Lecture 61: Nervous System Pathology 5

primary neoplasms of the CNS in domestic animals occur most frequently in

dogs

embryonal tumor

• originate from primitive cells in the CNS

• described sporadically in cattle, horses, and dogs

• found most commonly in young animals and are aggressive biologically 

what type of embryonal tumors are most common in young animals?

medulloblastomas

medulloblastomas

arise in the cerebellum, usually in close proximity to the vermis, and invade into adjacent structures

macroscopic lesions for medulloblastomas

• well circumscribed, soft, gray to pink masses

• usually do not cause hemorrhage and/or necrosis or form cysts

• expansile growth can compress the fourth ventricle causing obstructive hydrocephalus

• metastasize throughout the ventricular system

what is this?

medulloblastoma → white to tan, homogenous mass that compresses the cerebellum and brainstem 

astrocytoma

• reported most commonly in dogs and cats, rarely in horses, cattle, and pigs

• brachycephalic breeds are the most commonly affected and have peak incidence from ages 5-11

• common sites include the cerebral hemispheres

true or false: astrocytomas are 20-30% incidence of all gliomas.

true

lesions of astrocytomas

• often displace normal tissue

• poorly defined, firm and white to pink (lower grade)

• regions of hemorrhage, necrosis, cavitation (higher grade)

what is this?

astrocytoma

• right hemisphere contains a poorly demarcated, nonencapsulated, expansile mass

• lesion has displaced the midline to the left and compressed the right lateral ventricle

oligodendroglioma

• most common in dog

• most common glioma

• predilection for brachycephalic breeds

• age range 5-11

• occur in all areas of the cerebrum and brainstem, especially in close proximity to the lateral ventricles

what is the most common glioma?

oligodendroglioma

oligodendroglioma lesions

• well-demarcated mass of variable size 

• gray to pink-red and soft to gelatinous with areas of hemorrhage 

• larger tumors, the central area may be cystic 

what is this?

oligodendroglioma → tumor is arising in a periventricular location and is gray, soft, and gelatinous

what is this?

oligodendroglioma → tumor is gray, soft, and gelatinous

ependymoma

• most common in the cat

• involve the lateral as well as third and fourth ventricles

• can occur in central canal of spinal cord

• can metastasize to subarachnoid space due to flow of CSF

lesions for ependymoma

• large expansile intraventricular masses with generally well-demarcated margins

• soft and gray-white to red, depending on blood content

• smooth cut surface in dogs

• more granular cut surface in cats

• aggressive tumors show invasion into the normal tissue at its margins

what is this?

ependymoma → third ventricle contains a moderately well demarcated expansile mass that has invaded normal tissue ventral to it; moderate hydrocephalus in both lateral ventricles

choroid plexus tumors

• most common in dogs

• 5-10% of all primary brain tumors in middle aged to older dogs

• breed predilection reported for golden retrievers 

• occurs most frequently in fourth ventricle

lesions of choroid plexus tumor

• well-defined, expansive, granular to papillary growth located within ventricular system

• gray-white to red and compresses the adjacent nervous tissue

• can develop to hydrocephalus due to obstruction

what is this?

choroid plexus carcinoma → lateral ventricle contains an expansile mass that has partially filled the ventricular lumen and is associated with midline shift

what is this?

choroid plexus carcinoma → 3rd ventricle has expansile mass with metastasis

what is the most common neoplasm of the CNS in dogs and cats?

meningiomas

meningiomas

• occurs in dogs between 7 and 14 years of age and in cats 10 years old or older

• dog → basal and lateral area of the brain, surface of the spinal cord

• cats → cerebral hemispheres, over the cerebellum

where do meningiomas arise from?

the arachnoid cell layer and project into subdural space

since meningiomas grow slowly, what can they cause?

pressure atrophy of the adjacent nervous tissue

lesions of meningiomas

• solitary and vary in size

• well defined, spherical, lobulated, or plaque-like in shape

• firm, encapsulated, gray-white

• cut surface has soft, red, brown, or gray areas of hemorrhage and necrosis

lesions of meningiomas in cats

most always compressive and not invasive → can be shelled out

what is this?

meningioma → surface of the right parietal cortex is a mass that has compressed and distorted the adjacent parenchyma

what is this?

meningioma → occupies the longitudinal fissure and displaces the left and right cerebral hemispheres laterally

what is this?

meningioma with the neoplasm shelled out

lymphosarcoma

primary CNS lymphoma occurs in all domestic animal species → most common in dog and cat

in cattle, there can be manifestations of bovine leukemia virus that can result in

lymphosarcoma → presents as an extradural white to yellow lobulated compressive mass in spinal canal

what is this?

lymphosarcoma → beige mass within the meninges on the left side of spinal cord

histiocytic sarcoma

• hematopoietic neoplasm that can present either as a primary CNS tumor or as part of disseminated disease

• primary tumor presents as a meningeal mass that compresses and invades the underlying neuroparenchyma

metastatic tumors

• most common in dogs

• mammary gland carcinoma and pulmonary carcinoma in dog occur most frequently

what is one of the most common metastasizing sarcomas in the dog and the most common metastasizing tumor to the brain?

hemangiosarcoma

what is this?

metastatic hemangiosarcoma → prominent hematogenous metastases, which appear as black nodules of various sizes distributed throughout the brain

in an unfixed specimen, what color would the nodules of metastatic hemangiosarcoma be?

red to dark red 

what is this?

metastatic mammary carcinoma → right cerebral hemisphere contains a well-demarcated mass which has caused enlargement of the right cerebral hemisphere and compression of right lateral ventricle

the leptomeninges of animals with heavily pigmented skin can have

melanin

true or false: congenital meningeal melanosis produces no clinical impairment in affected animals.

true 

what is this showing?

black pigmentation of the leptomeninges overlying the olfactory poles and dorsal aspect of the frontal lobe

equine encephalomyelitis

• infection occurs via mosquitoes

• primary target cell for infection and injury is neurons

• inflammation in gray matter of brain and spinal cord

EEE, WEE, and VEE

induce an encephalomyelitis that has similar characteristics

lesions for equine encephalomyelitis

• uncommon and nonspecific

• cerebral hyperemia, edema, petechiation, focal necrosis, and increased CSF in subarachnoid space

• gross lesions found in gray matter

what is this?

equine encephalomyelitis → thalamus has dark red to black discoloration as a result of congestion and hemorrhage 

what is this?

equine encephalomyelitis → red to brown discoloration of the gray matter in the dorsal and ventral horns; focused more heavily on the gray matter

west nile virus

• mosquito-borne

• causes acute polioencephalomyelitis in humans, birds, and horses → targets gray matter of spinal cord

• ubiquitous in lower 48 states of US

lesions of west nile virus

• usually involve gray matter

• hyperemia and petechiation to prominent hemorrhage → brain stem and gray matter of thoracolumbar spinal cord 

what is this showing?

west nile virus

equine herpesvirus

• important cause of equine abortion, perinatal foal infection and death, and rhinopneumonitis, in addition to myeloencephalitis

• neurologic form can affect zebras

• vasculitis is the principle lesion → endotheliotropic

how does equine herpesvirus cause vasculitis?

• inhalation of virus

• virus infects epithelial cells of the nasopharynx and spreads to local lymphoreticular tissue, where it infects lymphocytes and macrophages

• transferred to endothelial cells of CNS

• vasculitis 

what is the characteristic lesion in the CNS caused by EHV-1 infection?

vasculitis affecting endothelial cells of small blood vessels with thrombosis and resulting in focal CNS necrosis

lesions of EHV-1 occur in both

gray and white matter of the spinal cord and brain with regions of hemorrhage and necrosis

what is this?

EHV-1 → focal or multifocal areas of hemorrhage and/or necrosis

equine protozoal myeloencephalitis 

• caused by protozoa sarcocystis neurona, with less common isolates of neospora hughesi 

• pathogen enters body through ingestion of sporocysts

• protozoa shed in opossum feces

lesions of equine protozoal myeloencephalitis

• variably sized dark red-brown foci of necrosis and hemorrhage

• white and gray matter with random distribution

• more common in spinal cord

• brain → most common in brainstem

what is this?

equine protozoal myeloencephalitis → large focus of hemorrhage and necrosis in the caudal brain stem caused by sarcocystis neurona

what is this?

equine protozoal myeloencephalitis → prominent focal hemorrhage and necrosis are present in the right lateral funiculus and in the right and left lateral ventricle 

halicephalobus gingivalus

• free-living rhabditiform nematode that can infest the nasal cavity, CNS, and kidneys of horses

• tan-white, multifocal to diffuse foci

• results in foci of granulomatous and eosinophilic inflammation with associated nematodes

what is the primary predisposing factor of equine degenerative myeloencephalopathy?

dietary insufficiency of alpha-tocopherol (vitamin E)

equine motor neuron disease 

• associated with a vitamin E deficiency 

• develops in middle-aged to older horses 

• lacks a known genetic component 

• affects animals sporadically within a herd

• severe neurogenic muscle atrophy 

what can be used to support the diagnosis of equine motor neuron disease?

biopsy of the sacrocaudalis muscle to look for neurogenic muscle atrophy

what are clinical signs of equine motor neuron disease?

short-striding gait, muscle fasciculations, and narrow-based stance

leukoencephalomalacia 

• softening of white matter of brain

• ingestion of moldy feed composed of corn or corn by-products contaminated with fusarium verticillioides 

• primary toxin is fumonisin B1

lesions of leukoencephalomalacia

• white matter of the cerebral hemispheres most common

• can impact brainstem and cerebellum

• edema, brain swelling is marked with flattening of cerebrocortical gyri

• gross lesion at time of death is malacia and liquefaction of the affected white matter

• gray matter is spared

what can be the sole manifestation of leukoencephalomalacia?

hepatotoxicity

what is this?

leukoencephalomalacia → white matter of the frontal and parietal lobes is malacic due to necrosis, gray matter is not affected 

what is this?

leukoencephalomalacia → hemorrhages concentrated on white matter and yellow discoloration of white matter (soft)

horses grazing on yellow star thistle or russian knapweed for 1 month or longer during hot months develop a disorder called

nigropallidal encephalomalacia

lesions of nigropallidal encephalomalacia 

• sharply demarcated foci of yellow discoloration and malacia in the globus pallidus and substantia nigra

• lesions are bilateral and vary in severity

affected horses with nigropallida encephalomalacia

• have persistent chewing movements

• have difficulty in prehension of feed and drinking water

what is this?

nigropallidal encephalomalacia → lesion caused by yellow star thistle poisoning

cholesteatoma

• form in the choroid plexus of the lateral ventricles in horses as an aging change

• lesion thought to result from edema and minor but repeated hemorrhages within the choroid plexuses, which result in cholesterol deposits

• masses are incidental but can cause acquired hydrocephalus

lesions of cholesteatoma

• tan to yellow-brown firm masses with a smooth, often glistening surface

• occasionally the masses are mineralized

• can have associated granulomatous response

what is this?

cholesteatoma → choroid plexus of lateral ventricle contains an expansile mass consisting of cholesterol and a granulomatous inflammatory response

postanesthetic myelopathy 

• a hemorrhagic myelopathy secondary to general anesthesia in which the animals are placed in dorsal recumbency 

• after surgery, they are unable to stand

• hemorrhage throughout gray matter of spinal cord

• lumbosacral area most common

• corresponds to neuronal necrosis

postanesthetic myelopathy lesion

develops secondary to the weight of the animals blocking normal venous drainage from the vertebral sinuses, leading to an infarctive lesion in the spinal cord

what is this?

postanesthetic myelopathy