Page 1135 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1110 CHAPTER 10

VetBooks.ir CHOLESTEROL GRANULOMA 10.63
(CHOLESTEATOMA)

Cholesterol granulomas, also known as cholesteato-
mas, are found incidentally in the choroid plexuses of
up to 20% of older horses. They occur more com-
monly in the fourth ventricle, but usually reach a larger
size in the lateral ventricles and are thus more likely to
cause clinical signs. They appear as brownish nodular
thickenings and microscopically consist of abundant
cholesterol crystals interspersed with haemosiderin,
empty clefts and an inflammatory reaction consist-
ing of giant cells and macrophages (Fig. 10.63). In
a minority of cases, compression of brain tissue or an
obstructive hydrocephalus may result. Clinical signs
are insidious in onset and include altered behaviour,
depression, somnolence, seizures, ataxia, weakness
and unconsciousness. There is no effective treatment. Fig. 10.63 Cholesterol granulomas in the lateral
ventricles of a 20-year-old mare. The mare had a
GOMEN DISEASE history of seizures. (Photo courtesy M Saulez)

Gomen disease is a progressive degenerative cerebel-
lar disease, recognised in the northwest part of New breeds. Both halothane and isoflurane anaesthe-
Caledonia in the South Pacific, that causes mild to sia have been used in reported cases. Signs range
severe ataxia. It occurs in indigenous and introduced from difficulty standing to tetraplegia with flac-
horses that are allowed to roam free, with confined cid paralysis and anaesthesia of the hindlimbs.
horses generally unaffected. Signs may take 1–2 years Characteristically, horses move into a dog-sitting
to develop following introduction to an endemic position. Affected horses became recumbent or
area. Prominent signs include ataxia and a wide- remained in lateral recumbency until euthanasia
based stance referable to cerebellar involvement and 1–8 days later. Necropsy revealed haemorrhage and
weakness, probably due to brainstem or spinal cord congestion of the meninges and spinal cord, and
involvement. The condition is progressive, with most degrees of malacia of grey matter over at least sev-
horses dying or being euthanased within 3–4 years. eral spinal cord segments at sites anywhere from the
Gross examination of the brain reveals cer- caudal cervical to caudal sacral spinal cord. These
ebellar atrophy, with severe depletion of Purkinje changes are consistent with hypoxic and ischaemic
neurons visible histologically. There is moderate neuronal damage. The syndrome is thought to
to severe lipofuscin pigmentation of neuron cell involve a number of factors including systemic arte-
bodies throughout the brain and spinal cord. This rial hypotension, local venous congestion caused by
is considered greater than normally expected in halothane anaesthesia and compression of the cau-
healthy horses of a similar age. The pathogenesis dal vena cava by abdominal viscera. The prognosis
is unknown, but is thought to involve a metabolic was hopeless in the cases that have been described,
disorder, perhaps resulting from toxicity. but milder cases may not be recognised.

POST-ANAESTHETIC MYELOPATHY STRINGHALT

Post-anaesthetic myelopathy has been reported Definition/overview
particularly in young heavy horses, although there Stringhalt is a disorder that is characterised by an
have been reports of cases in many other horse abnormal gait with involuntary and exaggerated