Developmental Defects + Neoplasia

Timing of developmental defects

• timepoint of insult + severity of insult → outcome of defect in neural tube closure

  • early enough insult = fetal-fatal

• brainstem → cerebrum → cerebellum

• early + severe = aplasia

• early + moderate = segmental aplasia

• later: hypoplasia

• all changes accompanied by some degree of dysplasia

Dysraphism

• defect in neural tube closure, can also result in vertebral body defects

  • spinal cord induces surrounding mesoderm to form correctly, brain induces closure of the overlying skull bones

• causes myelodysplasia ± gross changes in CNS

• Dx: CT, rads

BVDV

• causes enteric signs in adults & variable lesions in fetus

• <100 days: fetal-fatal

• early 100-170: complete aplasia of the cerebrum based on timing, cranioschisis, mandibular lesions, microophthalmia, meningocoele

• middle: porencephaly (hole in brain)

• late 100-170: cerebellar aplasia/hypoplasia

• >170 days: immune

Meningomyelocoele

• spinal cord tissue has open access to overlying integument

Cranioschisis

• developmental defect in formation of the skull bones

Radiomimetic

• any agent that causes rapid death of rapidly dividing cells

Feline panleukopenia

• causes cerebellar hypoplasia + dysplasia

• non-progressive, causes wobbliness in kittens

Cerebellar abiotrophy

• fully developed cerebellum undergoes degenerative changes w/o dysplasia

• on histo: degeneration & necrosis

Hypomyelinosis

• oligodendrocytes are normal other than failure of myelin production

• on histo: less blue w/luxol fast blue

Border Dz virus infection

• infection of ewe mid-gestation causes infection of fetal thyroid follicular cells

• failure of T3-4 to induce myelin formation

Swayback

• in utero deficiency of copper → generalized hypomyelinogenesis ± neurons unable to support axons

• causes holes in brain where white matter should be

Enzootic ataxia

• post-natal copper deficiency → selective loss of axons & myelin in the spinal cord

• causes axon degeneration

Hydrocephalus

• impeded CSF flow + increased intracranial pressure + atrophy of periventricular tissues

• may be bottlenecked @ mesencephalic aqueduct (ventricle 3-4) + lateral apertures (4th ventricle → subarachnoid space)

• acute rapid increase in pressure is life-threatening, partial obstruction/congenital stricture causes gradual increase in pressure that can be adapted to (bones not yet closed, can expand)

• can lead to periventricular edema → edema cycle

• causes demyelination around the ventricles

CNS neoplasia

• glial & mesenchymal most common

• primitive neuroectodermal tumors in young animals

• secondary/metastatic tumors common in CNS

• meningeal tumors common

• lymphoma can be primary in CNS