Page 291 - Atlas of Small Animal CT and MRI

3.1

Developmental disorders

Anomalies of the vertebral column compression atrophy, even in patients without overt
neurologic deficits. An uncommon vertebral anomaly,
Vertebral malformation caudal articular facet hypoplasia or aplasia in the
Malformations of the vertebrae are common, and thoracolumbar vertebral column, has been reported
although some are clinically significant, many are seen as with spinal cord compression due to contralateral facet
incidental findings on imaging studies. Malformations and ligamentum flavum hypertrophy. 6
can be categorized as simple or complex, and a recent The CT appearance of vertebral anomalies will vary
review of spinal anomalies proposed specific classifica­ depending on the specific malformation, but common
tion of anomalous vertebrae based on a similar scheme findings include alteration in vertebral shape, reduced
used in people. Those anomalies that occur during the attenuation when mineralization is incomplete, and ver­
1,2
early embryonic period include centrum median cleft tebral column curvature abnormalities. Vertebral canal
(butterfly vertebrae), true hemivertebrae, mediolateral stenosis suggests spinal cord impingement or compres­
wedged vertebrae, and transitional vertebrae. Anomalies sion, which can be documented using CT myelography
that develop during the later fetal period include block (Figures 3.1.1, 3.1.2). Lumbosacral transitional vertebrae
vertebrae, articular process hypoplasia, and centrum can predispose to cauda equina syndrome (Chapter 3.5),
hypoplasia or aplasia (dorsoventral wedged vertebrae). and asymmetrical transitional vertebra at this level can
1–3
Vertebral anomalies can be further classified as arising result in pelvic rotation leading to coxofemoral malar­
from defects in formation (e.g. wedged, hemi‐, and ticulation (Figure 3.1.3).
butterfly vertebrae) versus incomplete or absent segmen­ MR features are similar to those seen with CT, and
tation (e.g. block vertebrae). spinal cord pathology is often more clearly detected
German Shepherd Dogs are overrepresented for (Figure 3.1.2).
developing transitional vertebrae at the lumbosacral
junction. Certain screw‐tailed breeds, such as Bulldogs,
4
French Bulldogs, Pugs, and Boston Terriers, are highly Craniocervical junction malformation
predisposed to complex vertebral anomalies, particularly The term craniocervical junction malformation
in the midthoracic region. Vertebral anomalies can includes anomalies of the occipital bone and the first
5
result in a combination of scoliosis, kyphosis, lordosis, two cervical vertebrae. The most common of these
7
or rotational spinal abnormalities; can cause spinal canal disorders, Chiari‐like malformation, is discussed in
stenosis; and may predispose to spinal injury from what Chapter 2.3. Other malformations involving the occip­
might otherwise be clinically insignificant trauma. In ital bone and atlanto‐occipital overlap are described
animals with vertebral canal stenosis, spinal cord in Chapter 1.4. Chiari‐like malformation aside, cranio­
diameter is often focally decreased as a result of chronic cervical junction malformations primarily affect

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.
281