VD and DV Projections

Choosing between a DV and VD projection is more a function of hospital protocol or personal preference than clinical need. To obtain the VD view, the animal is placed in dorsal recumbency.

Figure 4-2

A, Patient positioning to obtain an oblique view of the middle ear. The resultant radiograph is named the left 20-degree ventral-right dorsal oblique view, which describes the entrance and exit points of the primary beam. The asterisk indicates the point where the primary x-ray beam enters the patient. B, Patient positioning to obtain a right 20-degree ventral-left dorsal oblique radiograph. The arrow indicates the trajectory of the primary beam.

Continued

Figure 4-2—cont'd

C, Left 20-degree ventral-right dorsal oblique radiograph of the middle ear. The right bulla is displaced ventrally (white arrowheads). Only a faint outline of the wall of the left bulla can be seen (black arrowheads) with the left external acoustic meatus located dorsally (black arrows). There is superimposition of the right stylohyoid bone over the right tympanic bulla. The angu­lar process of the right hemimandible (white arrow) is visible ventral to the right temporo­mandibular joint (curved arrow).

midline halfway between the external acoustic meatuses (Figure 4-3, A). The animal is placed in sternal recumbency to obtain a DV view. The primary beam is directed vertically centered at a point where an imaginary line connecting the bullae inter­sects with the midsagittal plane. The body of the mandible should be parallel to the cassette, to avoid distortion. The tongue should be pulled forward and maintained on the midline.

Figure 4-3

A, Patient positioning to obtain a VD view of the middle ear. The asterisk indicates the entrance point of the primary x-ray beam. Choosing between a VD and a DV view is more a function of hospital protocol or personal preference than clinical need. B, VD radiograph of the middle ear. The most caudal walls of the tympanic bullae (black arrowheads) are noted caudal to the more radiopaque petrosal portions of the temporal bones (asterisks). Rostral to the mastoid process (white arrowheads) lies the external acoustic meatus. The paracondylar process (white arrows) projects caudally. C, DV radiograph of the middle ear. The soft tissue exposure technique allows visualization of the external ear canals (arrows). The walls of the tympanic bullae (arrow­heads) surround the petrosal portions of the temporal bones (asterisks).

horizontal portion of the external acoustic canals (Figure 4-3, C), which are noted as well-defined lucent structures. The canals tend to be wider laterally as the auricular cartilage expands to form the pinna. The average diameter of the proximal end of the annular cartilage is 4.1 ± 0.7 mm in dogs in which the tympanic membrane is visible otoscopically.¹