Page 275 - Small Animal Internal Medicine, 6th Edition

CHAPTER 14
VetBooks.ir

Diagnostic Tests for the

Nasal Cavity and

Paranasal Sinuses

NASAL IMAGING cats with possible tooth root abscess. Because nasal signs
may be the only indication of tooth root disease, imaging is
Nasal imaging is a key component of the diagnostic assess- indicated for patients without an obvious diagnosis from CT
ment of animals with signs of intranasal disease, allowing and rhinoscopy.
assessment of bone and soft tissue structures that are not The intraoral view is taken with the animal in sternal
visible by physical examination or rhinoscopy. Nasal radiog- recumbency. The corner of a nonscreen film is placed above
raphy, the type of imaging most readily available in general the tongue as far into the oral cavity as possible, and the
practice, is described in some detail. However, computed radiographic beam is positioned directly above the nasal
tomography (CT) provides images that are superior to radio- cavity (Figs. 14.1 and 14.2). The frontal sinus view is obtained
graphs in most cases and has widespread availability. The with the animal in dorsal recumbency. Adhesive tape can be
role of magnetic resonance imaging (MRI) in the evaluation used to support the body and draw the forelimbs caudally,
of canine and feline nasal disease has not been well estab- out of the field. The head is positioned perpendicular to
lished, but it likely provides more accurate images of soft the spine and the table by drawing the muzzle toward the
tissue than are provided by CT. MRI is not used routinely on sternum with adhesive tape. Endotracheal tube and anes-
account of its limited availability and relatively high expense. thetic tubes are displaced lateral to the head to remove them
High-quality dental imaging is indicated for patients in from the field. A radiographic beam is positioned directly
which CT and rhinoscopy do not provide an obvious diag- above the nasal cavity and frontal sinuses (Figs. 14.3 and
nosis. Dental radiographs can be more sensitive than CT for 14.4). The frontal sinus view identifies disease involving the
the diagnosis of tooth root disease. frontal sinuses, which in diseases such as aspergillosis or
Because nasal imaging rarely provides a definitive diag- neoplasia may be the only area of disease involvement. The
nosis, it is usually followed by rhinoscopy and nasal biopsy. tympanic bullae are best seen with an open-mouth projec-
All of these procedures require general anesthesia. Nasal tion in which the beam is aimed at the base of the skull (Figs.
imaging should be performed before, rather than after, these 14.5 and 14.6). The bullae are also evaluated individually
procedures for two reasons: (1) The results of nasal imaging by lateral-oblique films, offsetting each bulla from the sur-
help the clinician direct biopsy instruments to the most rounding skull.
abnormal regions, and (2) rhinoscopy and biopsy cause Nasal radiographs are evaluated for increased fluid
hemorrhage, which obscures soft tissue detail. density, loss of turbinates, lysis of facial bones, radiolu-
cency at the tips of the tooth roots, and the presence of
RADIOGRAPHY radiodense foreign bodies (Box 14.1). Increased fluid density
Nasal radiographs are useful for identifying the extent and can be caused by mucus, exudate, blood, or soft tissue
severity of disease, localizing sites for biopsy within the nasal masses such as polyps, tumors, or granulomas. Soft tissue
cavity, and prioritizing the differential diagnoses. The dog or masses may appear localized, but the surrounding fluid often
cat must be anesthetized to prevent motion and facilitate obscures their borders. A thin rim of lysis surrounding a
positioning. Radiographic abnormalities are often subtle. At focal density may represent a foreign body. Fluid density
least four views should be taken: lateral, ventrodorsal, intra- within the frontal sinuses may represent normal mucus
oral, and frontal sinus or skyline. The intraoral view is par- accumulation caused by obstruction of drainage into the
ticularly helpful for detecting subtle asymmetry between the nasal cavity, extension of disease into the frontal sinuses
left and right nasal cavities. Radiographs of the tympanic from the nasal cavity, or primary disease involving the
bullae are obtained in cats to determinate extension of frontal sinuses.
disease into the middle ear, particularly with nasopharyngeal Loss of the normal fine turbinate pattern in combination
polyps. High quality dental films are indicated in dogs and with increased fluid density within the nasal cavity can occur

247