Page 927 - Problem-Based Feline Medicine

42 – THE WEAK AND ATAXIC OR PARALYZED CAT 919

Pathogenesis abnormal formation and/or protrusion of the
meninges and/or spinal cord.
Spinal cord and vertebral anomalies are classified into
– Pathogenesis may involve initial failure of clo-
abnormalities originating in the tissues of mesodermal
sure or the reopening of a previously closed neu-
origin (vertebral body and intervertebral disc) and
ral tube.
those arising from tissues of ectodermal origin (spinal
– Spina bifida occulta represents an incomplete
cord and meninges).
closure of one or more vertebral arches without
Malformations of mesodermal origin. protrusion of meninges or spinal cord.
● Block vertebrae. – Spina bifida manifesta includes meningocele
– Caused by improper segmentation of somites, (meningeal herniation through the vertebral arch
resulting in stable vertebral fusion. defect) and meningomyelocele (herniation of
● Butterfly vertebrae. the spinal cord and meninges).
– Abnormal persistence of the notochord (the – The meningeal and/or spinal cord herniation may
embryological precursor of intervertebral discs), or may not communicate with the environment.
producing a midline cranial to caudal cleft in the ● Sacrococcygeal dysgenesis of Manx cats.
vertebral body (when viewing the vertebra from – An autosomal semi-lethal dominant trait,
the dorsoventral direction). providing the genetic basis for the absent tail
● Hemivertebrae. as well as numerous vertebral and spinal cord
– Produced by fusion of one lateral somite to one abnormalities.
on the contralateral side that is not directly – Homozygotes usually do not survive.
opposed or by a lack of vascularization, lead- – There are four phenotypic subgroups – a com-
ing to a failure of ossification in part of the ver- plete absence of coccygeal, sacral +/− caudal
tebral body. This produces a wedge-shaped lumbar vertebrae (the most severe); fused caudal
vertebra, and scoliosis, lordosis or kyphosis. vertebrae; mobile but kinked caudal vertebrae;
● Transitional vertebrae. and a normal tail.
– Sacralization of the last lumbar vertebra is the
most common in cats. In this condition, the last Clinical signs
lumbar vertebra has characteristics of both lum-
bar vertebrae and the sacrum. Clinical signs are dependent on the type of congenital
● Atlantoaxial subluxation. malformation and its location.
– Results from hypoplasia or aplasia of the dens
Block vertebrae are usually stable.
with secondary atlantoaxial instability.
● Occasionally they can be stenotic or angulated,
– It is either caused by a developmental failure
causing extradural spinal cord compression.
of dens ossification or an ischemic necrosis
● Disc extrusion can occur at disc spaces immediately
and partial resorption of the dens as a result of
cranial and caudal to the block vertebrae.
trauma.
– The cranial portion of the axis is displaced into Butterfly vertebrae are generally incidental findings.
the spinal canal producing cord compression.
Hemivertebrae commonly lead to scoliosis, lordosis
Malformations of ectodermal origin. or kyphosis.
● Abnormalities of the vertebral arch and spinal cord ● Signs are due to spinal cord compression or
are primarily influenced by neural tube devel- repeated trauma associated with vertebral instabil-
opment. ity. Instability produces osseous changes that sec-
● The most common anomaly is spina bifida. ondarily compress the spinal cord.
● Spina bifida. ● Signs may be acute, chronic, progressive or inter-
– The defects of spina bifida vary from incom- mittent, but are usually first noted within the first
plete fusion of the vertebral arch to incom- 1–2 years of life.
plete fusion of the neural tube, resulting in ● Conformation may be visibly or palpably abnormal.