Page 293 - Atlas of Small Animal CT and MRI

Developmental Disorders 283

osteochondrosis, male dogs and Boxer, Rottweiler, and discussion. Errors of ectoderm, mesoderm, and neuro­
German Shepherd Dog breeds are overrepresented. ectoderm development and differentiation, primarily
Clinical signs are those of cauda equina neuropathy, and associated with incomplete dorsal migration and closure,
mean age at presentation is 6.3 years. Approximately result in a grouping of related disorders under the
90% of lesions involve the craniodorsal margin of the overarching term spina bifida, which often involves the
body of the sacrum, while the remainder involve the caudal lumbar and sacral region.
caudodorsal margin of the body of the last lumbar Spina bifida can be further subclassified as spina bifida
vertebra. 23 occulta or spina bifida cystica. Spina bifida occulta is
On CT images, lumbosacral osteochondrosis lesions limited to incomplete dorsal closure of affected vertebra
appear as one or more separate, bone‐attenuating bodies and is periodically seen on imaging studies as an
associated with an underlying defect within the sub­ incidental finding. Spina bifida cystica includes dorsal
chondral bone of the parent vertebra. Osteochondrosis meningeal defects leading to meningocele alone or the
lesions may be isolated or associated with other develop­ most clinically significant form that includes defective
mental or degenerative processes of the lumbosacral meningeal and cord development resulting in mye­
junction (Figure 3.1.11). 24 lomeningocele. Spina bifida can further be characterized
In a report of MR features of lumbosacral osteochon­ as closed or open to the external environment.
drosis in seven dogs, affected endplates were predomi­ Sacrocaudal dysgenesis of the Manx cat is a complex
nantly T1 spin‐echo hypointense, T1 gradient‐echo spinal neural tube defect that includes developmental
hyperintense, variably T2 hyperintense, and contrast abnormalities of the sacral and caudal vertebrae and
enhanced. Concurrent intervertebral disk disease was associated spinal cord segments, which can include
present in five of seven dogs. 26 meningomyelocele and can be closed or open. Other
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manifestations of abnormal neural tube development,
Intradural arachnoid diverticula such as spinal duplication, are rare. 37

Intradural arachnoid diverticula, sometimes termed Spina bifida occulta
arachnoid or subarachnoid cysts, are focal, subdural, The specific CT or MR imaging feature of spina bifida
and usually dorsally located dilatations containing
cerebrospinal fluid and most often confluent with the occulta is incomplete closure of the dorsal arch and
spinous process of one or more vertebrae (Figure 3.1.13).
subarachnoid space. The etiology of intradural arach­
noid diverticula is not known, but when seen in young The meninges and spinal cord should appear unaffected.
animals they are thought to be developmental. A Spina bifida cystica
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broader discussion of the various forms of arachnoid
diverticula, both developmental and acquired, is MR imaging features of meningocele include T1 hypoin­
included in Chapter 3.5. In young dogs, presumed tense, STIR and T2 hyperintense dorsal dilation of the
developmental arachnoid diverticula commonly occur subarachnoid space in the region of the lumbosacral
in the C2–C4 region in large breeds and in the thora­ junction. The terminal spinal cord and associated spinal
columbar region in all breeds. 28–31 Male dogs and Pug, nerves remain within the vertebral canal. Meningocele is
French Bulldog, and Rottweiler breeds are overrepre­ also present in patients with myelomeningocele, but the
sented. Imaging features of intradural arachnoid terminal spinal cord or the associated spinal nerves are
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diverticula are described in Chapter 3.5 (Figure 3.1.12). displaced dorsally into the meningocele. If the lesion is
open, sagittal or transverse STIR or T2 images can be
Spinal neural tube defects (spinal dysraphism) used to document a communicating tract as a linear
hyperintensity (Figures 3.1.14, 3.1.15).
Neural tube defects result from abnormal closure or
failure of closure of the developing neural tube. Closure Spinal dermoid sinus
errors in the rostral part of the tube lead to cranial Dermoid sinus is an uncommon disorder that also
defects, while those that occur caudally lead to vertebral results from neural tube closure errors. Failure of normal
column and spinal cord anomalies. Folate deficiency is cell separation and differentiation into developing
one well‐established cause of the disorder in people, and spine and skin leads to a dorsal sinus that histologically
a hereditary link has been identified in neural tube contains skin elements, such as hair follicles and
defects described in Weimaraner dogs. 32–35 sebaceous glands. The sinus can have a closed end at its
Terminology and classification of the various spinal most internal extent or connect to the meninges or
neural tube defects are both inconsistent and confusing, spinal cord via a closed or patent tract. A grading scheme
and we choose to use a simplified scheme for this has been proposed, ranging from I to IV depending on

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