Cerebrospinal fluid builds up and causes pressure atrophy of the overlying nervous tissue, allowing the ventricles to dilate Acquired or congenital •Acquired caused by obstruction from neoplasms or secondary to inflammation •Congenital is most common in the dog, especially toy breeds |
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Hydranencephaly/ Porencephaly
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Porencephaly is the formation of a fluid-filled cavity in the cerebrum caused by necrosis and loss of the nervous tissue
Hydranecephaly is a more severe form of porencephaly in which most of the white matter of the cerebrum is lost and the lateral ventricles expand to fill the empty space Most commonly caused by in utero viral infections that destroy the developing brain •Blue tongue virus infection in sheep is the most common cause •Border disease in sheep and bovine virus diarrhea can occasionally cause porencephaly |
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Cerebellar hypoplasia
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Failure of the cerebellum to develop to normal size
Usually caused by an in utero infection •Bovine virus diarrhea in cattle •Feline panleukopenia in cats Affected animals have a hypermetric gait at birth, tremors and loss of balance |
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Abiotrophy
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Atrophy of the cerebellum after the organ has attained normal size
Occurs most often in the dog Signs develop several months after birth Cerebellum is usually grossly normal |
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Swayback
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Caused by a deficiency of copper during pregnancy in sheep
Necrosis of white matter and hydranencephaly |
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Enzootic ataxia
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Also caused by copper deficiency and is more common than swayback
Axonal degeneration Occurs several weeks after birth |
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Hypomyelinogenesis
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Failure of myelin to develop
Affected animals have tremors and shake at birth Causes •Inherited disease in pigs and dogs •Border disease in sheep causes hairy shakers – animals that shake and have abnormal wool that is more like hair |
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Spina bifida
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Failure of the spine to close properly during development
Affected animals have open areas in the bony spine through which meninges or spinal cord may protrude |
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Hydromyelia
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-dilation of the central canal of the spinal cord
-lined by ependymal cells |
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Syringomyelia
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The formation of a syrinx or cavity in the spinal cord
It is not lined by ependymal cells –this is how you can tell it apart microscopically from hydromyelia |
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Edema of the Brain
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Not usually seen grossly
When severe and diffuse, there is swelling of the brain with flattening of the gyri The cerebellum is forced into the foramen magnum and becomes narrowed into a cone shape Types •Intercellular (vasogenic) oOften focal oSeen with neoplasia, inflammation, and trauma •Intracellular (cytotoxic) oOccurs with toxic insults such as salt and lead toxicity as part of the neuronal necrosis that occurs with these diseases oAlso seen with hepatoencephalopathy, which is a neurologic disease occurring secondary to liver disease Microscopic •Results in holes in the neuropil (normal, pink staining neural tissue) |
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Infarcts of the nervous system
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Because of the artery type, the brain and spinal cord are more sensitive to ischemia and emboli
•Neural tissue also does not have multiple blood supplies Areas of infarction are grossly pale, tan to yellow, and swollen •Lesions are sharply demarcated because blood supply is so specific There may be hemorrhage in which case the lesions are red Causes -Feline ischemic encephalopathy -emboli -fibrocartilagenous emboli |
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Feline ischemic encephalopathy
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oDisease of cats producing areas of necrosis in the cerebrum , which are infarcts
Cause is unknown, but is assumed to be vascular in origin oAffected cats may have ataxia, seizures, blindness and behavioral changes |
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Bacterial emboli
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In cases of septicemia, bacterial emboli may localize in the brain, producing multifocal hemorrhagic infarcts and encephalitis
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Fibrocartilagenous emboli
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Emboli of intervertebral disk that gets into the ventral spinal artery
Lodge in the spinal cord of pigs and dogs, causing infarction Affected animals often have posterior paralysis that has occurred suddenly |
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Hemorrhage and contusion (bruising) of the nervous system
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Usually caused by trauma
Hemorrhage may be epidural, subdural, or within the parenchyma Can also see in some cases of necrosis or infarction |
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Lysosomal storage diseases
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•Group of inherited diseases each caused by an absence or deficiency of a single enzyme in a pathway of enzymes that breakdown cellular organelles within lysozymes in the normal process of cell turnover
oInherited as an autosomal recessive and the disease is seen in the homozygote (heterozygote is normal) oOccasionally a storage disease can be acquired due to inhibition of the enzyme due to a toxin •Missing enzyme in any of these pathways leads to accumulation of substrate within the lysosome and cellular dysfunction •Dogs and cats are most commonly affected with a few affecting cattle and sheep •Clinical signs appear shortly after birth oAtaxia, incoordination, and tremors oProgression to death over many months •No gross lesions in the brain •Microscopically neurons are filled with substrate which is often foamy and granular in appearance, sometimes showing accumulation of lipofuscin |
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Transmissible Spongioform encephalopathy
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•A group of neurologic diseases in which clear vacuoles form microscopically within neurons and the neuropil
oMicroscopic appearance of numerous holes in the brain, like a sponge •Examples oScrapie in sheep oBovine spongiform encephalopathy •Caused by a prion – an infectious particle consisting only of protein •Infection occurs when animals are young, but clinical disease is not seen for at least 2 years •Clinical signs oBehavior changes oAtaxia oPruritis in sheep oProgression to emaciation and death over many months to a year •No gross lesions |
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Chromatolysis
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•Dispersion of the Nissl substance within neurons
oGives the cytoplasm a ground glass appearance oCell body becomes pale and pink staining •Occurs when the axon of the neuron is damaged and is seen in many of the axonal degenerations •Caused by a gearing up of metabolism of the cell body and dispersal of ribosomes |
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Wallerian degeneration - general
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•caused by compression that leads to degeneration of the axons in the white matter and loss of myelin
•No gross lesions usually seen •Microscopically oAxons are lost, fragmented, or swollen oMyelin sheaths are swollen, leaving vacuoles throughout the white matter Vacuoles contain axons in the center, which is a key for diagnosis Macrophages are seen in the empty axon sheaths •Gitter cells •Engulf degenerated axon and myelin Reactive astrocytes are present •Proliferate and fill in spaces fromm necrosis |
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Causes of Wallerian degeneration
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oHerniation of the intervertebral disk
Most important cause of spinal cord compression Usually occurs in chondrodystrophoid breeds Dog develops sudden posterior paralysis and pain oCervical vertebral stenotic myelopathy Wobbler syndrome in the horse The cervical vertebrae may be malformed resulting in stenosis of the spinal canal Could also have damaged articular facets leading to increase movement of the vertebrae |
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Toxins that cause axonal degeneration
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•Organophosphates
oMost important toxin that can cause axonal degeneration oAmong other things, cause delayed neurotoxicity several weeks after exposure Distal axons in the central and peripheral nervous system degenerate Clinical signs of ataxia, weakness, proprioceptive deficits, and paralysis •Copper deficiency oIn the neonatal lamb oEnzootic ataxia oWallerian degeneration of the spinal cord and chromatolyis are seen |
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Degenerative myelopathy
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•An important group of diseases affecting primarily dogs and horses that is of unknown cause
oMost common in the horse Young horses (6 months to 2 years) develop progressive ataxia in all 4 limbs All levels of the spinal cord and all funiculi have Wallerian degeneration oOccurs in old German Shepherds Causes progressive posterior paresis |
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Necrosis of neruons - general
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Occurs commonly in a variety of diseases
Typically no gross lesions are seen Microscopic •Necrotic neurons are shrunken and red instead of blue Often there is associated edema and softening of the gray matter |
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Polioencephalomalacia
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Refers to necrosis of the cerebral cortical gray matter
Occurs most commonly in ruminants, especially in cattle •Associated with a deficiency of thiamine •Thiamine is normally produced in the rumen oAlteration of the rumen flora in favor of thiaminase-producing bacteria and/or a decrease in thiamine production results in disease Associated with high concentrate diets Cattle with polio are often blind and have paresis, progressing to recumbency Grind their teeth and have opisthotonus and extensor rigidity |
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Additional toxicities that can cause polioencephalomalacia
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•Salt poisoning in pigs and sometimes ruminants
oAnimals deprived of water for an extended period may develop hypernatremia and altered osmolality upon sudden rehydration Causes brain edema and neuronal necrosis leading to polio •Lead toxicity oImportant cause of polio in ruminants oUsually results from ingestion of lead paint or licking of old batteries oClinical signs Animals are excitable and hyperactive They may bellow and have seizures Others are blind and stagger or are recumbent with tremors |
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Hypoxia and ischemia
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Common causes of neuronal necrosis
Neurons of the cerebral cortex and hippocampus and the Purkinje cells of the cerebellum are the most sensitive Severe ischemia may lead to infarction Can occur during prolonged seizures and anesthesia |
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Neonatal Maladjustment syndrome
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In the foal
Caused by hypoxia and ischemia during dystocia (causes necrosis of neurons) “Dummy foals” •Foals fail to suckle, wander, and have seizures and convulsions beginning soon after birth |
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Leukoencephalomalacia
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Necrosis of the white matter of the brain with softening
Occurs in the horse with ingestion of moldy corn infected with the fungus Fusarium •The fungus produces a toxin (fumonisin B) which causes vascular damage in the white matter Grossly the cerebral cortical white matter is edematous and thickened with hemorrhage and yellowing Affected horses have a sudden onset of staggering, weakness, circling, depression, and head pressing •Terminally there are seizures and hyperexcitability •Death occurs in several hours to 2-3 days |
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Clostridium perfringens type D infection
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In sheep
Causes enterotoxemia with hemorrhagic enteritis In some animals that recover a secondary neuronal necrosis with hemorrhage develops in the basal ganglia, cerebellar peduncles, and internal capsule •Bilaterally symmetrical •Disease is called focal symmetrical encephalomalacia •Toxin damages blood vessels |
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Equine motor neuron disease
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Degeneration and necrosis of the neurons in the ventral horns of the spinal cord
The cause is unknown, but some cases respond to vitamin E supplementation |
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Poliomyelomalacia
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Pigs
Necrosis of the ventral horn of the cervical and lumbar spinal cord Caused by selenium toxicity Affected animals have posterior paralysis and quadripelegia |
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Inflammation of the nervous system - general
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Inflammation in the nervous system usually indicates an infectious disease is present
A general response to injury in the CNS is perivascular cuffing by inflammatory cells, usually lymphocytes •This reaction is seen in necrosis and ischemia/hypoxia diseases as well as inflammatory diseases |
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Meningitis
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•Bacterial infections typically produce meningitis, which is inflammation of the leptomeninges, pia, and arachnoid
•Neutrophils are a predominant component of the reaction •The reaction may extend into the neuropil and then is called menigoencephalitis •Gross lesions are not usually seen with meningitis but if the inflammation is severe, the meninges will appear opaque white, yellow, or green |
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Abscesses
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•Bacteria may produce a focal abscess which can be epidural, subdural, or within the nervous tissue
•Occasionally bacterial will localize in the ependyma and the choroid, producing ependymitis and choroiditis oGrossly, exudate may be seen in the ventricles |
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Listeria
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•Important infection in ruminants
•Organism enters the brainstem from the mouth along the cranial nerves oTrauma in the mouth allows the organism to enter oOften from infected silage •Produces a purulent encephalitis with microabscesses •Affected animals circle, are depressed, and have head pressing •Paralysis of the 7th nerve may produce unilateral drooping of the ear, lip, or eyelid |
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Histophilus somni
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•Causes an important infection in cattle called thrombotic meningoencephalitis
•Bacteria is normal flora of the respiratory tract, but can cause pneumonia and septicemia oLocalization in the brain is the most common form of the disease Produces a vasculitis with thrombosis of cerebral vessels Grossly, multifocal hemorrhages are seen which are infarcts Often arthritis and pneumonia •The disease affects young feedlot cattle with a variety of neurologic signs •Death is usually rapid |
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Viral infections of the CNS
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•Viral infections of the CNS typically produce no gross lesions but do have a characterisitic set of microscopic lesions that identify the infection as viral
oLymphocytic and plasma cell perivascular cuffing Surround the vessels like a cuff oChromatolysis and necrosis of the neurons oMicroglia proliferate forming small aggregates called glial nodules Little clusters of blue staining cells -examples --rabies --pseudorabies --equine viral encephalitis --retrovirus infection --canine distemper --equine herpes virus 1 --west nile virus |
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Rabies
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•Caused by rhabdovirus
•Transmitted by bite wounds •Foxes and skunks are the primary reservoir •Microscopic oRabies produces eosinophilic intracytoplasmic accumulations of virus called Negri bodies oEncephalitis can vary Much inflammation in carnivores with few Negri bodies Minimal inflammation in ruminants and lots of Negri bodies •Clinical signs oNo specific clinical signs occur with rabies and the disease can mimic many other neurologic diseases oAnimals may be dummy-like and docile or aggressive oLameness or paresis may be the only clinical sign oAnimals die within 10 days of showing signs |
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Pseudorabies
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•Herpes virus infection of swine
•Maintained in enzootic areas of pigs where it produces a highly contagious by usually asymptomatic infection •Other pigs develop neurologic disease, the severity of which depends on the age of the pig oYoung pigs develop severe disease and die oAdults have mild respiratory signs •Transmission of the disease to other animals from swine typically produces a fatal neurologic disease characterized by intense pruritis oIntranuclear viral inclusions are seen in neurons of affected animals |
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Equine viral encephalitis
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•Significant disease of the horse caused by an arbovirus and transmitted by mosquitoes
•Birds are natural reservoir •Horse is a dead-end host and incapable of transmitting the infection •Clinical signs oAffected horses are often somnolent, blind, and may circle oParalysis develops and death within 1-2 days |
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Retrovirus infection
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•In sheep and goats
•An unusual viral encephalomyelitis in that the lesions are predominantly demyelination with perivascular cuffs •Caprine arthritis encephalitis virus in goats oProduces encephalomyelitis in young kids oCauses arthritis and interstitial pneumonia in older goats •Lesions are mostly in the spinal cord and lead to paralysis and ataxia |
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Canine distemper
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•Caused by a mobillivirus
•Neurologic disease usually follows a clinical or subclinical infection of the respiratory and intestinal tracts oDisease produces neuronal necrosis in gray matter and demyelination in white matter oIntranuclear and intracytoplasmic inclusions occur in neurons and astrocytes Presence of inclusion bodies in both the nucleus and the cytoplasm is diagnostic •Clinical signs are variable as the lesions are widespread oMyoclonus (repetitive contraction) of the masticatory muscles is often a characteristic feature |
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Equine herpes virus 1
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•Mainly causes abortion in the horse
•Less often can produces neurologic disease oVasculitis with hemorrhages visible grossly in the spinal cord and brain oAffected animals have paresis, ataxia, and become recumbent |
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West Nile Virus
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•Flavivirus affecting mainly birds and horses
oHorses have paresis and paralysis •The lesion is a poliomyelitis (inflammation of the gray matter) and encephalitis |
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Fungal infections
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Introduction
•Fungal infections typically produces a granulomatous or pyogranulomatous inflammation •Gross lesions are usually not seen Cryptococcus •This fungal infection in the cat is the most important fungal disease in animals affecting the nervous system •Yeast infection enters through the nasal mucosa and can extend into the brain through the cribiform plate producing a meningitis or meningoencephalitis •Microscopically has a “soap bubble” appearance of the brain which is unique to this organism |
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Parasite infections
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•Parasite infections produce multifocal inflammation and necrosis of white and gray matter often with some eosinophils in the lesion
•Gross lesions are not usually seen -examples --Equine protozoal myelitis --parelaphostrongylus tenuis --halicephalobus deltrix |
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Equine protozoal myelitis (EPM)
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•Common disease of the horse caused by Sarcocystis neurona
•Transmitted from the opossum •Produces multifocal inflammation in the gray or white matter with occasional eosinophils •Horses have paralysis, paresis , and ataxia |
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Parelaphostrongylus tenuis
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•Nematode that is transmitted to sheep and llamas from the white tail deer
oNo clinical disease in the deer •Infection is limited to the spinal cord •Common cause of paresis, paralysis and ataxia in sheep and llamas |
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Halicephalobus deltrix
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•Free living nematode that infects the nasal cavity, brain, and kidney of horses
•The larva may penetrate the skin and migrate hematogenously to the brain |
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Granulomatous meningoencephalitis
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•Common disease of the dog
oMost nervous disease in small animals are this •Often produces no gross lesions •The lesions affect principally the white matter and consist of cuffs of lymphocytes and plasma cells with some macrophages •Results in death or euthanasia -cause is unknown |
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Cauda equina neuritis
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•Disease of the horse affecting the nerves of the cauda equina
•Grossly the nerves are thick and discolored gray to brown due to hemorrhage •Granulomatous inflammation with fibrosis •Horses show incontinence, perineal anesthesia, and tail paralysis -cause is unknown |
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Glial cell tumors
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Astrocytoma
•The most common tumor of the glial cells (and the second most common tumor in the CNS) •Most common in the brachycephalic breeds of dog •Located in the cerebral cortex •Tan, gray, or white and compress adjacent tissue •May be well delineated or poorly defined grossly Oligodendroglioma •Tumors of the oligodendroglia •Very rare |
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Choriod plexus tumors
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Adenoma or adenocarcinoma
Rare Very vascular and red grossly Usually in the 4th ventricle |
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Meningioma
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The most common tumor of the CNS
Seen in the dog and cat A white to gray fibrous mass on the surface of the brain, •Usually ventral in dogs •Usually dorsal in cats |
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Ependymoma
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Rare tumor of ependymal cells
Within the ventricle White, gray, or tan as opposed to the choroid plexus tumor which is red |
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Neuroblastoma/ medulloblastoma
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Rare tumors arising from primitive neurons
See most often in young animals (since they’re congenital) in the medulla Usually well demarcated, gray to pink |
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Ganglioneuroma
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Rare tumor of neurons in the peripheral nervous system
Firm, white nodules and occur in any ganglion |
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Peripheral nerve sheath tumor
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Also called a Schwannoma
Uncommon tumor of the peripheral nerve system Occurs most often in the dog •The skin is the usually site, followed by the brachial plexus where it causes unilateral limb paralysis Also seen in cattle as multiple masses most often affecting intrathoracic nerves Tumor is firm and white |
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Cholesterol granuloma
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Occurs in the lateral ventricle of the horse
Cause is unknown Usually an incidental finding, but large nodules may obstruct the ventricle and cause hydrocephalus (but not commonly) |
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Dural ossification
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The formation of mineralized plaques in the dura of older dogs that often form bone
Usually incidental findings with no clinical signs Some dogs may have pain with flexion of the spine |
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Things that cause microscopic holes in nervous tissue
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oEdema
oArtifact Because of high lipid content Holes are all the same size and evenly distributed oTransmissible spongiform encephalopathy Holes in the neuropil and neurons oAxonal degeneration |
