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==The Forebrain==
* The nervous system can be classified functionally to:
*# The intercranial structures
*# The spinal cord
*# The peripheral nervous system.
* The intercranial structures can be further divided into the '''rostrotentorial''' and '''caudotentorial''' structures.
** The rostrotentorial structures consist of the cerebral hemispheres, basal nuclei, diencephalon and the rostral portion of the midbrain.
*** Collectively, these are the forebrain.
* The forebrain is responsible for many functions associated with or requiring consciousness.
==Clinical Signs==
===Seizures===
* Seizures are a classical sign of rostrotentorial disease.
===Altered Mentality/ Behaviour===
* The forebrain contains significant components of the limbic system, which are responsible for emotion.
** Intercranial disease may therefore give rise to abnormal behaviour and aggression.
===Circling, Head Pressing, Compulsive Walking===
* These behaviours are associated with unilateral rostrotentorial disease.
* There is a tendency to circle '''towards''' the side of the lesion.
===Head Aversion===
* Head aversion is also known as head turn.
* Turn is usually towards the side of a unilateral lesion.
===Menace Deficit===
* There may be a deficit in the menace response on the opposite side to a unilateral lesion.
** However, the pupillary light reflex (testing optic nerve function) and facial nerve function are found to be normal.
* The lack of a contralateral menace response is associated with poor or absent vision.
** The menace reflex is a learned response, and requires forebrain processing of visual information.
** The sign is contralateral because there is significant decussation of the visual fibres at the optic chiasm in animals.
* There may also be a reduction in the medial visual field in the eye ipsilateral to the lesion.
** This combination of visual field abnormalities is known as '''hemianopia'''.
===Facial Sensation Deficit===
* There may be a deficit in facial sensation on the side contralateral to a unilateral lesion.
** This is because CN V sends facial sensory signals to the opposite parietal cortex via the thalamus.
===Hemiparesis===
* Hemiparesis may be a sign of forebrain disease.
* Many tracts cross at various levels in the CNS, however functional crossover occurs at the level of the causal mesencephalon and rostral pons.
** Unilateral lesions rostral to this level give contralateral hemipareis.
** Unilateral lesions caudal to this level give ipsilateral hemiparesis.
==Differential Diagnosis==
* Remember that the age and breed of the animal are important.
** Animals present with congenital abnormalities within their first year of life.
** Young animals are also more predisposed to:
*** Infections - due to their immature immune systems and lack of vaccinations.
*** Intoxications - due to their innate curiosity and propensity to explore with their mouths.
*** Traumatic injury - due to both their curiosity and lack of road sense.
** Geriatric animals tend to suffer the same kind of neurological problems as other adult animals.
*** Infectious, inflammatory and metabolic disorders.
** Elderly animals are more likely to suffer from:
*** Neoplasi
*** Vascular problems
*** Degenerative disorders
* It must be determined whether the suspected lesion is due to a systemic disease, or to a structural change in the intracranial nervous system.
** Structural change can be detected by CT or MRI scanning.
* The following causes must be considered and eliminated.
===Common Diseases Affecting the Forebrain===
====Degenerative Diseases====
* Storage diseases
* Cognitive dysfunction syndrome
====Anomalies====
* Hydrocephalus
* Hydraencephaly
* Lissencephaly
====Metabolic Diseases====
* Hepatic encephalopathy
** Most commonly seen with congential liver shunts or with sever liver failure.
* Renal encephalopathy
* Pancreatic disease
* Glucose abnormalities
** Insulinoma
** Diabetes Mellitus
* Hypo- and hyper-thyroidism
* Hypoxia, for example due to:
** Anaemia
** Cariopulmonary disease
** Severe URT obstruction
* Hypertension
* Ion inbalances
** Hypocalcaemia
** Hypokalaemia
*** For example in chronic renal failure or hyperaldosteronism
** Hypophosphataemia
** Hypomagnesaemia
*** E.g. in hepatic lipidosis or re-feeding syndrome.
====Neoplasia====
* Primary brain tumours
* Metastatic tumours
* Local extension of tumours
====Nutrtional Conditions====
* Thiamine deficiency
====Infectious Causes====
* Canine distemper
* FIP
* Toxoplasmosis
* Fungal disease
* Rickettsial diseases
* Rock Mountain spotted fever
* Ehrlichia
* Bacterial infections
* Parasitism
====Trauma====
* Head trauma
====Toxicity====
* Metranidazole
* Lead
====Vascular====
* Arteriovenous malformation
* Infarction
* Feline ischaemic encephalopathy
* Haemorrhage
* Hypertension
==Diagnosis==
* Diagnosis must encompass the following:
===History===
* Aside from the normal history, there are several very important questions to be asked:
** Has there been any possible exposure to toxins or trauma?
** What is the animal's diet?
** Are the litter mates normal?
** Are there any specific clinical signs that may relate to a particular diagnosis?
** E.g. hypersalivation - commonly seens in young animals with portosystemic [[Liver - Anatomy & Physiology|liver]] shunts.
===Physical Examinations===
* Check for signs of systemic disease.
** Ocular changes with FIP, toxoplasmosis, FeLV or lysosomal storage diseases.
** Ascites with with FIP, liver or cardiac disease.
===Neurological Examination===
* This should include CN examination, postural reactions, spinal reflexes and sensory examination.
===Blood and Urine Tests===
* Blood tests should include haematology and serum biochemistry.
* These are particularly helpful in the diagnosis of many systemic and especially metabloic conditions.
===Infectious Disease Tests===
* E.g. FeLV and FIV, toxoplasma IgM and IgG tests.
===CSF Analysis===
* Particularly useful in the diagnosis of:
** Inflammatory diseases
*** E.g. FIP
** Lymphoma
===Imaging===
* Radiographs of the chest and abdomen
* Abdominal ultrasonography
* MRI or CT scans
** Examine the structure of the brain and determine presence or absence of inflammation or neoplasia.