Metastasis to ipsilateral medial retropharyngeal and deep cervical lymph nodes in 22 dogs with thyroid carcinoma

Abstract

Objective To determine the rate of nodal metastasis to the medial retropharyngeal (MRP) and deep cervical lymph nodes in dogs surgically treated for thyroid carcinoma. Study design Retrospective study. Animals Twenty‐two client‐owned dogs. Methods Medical records between July 2015 and October 2019 at the Universities of Missouri and Florida were reviewed. Dogs that underwent thyroidectomy with concurrent elective MRP lymphadenectomy ± deep cervical lymphadenectomy were included. Tumor site, preoperative staging, and histopathological findings were recorded. Results Twenty‐two dogs with 26 total thyroid carcinomas were included. Primary tumors were lateralized in 19 dogs, bilateral in two dogs, and bilateral and midline ectopic in one dog. All dogs underwent ipsilateral MRP resection, including bilateral resection in dogs with bilateral tumors. Three contralateral MRP lymph nodes were excised from dogs with unilateral carcinomas. Four deep cervical lymph nodes and one superficial cervical lymph node were excised. Metastases were identified in 14 lymph nodes in 10 of 22 (45%) dogs. All four excised deep cervical lymph nodes and one contralateral MRP lymph node were identified as metastatic. Size of deposit could be classified in 13 of 14 metastatic lymph nodes. Macrometastasis was detected in seven lymph nodes, micrometastasis was detected in one node, and isolated tumor cells were detected in five lymph nodes. Conclusion Regional metastasis was common within the lymph nodes sampled in this population of dogs with thyroid carcinoma. Clinical significance These results provide evidence to justify further exploration of a larger population to verify the rate of regional metastasis and determine the prognostic impact of nodal metastasis.

To map or not to map the cN0 neck: Impact of sentinel lymph node biopsy in canine head and neck tumours

“…[36][37][38] Recently, metastases to surgically excised deep cervical lymph nodes have been described in 45% of dogs with thyroid carcinoma, several of which had negative prognostic factors such has bilateral tumours, lymphatic or vascular invasion and capsular invasion. 39 Conversely, the four thyroid tumours included in the present study were early-stage and no negative prognostic factors were recognized, except for the ectopic location of one thyroid carcinoma. 36 Although the impact of recognized prognostic variables and tumour stage on the likelihood of lymphatic spread has not been assessed yet for canine thyroid carcinoma, it is reasonable to assume that early stage tumours without negative prognostic factors may have a lower risk of lymphatic dissemination.…”

Outcome and postoperative complications in 73 dogs with thyroid carcinoma with gross vascular invasion managed with thyroidectomy

“…Canine thyroid carcinoma has been associated with a high metastatic rate, with 38% of dogs diagnosed with distant metastasis at the time of presentation, most often to the lungs 2,10 . The most common sites of regional metastasis include the medial retropharyngeal and deep cervical lymph nodes, although mandibular, superficial cervical, and mediastinal lymph node metastasis have also been reported 11,12 …”

Multiorgan metastases with massive bone involvement of a medullary thyroid carcinoma in a dog

“…Deep cervical LNs, together with retropharyngeal LNs, have been reported to be the most common sites of nodal metastasis of canine thyroid carcinoma. 8,18 It is, therefore, possible that some neoplastic cells may have reached these sites from the primary tumor, even before diagnosis, entering a state of quiescence. The phenomenon of tumor dormancy is well-acknowledged in human thyroid cancer and has therapeutic implications.…”

“…Only after the onset of symptoms, TBCT revealed presumptive nodal metastatic disease, which included a nodular lesion at the entrance to the chest, consistent with deep cervical lymphadenopathy or ectopic thyroid tissue. Deep cervical LNs, together with retropharyngeal LNs, have been reported to be the most common sites of nodal metastasis of canine thyroid carcinoma 8,18 . It is, therefore, possible that some neoplastic cells may have reached these sites from the primary tumor, even before diagnosis, entering a state of quiescence.…”