Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

C H A P T E R F I V E
The Skull
RADIOLO GY AND ULTRASONO GRAPHY OF THE SKULL
Skull or head radiographs are indicated for the evaluation of patients with clinical signs
that suggest involvement of the bones, sinuses, nasal passages, teeth, eyes and orbit, brain,
oral cavity, and external soft tissues. The skull is a complex structure with many overlapping
shadows, and this can be intimidating when it becomes necessary to evaluate radiographs
of this area. Fortunately, the skull is a relatively symmetric structure and the right
and left halves can be compared directly, provided the patient is positioned carefully and
symmetrically. Artifacts created by off-axis radiographs can mimic or obscure abnormalities.
Special radiographic projections have been described for evaluation of specific areas.
These are extremely valuable and should be used when clinical signs suggest an abnormality
in those portions of the head.
Ultrasonography has limited value in evaluation of the head. It is used frequently for
evaluation of the eye and orbit, for evaluation of soft-tissue masses or swelling, and for
evaluation of the brain, either through an open fontanelle or through a traumatic bony
defect in the calvarium. The use of computed tomography (CT) and magnetic resonance
imaging (MRI) is steadily increasing as the access to these modalities becomes more available
and affordable. In many cases, either of these modalities obviates the use of standard radiographic
procedures.
RADIOGRAPHIC POSITIONING
Multiple projections of the skull are necessary for full evaluation of pathologic change. The
commonly used radiographic views are the lateral, ventrodorsal, and dorsoventral. Other
views that may be helpful in evaluating specific structures include the open-mouth lateral,
lateral oblique, intraoral ventrodorsal, open-mouth ventrodorsal, intraoral dorsoventral,
intraoral dental studies with “bite” film, frontal, open-mouth frontal, and modified occipital.
To obtain the precise positioning required to evaluate the views of the skull, the radiographs
must be taken with the patient anesthetized and the skull given the necessary support.
L AT E R A L V I E W
The standard lateral view of the skull is obtained by positioning the skull in true lateral
recumbency; this results in superimposition of the paired structures (e.g., mandibles,
osseous bullae) (Fig. 5-1). Positioning is accomplished by elevating the nose rostrally and
rotating the head dorsally using radiolucent supporting material, such as a wedge-shaped
piece of radiolucent foam placed under the mandibles. Failure to do this will result in an
oblique view. The true lateral position is particularly useful in evaluating the nasal area and
calvarium.
V E N T R O D O R S A L V I E W
When making the ventrodorsal view of the skull, the animal is positioned in dorsal recumbency
with its head and cervical spine in a straight line and the palate parallel to the film
(Fig. 5-2). There should be no obliquity to either the left or right. Radiographically, the
position of both mandibles and the shape of the frontal sinuses should be symmetric. This
view is useful for evaluating the mandibles, calvarium, zygomatic arches, and temporomandibular
joints.
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