Page 13 - Atlas of Small Animal CT and MRI

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Nasal cavity and paranasal sinuses

Normal anatomy Developmental disorders

Symmetry of the thin, scrolled nasal turbinates is an The nasal septum and turbinates can occasionally appear
important aid to detecting abnormalities in the nasal asymmetrical in otherwise normal dogs and cats. These
cavities. The turbinates are more densely formed rostrally anomalies are often clinically insignificant but can
and become thicker with more interspersed airspaces sometimes lead to impaired airflow or obstruction.
caudally. The turbinates are surrounded by mucosa but Brachycephalic dogs and cats may also have poorly
are themselves thin bone. Thin collimation is required to developed or malformed turbinates and paranasal
appreciate their structure in CT images. The nasal sinuses that predispose them to other sinonasal disor-
sinuses should be air filled with a thin or undetectable ders. The sinuses may be partially developed, asymmet-
mucosal lining. A comparison of CT and MRI of the rical, or absent on one or both sides. Cats occasionally
normal nasal cavities and paranasal sinuses to gross have marked distortion of turbinates that may represent
cross‐sectional anatomy has been reported in mesatice- abnormal growth resulting from severe viral rhinitis at
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phalic dogs (Figures 1.1.1, 1.1.2), and computed tomog- an early age. Early trauma while skull growth is still
raphy of the normal nasal cavity and nasolacrimal occurring can also lead to distortion of nasal anatomy.
drainage system has been described in cats. 2,3 Such patients are often prone to recurring rhinitis as
adults. In brachycephalic cats, the nasal bones become
Normal nasal cycle dorsally rotated and reduced in size, and the course of
the nasolacrimal duct becomes altered. 6
The nasal cycle is a normal physiologic phenomenon Nasopharyngeal stenosis, a narrowing of the naso-
with a periodicity of 2–3 hours, which has been described pharynx caudal to the choana, occurs most commonly
in dogs. This frequent, alternating cycle is thought to as a congenital condition. It may also be secondary to
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allow nasal mucosa to recover from the minor trauma of inflammation, trauma, or tumors. The regions of stenosis
conditioning inspired air. Many dogs with otherwise nor- are very narrow and require thin‐slice CT images to
mal nasal CT or MR examinations will display asymmetry detect. Sagittal reformatted images are helpful for identi-
of the nasal mucosa reflected by apparent unilateral fying and quantifying the stenosis (Figure 1.1.4).
mucosal congestion (Figure 1.1.3). The asymmetry is due
to unilateral vasoconstriction causing increased mucosal Inflammatory disorders
perfusion on the contralateral side resulting in mucosal
thickening and increased resistance to airflow. In patients Foreign body rhinitis
exhibiting the nasal cycle, the mucosal thickening on Imaging diagnosis of nasal foreign body rhinitis often
the affected side is uniform, and there is no evidence of depends on whether the foreign object can be directly
underlying turbinate involvement. visualized. When the object is not seen, as is often the

Atlas of Small Animal CT and MRI, First Edition. Erik R. Wisner and Allison L. Zwingenberger.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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