Page 459 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 23 Cancer of the Gastrointestinal Tract 437

only 55% of 31 cats and dogs with metastasis to the regional LNs control. More aggressive surgeries such as mandibulectomy, max-
had metastasis to the mandibular LNs. 149 CT and PET/CT can illectomy, and orbitectomy are generally well tolerated by cats and
dogs. These procedures are indicated for all aggressive and/or inva-
be useful to determine LN metastasis and guide further diagnos-
VetBooks.ir tics. 143,147,148 LN aspiration should be performed in all animals sive oral tumors, particularly lesions with extensive bone invasion,
with poor sensitivity to RT (Tables 23.3 and 23.4).
with oral tumors, regardless of the size or degree of fixation of the
13–24,161–164
LNs. 34,149 The accuracy of LN aspirates for the detection of meta- Margins of at least 2 cm are generally necessary for malignant
static cancer in cats and dogs is 77%. 152 Resection of some or all of cancers such as SCC, MM, FSA, and OSA in the dog. If pos-
the regional LNs has been described and, although the therapeu- sible, FSA in the dog and SCC in the cat should be treated with
tic benefit of this approach is unknown, it may provide valuable surgical margins greater than 2 cm because of high local recur-
staging information. 148–151 The major concerns with nontargeted rence rates. Bone reconstruction after bony resection has been
LN resection are the possibility of missing a metastatic lesion and described, 165–172 but is rarely necessary in dogs because of good
the potential morbidity associated with excision of multiple LNs. postoperative function and cosmetic appearance with mandibu-
Lymphatic drainage of the oral cavity is highly variable in humans lectomy alone. 13–24 Furthermore, a high complication rate has
and likely in dogs and cats, 151 and the first draining LN can be been reported after reconstruction and these complications often
ipsilateral or contralateral to the tumor and include any one of require revision surgeries for their management. 24,172 In contrast
the mandibular, medial retropharyngeal, parotid, or minor LNs, to dogs, cats frequently have poor postoperative function after
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such as the buccal LN. 149,151 For these reasons, sentinel LN (SLN) mandibulectomy and hence mandibular reconstruction may
mapping and biopsy is becoming the preferred technique for LN improve postoperative functional outcome in cats. 173 Rostral
staging of oral tumors. and segmental resections (e.g., mandibulectomy and maxillec-
SLN mapping and biopsy is the assessment of LN metastasis tomy) may be sufficient for benign lesions and rostral SCC in
without more aggressive en bloc surgical excisions of the regional dogs. Rim resections, in which the ventral cortex of the mandible
LNs. The SLN is the first draining LN and the status of this LN is preserved, may be possible for small benign tumors localized
is representative of the entire LN bed. Furthermore, the SLN is to the alveolar margin of the mandible (Fig. 23.7). 174–176 Larger
not necessarily the regional anatomic LN. In one study of dogs resections, including hemimandibulectomy, hemimaxillectomy,
with cutaneous mast cell tumors, the SLN was different from the orbitectomy, and radical maxillectomy, are necessary for more
regional anatomic LN in 40% of dogs. 153 Methods to detect SLN aggressive tumors, especially FSA, and malignant tumors with a
in people with head and neck cancer include lymphoscintigraphy, more caudal location. 13–24,161–164 Although these large resections
intraoperative blue dyes, and intraoperative gamma probes. 154 carry some morbidity, owner satisfaction with the cosmetic and
Lymphoscintigraphy, intraoperative dyes, and contrast-enhanced functional outcomes is in excess of 85%. 13–24,90,161–164 Cosme-
ultrasonography have been described in dogs with various tumors, sis is usually very good after most mandibulectomy and maxil-
including head and neck cancer. 154,155 The use of lipid-soluble and lectomy procedures (Fig. 23.8), but can be challenging with
water-soluble contrast agents has also been reported as methods of aggressive bilateral rostral mandibulectomies and radical max-
detecting the location of the SLN preoperatively, and then com- illectomies. 13–24,161–164,177 Blood loss and hypotension are the
bining this with methylene blue to aide in the identification of the most common intraoperative complications, particularly during
SLN intraoperatively (Fig. 23.6). 156 The advantage of this latter caudal or aggressive maxillectomy procedures. 21,162,177 Postop-
technique is that radioactive materials are not required and hence erative complications include incisional dehiscence and oronasal
this is a more widely applicable SLN mapping technique. fistula formation, epistaxis, increased salivation, mandibular drift
and malocclusion, lip trauma, infection, and difficulty prehend-
Clinical Staging: Distant Metastasis ing food, particularly after bilateral rostral mandibulectomy cau-
dal to the second premolar teeth. 13–24,161–164,177 Elastic training,
The final step in the clinical staging of animals with oral tumors consisting of an orthodontic elastic rubber chain between an
is imaging of the thoracic cavity for metastasis to the lungs. orthodontic button on the lingual aspect of the intact mandible
Three-view thoracic radiographs (right and left lateral projections, tooth and buccal aspect of the maxillary fourth premolar tooth,
and either dorsoventral or ventrodorsal projection) are gener- has been described to maintain occlusion and prevent mandibular
ally recommended. CT scans should be considered for animals drift after mandibulectomy in dogs. 178 Enteral feeding tubes are
with highly metastatic tumor types, such as oral MM, as they are not usually required after oral surgery in dogs; however, they are
significantly more sensitive in detecting pulmonary metastatic recommended for cats treated with any type of mandibulectomy
lesions compared with radiographs. 157–160 Based on these diag- because eating can be difficult for 2 to 4 months after surgery and
nostic steps, oral tumors are then clinically staged according to the 12% of cats never eat voluntarily after mandibulectomy. 89,90
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WHO staging scheme (see Table 23.2). Local disease control is the goal of treatment for most animals
with oral tumors. Regional LN resection has been described in
Treatment cats and dogs; although it adds to clinical staging information,
its effectiveness in controlling local and metastatic disease is
Surgery unknown. 148–151
Surgery and RT are the most common treatments used for the Radiation Therapy
local control of oral tumors. Surgical resection is the most eco-
nomic, expeditious, and curative treatment. The type of oral RT can be effective for locoregional control of oral tumors. RT can
surgery depends on tumor histology and location. Except for be used as a primary treatment, with either palliative or curative
peripheral odontogenic fibromas, most oral tumors have some intent, as an adjunct for incompletely resected tumors, or as an
underlying bone involvement and surgical resection should adjunct for locally aggressive tumors regardless of the completeness
include bony margins to increase the likelihood of local tumor of excision, such as oral FSA. MM, 42–49 canine oral SCC, 80,81,179