cell carcinoma involving thyroid gland is an extremely rare
condition. To label a thyroid tumor as squamous cellcarcinoma the
tumor should be entirely composed of tumor cells with squamous
differentiation. This condition should be differentiated from:
carcinoma thyroid containing patches of sqamous epithelium
carcinoma of thyroid containing patches of squamous elements
carcinoma thryoid which may contain both adeno and squamous
of squamous cell carcinoma thyroid:
squamous cell carcinoma thyroid
involvment of thyroid gland by tumor extention from adjacent
involvmement of thyroid gland from adjenct sites like lungs, head
and neck, GI tract
squamous cell carcinoma involving thyroid gland is an extremely rare
condition affecting about 1% of all the primary thryoid malignancies.
Histologically the thyroid gland does not normally contain squamous
epithelium that is the reason why this condition is pretty rare.
Several hypothesis have been proposed to explain the genesis of
squamous cell carcinoma in the thyroid gland.
& Harvey theory:
is one of the earliest theories proposed to account for the
development of squmaous cell carcinoma in the thyroid gland. This
theory is based on the concept that embryonic remnant of thyroglossal
cyst contained squamous elements. Under normal circumstances
thyroglossal duct involutes. Persistence of this duct and the related
squamous elements happens to be the crux of this theory. Anatomically
the lower portion of thyroglossal duct happens to be the pyramidal
lobe of thyroid gland. If this theory is true then squamous cell
carcinoma of thyroid gland should commonly involve the pyramidal
lobe. In reality this tumor is commonly seen in the lateral lobes of
thyroid thus puts a question mark on the validity of this theory.
arch elements which include ultimobranchial body and thymic
epithelium could probably be the source for squamous elements in the
happens to be the more recent one. It says that squamous elements
seen in the thyroid gland could have arisen due to metaplasia of
normal thyroid cells. Even this theory has its own achilles tendon.
The commonest cause for squamous metaplasia in thyroid gland happens
to be Hashimoto's thyroiditis. Studies have shown that it is rare for
these patients to develop squamous cell carcinoma of thyroid gland.
suggested that squamous elements could reach the thyroid gland as
direct invasion from adjacent areas like larynx, pharynx and
oesophagus. He demonstrated this theory by injecting methylene blue
dye in the pyriform fossa before performing thyroidectomy. Superior
portion of the thyroid gland was found stained by the dye. This
demonstrates that there is a communication between these areas for
potential tumor spread.
these tumors are very aggressive, infact as aggressive as anaplastic
carcinoma. These patients usually present with rapidly increasing
neck mass with evidence of involvment of strap muscles, tracheal
compression and oesophageal compression.
differentiation of thyroid mass from other neck lumps
in assessing adjacent organs like larynx and oropharynx
oesophageal and tracheal involvement
very poor because of its radioresistance.
thyroidectomy followed by irradiation is the accepted modality.
Patients with secondary deposits in the cervical nodes should undergo
neck dissection procedures.