Patología de la Tiroides: Visión General

Thyroid Pathology: General Overview

• Thyroid pathology encompasses a range of diseases affecting the thyroid gland

Thyroid Gland: Anatomy

• The thyroid gland is a bilobed organ located in the lower anterior neck
• Composed of two lateral lobes connected by an isthmus
• The shape of the adult thyroid resembles a butterfly or the capital letter H
• Each lobe exhibits a pointed upper pole and a blunted lower pole
• Understanding surgical specimen submission (lobectomy, hemithyroidectomy, total thyroidectomy) is crucial for pathologists
• Thyroid biopsies, often combined with ultrasound, are frequently performed
• Historical context: English name derives from Greek "thyreoeides," German name "Schilddrüse" meaning "shield gland." Leonardo da Vinci is credited with the first anatomical depiction of the thyroid, and Thomas Wharton named it due to its location near the thyroid cartilage.

Pyramidal Lobe

• A vestige of the inferior portion of the thyroglossal duct
• A small conical projection of thyroid tissue extending from the isthmus upward to the hyoid bone, often positioned on the surface of the thyroid cartilage
• Present in approximately half of all thyroid glands
• Average length is 24 mm, with some pyramidal lobes exceeding 20 mm
• Typically attached to the left side of the isthmus or to the left lobe itself

Thyroid Gland: Histology

• Composed of thyroid follicles, each lined by a single layer of cuboidal to low columnar epithelium
• The lumen of the follicles usually contains colloid, which can appear scalloped or densely eosinophilic depending on activity levels
• Stroma, including C cells (formerly known as parafollicular cells), are also present
• C cells produce calcitonin

Thyroid Gland: Physiology

• The regulation of thyroid hormones (T3 and T4) is a complex process involving the hypothalamus and pituitary gland
• The hypothalamus releases TRH (thyrotropin-releasing hormone), which stimulates the anterior pituitary to synthesize and release TSH (thyroid-stimulating hormone)
• TSH in turn stimulates the thyroid gland to produce T3 and T4
• T3 and T4 exert a negative feedback loop on the hypothalamus and pituitary, regulating their respective secretions

Sanderson's Polsters

• Collections of small follicles projecting into the lumen of larger follicles
• Can mimic papillary carcinoma

Oncocytes (Hürthle Cells)

• Large cells characterized by abundant, deeply eosinophilic cytoplasm and numerous mitochondria.

Positive Stains

• Follicular cells stain positively for thyroglobulin, TTF1, and low molecular weight keratin.
• Colloid stains positively for thyroglobulin.
• C cells stain positively for calcitonin, neuron-specific enolase, chromogranin A, and synaptophysin.

Thyroglossal Duct Cyst (TGD)

• Congenital anomaly of the thyroid gland
• The most common congenital neck mass
• Due to the persistence and cystic dilation of the thyroglossal duct.
• External surfaces are usually smooth and rounded.
• Contents can range from clear mucus to viscous gel, varying in color (clear, yellowish tan, reddish brown, and grayish white). Infected cysts may contain pus.
• Histologically, lining can vary: Ciliated pseudostratified columnar (respiratory), squamous, or cuboidal epithelium. Cysts often lack epithelium in some areas, reflecting inflammation. Thyroid follicles may be present in cyst or duct wall.

Hashimoto's Thyroiditis

• An autoimmune disease characterized by inflammation of the thyroid gland
• Predominantly affects women (90-95%) typically between the ages of 45 and 65, with familial clustering.
• More frequent in white individuals compared to black individuals.
• Often characterized by a painless, gradual onset of impaired thyroid function (hypothyroidism).
• Frequently results in an enlarged thyroid gland (goiter), though not always.

Graves' Disease ("Basedow Disease")

• An autoimmune disorder leading to hyperthyroidism
• Named after Robert J. Graves
• Commonly affects middle-aged women
• Characterized by increased thyroid hormone production
• Associated with symptoms such as diffuse goiter, infiltrative ophthalmopathy, and, less frequently, infiltrative dermopathy.

Multinodular Goiter

• The most common thyroid disease
• Characterized by an enlarged thyroid gland with multiple nodules
• Nodular enlargement with distorted outer surfaces
• Can cause compression of the trachea, esophagus, or blood vessels
• Frequently asymptomatic and euthyroid.
• Iodine deficiency is the most common worldwide cause.
• Serum thyroid-stimulating hormone (TSH) decreases with increasing goiter size as TSH is negatively correlated with the size of the goiter

Follicular Adenoma

• A benign tumor of the thyroid gland
• Often presents as a solitary "cold" nodule.
• Usually encapsulated, but size variations exist (1-10 cm)
• Solid, fleshy, and tan to light brown in appearance

Follicular Carcinoma

• A malignant tumor of the thyroid gland, comprising 6-10% of thyroid carcinomas
• Usually a solitary 'cold' nodule, warranting extensive sampling of the capsule.
• Three subtypes distinguished by invasiveness: minimally invasive, capsular invasion only, and widely invasive
• Grossly, shows solid, tan-brown solid cut surface, possible cystic changes, and hemorrhage

Oncocytic (Hürthle Cell) Tumors

• A type of follicular neoplasm characterized by the presence of a significant proportion of oncocytes (Hürthle cells)
• Oncocytes are characterized by abundant, granular eosinophilic cytoplasm and prominent mitochondria in high numbers.
• Malignant if the tumor demonstrates capsular and vascular invasion

Papillary Carcinoma

• The most common thyroid malignancy in adults (75-80%)
• Frequently presents as a painless nodule or mass in the neck.
• Frequently, diagnosed by FNA
• Often associated with occult tumors at autopsy (1 to 10 mm). Can be multicentric (46%) or exhibit nodal metastases (14%).

Psammoma Bodies

• Mineral-containing calcifications frequently observed within the fibrous stroma between papillary tumor cells
• Commonly found in papillary thyroid carcinoma.

Medullary Carcinoma

• A neuroendocrine tumor derived from C cells (formerly called parafollicular cells) in the thyroid.
• Either sporadic (nonhereditary) or familial (hereditary)
• Sporadic cases may result in a single tumor, whereas familial cases are more commonly bilateral
• May have bilateral, multicentric growth
• Frequently diagnosed via screening tests for calcitonin or for RET oncogene mutations
• Frequently identified by an analysis of serum calcitonin levels
• Usually a single circumscribed, non-encapsulated, gray-tan mass
• Variety of morphologies may resemble other thyroid malignancies.

Secondary Tumours/Metastases

• These tumors arise from other sites and spread to the thyroid through direct extension or via blood vessels
• Not a common finding
• Most often detected in individuals with known, pre-existing malignancies

Poorly Differentiated Thyroid Carcinoma

Anaplastic Carcinoma

• A highly aggressive, undifferentiated thyroid cancer
• Rare, accounting for a small percentage (2-5%) of thyroid cancers but contributing approximately 40% of cancer-related deaths
• Rapidly enlarging, bulky neck mass

Classification of Thyroid Carcinoma

Este cuestionario ofrece una visión general de la patología tiroides, incluyendo su anatomía y las características del órgano. Explora aspectos como la lobectomía y la importancia de las biopsias en el diagnóstico, además de su contexto histórico. Ideal para aquellos interesados en la anatomía y enfermedades de la glándula tiroides.