The Skull
 

There are three types of skulls in dogs relative to the proportions of the facial bones and the cranial vault. This variation must be taken into account when viewing normal skull films doliocephalic: larger facial component (ie; long nosed breeds such as the collie); mesocephalic (e.g. the beagle); brachiocephalic: shorter facial component (e.g. Boston terrier). Some indications for the skull radiographs are neurological problems (hydrocephalus), nasal or mandibular problems (fractures), maxilla (rhinitis, neoplasm), primary tumours of the skull (soft tissue swelling), mass behind the eye, teeth diseases and middle ear problems.

Cat differences: The cat skull is constructed differently from the dog and these differences must be known. Cats have a greater doming on the frontal and nasal bones, smaller frontal sinuses (may be absent in Persians), more complete bony orbits and wider skulls because the zygomatic arches are wider.

Nasal cavity: In the DV view, compare each side for opacity or lucency. Increased soft tissue caused by inflammation or an increase in opacity. When there is a difference in the opacity of one side of the nasal cavity (haminasum) compared with the other, examine for detail of the nasal conchae.

Teeth: Visualise the crown, root and pulp cavity. Note the presence or absence of the lamina dura. This is the side of the alveoli through which the beam passes. This makes it appear as a white line separated by a space (periodontal space) from the tooth root. The periodontal space lies between the lamina dura and the tooth root and is occupied by the periodontal membrane.

Pharynx: Radiographically, its soft structures are contrasted against the air opacity. The pharynx is located ventral to the vertebrae C1-C2 and is best visualised on a lateral projection.
Structures of the pharynx are:
Soft palate: separates the oropharynx from the nasopharynx and can be seen radiographically.
Nasopharynx: air-filled area above the soft palate.
Oropharynx: air filled continuation of the oral cavity below the soft palate.
Laryngopharynx: the common part of the pharynx filled by the larynx in the lateral view.
Hyoid bones: suspend the larynx from the skull - stylohoid, epihyoid, ceratohyoid , basihyoid, and thyrohyoid. As bones, they are visible radiographically. The most common clinical radiographical findings are fractures.
Basihyoid: seen end on in the lateral projection; making it appear very white (dense).
Laryngeal cartilages: make up the skeleton of the larynx-epiglottis, thyroid, cricoid and arytenoid. With  age the cartilages can mineralise, espically in larger or chondrodystrophic breeds. The cricoid cartilage is the first to become calcified.
Cricoid cartilage: the easiest to see.
Epiglottis: also easy to see at the rostral end of the larynx. In the horse the normal position of the tip of the epiglottis is dorsal to the soft palate.

Radiographing the Skull
Skull films are difficult to read because of the confusing overlap of structures of different densities. Use a skull specimen to help read skull radiographs and radiographic projections. All skull radiographs should be carried out under general anaesthesia because they require perfect positioning.  Many different positions are used in skull radiography to look at the different structures. The  dorsoventral and lateral are standard views. Open mouth lateral oblique views of the mandible(Fig. 1) or maxilla (Fig. 2)  are shot at a 45° angle to separate the teeth of the opposite jaws. Occlusal views are shot by placing the cassette in the mouth and directing the beam in a DV (Fig. 3) or VD (Fig. 4)  direction. This isolates the upper or lower jaw respectively from the other jaw.
There are different views to highlight specific structures:

Positioning terms & techniques

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