Radiographs of the head are useful when evaluating for injuries or disease processes of the skull, jaws, teeth, nasal cavity, and paranasal sinuses in horses.
Examples include, but are not limited to, dental or periodontal disease of the cheek teeth, head trauma, sinusitis, and neoplasia.
Common clinical signs for which skull radiographs may be indicated include nasal discharge or epistaxis (especially unilateral), swellings of the face, odor or draining tracts, bony changes, or difficulty eating.
When skull radiographs are indicated, here are some common guidelines to follow for procedures, views, and interpretation.
Performing Radiographs of the Head in a Horse
A systemic approach to an x-ray study can help improve efficiency and ensure nothing is missed. This should include…
All necessary equipment, including a generator with enough power for skull radiographs, a large sensor (while intraoral plates are available for dental evaluation, here we’ll discuss extraoral views), and any props that may be needed to aid with views or positioning.
Knowing which views are needed (more on this below).
Having a technique chart or reference for settings. While the numbers can vary depending on the machine/equipment, commonly kVp is set between 70-100 and mA between 3-20.
Sedation is generally recommended unless there is a medical contraindication.
If possible, remove the horse’s halter or anything else on the head that could create an artifact or cover-up details in the x-ray image.
In some cases, it may be worthwhile for radiographs to be accompanied by (or followed up with) additional diagnostic tests, such as ultrasound or endoscopy.
Which Radiographic Views of the Equine Skull Should be Taken?
These are the most common views that are typically used for an equine skull study…
Lateral: This is a good screening shot to look for abnormalities (such as fluid or opacity) in the nasal cavity and paranasal sinuses. Bony and dental structures will be superimposed, but obvious abnormalities (such as tooth root abnormalities) might also be noted here. The cassette is centered over the 4th upper cheek tooth or rostral aspect of the facial crest, and a horizontal beam is used.
Ventrodorsal (or Dorsoventral) Oblique: Oblique views are valuable for reducing superimposition. A VD or DV technique can be used.
A VD oblique aids in evaluating mandibular structures, as well as in viewing the maxillary sinuses with less superimposition. The cassette is centered at about the same location as the lateral shot, but more dorsally to create obliquity. The x-ray tube is placed ventrolateral to the mandible so that the beam is at approximately a 45-degree angle on the opposite side of the face.
A DV oblique is helpful for evaluating sinus structures and maxillary cheek teeth. This view is basically the reverse of the VD, with the cassette positioned below the jaw and the x-ray beam pointing down at approximately a 45-to-60-degree angle on the opposite side of the face.
Dorsoventral: This view provides a lot of information about the sinuses, nasal passages, and nasal septum, especially for comparing right to left. Teeth and bony structures may also be evaluated, although overlap of these structures is to be expected. For this shot, position the cassette ventral to the head, centered under the mandibles. Then position the beam perpendicular to the cassette.
Additional views may be obtained as needed, especially more focal shots and additional angles to isolate an area in question.
For more detailed guidance on views for evaluating specific areas of the skull, this article is highly recommended: 101-eve-v25-i12-fm-toc.indd (aaep.org)
Interpreting Radiographs of the Equine Skull
Fortunately, the contrast between air (the nasal passages and paranasal sinuses) and bone creates good radiographic contrast. On the other hand, the complex structures of the skull, combined with superimposition of those structures, can make radiographic interpretation challenging.
For the best results, always use markers to identify which side of the head is being evaluated in the shot and differentiate between right and left, especially in oblique views (for example, RDLV—right dorsal to left ventral oblique).
Also, obtaining bilateral views is helpful for lateral and oblique shots, since it allows for comparison between sides.
Always evaluate the entire radiograph, and be on the lookout for asymmetry.
As with any x-ray study, clinical experience and good radiography reference images can help a vet identify what is normal versus abnormal.
Consultation with a radiologist can be helpful as well.
By having a system for skull radiographs, knowing which views to take, and becoming familiar with the interpretation of these x-ray studies, a vet can determine the next step for a horse showing symptoms of a problem with the head or teeth.
Written by: Dr. Tammy Powell, DVM
