Dog Owner's Home Veterinary Handbook.pdf - Mr. Walnuts

Lissencephaly is a condition seen rarely in Lhasa Apsos, Irish Setters, Wire
Fox Terriers, and Samoyeds. The brain is smooth without the gyri or folds normally
seen. Affected dogs may show behavioral abnormalities, including difficulty
housetraining and sometimes seizures.
HYDROCEPHALUS
Hydrocephalus is caused by the excessive accumulation of cerebrospinal fluid
in the ventricles of the brain. The enlarged ventricles damage the cerebral cortex
by compressing it against the skull. Most cases are congenital. Some are
acquired through trauma, brain infections, or tumors.
Breeds with an increased risk of congenital hydrocephalus include the
Maltese, Yorkshire Terrier, Chihuahua, Lhasa Apso, Pomeranian, Toy Poodle,
Cairn Terrier, Boston Terrier, Pug, Pekingese, and Bulldog.
Hydrocephalus causes seizures, partial or complete blindness, and dementia.
The diagnosis is made by skull X-rays, ultrasound of the ventricles and, in difficult
cases, by CT scan or MRI. A characteristic enlargement of the dome of
the skull occurs in congenital hydrocephalus, but this may not be seen until
the puppy is several months old.
An increase in ventricular size without clinical signs has also been noted.
This is called subclinical hydrocephalus. In certain lines of toy breeds with a
high incidence of clinical and subclinical hydrocephalus, EEG screening and
breeding only dogs with normal EEGs has reduced the incidence of hydrocephalus.
Treatment: This is directed toward decreasing the production of cerebrospinal
fluid with corticosteroids and diuretics. Surgery has been beneficial
is some cases. The long-term prognosis is favorable if diagnosis and treatment
is begun before the brain is damaged. Nonetheless, affected dogs often appear
dull and have a limited ability to learn.
Seizure Disorders
THE NERVOUS SYSTEM • 367
A seizure is caused by an abnormal burst of electrical activity within the
brain, commonly in one of the cerebral hemispheres. The electrical activity
sometimes spreads out and involves other areas, including the midbrain.
A typical grand mal seizure is preceded by a period of altered behavior,
called the aura. During the aura dogs may be restless and anxious, cry out,
demand affection, or seek seclusion. The actual seizure normally lasts less
than two minutes, and is characterized by collapse with rigid extension of the
legs. The dog becomes unconscious and may stop breathing for 10 to 30 seconds.
This is followed by rhythmic jerking of the legs (which resembles running
or paddling). Some dogs also chomp, chew, drool, or urinate and