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Types of Thyroid Tumors, Papillary thyroid carcinoma and Reasons for total thyroidectomy

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Thyroid tumors are abnormal growths or masses in the thyroid gland, a butterfly-shaped gland located at the base of your neck. These tumors can be benign (non-cancerous) or malignant (cancerous).

Types of Thyroid Tumors

1. Benign Tumors of the Thyroid

Epithelial Tumors:

  1. Papillary adenoma (fetal of microfollicular adenoma).
  2. Follicular adenoma (cystadenoma or colloid adenoma).

Mesenchymal Tumors:

  1. Lipoma.
  2. Leiomyoma.
  3. Hemangioma.

Other Tumors: Teratoma (mainly in children).

Papillary thyroid carcinoma

Papillary thyroid carcinoma

2. Malignant tumors of the thyroid (Thyroid Cancer)

Background:

Thyroid tumors of follicular cell origin:

Differentiated Thyroid Cancer:

  • Papillary thyroid carcinoma.
  • Follicular thyroid carcinoma.
  • Hurthle cell carcinoma.
  • Variants of papillary cell carcinoma, poorly differentiated thyroid carcinoma.

Undifferentiated carcinoma

Background: Thyroid tumors

  1. Parafolicular cell origin: Medullary thyroid carcinoma (Sporadic, Familial).
  2. Stromal origin: Lymphoma, Sarcoma, and Metastases.

When to be suspected?

Thyroid cancer is suspected in the presence of an enlarging painless lesion with one or more of the following:

  • Radiation exposure.
  • Male gender, older age, and younger age.
  • Rapid increase in size.
  • Previous thyroid cancer.
  • Lymphadenopathy
  • Evidence of local invasion (vocal cord paralysis, dysphagia, or firm, fixed nodules)
  • Familial syndrome.

Incidence

  • (Papillary or papillary/follicular= 80%.
  • Follicular= 15%
  • Medullary = -2-10%
  • Anaplastic 5-15%
  • Lymphoma= rare.
  • Metastatic= rare.

Classification

  • Differentiated tumors of follicular origin (90-95%): Papillary carcinoma, follicular carcinoma, Hurtle cell carcinoma.
  • From parafollicular cells (2-10%): Medullary thyroid carcinoma (MTC).
  • Poorly differentiated (5-15%): Anaplastic thyroid carcinoma (ATC).

Oncogenes associated with Thyroid Carcinoma

  • RET oncogene: Papillary (PTC) & MTC.
  • Mutated RAS oncogene: Follicular thyroid carcinoma (FTC).
  • Mutated p53 gene: Anaplastic thyroid carcinoma (ATC).

Papillary thyroid carcinoma (PTC)

Incidence

  • It is the most common histological variety of thyroid malignancy (80%) and is considered the predominant thyroid cancer in children.
  • May be due to radiation exposure of the neck.
  • Age: Peak incidence is in the third decade of life.
  • Gender (female: male 3:1).

Pathology

  • It is composed of complex papillary projections with a fibrovascular core.
  • The hall mark diagnostic features are Psammoma bodies (laminated calcified spheres) and Orphan Annie eye Nuclei or ground glass nuclei (nuclei that contain finely dispersed chromatin, which imparts an optically clear or empty appearance). 
  • The incidence of multi-focality is 80%.
  • It has a propensity to spread to LNs in 30-50% of patients, albeit with no effect on survival. Hematogenous spread is late to the lungs and bones.

Clinico-pathological Forms of PTC

Based on tumor size and extent, 3 clinico-pathological forms of PTC are recognized, all of which may be associated with LN metastases and intra-thyroidal blood vessel invasion or occasionally metastases.

  1. Minimal or occult: micro carcinoma: 1 cm or less, no capsular invasion, unpalpable, and usually an incidental finding or at autopsy.
  2. Intra-thyroidal tumors: >1cm, confined to the thyroid gland with no extra-thyroidal invasion.
  3. Extra-thyroidal tumors: Locally advanced with invasion through the capsule into adjacent tissues.

Diagnosis

Symptoms and signs:

  • Euthyroid, slowly growing, painless mass.
  • Manifestations of local invasions (late): Dysphagia, dyspnea, hoarseness of voice.
  • Palpable cervical LN: More apparent than primary lesion (occult tumor).
  • Distant metastases (uncommon): lung metastases in children.

Investigations

Ultrasonography (US)

Sonographic features that are helpful are:

  1. Calcifications: Thyroid microcalcifications, which are Psammoma bodies, are 10 – 100m round laminar crystalline calcific deposits. They are one of the most specific features of thyroid malignancy, with a specificity of 85%.
  2. Local invasion of adjacent soft tissue & LN metastases are highly specific for thyroid cancer. The US features that raise suspicion of LN metastases include a rounded bulging shape, increased size, replaced fatty hilum, irregular margins, heterogeneous echo-texture, calcifications, cystic areas, and vascularity throughout the LN instead of normal central hilar vessels at Doppler imaging.
  3. Shape: The shape of a thyroid nodule is a potentially useful US feature in that a solid thyroid nodule that is taller than it is wide (i.e. greater in its anteroposterior dimension than its transverse dimension) has a 90% specificity for malignancy.
  4. Vascularity (color or power Doppler US): The most common pattern of vascularity in thyroid malignancy is marked intrinsic hyper-vascularity, which is defined as flow in the central part of the tumor that is greater than that in the surrounding thyroid parenchyma.
  5. Hypoechoic solid nodule: Malignant nodules, both carcinoma & lymphoma, typically appear solid & hypoechoic when compared with normal thyroid parenchyma.

FNAC (specific and sensitive for PTC, MTC, and ATC).

CT/MRI in patients with extensive local or sub-sternal extension.

Surgery

  • Hemithyroidectomy (lobectomy with isthmectomy) is acceptable for minimal PTC.
  • Total thyroidectomy if size >4cm, age (male>40 y, female > 50 y & angio invasion.
  • Total thyroidectomy + Neck dissection if there is proof of metastatic cervical LNs.

Reasons for total thyroidectomy

  1. 80% is multifocal.
  2. To decrease the incidence of anaplasia in any residual tissue.
  3. Facilitate the Dx of unsuspected metastatic disease by RAI scanning or treatment.
  4. Greater sensitivity of blood thyroglobulin level to predict recurrent or persistent disease.

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