Page 183 - Atlas of Small Animal CT and MRI

2.4

Trauma, hemorrhage, and vascular disorders

Head trauma accurate retrospective determination of the acute onset of
a single bleeding episode, veterinary patients often have
Common causes of acute head trauma include high‐ multiple sequential bleeds from a primary lesion, con-
impact automobile collisions, violent blunt‐force and founding the accuracy of staging. The information in
missile penetrating (gunshot) injury, bite wounds, and Table 2.4.1 is extracted from the human MRI literature,
lower‐impact injury from falls and collisions. but it should approximate hemorrhage‐staging patterns
Skull fractures can be nondisplaced or displaced, and in veterinary patients using unenhanced spin‐echo T1
the latter may lead to higher brain morbidity when and T2 intensities (Figures 2.4.3, 2.4.4, 2.4.5). In addi-
2–5
depressed (Figure 2.4.1). Fractures are variable in appear- tion, T2* gradient echo sequences can be used to detect
ance and depend on both the source of trauma and the signal void from susceptibility of blood degradation
impact site. Because the neurocranium forms a rigid products at most stages, though the susceptibility “bloom”
box, comminuted fractures are common, particularly in sometimes overstates the actual hemorrhage volume.
skeletally mature animals whose sutures have fused. Because hematoma density is greater than that of normal
Computed tomography is generally the imaging brain parenchyma, acute to subacute hemorrhage is
modality of choice for initial evaluation of head injury in hyperattenuating compared to brain parenchyma on
people because it can be rapidly performed and accurately unenhanced CT images. Density gradually reduces to
detects skull fractures and intracranial hemorrhage. become isoattenuating with brain parenchyma over
Magnetic resonance imaging is preferred when clinical many days to weeks. 2–5
signs are not explained by CT findings or in patients with
subacute to chronic brain trauma. Experience suggests
1
that a similar approach should be used in veterinary Extraaxial hemorrhage
patients (Figure 2.4.2).
Extraaxial hemorrhage is classified as epidural, subdural,
or subarachnoid, although in our experience subarach-
Staging hemorrhage
noid hemorrhage is less frequently recognized.
Much emphasis has been placed on the importance of
staging intraaxial intracranial hemorrhage in human Epidural hematoma
medicine using MRI. In our experience, while it is an Epidural hematomas are most often traumatic in origin,
interesting intellectual exercise, staging of intraaxial arise in the potential space between the cranium and the
hemorrhage in our veterinary patients is often less dura mater, and typically occur from meningeal arterial
rewarding, as it seldom alters imaging diagnosis or hemorrhage. Epidural hematomas are described as
patient management. In addition, while guidelines for having a characteristic biconvex or lenticular shape on
staging intracranial hemorrhage in people are based on cross‐sectional images (Figure 2.4.6). Acute epidural

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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