Page 785 - Clinical Small Animal Internal Medicine

69 Central Nervous System Trauma 753

the retina, optic nerves, optic chiasm, and rostral brain- exaggerated responses to routine stimuli often con-
VetBooks.ir stem. The presence of miosis may indicate a lesion in the firms prosencephalon damage. It is important to note
that the patient’s blood pressure, oxygenation status,
diencephalon, as the sympathetic innervation to the eye
originates in the hypothalamus. The peripheral sympa-
ness and so the latter should be reevaluated after cor-
thetic innervation to the eye can also be affected by and temperature may all affect its level of conscious-
injury anywhere along its pathway through the brachial rection of the former vital parameters.
plexus, anterior mediastinum, cervical soft tissues, and After evaluation, the patient should be assigned a score
tympanic bulla which often causes concurrent third eye- for each category to determine its overall coma score.
lid elevation, enophthalmos, and ptosis as part of a This score can be used to monitor for improvement or
Horner syndrome. A miotic pupil may also be seen deterioration of neurologic status, guide diagnosis and
with ocular injury and spasm of the ciliary muscles of treatment decisions (see later), and provide information
the iris; therefore, an ocular cause of miosis should be about prognosis.
investigated.
Bilateral mydriasis that is unresponsive to light can
indicate permanent midbrain damage or brain hernia- Confirmation of Injury and Diagnosis
tion and a poor prognosis. Other causes of mydriasis A diagnosis of head trauma is based primarily on a
include decreased cerebral perfusion, postictal changes, compatible history and clinical signs of intracranial neu-
trauma to the iris or retina, periorbital trauma or hema- rologic dysfunction. However, additional tests can be
toma and previous ocular abnormalities. used to confirm location and extent of injury. It is impor-
Progression from miosis to mydriasis indicates a dete- tant to understand that advanced imaging of the brain
riorating neurologic status and is an indication for imme- (computed tomography and magnetic resonance imag-
diate, aggressive therapy. Unilateral changes in pupil size ing) should be reserved for patients that do not respond
may be seen early in deterioration. Paralysis of cranial to initial treatment or who deteriorate despite aggressive
nerve (CN) III can lead to mydriasis, loss of direct pupil- therapy. Both of these imaging modalities require anes-
lary light reflex, ptosis, and ventrolateral strabismus. The thesia, which can destabilize the head trauma patient,
CN III nucleus is located in the midbrain so damage to unless the patient is in a coma on presentation.
this nucleus can be seen as a result of midbrain injury or Significant injury to the brain can occur, leading to
compression secondary to transtentorial herniation. neurologic signs without causing skull fractures or
The oculocephalic reflex (physiologic nystagmus) is hematoma formation. Advanced imaging of the brain
tested by moving the animal’s head in vertical and hori- may be performed to evaluate for fractures, hemorrhage,
zontal planes to assess brainstem function and function or parenchymal lesions; however, changes may not be
of the cranial nerve nuclei innervating the extraocular seen even in a patient with severe neurologic deficits.
eye muscles. If the animal’s head cannot be moved with- Imaging modalities available include skull radiography,
out risk, a visual stimulus such as food or the owner ultrasonography, computed tomography (CT), and mag-
should move around the animal. Absence of the oculoce- netic resonance imaging (MRI). Advanced imaging can
phalic reflex reflects injury to the brainstem. This reflex be helpful in identification of hematomas (extraaxial vs
may also be delayed with cerebral injuries. intraaxial), calvarial fractures, edema, and parenchymal
contusions.
Assessment of Consciousness
A patient’s level of consciousness provides information Skull Radiographs
regarding function of the cerebral cortex and the Skull radiography may reveal calvarial fractures, but
ascending reticular activating system (ARAS) of the provides no information regarding the brain parenchyma
brainstem. Consciousness can be described as normal, (Figure 69.11). Radiographs of the skull can be difficult
depressed or obtunded, stuporous, or comatose. An to interpret due to the irregularity of the skull bones and
animal in a stupor is partially or completely uncon- require anesthesia for accurate positioning, which may
scious, but will respond to noxious stimuli. A patient in be contraindicated in the acutely injured patient.
a coma is unconscious and cannot be roused with nox- Radiography should not be limited to the skull following
ious stimuli. Coma typically indicates severe cerebral head trauma. Radiographs of the vertebral column, tho-
injury or brainstem damage, which carries a guarded rax, and abdomen are indicated to evaluate for evidence
prognosis. These terms describe different levels or of other injuries.
“quantities” of consciousness and provide information
regarding degree of cerebral impairment. The quality Advanced Imaging
of consciousness may be more difficult to objectively Computed tomography allows superior evaluation of
evaluate. Inappropriate activity suggesting confused or bony structures and is preferred over conventional