Do you still take skull radiographs for nasal disease?
Probably not, if you’ve had experience with the detail and specificity of CT for nasal disease. In our clinic, animals with signs of nasal or sinus disease are scheduled directly for CT imaging and rhinoscopy. Between these two modalities, we can usually come to a high probability diagnosis that distinguishes between fungal rhinitis, nasal neoplasia, and other types of rhinitis.
Nasal neoplasia is often underestimated clinically.
Nasal neoplasia is common in dogs, and the extent of the disease is often underestimated clinically and on direct imaging. CT allows us to evaluate bone lysis, sinus invasion and sinusitis, and destruction of the cribriform plate and calvarium. These findings often have a direct impact on prognosis and treatment options.
Get familiar with the various appearances of nasal disease and make it a mainstay of your practice.
The Atlas of Small Animal CT and MRI has a section devoted to nasal imaging, which describes a variety of nasal diseases and imaging characteristics. Here’s an excerpt from the text, and a figure of nasal carcinoma. Hope you enjoy it!
Neoplasia
Carcinomas are the most common nasal neoplasm in dogs, and lymphoma is the most common nasal tumor in cats. Most cats with nasal lymphoma are presented with localized stage I disease, although some may have nasal manifestations of multicentric lymphoma. Carcinomas include squamous, transitional, and adenomatous forms. Other tumor types periodically encountered include soft tissue sarcomas, such as hemangiosarcoma; primary bone tumors, including chondrosarcoma, fibrosarcoma, osteosarcoma, and osteochondrosarcoma; and other round cell tumors, such as plasma cell tumor.
Virtually all patients with nasal neoplasia have a soft tissue mass, although tumor margins are often poorly delineated because of summation with adjacent nasal mucosa and underlying disrupted turbinates. Discrete masses recognized on rhinoscopy may not be evident on cross‐sectional imaging even when thin‐section images are acquired. Mineralization may be evident either because of retention of turbinate remnants or, in the case of osteogenic tumors, from the presence of new tumor related bone. Most nasal tumors are bilateral, although the distribution may be asymmetrical. Carcinomas typically arise in the mid to caudal aspect of the nasal cavity, while lymphomas are most often centered on the ventral nasal meatus and the nasopharynx. Neuroendocrine tumors arising from the nasal cavity typically arise on or adjacent to the cribriform plate of the ethmoid bone, extending both rostrally into the nasal cavity and caudally into the cranial vault.
Nasal tumor contrast enhancement is variable and often does not assist in delineating intranasal tumor margins because of the concurrent contrast enhancement of adjacent nasal mucosa. Contrast medium is more useful for delineating extranasal tumor margins in patients with extensive nasal cavity bone destruction or frontal sinus tumor extension.
Nasal tumors often extend into the sphenoid and frontal sinuses, but more often nasal masses cause obstructive frontal sinusitis because of occlusion of the communicating duct between the frontal sinus and nasal cavity. Tumor extension can be distinguished from obstructive sinus disease using contrast‐enhanced imaging to differentiate vascularized mass from fluid or exudative sinus collections.
Ecto‐ and endoturbinate destruction is routinely present because of tumor mass replacement. Destruction of dense frontal, maxillary, vomer, and palatine bone is common and, in general, appears to be more pronounced with nasal carcinomas and soft‐tissue sarcomas, although aggressive destruction occurs with lymphoma as well. Cribriform plate destruction is a common feature of aggressive nasal tumors and should be carefully assessed since this has implications regarding therapeutic options and prognosis. Large destructive lesions are easily recognized. Smaller fenestrations are best evaluated using a combination of thinly collimated axial and dorsal plane reformatted images when CT is used and with thin dorsal plane 3D SPGR images using MR. Contrast‐enhanced images can be useful when using either modality to detect meningeal enhancement in those patients with suspected intracranial encroachment. CT and MRI are equally effective in diagnosing nasal neoplasia, although CT has a slight increase in sensitivity for detecting bone lysis.
Homework
If you use CT or MR on a regular basis to diagnose nasal disease, be sure to compare and contrast between the different types of tumors and rhinitis. If this is new to you, it’s a fascinating area to learn about. The Atlas of CT and MRI is available through Amazon, and has 26 figures showing case examples to further your learning. Check it out if this article was helpful!
See you next time,
Allison Zwingenberger
Co-Author, Atlas of Small Animal CT and MRI
P.S.
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