Page 1082 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Nervous system 1057

VetBooks.ir horses, and abnormal activity such as diffuse high volt- The technique has been advocated as a means of
assessing the functional significance of suspected
age or diffuse or multifocal paroxysmal activity. These
abnormalities could be associated with intracranial
diagnostic techniques such as CSF analysis, magnetic
lesions such as hydrocephalus, encephalitis, menin- intracranial disorders in horses, but does not replace
gitis and abscessation (Streptococcus equi subsp. equi). resonance imaging (MRI) and CT.

NEUROLOGICAL DISEASES

CONGENITAL DISORDERS Clinical presentation
Hydrocephalic animals are often born dead, or are
HYDROCEPHALUS born weak and die shortly after birth, and this is usu-
ally associated with dystocia in the mare. Animals
Definition/overview that survive may have a varied presentation. Clinical
Hydrocephalus is the accumulation of excessive abnormalities relate to compression of the cerebral
volumes of CSF in the brain or cranial cavity. If cortex. In neonates, poor suckle reflex, blindness,
affecting the ventricular system, it is termed inter- lack of affinity for the mare, depression, ill-thrift and
nal hydrocephalus, whereas that affecting the sub- growth retardation may be present (Fig. 10.15). The
arachnoid space is termed external hydrocephalus. It head may be grossly enlarged and dome shaped, but
is rare in horses but is most often seen in neonatal this is not consistent or always apparent (Fig. 10.16).
foals as a congenital malformation. A mildly dome-shaped skull can more commonly
be the result of intrauterine growth retardation or
Aetiology/pathophysiology immaturity.
An inherited defect has been proposed in some
horse breeds. Very recently, a nonsense genetic
mutation was linked to hydrocephalus in the
Friesian horse. In this breed, it is thought that 10.15
the hydrocephalus is associated with obstruc-
tion of the normal absorption of CSF, due to
abnormal development of the jugular foramen.
Hydrocephalus can also be acquired following
conditions such as meningitis or haemorrhage.
Hydrocephalus can be classified as normotensive
or hypertensive. Normotensive hydrocephalus is
usually incidental to loss of brain parenchyma,
after destructive pre-natal or post-natal infection
or injury. The CSF volume expands passively to
fill the space that is normally occupied by the brain
tissue. Hypertensive hydrocephalus is a result of
obstruction of the CSF conduit between the sites
of production, in the third and lateral ventricles,
and the sites of absorption by the arachnoid villi Fig. 10.15 Hydrocephalus in a 6-week-old male
in the subarachnoid space. Blockage may be due foal. The foal was unable to lift his head and pull his
to hypoplasia or aplasia of a part of this system or tongue into the mouth. The foal suffered from severe
it may be acquired. The increased CSF pressure perinatal asphyxia and developed necrosis of the
results in dilation of the third and lateral ventri- cerebrum. CSF took the place of the lost parenchyma.
cles, with resulting tissue damage. This was a case of compensatory hydrocephalus.
(Photo courtesy FT Bain)