Page 15 - Atlas of Small Animal CT and MRI

Nasal Cavity and Paranasal Sinuses 5

successful treatment. In our experience, this parameter Virtually all patients with nasal neoplasia have a soft‐
can be evaluated using either CT or MRI. However, tissue mass, although tumor margins are often poorly
thin‐section CT viewed in both the transverse and delineated because of summation with adjacent nasal
reformatted dorsal planes seems to be more sensitive mucosa and underlying disrupted turbinates. Discrete
for detection of small, focal, destructive ethmoid masses recognized on rhinoscopy may not be evident on
fenestrations. Although the majority of patients have cross‐sectional imaging even when thin‐section images
unilateral disease, some animals have bilateral imaging are acquired. Mineralization may be evident either
findings. In general, this constellation of cross‐sectional because of retention of turbinate remnants or, in the case
imaging features, while not pathognomonic, is highly of osteogenic tumors, from the presence of new tumor‐
accurate for the diagnosis of canine aspergillosis related bone. Most nasal tumors are bilateral, although
(Figures 1.1.14, 1.1.15, 1.1.16). 11–15 the distribution may be asymmetrical. Carcinomas typi-
Feline aspergillosis is uncommon but occurs cally arise in the mid to caudal aspect of the nasal cavity,
frequently enough that it must be included in a differen- while lymphomas are most often centered on the ventral
tial of feline nasal disease. In our clinical experience, nasal meatus and the nasopharynx. Neuroendocrine
imaging features include bilateral involvement, moderate tumors arising from the nasal cavity typically arise on or
to marked nasal turbinate destruction, and a greater adjacent to the cribriform plate of the ethmoid bone,
degree of fluid and mucosal hyperplastic replacement extending both rostrally into the nasal cavity and
compared to dogs. Maxillary and/or frontal bone caudally into the cranial vault.
remodeling and bone destruction can be seen. Contrast‐ Nasal tumor contrast enhancement is variable and
enhanced images accentuate the difference between often does not assist in delineating intranasal tumor
noncontrast‐enhancing nasal exudates and adjacent margins because of the concurrent contrast enhance-
contrast‐enhancing nasal mucosa. Frontal sinus involve- ment of adjacent nasal mucosa. Contrast medium is
ment is also seen, but sinus contents appear more fluid more useful for delineating extranasal tumor margins in
and fungal masses are not as prevalent. A common find- patients with extensive nasal cavity bone destruction or
ing is the presence of a mass lesion in the nasopharynx, frontal sinus tumor extension.
which on endoscopic exam is found to be granuloma- Nasal tumors often extend into the sphenoid and
tous reactive tissue. 16 frontal sinuses, but more often nasal masses cause
Feline nasal cryptococcosis appears to occur in two obstructive frontal sinusitis because of occlusion of the
forms. The first is that of localized rhinitis, and the communicating duct between the frontal sinus and nasal
second is that of nasal extension of more aggressive cavity. Tumor extension can be distinguished from
regional or systemic fungal disease. In cats with local- obstructive sinus disease using contrast‐enhanced
ized cryptococcal rhinitis, the disease is bilateral and imaging to differentiate vascularized mass from fluid or
nondestructive. Turbinates do not appear disrupted; exudative sinus collections.
however, the normally air‐filled interstices between the Ecto‐ and endoturbinate destruction is routinely
turbinates appear fluid filled. In the more aggressive present because of tumor mass replacement. Destruction
form, fungal granulomas can produce space‐occupying of dense frontal, maxillary, vomer, and palatine bone is
masses that can erode adjacent bone and may extend common and, in general, appears to be more pronounced
caudally through the cribriform plate (Figure 1.1.17). with nasal carcinomas and soft‐tissue sarcomas, although
aggressive destruction occurs with lymphoma as well.
Cribriform plate destruction is a common feature of
Neoplasia
aggressive nasal tumors and should be carefully
Carcinomas are the most common nasal neoplasm in assessed since this has implications regarding thera-
dogs, and lymphoma is the most common nasal tumor in peutic options and prognosis. Large destructive lesions
cats. Most cats with nasal lymphoma are presented with are easily recognized. Smaller fenestrations are best
localized stage I disease, although some may have nasal evaluated using a combination of thinly collimated
manifestations of multicentric lymphoma. Carcinomas axial and dorsal plane reformatted images when CT is
include squamous, transitional, and adenomatous forms. used and with thin dorsal plane 3D SPGR images using
Other tumor types periodically encountered include soft‐ MR. Contrast‐enhanced images can be useful when
tissue sarcomas, such as hemangiosarcoma; primary bone using either modality to detect meningeal enhance-
tumors, including chondrosarcoma, fibrosarcoma, osteo- ment in those patients with suspected intracranial
sarcoma, and osteochondrosarcoma; and other round cell encroachment. 9,17–20 CT and MRI are equally effective
tumors, such as plasma cell tumor (Figures 1.1.18, 1.1.19, in diagnosing nasal neoplasia, although CT has a slight
1.1.20, 1.1.21, 1.1.22, 1.1.23, 1.1.24, 1.1.25, 1.1.26). increase in sensitivity for detecting bone lysis. 21

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