Mechanism of Thyroid Gland Invasion in Laryngeal Cancer and Indications for Thyroidectomy

Abstract

Invasion of thyroid gland (TG) by laryngeal cancer is rare. However, ipsilateral hemithyroidectomy is routinely performed during total laryngectomy (TL) for laryngeal cancers. Even hemithyroidectomies are associated with hypothyroidism in 23-63% and hypoparathyroidism in 25-52%. Most of the studies on laryngectomy have advised thyroidectomy for T3 and T4 lesion, transglottic growth, subglottic disease or extension and involvement of anterior commissure. The role of tumour differentiation in TG invasion is unknown. The cases with TG invasion have been reported to have poorer prognosis. This is a retrospective study of 45 patients undergoing thyroidectomy along with TL. Of these, five had TG invasion. Extra-laryngeal soft tissue involvement [RR 1.89 (1.02, 4.24)] and transglottic growths [RR 1.18 (1.02, 1.36)] had a significant association with TG invasion. The mode of spread, contiguous or non-contiguous, depended on tumour differentiation. Well differentiated cancers had propensity for contiguous spread and moderately differentiated cancers for non-contiguous spread (p = 0.05). The 5 years survival of T4a cases was 30%. The difference in survival between TG invasion (p = 0.618), cartilage invasion (p = 0.111) and soft tissue infiltration (p = 0.474) was statistically insignificant. Anatomically direct TG invasion can only occur through extralaryngeal soft tissue which is includes cricopharyngeus and cricothyroid muscles. We recommend thyroidectomy only when these muscles are involved by the tumour in case of well differentiated cancers. The probability of TG invasion increases with transglottic growths with subglottic extension more than 10 mm. We recommend ipsilateral hemithyroidectomy in less differentiated cancers as they have propensity for non-contiguous spread.

Evidence‐based management of the thyroid gland during a total laryngectomy

“…Thyroid gland invasion is part of the extension of anterior extralaryngeal cancer . As reported by Chen et al, the most common route of extralaryngeal spread of glottic SCC is through the cricothyroid membrane .…”

“…Thyroid gland invasion is part of the extension of anterior extralaryngeal cancer. 1,2,[9][10][11][12][13][14] As reported by Chen et al, the most common route of extralaryngeal spread of glottic SCC is through the cricothyroid membrane. 15 CT scan sensitivity is low for thyroid cartilage or cricothyroid membrane invasion, which were associated with TGI in our series.…”

“…[16][17][18][19][20] SCC originating from the subglottis then logically signify a higher risk of TGI, and the glottic lesions with anteroinferior spread may be considered as a risk factor for TGI, as reported by Mendelson et al 4 In our series, subglottic extension was not associated with a higher risk of TGI as previously reported by some authors, nor with major extension to the cricoid mucosa or to the trachea. 1,2,4,9,12,21,22 However in the literature, the limit between the glottis and subglottis is variable and ranges anywhere from 0 to 10 mm below the free edge of the true vocal cords. 4,13 Moreover, the precise definition of subglottic extension used was not reported by all authors.…”

How reliably can computed tomography predict thyroid invasion prior to laryngectomy?

“…It has been shown that involvement of the subglottis carries a significantly higher risk of thyroid invasion . It has also been suggested that poorly differentiated cancers may have a propensity for thyroid invasion, although currently the evidence to support this is low …”

“…2,4,[6][7][8] It has also been suggested that poorly differentiated cancers may have a propensity for thyroid invasion, although currently the evidence to support this is low. 9 This study aimed to test the usefulness of preoperative computed tomography (CT) in predicting histological involvement of the thyroid. The alternative hypothesis was, therefore, that preoperative CT has a high positive and negative predictive value for thyroid involvement prior to total laryngectomy.…”