Page 175 - Atlas of Small Animal CT and MRI

2.3

Developmental disorders

Anomalous development of the brain Clinical signs include pain, positional pain, hyperesthe­
sia, and neurologic deficits, but severity of clinical signs
Brain malformation in the dog and cat can be induced by correlate poorly to imaging findings. 10
trauma, toxins, inflammatory disorders, serendipitous On CT images, the caudal fossa will appear smaller
in utero aberrations, and genetic defects. Brain develop­ than normal, which may be best appreciated on sagittally
ment can be broadly divided into five progressive stages reformatted images. Obstructive hydrocephalus and
of dorsal induction—ventral induction, neuronal prolif­ syringohydromyelia may also be seen. Similar features
3,6
eration, differentiation and histogenesis, neuronal will be seen on MR images, and a sagittal T2 sequence is
migration, and myelination. Anomalies can arise during often best for detecting ventricular and central canal dis­
1
any one of these stages, and the type of anomaly will tension and for recognizing cerebellar displacement and
reflect the predominant development activity at the time. foraminal herniation (Figures 2.3.1, 2.3.2). 9–11
Most significant anomalies are rarely imaged with CT
or MRI since many patients die or are euthanized early Cerebellar hypoplasia
in life. Although classification schemes for developmental Cerebellar hypoplasia has been reported in cats as a
brain anomalies vary widely, we have chosen to organize sequela to in utero parvovirus infection. 12–14 The disorder
this section into hindbrain herniations and malforma­ has also been reported in dogs, but a distinction between
tions, diverticulation and cleavage disorders, malforma­ cerebellar hypoplasia and cerebellar atrophy from degen­
tions of cortical development, and nonneoplastic cysts. 2 eration may be challenging antemortem. 15–18 On MR

images in people, the cerebellum is small and may appear
Hindbrain herniations and malformations to float in an expanded subarachnoid space. The number
19
Chiari‐like malformation of folia may also be reduced. Similar gross features have
Chiari‐like malformation is due to reduced volume of been reported in domestic animals (Figure 2.3.3).
the caudal cranial fossa, resulting in cerebellar to caudal
cranial fossa volume mismatch. The disorder occurs Cerebellar vermian hypoplasia
3–7
primarily in Cavalier King Charles Spaniels, but other Cerebellar vermian hypoplasia is a rare disorder in
small and toy breed dogs can be affected. 3,4,8 The reduced which the cerebellar vermis is hypoplastic or absent. In
caudal fossa volume results in crowding and reposition­ some patients, the cerebellar hemispheres and flocculus
ing of the cerebellum, which may sometimes encroach may also be involved and the caudal cranial fossa can be
20
on or herniate through the foramen magnum. Cerebellar enlarged. The anomaly is analogous to Dandy–Walker
crowding also causes extramural compression of the syndrome in people.
fourth ventricle and central canal, which leads to On unenhanced CT images, the cerebellar vermis is
obstructive hydrocephalus and syringohydromyelia. hypoplastic or absent, leaving a potential space filled by
3,9

Atlas of Small Animal CT and MRI, First Edition. Erik R. Wisner and Allison L. Zwingenberger.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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