Cancer of the nervous system

Nervous system

The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

 is common in domestic canids, and includes primary neoplasia of the peripheral nervous system, primary neoplasia of the central nervous system and various metastatic

Metastasis

Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...

 cancers. Some of the most common of the central nervous system tumors are several types of primary (originating from brain tissue) canine brain tumors. Examples of these include: meningiomas, astrocytomas, glioblastomas, oligodendriomas, choroid plexus papillomas, and pituitary adenomas. Breeds predisposed to brain tumors include: Boxer Dog, Pug, English Bull Dog, Boston Terrier, and Golden Retrievers.

Meningiomas

Meningiomas

Meningioma

The word meningioma was first used by Harvey Cushing in 1922 to describe a tumor originating from the meninges, the membranous layers surrounding the CNS ....

 (arising from the meninges, a neural crest-derived cell) are the most common brain tumor of dogs, accounting for 40% of all primary brain tumors. Golden Retrievers as well as other dolichocephalic (long-nosed) breeds are particularly susceptible.

Astrocytomas and glioblastomas

Astrocytomas

Astrocytoma

Astrocytomas are a type of neoplasm of the brain. They originate in a particular kind of glial-cells, star-shaped brain cells in the cerebrum called astrocytes. This type of tumor does not usually spread outside the brain and spinal cord and it does not usually affect other organs...

 are the most common neuroectodermal tumor of dogs. Glioblastomas are considered a subset of astrocytomas--a particularly damaging, invasive, and undifferentiated type. Canine glioblastomas are particularly interesting as they are extremely similar to glioblastomas in humans. Studies are underway to use and develop the dog as a model of this devastating disease of humans in the hope that characterizing and successfully treating these tumors in dogs may lead to improved therapies for humans afflicted with this disease. Interestingly, brachycephalic

Cephalic index in cats and dogs

Cephalic index is the charting of or classification of the Cephalic ratio; the cranial width as compared to cranial length. The cephalic index refers to the cranium and its relative size, comparing cranial length to cranial width....

 (short-nosed) breeds such as the Boxer, Pug, Boston Terrier and Bulldog have a marked (25 times the normal occurrence) predilection for developing primary brain tumors to include glioblastomas.

Pituitary gland adenoma

Pituitary gland tumors are very common in the canine. A productive form arising from the anterior pituitary is the primary cause of Cushing's disease of dogs. This tumor causes excessive production of cortisol

Cortisol

Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...

 from the adrenal cortex

Adrenal cortex

Situated along the perimeter of the adrenal gland, the adrenal cortex mediates the stress response through the production of mineralocorticoids and glucocorticoids, including aldosterone and cortisol respectively. It is also a secondary site of androgen synthesis.-Layers:Notably, the reticularis in...

 which leads to the classic signs of alopecia (hair loss), polyuria (excessive urination), polydipsia (excessive water drinking), and a pot-bellied appearance of the abdomen due to muscle break down. See picture here.

Clinical signs

Two of the most important signs a dog may have an intracranial brain tumor are seizure

Seizure

An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...

and unexplained behavioral changes. Seizures manifest as a 1-2 minute display of a combination of the following: loss of consciousness, lateral recumbency (dog lying on its side), paddling of the legs, tremors, and involuntary urination/defecation. Often, the only signs an absent owner may have of a pet dog that has had a seizure is unexplained soiling of the floor by a normally house-broken pet. Behavioral changes can manifest in many ways to include nervousness, barking in the corner (dementia), pacing, aggressiveness or irritation, or deviation from normal routines. "Doggy headaches" can manifest as head pressing against walls, doors, or even owners themselves. Other signs that may be encountered are ataxia (uncoordinated ambulation), circling, blindness, lethargy, and disorientation.

Treatment

Unfortunately, at this time, there is no true cure (100% remission) for brain tumors in dogs (or any species for that matter.) In practice, brain tumors are generally considered to be malignant due to the delicate and poorly regenerative nature of neurons and restriction of the brain to the finite space of the cranium which does not allow tumor growth devoid of collateral damage to brain parenchyma. Therefore, general long-term prognosis for canine brain tumors is poor. Current treatment of brain tumors revolves around four main modalities: surgery, radiation, chemotherapy, and palliative (pain relieving) care. Depending on the type, extent, and location of the cancer, any one or combination of these techniques may be employed. For instance, the first line treatment for meningiomas is surgery but may be coupled with chemotherapy in an attempt to improve survival time. Intercranial tumors (such as glioblastoma) more commonly rely on radiation therapy as surgical access to the tumor may be prohibitively dangerous. Palliative care tends to include corticosteroids to help reduce swelling and edema around tumors as well as anti-convulsant medications to control seizuring.