Forebrain Diseases Flashcards
What are the 5 pairs of arteries that make up the blood supply to the brain?
- 4 from the cerebral arterial circle (Circle of Willis)
- Rostral cerebral
- Middle cerebral
- Caudal cerebral
- Rostral cerebellar
- 1 from the basilar artery
- Caudal cerebellar
Blood is supplied to the rostral half of the brain in canines by what artery? Caudal half of the brain?
- Rostral: internal cartoid a.
- Caudal: vertebral a.
In cats, the entire brain is supplied by what artery? How is the basilar artery’s function different in cats?
Maxillary artery; Basilar artery actually carries arterial blood AWAY
In cows, their entire brain is supplied by a mixture of blood from which two arteries?
maxillary and vertebral a.
What are clinical signs and exam findings with forebrain diseases?
- Seizures
- Altered mentation
- Behavioral change, dementia
- Loss of training
- Pacing, wandering
- Wide circles (same side)
- Head turn (same side)
- Postural reaction deficits (opposite side)
- Visual impairment, cortical blindness - (opposite side)
- Head pressing, star-gazing, fly biting
- +/- hemiparesis, hemi-neglect
With forebrain disease, typically animals will have a normal gait, but may have what?
proprioceptive ataxia
What are clinical signs NOT associated with forebrain disease?
- Head tilt
- Nystagmus
- Stupor, coma
- Ataxia
- Abnormal spinal reflexes
- Significant CN deficits
- Intention tremors
Why are postural reaction deficits on the contralateral side with forebrain disease?
decussation of proprioceptive tracts occurs anatomically in the medulla oblongata
Why are visual defects on the contralateral side of a forebrain lesion?
because decussation occurs at the optic chiasm
What is your diagnostic work-up for forebrain disease?
- thorough hx and neuro exam are key!
- MDB, +/- Abdo/thoracic imaging
- MRI (> CT for brain imaging)
- CSF analysis
- +/- infectious dz testing
What are some degenerative diseases of the forebrain?
lysosomal storage disease, leukodystrophy, and cognitive dysfunction
Describe lysosomal storage disease
- accumulation of metabolic by-products due to defective enzyme
- leads to cellular dysfunction
- often autosomal recessive
Describe leukodystrophy
- metabolic genetic dz
- affects white matter
Describe cognitive dysfunction (CD)
- mostly dogs >9yrs
- +/- model for human Alzheimer’s
- accumulations of beta-amyloi in brain
- coalesce to form neuritic plaques
- most prominent in frontal cerebral cortex and hippocampus
What are the clinical signs of CD?
- progressive cognitive impairment
- inactivity, abnormal sleep/wake cycle
- wandering/pacing
- dementia, urinary/fecal incontinence
- anxiety
- lost in familiar environments, failure to recognize familiar people/animals
- decr interaction
- hearing loss, vocalization
- cats may show aggression
How do you diagnose and treat CD?
- Dx: hx, CS, and excluding other causes
- may or may not have abnormalities on MRI (e.g. cerebral atrophy, ventricular enlargement, microhemorrhages & infarcts)
- Tx: no known cure
- Selegiline (L-deprenyl) = MAO inhibitor
- Holistic tx
What are considered anomalous forebrain disorders?
Congenital hydrocephalus and epilepsy
Describe congenital hydrocephalus
- Toy and brachycephalic breeds
-
Excessive CSF in ventricular system
- flow obstruction vs. insufficient absorption
- Destruction of ependymal lining of ventricles
- Neuronal injury in cerebral cortex & compromise of cerebral vasculature
- Damage periventricular white matter
- often dogs are asymptomatic
- can cause dysfunction from compression and stretching of brain parenchyma
What are your general exam findings with congenital hydrocephalus?
- dome shaped head
- open fontanelle or larger calvarial defect
- ventrolateral strabismus aka “sun set sign”
- likely due to orbital malformation
- Neuro exam findings:
- typically apparent from 6 mo old
- behavior change, obtundation, dementia, circling, pacing, restlessness, seizures (not common)
What is the treatment for congenital hydrocephalus?
- reduction of CSF production
- Pred
- Proton pump inhibitor (Omeprazole)
- Furosemide
- Surgical:
- ventriculoperitoneal shunt
Can NOT address cerebrocortical damage
Describe primary epilepsy
- no identifiable brain abnormality
- typically pure-bred dogs
- genetic basis likely
- Generally 1-5 yrs
- seizures mostly generalized, can be partial
- seizures often at rest/sleep
- seizure frequency highly variable
- documented in cats
What is the primary treatment for epilepsy? What are a few examples of emergency anti-convulsants?
Primary tx:
- Phenobarb
- KBr
- Levetiracetam (Keppra)
- Zonisamide
Emergency anti-convulsants:
- Phenobarb
- Diazepam IV/per rectum
- Levetiracetam
What are two examples of forebrain metabolic diseases?
Hepatic encephalopathy and hypoglycemia
Describe the causes and clinical signs of hepatic encephalopathy
Causes:
- Liver failure
- PSS
CS:
- obtundation
- pacing
- head pressing
- visual deficits
- seizures (infrequent)
*signs may be assoc. w/ feedings
How might you diagnose and treat hepatic encephalopathy?
Dx:
- Hx
- pre & post-prandial bile acids
- Elevated ALT, ALP, NH3
- Ammonium biurate crystals in urine
- visualization of PSS on U/S or CT
- Mesenteric portography
- per-rectal scintigraphy
Tx:
- surgical shunt attenuation
- low protein diet
- lactulose (binds NH3)
- abx
Describe the causes and clinical signs of hypoglycemia?
Brain is COMPLETELY dependent on glucose for metabolism
Causes:
- glycogen depletion in very young/small puppies and kittens
- excess insulin secretion (insulinoma)
- insulin overdose in diabetics
- Addison’s
- liver failure
- toxins (xylitol)
CS: tremors, vocalization, altered mental status, seizures, visual dysfunction
What are the most common primary forebrain neoplasms?
Primary tumors
- Meningioma (both dogs and cats)
- Glioma (oligodendoglioma, astrocytoma)
- Choroid plexus tumors
- LSA
- Histiocytic sarcoma
What are the most common secondary forebrain neoplasms?
- Hemangiosarcoma
- Mammary, pulm, prostatic adenocarcinoma
- LSA
- Melanoma
- Nasal & frontal sinus carcinoma
- Calvarial tumors
- Pituitary tumors
- Peripheral Nerve Sheath Tumors (CN V)
T or F: a defiinitive diagnosis for any brain tumor can be made just by imaging it
F; cannot be made without histopath
What are the signalment, clinical signs, and treatment options for forebrain neoplasms?
Signalment: typically older dogs (>5yrs), any breed
CS:
- variable - often seizures
- behavior change, circling, head pressing, visual deficits, hemi-attention
- CP deficits
- Often gradual development
- Endocrine signs w/ pituitary tumors
Tx: surgery, radiation, chemo
What are 3 nutritional forebrain diseases?
- Thiamine deficiency (cats on all-coldwater fish diets)
- Hypoglycemia
- Hypocalcemia
What are a few immune-mediated/inflammatory diagnoses for forebrain disease?
- Necrotizing Leukoencephalitis (NLE) - Yorkies
- Necrotizing meningoencephalitis (NME) - Pugs
- Granulomatous meningoencephalitis (GME)
*All of these can ONLY be made with histopath!
Catch-all term: meningoencephalitis of unknown etiology (MUE)
What are examples of infectious causes of forebrain disease?
- Bacterial (Staph, Strep, E.coli, Klebsiella)
- Protozoal (Toxo, Neospora)
- Viral (Rabies, Distemper, Coronavirus - FIP)
- Fungal (Crypto)
- Rickettsia (Erlichia canis, Rickettsia rickettsii)
- Parasitic (aberrant migration - Dirofilaria, Baylisacaris, Cuterebra, Taenia)
What are 5 horse-specific infectious conditions that cause forebrain disease?
- Equine infectious encephalitidies - horses do not become contagious
- Mosquito-borne Alphavirus
- EEE (Eastern Equine Enchephalitis)
- WEE (Western)
- VEE (Venezuelan)
- Mosquito-borne Alphavirus
- Equine protozoal myeloencephalitis (EPM): Sarcocystis neurona - typically localize to SC
- West nile virus encephalomyelitis - Flavivirus
- EHV myeloencephalopathy
- Rabies
How do you diagnose and treat infectious forebrain diseases?
Dx:
- CSF analysis: sig. pleocytosis, elevated protein levels
- serology
Tx: drugs must cross BBB
- Abx: potentiated sulfas, doxy, clindamycin
- immune suppression: pred, cytosin arabinoside, procarbazine, cyclosporine
What are some toxins that can cause forebrain disease?
- Xylitol
- Narcotic and “recreational” drugs
- Ivermectin
- Bromethalin (rodenticide)
- Metaldehyde (snail bait)
- Caffiene/methylxanthines
- Lead
- Strychnine
- OPs
- Pyrethrins (cats)
What are some examples of traumatic causes of forebrain disease?
- Neonates - narrow birth canal, oversized cranium, forced whelping/fetal extraction
- small breeds - fall/dropped, mishandling/stepped on, HBC, blunt trauma, penetrating trauma
- large breeds - HBC, blunt trauma, penetrating trauma
- felines - high rise fall, HBC, blunt trauma, penetrating trauma (more at risk b/c thinner calvarium and reduced muscle mass)
What are the causes of brain infarcts (strokes)?
- non-hemorrhagic vs. hemorrhagic (less common)
- Hypertension
- primary (rare)
- secondary (Cushings, renal dz, pheochromocytoma)
- Cardiac dz
What are the causes and clinical signs of brain infarcts, and how would you treat them?
Causes:
- hypercoagulability
- hyperviscosity (polycythemia vera, mult myeloma)
- intravascular neoplasia (LSA, hemangiosarc)
- Atherosclerosis (hypothyroid, hyperlipidemia, diabetes) - Schnauzers
CS: typically per-acute to acute, may be transient
Tx: treat underlying cause!, supportive care if no cause found
