PATHO LICK

Neuron

Highly specialized nerve cell responsible for electrical and chemical signal transmission, most sensitive cell to hypoxia, requires continuous oxygen and glucose.

Ischemic Cell Change

Acute neuronal degeneration following ischemia, stroke, severe trauma, or prolonged cardiac arrest, key phrase, no blood → no oxygen → shrunken neuron → neuronal death.

Chromatolysis

Reversible neuronal response to axonal injury, Nissl bodies disperse, cell body swells, nucleus displaced eccentrically, indicates the neuron is attempting repair.

Inclusion Bodies

Abnormal intracellular neuronal structures usually caused by viral infections, key example, Negri bodies = Rabies.

Degenerative Cytoplasmic Inclusions

Accumulation of abnormal intracellular material due to chronic neuronal injury or metabolic disorders, example, Lafora bodies → myoclonic epilepsy.

Lipofuscin

Golden-brown wear-and-tear pigment within neurons associated with aging, usually incidental and not clinically significant.

Glial Cell Reaction (Gliosis)

Swelling, hypertrophy, and proliferation of glial cells after CNS injury, best indicator of nervous tissue injury.

Gitter Cells

Activated microglial phagocytes that remove dead neurons during neuronal necrosis, perform neuronophagia.

Neuronophagia

Phagocytosis of dead neurons by microglia (Gitter cells) during neuronal necrosis, key phrase, dead neuron surrounded and engulfed by microglia.

Satellitosis

Accumulation of astrocytes and microglia around injured neurons, common in viral encephalitis and neurodegenerative diseases, indicates impending neuronal death.

Fibrinous Inflammation

Fibrin deposition within the CNS due to severe meningeal or deep brain injury, usually limited to the meninges or deep brain lesions.

Purulent Inflammation

Suppurative inflammation with pus and neutrophils (PMNs) caused by pyogenic bacterial infection, key phrase, PMN infiltration in neuropil.

Lymphocytic Inflammation

Predominantly lymphocytic inflammatory response caused by viral infections, most common CNS inflammatory pattern.

Perivascular Cuffing

Lymphocytes surrounding blood vessels, hallmark of viral encephalitis.

Encephalitis

Inflammation of the brain parenchyma caused by infectious or immune-mediated diseases.

Meningitis

Inflammation of the meninges, affects the dura mater, arachnoid mater, and pia mater.

Leptomeningitis

Inflammation of the pia mater and arachnoid mater, key phrase, inflammation of the leptomeninges.

Myelitis

Inflammation of the spinal cord.

Encephalomyelitis

Inflammation involving both the brain and spinal cord.

Hypomyelination

Insufficient myelin production due to failure of oligodendrocytes (CNS) or Schwann cells (PNS), causes slower nerve conduction.

Dysmyelination

Abnormally formed myelin due to defective myelin formation, myelin is present but structurally abnormal, resulting in inefficient nerve conduction.

Demyelination

Loss of previously normal myelin due to acquired myelin injury, key phrase, myelin lost after formation, gross finding, malacia, microscopic findings, vacuolation (spongy appearance), little or no myelin, axonal loss.

CNS Infarction (Infarct)

Localized neuronal necrosis due to interrupted blood supply from arterial obstruction, vascular compression, cardiac arrest, severe hypotension, hypoxia, toxins, or nutritional deficiencies, key phrase, artery blocked → central neurons die first, surrounding neurons initially survive, dying neurons release glutamate causing calcium influx, excitotoxicity, and infarct expansion.

Arterial Obstruction

Blockage of cerebral blood flow by embolus or thrombosis, common cause of CNS infarction.

Vascular Compression

Reduced blood flow due to external vessel pressure, commonly from intervertebral disc herniation.

Hypoxic-Ischemic Injury

Neuronal injury from cardiac arrest, severe hypotension, or hypoxia, neurons are highly affected because of their high oxygen requirement.

Toxic-Hypoxic Injury

Neuronal damage from impaired oxygen utilization caused by carbon monoxide poisoning or cyanide poisoning, produces CNS hypoxia despite adequate blood flow.

Nutritional/Toxic Infarction

Ischemic neuronal injury associated with toxins or nutritional deficiencies, contributes to infarction or neuronal degeneration.

Excitotoxicity

Secondary neuronal death caused by excess glutamate, leading to Ca²⁺ influx, additional neuronal death, and enlarged infarct.

Sudden Occlusion

Acute interruption of blood supply due to embolus or Hansen Type I disc herniation, causes rapid neuronal death within minutes and severe infarction.

Gradual Occlusion

Slow reduction in blood flow from progressive vascular obstruction, allows collateral circulation, reducing infarction severity, may result in brain atrophy instead of infarction.

Vasogenic Edema

Most common cerebral edema in animals, extracellular fluid accumulation due to BBB disruption from inflammation, hematoma, brain contusion, infarction, cerebral hypertension, or brain neoplasms, key phrase, BBB breakdown → leakage of fluid, proteins, and ions into white matter, mainly extracellular edema, astrocytes may swell.

Cytotoxic Edema

Intracellular fluid accumulation caused by ischemia or hypoxia → ATP depletion → Na⁺/K⁺-ATPase pump failure, key phrase, ATP decreases → Na⁺ retained → water follows → hydropic degeneration, occurs without BBB disruption.

Frenzy

Extreme excitement or aggression with unprovoked attacks, associated with cerebral lesions, commonly rabies.

Catalepsy

Trance-like state with loss of voluntary movement, rigid posture, and poor response to stimuli due to CNS dysfunction.

Mania

Persistent abnormal excitement or aggression caused by lesions of the frontal lobe, temporal lobe, or limbic system, commonly rabies, characterized by wandering, excessive vocalization, and pen biting.

Tremors

Rhythmic involuntary shaking of the body or limbs due to abnormal nervous system activity.

Convulsions (Seizures)

Violent involuntary muscle contractions caused by abnormal electrical activity in the CNS, indicate neurologic dysfunction.

Torticollis

Twisting of the head and neck due to neurologic disease, common in Newcastle disease.

Star-Gazing Stance

Persistent upward head posture caused by lesions of the cerebellum or vestibular system.

Spastic Paralysis

Complete loss of voluntary movement with increased muscle tone (hypertonia) due to Upper Motor Neuron (UMN) lesion, characterized by stiff, rigid muscles.

Flaccid Paralysis

Complete loss of voluntary movement with decreased muscle tone and hyporeflexia due to Lower Motor Neuron (LMN) lesion, characterized by limp muscles.

Paresis

Partial paralysis or muscle weakness, commonly due to spinal cord disease, differentiate from orthopedic disease.

Paresthesia

Abnormal sensation including tingling, itching, or burning caused by peripheral nerve damage, represents sensory dysfunction.

Blindness

Loss of vision caused by disease affecting the eye, optic nerve, or brain, may require a neurologic examination.

Ataxia (Incoordination)

Loss of coordinated movement causing a staggering or drunken gait, due to lesions of the pons, medulla, cerebellum, or spinal cord, may show a sawhorse stance to maintain balance.

Traumatic CNS Injury

Mechanical injury to the brain and/or spinal cord caused by compression, stretching, twisting (rotational forces), laceration/tearing, or sudden acceleration/deceleration, damages neurons, axons, and blood vessels, key phrase, primary mechanical injury + secondary ischemic injury.

Compression Injury

CNS tissue compressed by external force causing neuronal and vascular damage.

Stretching Injury

Excessive stretching of neurons and axons due to traumatic force, results in axonal injury.

Twisting (Rotational) Injury

Rotational force causes shearing of nervous tissue, major cause of diffuse axonal injury.

Laceration/Tearing Injury

Physical tearing of CNS tissue due to severe trauma, produces direct neuronal and vascular disruption.

Acceleration-Deceleration Injury

Rapid movement causes the brain to shift within the skull, commonly from motor vehicle accidents, falls, or blunt trauma, leading to contusions, hemorrhage, and diffuse axonal injury.

Axonal Injury (Diffuse Axonal Injury)

Damage or tearing of axons due to shearing forces from rotational trauma, key phrase, angular rotation, important cause of severe neurologic deficits.

Cerebral/Spinal Cord Hemorrhage

Bleeding within the brain or spinal cord due to traumatic vascular injury, causes compression and secondary ischemia.

Hematoma

Localized collection of blood within the CNS or subarachnoid space caused by ruptured blood vessels after trauma, contributes to increased intracranial pressure and neurologic dysfunction.

Neuronal Degeneration

Progressive neuronal death following trauma due to secondary ischemia after vascular injury, develops after the primary mechanical damage.

Angular Rotation Injury

Twisting movement of the brain producing shearing forces, tears axons and blood vessels, resulting in diffuse axonal injury.

Vertical Rotation Injury

Up-and-down movement stretches nervous tissue, neurons, and blood vessels.

Lateral Rotation Injury

Side-to-side movement produces shearing and tensile forces, causing additional axonal and vascular injury.

Caudal Displacement Injury

Brain moves forward or backward and strikes the skull during rapid acceleration/deceleration, causing brain contusions (bruising).

Coup Injury (Impact Injury)

Brain injury occurs at the site of impact following a direct blow to the head.

Contrecoup Injury (Repercussion Injury)

Brain rebounds and strikes the opposite side of the skull after impact, causing injury opposite the site of impact.

Intervertebral Disc Disease (IVDD)

Degeneration of the intervertebral discs resulting in spinal cord compression, caused by disc degeneration, aging, premature degeneration, or chronic spinal instability, key phrase, loss of disc cushioning → spinal cord compression.

Disc Degeneration

Progressive deterioration of the annulus fibrosus and nucleus pulposus due to aging or premature degeneration, predisposes to disc extrusion or disc protrusion.

Hansen Type I IVDD (Disc Extrusion)

Acute rupture of the annulus fibrosus with extrusion of calcified nucleus pulposus into the spinal canal due to premature disc degeneration, key phrases, slipped disc, acute onset, severe pain, spinal cord compression, paralysis, common in chondrodystrophic breeds including Dachshunds, Beagles, and French Bulldogs.

Disc Extrusion

Sudden displacement of disc material into the spinal canal due to rupture of a degenerated disc (Hansen Type I), causes acute spinal cord compression.

Hansen Type II IVDD (Disc Protrusion)

Chronic bulging of the annulus fibrosus into the spinal canal due to age-related degeneration or chronic spinal instability, key phrases, slow progression, chronic compression, mild pain, stiffness, difficulty rising, progressive ataxia or coordination deficits, more common in large, older dogs.

Disc Protrusion

Gradual protrusion of the intervertebral disc without complete rupture due to chronic disc degeneration (Hansen Type II), produces chronic spinal cord compression rather than acute injury.

Lissencephaly

Congenital smooth cerebrum with absent or reduced gyri and sulci due to defective neuronal migration, key phrases, smooth brain and abnormal neuronal development before birth.

Rathke's Cleft Cyst

Fluid-filled cyst arising from Rathke's pouch remnants, developmental anomaly of the pituitary, key features, panhypopituitarism, stunted growth, bilateral alopecia, comedones, skin hyperpigmentation.

Hydrocephalus (Congenital)

Excessive CSF accumulation within the cerebral ventricles due to congenital obstruction or impaired CSF drainage, causes pressure atrophy of the cerebrum, gross findings, thin calvarium and enlarged fontanelles.

Hydrocephalus (Acquired)

Excessive ventricular CSF accumulation developing later in life due to neoplasms, inflammation, hemorrhage, or foreign bodies, key phrase, obstruction of CSF flow.

Cerebellar Hypoplasia

Underdeveloped cerebellum caused by viral destruction of mitotic cells in the external granule layer during late gestation or shortly after birth, examples include Feline Panleukopenia Virus in kittens, BVDV in calves, Classical Swine Fever Virus in piglets, key phrase, small cerebellum → ataxia and intention tremors.

Dysraphism

Congenital failure of neural tube fusion during embryonic development, umbrella term for anencephaly, cranium bifidum, spina bifida, and related defects.

Anencephaly

Congenital absence of most of the brain, especially the cerebral hemispheres, due to failure of the rostral neural tube to close, usually incompatible with life.

Prosencephalic Hypoplasia

Absence or severe underdevelopment of the forebrain with relatively preserved brainstem, due to failure of rostral neural tube development.

Maternal Teratogenic Neural Tube Defect

Congenital CNS malformations caused by maternal exposure to excess vitamin A or cyclophosphamide during pregnancy, may produce anencephaly or prosencephalic hypoplasia.

Cranium Bifidum

Failure of cranial bones to fuse resulting in a midline skull defect, allows protrusion of meninges and/or brain tissue.

Meningocele

Herniation of meninges and CSF only through a skull defect due to cranium bifidum, no brain tissue within the sac.

Meningoencephalocele

Herniation of meninges, CSF, and brain tissue, more severe because brain tissue protrudes.

Spina Bifida

Failure of vertebral arches to close due to dysraphism, vertebral counterpart of cranium bifidum, usually affects the lumbosacral region.

Spinal Meningocele

Herniation of meninges and CSF through a vertebral defect due to spina bifida, no spinal cord within the sac.

Meningomyelocele

Herniation of meninges and spinal cord through a vertebral defect, most severe form because neural tissue protrudes.

Spina Bifida Occulta

Failure of vertebral arch closure without herniation, mild form of spina bifida, spinal cord remains within the vertebral canal, may have absent skin over the defect with visible dura.

Microencephaly

Congenital abnormally small brain due to failure of normal embryonic brain development, key phrase, small brain, severe cases may have a simple hollow spinal cord from incomplete nervous system maturation.

Porencephaly

Small fluid-filled cavities (cysts or clefts) within the cerebral hemisphere caused by destruction of immature neuroblasts during fetal development, key phrase, cavity communicates with the subarachnoid space and may communicate with the lateral ventricle.

Hydranencephaly

Large fluid-filled cavities replacing much of the cerebral hemispheres, especially the white matter, due to failure of normal cerebral development during gestation, severe form of porencephaly, key phrase, cerebral hemispheres largely replaced by fluid-filled cavities.

Brain Abscess

Localized collection of pus within the CNS caused by pyogenic bacterial infection, early abscess contains thick granular exudate with surrounding hyperemia.

Streptococcal/Staphylococcal/Corynebacterial Abscess

Suppurative abscess caused by Streptococcus spp., Staphylococcus spp., or Corynebacterium spp., produces pale-yellow to yellow, watery to creamy pus.

Coliform Abscess

Suppurative abscess caused by Escherichia coli or Klebsiella spp., produces white to gray, watery to creamy pus.

Pseudomonas Abscess

Suppurative abscess caused by Pseudomonas spp., produces green to bluish-green exudate due to bacterial pigments.

Suppurative Bacterial Meningitis

Purulent inflammation of the meninges with neutrophilic exudate caused by pyogenic bacteria, common in horses, key findings, pale yellow-white subarachnoid exudate, PMN infiltration, bacteria, debris, edema fluid, flattened gyri from brain swelling.

Spinal Cord Abscess

Localized suppurative lesion within the spinal cord caused by extension from vertebral osteomyelitis, tail docking in lambs, or hematogenous spread, clinical signs include abnormal mentation, ataxia, head tilt, circling, and blindness.

Wallerian Degeneration

Degeneration of the distal axon and myelin sheath after axonal transection, crush injury, or spinal cord compression, key phrase, active breakdown of axon and myelin distal to injury.

Diskospondylitis

Infection of the intervertebral disc and adjacent vertebrae with osteomyelitis caused by bacterial emboli, common in pigs, key findings, vertebral abscesses, osteomyelitis, spinal cord compression, Wallerian degeneration, vertebral remodeling narrows spinal canal.

Leukoencephalomalacia (LEM)

Liquefactive necrosis (malacia) of the cerebral white matter caused by ingestion of moldy corn contaminated with Fusarium moniliforme (Fusarium verticillioides) producing fumonisins, occurs in horses, key phrases, fatal neurologic disease, white matter necrosis, frontal and parietal lobes affected, gray matter spared or minimally affected, gross finding, softening of cerebral white matter, especially around the lateral ventricles.

Medulloblastoma

Embryonal CNS tumor arising from embryonal cells, occurs in young dogs, cows, cats, and pigs, affects the cerebellum, gross appearance, well-circumscribed, soft gray-pink expansile mass, usually no hemorrhage, necrosis, or cysts.

Oligodendroglioma

Glial tumor arising from oligodendroglia, occurs in dogs, cats, and cows, affects the cerebrum, brainstem, and interventricular septum, gross appearance, well-demarcated, soft or gelatinous gray-pink to red mass, hemorrhage common.

Astrocytoma

Astroglial tumor arising from astroglia, occurs in dogs, cats, and cows, affects the pyriform lobe, cerebral hemispheres, thalamus-hypothalamus, midbrain, cerebellum, and spinal cord, gross appearance, poorly demarcated if well differentiated, anaplastic forms are softer with necrosis, hemorrhage, edema, and cavitation.

Ependymoma

Tumor of ependymal cells arising from the ventricular lining or central canal, occurs in dogs, cats, cows, and horses, affects the lateral ventricles more than the third or fourth ventricles and the central canal, may obstruct CSF causing hydrocephalus, gross appearance, soft gray-white invasive mass with hemorrhage and cavitation.