Page 527 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 24 Tumors of the Respiratory System 505

was associated with significantly worse DFS. If confirmed by fur- Feline laryngeal tumors include SCC, lymphoma, adenocarci-
ther studies, EGFR expression may be a prognostic indicator for noma, and poorly differentiated round cell tumors. 209,229–230 Benign
laryngeal masses have also been reported, such as lymphoplasmacytic
SNSCC, and targeted inhibition of EGFR may be a new approach
VetBooks.ir to treatment of patients with this rare cancer. inflammation, lymphoid hyperplasia, and polypoid laryngitis. 209,231
Primary masses of the trachea in cats include lymphoma, SCC,
SECTION C: CANCER OF THE LARYNX AND histiocytic sarcoma, neuroendocrine carcinoma, and adenocar-
Lymphoplasmacytic inflammation, lymphoid
209,232–238
cinoma.
TRACHEA hyperplasia, and epithelial polyp have also been reported. 209,239
The trachea can be secondarily invaded by adjacent tumors,
such as thyroid carcinomas, 240 or the lumen can be narrowed by
NICHOLAS J. BACON external compression from lymphomatous nodes. 241
Distant metastasis from primary laryngo-tracheal tumors is
Incidence and Risk Factors very rare.

Primary tumors of the larynx and trachea are uncommon in History and Clinical Signs
domestic animals. Laryngeal tumors comprise 0.02% of all biopsy
and necropsy specimens in dogs 206 and a literature review yielded Symptoms may be vague and may include dyspnea, stridor,
less than 30 dogs with tumors specifically affecting the cartilagi- voice change, exercise intolerance, coughing, gagging, dysphagia,
nous component of the larynx and trachea. 207 In a study of 2546 weight loss, wheezing, and anorexia. Some patients may present
insured animals in the United Kingdom in a 12-month period, in acute respiratory distress, including open-mouth breathing in
there were no reported cases of laryngeal or tracheal neoplasia. 208 cats. Clinical findings may be unremarkable, although occasion-
Dogs with tracheal masses are often under 2 years (benign car- ally patients with extratracheal compression may present with a
tilage dysplasias) or over 10 years (malignancies) of age. All sized palpable growth in the neck.
dogs are susceptible with both males and females affected. Arctic
breeds, such as the Alaskan malamute or Siberian husky, account Diagnostic Techniques and Workup
for 27% of canine laryngo-tracheal tumors. 207
Cats with laryngeal or tracheal masses are typically older with Hematology and biochemistry are likely to be unremarkable or
a median age of 12 years. Significant correlations have been found show nonspecific changes.
between Siamese and domestic long-haired cats and lymphoma, Radiographs of the neck and thorax may identify a solitary soft
and domestic long-haired cats and adenocarcinoma. 209 tissue space-occupying lesion or luminal stenosis within the inher-
ent negative contrast of the airway. Mineralization of tumors is
Pathology and Natural Behavior possible for osteochondromas in dogs. Cats with laryngeal and tra-
cheal masses have radiographic abnormalities in 88% of cases (Fig.
The larynx is a musculocartilaginous organ lined internally by 24.10). 209 Intraluminal tracheal masses may be able to be detected
stratified squamous mucous epithelium. Nearly half of its length ultrasonographically. 238 MRI has also been used to identify neo-
is occupied by the rostral epiglottic cartilage. The trachea runs plastic involvement of mucosal or submucosal layers. 216 CT will
from the larynx to its bifurcation at the carina, just cranial to the allow for precise localization of the mass within the lumen and
heart base. It is composed of approximately 35 C-shaped hyaline determine whether it has crossed the wall to affect surrounding
cartilages with the tracheal muscle running dorsally. The rings are local tissues.
interconnected by narrow fibro-elastic annular ligaments. The Direct access to the larynx allows for fine-needle aspirates or
lumen is lined by epithelium. 210 grab biopsies to be easily taken under light anesthesia. Superfi-
Benign lesions of the larynx are rare, and rhabdomyoma and cial biopsies, however, may give a false diagnosis of inflamma-
oncocytoma make up the majority of these tumors. There is cur- tory disease and normal squamous epithelium, when inflamed,
rently some uncertainty whether rhabdomyoma (striated muscle) can have many cytologic characteristics of malignancy. Rigid
and oncocytoma (epithelial origin) are in fact variants of the same or flexible endoscopes allow for direct visualization of tracheal
tumor in the canine larynx. 211,212 Other benign diseases include
chondroma, myxochondroma, congenital cysts in young dogs,
and lymphoplasmacytic and eosinophilic masses. 207,213
Rhabdomyosarcoma, SCC, adenocarcinoma, osteosarcoma
(OSA), chondrosarcoma (CSA), fibrosarcoma, mast cell tumor
(MCT), solitary extramedullary plasmacytoma, and granular cell
tumor have been reported in the canine larynx. 214–217
Young dogs, often 3 to 4 months of age, with active osteo-
chondral ossification sites, are at a higher risk of benign tracheal
chondromas, osteochondromas, and osteochondral dyspla-
sia. 207,218–221 These benign osteocartilaginous tumors grow
during development and stop growing at skeletal maturity. Leio-
myoma has been infrequently reported in the dog. 222,223 Tra-
cheal malignancies are more commonly located on the ventral
wall, and adenocarcinoma, MCTs, extramedullary plasmacy-
toma, OSA, CSA, and lymphoma have all been reported in the • Fig. 24.10 Soft tissue mass visible within the air-filled trachea of a cat,
canine trachea. 207,221,224–228 later diagnosed as a tracheal carcinoma.