PEER REVIEWED ImagIng EssEnTIals

SMALL ANIMAL & NASOFACIAL RADIOGRAPHY, INCLUDING THE & FRONTAL SINUSES Mary Wilson, RT(R), CT, MR, CV; Danielle Mauragis, CVT; and Clifford R. Berry, DVM, Diplomate ACVR University of Florida

Imaging Essentials provides comprehensive information on small animal radiography techniques. The following anatomic areas have been addressed in previous columns; these articles are available at todaysveterinarypractice. com (search “Imaging Essentials”). • Thorax • stifle joint and crus • Elbow and antebrachium • spine: cervical, thoracic, • abdomen lumbar • carpus and manus • scapula, shoulder, and • Pelvis humerus • Tarsus and pes

he anatomy of the skull and nasofacial area of Radiography of specific areas requires close attention to the dog and cat is complex, with cavities, sinuses, small details of anatomy that will aid in proper position- , , dental arcades, and cranial ing for each image. Improperly positioned radiographs can T cavity. In the 2-dimensional radiography image, lead to anatomic distortion of normal skull anatomy, re- the 3-dimensional skull creates a complex series of lines sulting in summation shadows unfamiliar to the reviewer and superimposed osseous structures. of the images, and possible false-positive diagnoses of ab- normalities.

THE NEED FOR ANESTHESIA INDICATIONS Radiographs of the skull are indicated for evaluation of although some basic skull views may be traumatic injuries, skull pain, epistaxis, soft tissue mass- obtained with heavy sedation, general anesthesia es, and for some related problems of the skull and nasal is required to achieve high-quality, precisely cavity, such as chronic and nasal discharge. If ad- positioned skull radiographs. Reasons include: vanced imaging is available, computed tomography (CT) • Projections made during the standard imaging can provide more specific and detailed information than series of skull radiographs require the dog or survey radiographs. Learn more about indications for CT cat’s mouth to be open when an exposure is by reading Advanced Imaging: Its Place in General made. Practice (January/February 2014), available at tvpjour- • When radiographing a trauma case in which nal.com. mandibular and maxillary fractures are present, a painful animal will not lie still even under heavy RADIOGRAPHIC EXPOSURE sedation. Exposures should be made using: Note: When specific skull fractures are present, • High mAs, with longer time station: Lowest mA that al- or trauma has occurred, placing stress on various lows use of a small focal spot in order to improve geo- areas of the skull to manipulate it for normal imaging metric sharpness and, thus, ability to see fine osseous positions is contraindicated. detail. For an average dog, the mAs is 10 to 15, with 55 to 65 kVp. tvpjournal.com March/April 2014 Today’s Veterinary Practice 47 | ImagIng EssEnTIals

to keep it parallel with the table. A A 3. Place the cervi- cal spine, thoracic limbs, and thorax in a lateral straight position relative to the skull. To ensure the patient is in lateral position: • Place your hand along the ventral mandi- B B ble, positioning your hand perpendicular to the table and the mandible. • Feel for the exter- nal occipital protu- berance along the caudodorsal margin of the skull (not as prominent in brachy- cephalic breeds). Figure 1. Mesaticephalic mixed breed dog • Compare the rela- positioned for lateral radiograph of the skull tive level with the and nasal cavity (A) and corresponding radio- mid dorsal aspect of graph (B). the nasal cavity and the tip of the ; Figure 2. Dog positioned for VD radio- this imaginary line graph of the skull and nasal cavity (A) • Grids: Use if areas thicker than 10 cm are being should parallel the and corresponding radiograph (B). imaged; otherwise, tabletop technique is rec- table. ommended. With digital radiology equipment, a grid should be used if areas thicker than 15 cm Collimation are being imaged. 1. Center the central beam to the mid cranium, with the collimator opened to just include the cranium and nasal BASIC POSITIONING cavity (crosshairs at level of the eyes). Depending on the Although basic positioning is similar, some variation in use dog’s skull type, the crosshairs may be cranial (dolicho- of sponges and tape will be required due to different skull cephalic), ventral (mesaticephalic), or caudal (brachyce- sizes and shapes of various canine and feline breeds. phalic) to the eye. • Dolichocephalic breeds (ie, Doberman pinscher) have 1. If the area of interest is lateralized to one side, place the long, narrower heads. side of interest closest to the detector in order to mini- • Mesaticephalic breeds (ie, beagle) have medium sized mize geometric magnification. However, oblique projec- and shaped heads. tions will be required to highlight this area of interest. • Brachycephalic breeds (ie, bulldog) have short, wide 1. Place the radiopaque marker ventral to the caudal man- heads, with foreshortening of the nasal cavity and ab- dible, separate from the patient on the table or radio- sence of frontal sinuses. graphic cassette. • Cats have more standard sized and shaped heads; howev- er, some brachycephalic cat breeds (ie, Persian) require the Ensuring Image Quality • same considerations as brachycephalic dog breeds. This view should extend from the rostral end of the nose (nasal planum) through the C1/C2 vertebrae. The images used in this article feature a mesaticephalic • The wings of the atlas (C1) and all aspects of the skull breed dog (mixed breed). (zygomatic arches, mandible, mandibular condyles, tem- poromandibular joints, tympanic bullae, etc) should be LATERAL PROJECTION OF SKULL & SINUSES (Figure 1) even and superimposed. Positioning • Achieving even superimposition is harder in brachy- 1. Place the patient in right lateral recumbency, with the cephalic breeds because their are much wider; nose and skull in an extended position. therefore, superimposing all structures may not be pos- 2. In dolichocephalic and mesaticephalic breeds, place a sible due to geometric distortion from the x-ray beam’s small rectangle sponge under the tip (end) of the nose divergent nature.

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VENTRODORSAL/DORSOVENTRAL PROJECTION VENTRODORSAL OPEN-MOUTH PROJECTION OF SKULL & SINUSES (Figure 2) OF NASAL CAVITY (Figure 3) Choosing ventrodorsal (VD) or dorsoventral (DV) po- Positioning sitioning is dependent on the breed of dog or cat (ie, 1. Place the patient in dorsal recumbency. VD for deep chested dogs and DV for brachycephalic 2. Extend the skull, allowing the external occipital pro- breeds). Key goals are to: tuberance to rest on the table (same as for closed- • Position the area of interest as close to the film/cas- mouth VD image). sette/detector as possible for best overall detail. 3. Place tape from one side of the table to the other, with • Reduce geometric magnification. the center portion of tape secured caudal to the max- • Ensure a straight radiograph that is symmetrical illary canine teeth, which helps keep the hard (right side and left side). parallel to the table. 4. Place a second piece of tape from one side of the table Positioning to the other, starting at the level of the mid abdomen, To obtain the VD projection: moving forward and around the mandible’s canine 1. Place the patient in dorsal recumbency. teeth, and taping to the same level on the other side 2. Extend the skull, with the external occipital protu- of the table. berance resting on a thin sponge to keep the head straight from side to side. 5. Open the mouth to full extension so the mandible is 3. Close the mouth and place a piece of tape across caudal to, or at the level of, the maxillary premolars. the maxilla, caudal to the canines, to keep the head 6. Tape the endotracheal tube with the mandible; care stable, if needed, which will create an artifact over should be taken to keep the endotracheal tube from this area. kinking during this imaging procedure. 4. Make sure the ventral aspect of the and the hard palate, which cannot be visualized when the Collimation patient’s mouth is closed, are parallel to the table. 1. Center the central x-ray beam in the middle of the 5. Use a positioning trough to help maintain the patient hard palate. in this position. 2. If possible, angle the tube head 10 degrees, in a rostral to caudal direction, relative to the patient’s To obtain the DV projection: 1. Place the patient in ventral recumbency. skull. If the tube head cannot be angled, do not 2. Extend the skull, with the mandibular rami placed on oblique the patient’s skull to minimize anatomic the table/cassette/detector or a thin radiolucent sponge distortion from geometric magnification. for stabilization. 3. Place the radiopaque marker along the right side of the patient’s skull. To ensure the patient is properly positioned: • Place your hands on either side of the skull, feeling for Ensuring Image Quality symmetry of the mandible and/or zygomatic arches. • The rostral extent of the image should be the nasal pla- • Check that your hand position, relative to either ana- num. tomic location, is equidistant from the table on both sides. S mall A n i mal kull & N asofac al Rad og r a p hy, Includ ng t h e asal C vit y Fr on Si nus s Collimation A B 1. Set the central x-ray beam to the midlevel of the zygomatic arch (at the level of the eyes), with the collimator opened to include the cranial aspect of C1 vertebra, neurocranium, nasal cavity, and just beyond the nasal planum rostrally. 2. Place the radiopaque marker on the right side of the patient, taking care to avoid superimposition over any part of the skull.

Ensuring Image Quality Figure 3. Dog positioned for • The rostral extent of the image should be the VD open-mouth radiograph of nasal planum. the nasal cavity (A) and cor- • The caudal extent should be the C1/C2 verte- responding radiograph (B). brae. Note: The tube head, which • Make sure the left and right sides of parts of is not seen in this image, was the skull are symmetrically positioned and not angled 10 degrees toward the obliqued; however, this is almost impossible in dog’s nose in order to obtain as much of the caudal aspect of dogs and cats that have skull trauma with mul- the nasal cavity as possible without mandibular superimposition. tiple fractures. tvpjournal.com March/April 2014 Today’s Veterinary Practice 49 | ImagIng EssEnTIals

• The caudal extent should be at the level of the super- • The caudal extent should be to the end of the nonscreen imposed mandible and osseous structures of the caudal film’s edge (as far caudal in the oral cavity as possible— skull. typically to the level of the ).

DORSOVENTRAL INTRAORAL PROJECTION OF ROSTROCAUDAL OBLIQUE SKYLINE PROJEC- NASAL CAVITY (Figure 4) TION OF (Figure 5) Positioning It is important to note that this view is only useful in dogs 1. If you have access to nonscreen film (old mammog- and cats that have frontal sinuses; brachycephalic breeds raphy film) that comes pre-wrapped, or use the edge do not commonly develop normal frontal sinuses. of a cassette, an intraoral image of the nasal cavity Use the lateral radiograph (Figure 1) to determine can be obtained with the dog in ventral recumbency. whether frontal sinuses—just dorsal and cranial to the 2. Extend the skull, with the mandibular rami positioned di- end of the neurocalvarium—are present. If gas-filled rectly on the table, and use a thin sponge to eliminate any sinuses are not present, this projection is not needed. degree of mandibular asymmetry. This is the same patient position as described for the DV projection of the skull. Positioning 3. Place the nonscreen film or small cassette in the patient’s This view is very similar to the open-mouth view, except mouth, between the maxilla and endotracheal tube: the nose is pulled caudal with the mandible, which situ- » To obtain better coverage, place the corner of the ates the frontal sinuses in a skyline profile. nonscreen film in first, which allows it to be posi- 1. Place the patient in dorsal recumbency. tioned further back in the mouth. 2. Flex the neck, placing the patient’s hard palate and » Nonscreen film that extends beyond the mouth may mandible perpendicular to the table and x-ray colli- need support from a sponge to keep it from bending mator system. toward the table. 3. Place small triangle sponges under the patient’s exter- Note: Technique for nonscreen film, which must be nal occipital protuberance to help maintain a symmet- manually or automatically processed, is 65 kVp and 150 ric position on the table. mAs; therefore, the patient needs to be under anesthesia 4. Use tape to hold the patient’s skull in place: flex the skull, and all personnel kept outside the room. place the tape on one side of the table at the level of the abdomen, pass the tape around the patient’s nose, and Collimation 1. Center the central x-ray beam between the nasal planum and right and left orbits. A 2. Place the radiopaque marker on the right side of the patient, within the collimated light beam, taking care to avoid superimposition over any part of the skull.

Ensuring Image Quality • The rostral extent of the image should be the nasal pla- num.

A B

B

Figure 4. Dog positioned for DV intraoral radiograph of the nasal cavity (A) and corresponding radiograph (B). Note: Nonscreen film has been placed inside the Figure 5. Dog positioned for rostrocaudal patient’s mouth between oblique skyline radiograph of frontal sinuses the endotracheal tube and hard palate. (A) and corresponding radiograph (B).

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then fasten the tape to the other side of the table at the the figures in this article as a guide as well as the in- same level. If the patient is in a positioning trough, place formation provided in the Ensuring Image Quality the tape along the outside of the trough. sections. 5. Take care to avoid: »» Kinking the endotracheal tube at the level of SUMMARY the oropharynx High-quality, correctly positioned and collimated ra- »» Over rotating the dorsal aspect of the calvar- diographs are critical for accurate assessment of the ium, which superimposes the cranial vault and nasal cavity and general survey of the skull. The pro- sinuses. jections discussed in this article form the basis for eval- 6. Make sure that the nose is perpendicular to the table uation of other areas, such as the tympanic bullae and when viewing the patient from the side. temporomandibular joints, which will be addressed in the next article in this column. n Collimation CT = computed tomography; DV = dorsoventral; VD = 1. Center the central x-ray beam between the eyes, just ventrodorsal dorsal to the bridge of the nose. Suggested Reading 2. Collimate on all sides to within a cm of the pa- Burk RL, Feeney DA. Small Animal Radiology and Ultrasonography: A tient’s . Diagnostic Atlas and Text, 3rd ed. Philadelphia: Saunders Elsevier, 2003. Kealy JK, McAllister H, Graham JP. Diagnostic Radiology and 3. Place the radiopaque marker on the right side of Ultrasonography of the Dog and Cat, 5th ed. Philadelphia: Saunders the patient. Elsevier, 2011. Sirois M, Anthony E, Mauragis D. Handbook of Radiographic Positioning for Veterinary Technicians. Clifton Park, NY: Delmar Cengage Learning, 2010. Ensuring Image Quality Thrall DE (ed). Textbook of Veterinary Radiology, 6th ed. Philadelphia: • The dorsal extent of the image should be the dor- Saunders Elsevier, 2012. sal skin surface. • The ventral margin should be the mid nasal cav- ity. Mary Wilson, RT(R), CT, MR, CV, • Make sure to open the field of view to include is a registered radiologic technologist with the American Registry of Radiologic skin-to-skin margins of the collimated area. Technologists. She manages the diagnos- tic imaging section at University of Florida QUALITY CONTROL College of Veterinary Medicine. Quality of Diagnostic Image Danielle Mauragis, CVT, is a radiology For quality control of any diagnostic image, use a sim- technician at University of Florida College of ple 3-step approach. Veterinary Medicine where she teaches diag- 1. Is the technique adequate, with appropriate expo- nostic imaging. She coauthored the Handbook sure and development? of Radiographic Positioning for Veterinary 2. Is the correct anatomy present within the image? Technicians and received the Florida Veterinary Medical Association’s 2011 Certified Compare the images you obtain with the images in Veterinary Technician of the Year Award. this article. Clifford R. Berry, DVM, Diplomate ACVR, is 3. Is positioning anatomically correct (Was correct ana- a professor in diagnostic imaging at University

tomic coverage obtained?), straight, and symmetric? of Florida College of Veterinary Medicine. His S mall A n i mal kull & N asofac al Rad og r a p hy, Includ ng t h e asal C vit y Fr on Si nus s Symmetry of the skull for VD/DV images is critical research interests include cross-sectional when evaluating all structures and osseous anatomy. imaging of the thorax, nuclear medicine, and Once it is determined that the technique is adequate, biomedical applications of imaging. He received make sure the appropriate anatomy is present and his DVM from University of Florida and com- pleted a radiology residency at University of California–Davis. positioning is correct, straight, and symmetric. Use

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