Equis ISSN 2398-2977

CNS: neoplasia

Synonym(s): Nervous tissue neoplasia

Contributor(s): Caroline Hahn, Graham Munroe, Anna Hollis


  • Primary neoplasia of nervous tissue in horses is exceptionally rare and other differential diagnoses should always be sought. Tumors of peripheral nerves and nerve sheaths are more common than CNS neoplasia. Tumors of the orbit may extend directly into the calvarium, causing brainstem signs.
  • The exception to this is pituitary pars intermedia dysfunction/pituitary adenoma which is extremely common in older horses and is discussed elsewhere.
  • Cause: unknown.
  • Signs: depend on cell origin, site and behavior of tumor; can be peracute but more usually chronic and progressive.
  • Diagnosis: history and clinical signs, neurological examination, radiography, ultrasonography.
  • Treatment: euthanasia is often indicated.
  • Prognosis: poor.
  • See also Eye: neoplasia - overview.



  • Unknown.

Predisposing factors


  • Melanoma more common in grey horses, even in non-dermal locations.


  • Primary nervous system neoplasias can be categorized according to their cellular origin:
    • Astrocytes, eg astrocytoma.
    • Nerve cells, eg ganglioneuroma.
    • Neuroepithelium, eg:
      • Ependymoma.
      • Choroid plexus papilloma.
      • Optic nerve neuroepithelioma.
      • Pineoblastoma.
      • Malignant medulloepithelioma.
      • Ocular medulloepithelioma.
    • Glial cells, eg:
      • Optic disc astrocytoma.
      • Retinoblastoma.
      • Microglioma.
    • Peripheral nerves, eg:
      • Neurofibroma, often found cutaneously: pectoral region, abdomen, neck, face.
      • Neurofibrosarcoma.
      • Schwannoma.
    • Nerve sheaths.
    • Mesodermal structures, eg:
      • Meningioma.
      • Neoplastic reticulosis.
      • Lipoma - mesencephalic aqueduct.
      • Meningeal lymphoma spinal cord.
      • Melanoblastoma cerebral meninges.
    • Endocrine organs, eg:
  • Secondary neoplasms may reach the nervous system via vascular metastasis or by direct infiltration through the cranial vault, vertebrae or osseous foramina, eg:
    • Lymphoma → compressive myelopathy.
      • Epidural space (thoracic, lumbar).
      • Brain.
      • Olfactory tracts.
      • Peripheral nerves.
    • Malignant pheochromocytoma Pheochromocytoma: epidural space.
    • Melanoma (white or gray horses) Skin: neoplasia - melanoma:
      • Spinal meninges.
      • Spinal cord.
      • Brain.
      • Epidural space.
    • Hemangiosarcoma Hemangiosarcoma: overview.
    • Adenocarcinoma:
    • Osteosarcoma:
      • Skull.
      • Vertebrae.
    • Osteoma:
      • Skull.
      • Vertebrae.
    • Plasma cell myeloma: bone marrow.
  • Extraneural neoplasia may encroach on or infiltrate peripheral nerves causing neurological signs, eg:
    • Osteosarcoma:
      • Skull.
      • Vertebrae.
    • Osteoma:
      • Skull.
      • Vertebrae.
    • Plasma cell myeloma Plasma cell myeloma: bone marrow.
  • Clinical signs of primary neoplasia depend on the type, site, nature and behavior of the neoplastic tissue.
  • Neurological clinical signs of secondary neoplasia are usually due to direct invasion, pressure-induced tissue destruction or blood supply compromise:
    • Secondary neoplasia is rare because although many tumors circulate through the bloodstream, few can gain access to the nervous system. For example, between 1970 and 2013, 12 cases of CNS lymphoma have been reported, only two of which had only CNS lymphoma present at post-mortem examination; the remaining 12 had multiple sites of lymphoma present.
    • Occasionally melanoma may metastasize to the central nervous system: melanomas are the most common tumors affecting the spinal cord.
  • Neurological clinical signs of extraneural neoplasia are usually due to nervous tissue compression.


  • May be peracute, but usually chronic and progressive.


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Further Reading


Refereed papers

Other sources of information

  • Knottenbelt D C, Patterson-Kane J C & Snalune K L (2015) Clinical Equine Oncology. Elsevier, London.
  • Hahn C N, Mayhew I G & Mackay R J (1999) Diseases of the Forebrain - Neoplasia. In: Equine Medicine and Surgery. Eds: Colahan P T, Mayhew I G, Merritt A M & Moore J N. Mosby Philadelphia. pp 911-912. ISBN: 0 8151 1743 4.