الفهرس 
EMBRYOLOGICAL DEVELOPMENTOnly 14 pages are availabe for public view
 |  | from | 197 |  |  |
| | | from | 197 | | |
Abstract
Cancer thyroid is the most common endocrine malignancy, it represenrs approximately 1% of new cancer diagnoses each year, about 5-10% of thyroid cancer patients die from their disease
Thyroid carcinomas arise from the 2 cell types present in the thyroid gland. The endodermally derived follicular cell gives rise to papillary, follicular, and probably anaplastic carcinomas. The neuroendocrine-derived calcitonin-producing C cell from neural cell crest that gives rise to MTCs,HCT arising from oncocytic cells were as Thyroid lymphomas arise from intrathyroid lymphoid tissue, whereas sarcomas likely arise from connective tissue in the thyroid gland.
Thyroid cancers are divided into adiffrentiated carcinoma which include papillary carcinomas, follicular carcinomas and medullary thyroid carcinomas (MTCs),undifferentiated anaplastic carcinomas, primary thyroid lymphomas, and primary thyroid sarcomas, Hurthle cell tumor is arare type of follicular carcinoma reffered to as oxyphilic type and accounts about 3-10% of FTC , Papillary carcinoma represents 80% of all thyroid neoplasms. Follicular carcinoma is the second most common thyroid cancer, accounting for approximately 10% of cases. MTCs represent 5-10% of neoplasms. Anaplastic carcinomas account for 1-2%. Primary lymphomas and sarcomas are rare.
Radiation exposure significantly increases the risk for thyroid malignancies, particularly papillary thyroid carcinoma. This finding was observed in children exposed to radiation after the nuclear bombings in Hiroshima and Nagasaki during World War II.
Low dietary intake of iodine does not increase the incidence of thyroid cancers overall. However, populations with low dietary iodine intake have a high proportion of follicular and anaplastic carcinomas also genetic alternations as (RET, RAS ,P53)are reported in DTC.
Thyroid carcinoma most commonly manifests as a painless, palpable, solitary thyroid nodule associated with hoarsness of voice , dysphagia and lymphadenopathy, Patients or physicians discover most of these nodules during routine palpation of the neck. Palpable thyroid nodules are present in approximately 4-7% of the general population, and most represent benign disease. High-resolution ultrasonography reportedly depicts thyroid nodules in 19-67% of randomly selected individuals. An estimated 5-10% of solitary thyroid nodules are malignant. Palpable and nonpalpable nodules of similar size have the same risk of malignancy.
The patient’s age at presentation is important because solitary nodules are most likely to be malignant in patients older than 60 years and in patients younger than 30 years. In addition, thyroid nodules are associated with an increased rate of malignancy in male individuals.
Ultrasonography is the imaging modality most commonly used to evaluate thyroid disease. This noninvasive study enables accurate evaluation of the thyroid gland. However, the usefulness of ultrasonography for distinguish between malignant and benign nodules is limited. Simple cysts found on sonograms are benign, but simple cysts are rarely found. Cysts are most commonly complex, with at least some solid component that could potentially harbor malignancy. Microcalcifications noted on sonograms are associated with thyroid malignancy. Ultrasonography is highly sensitive for thyroid nodules and can depict nodules only a few millimeters in size also US can guide for FNAC.
Radioiodine imaging can help in determining the functional status of a nodule. Nonfunctional nodules do not take up radiolabeled iodine-123 and appear as cold spots in the thyroid (cold nodules) Hyperfunctioning nodules take up radioiodine and appear as hot spots (hot nodules). Warm nodules appear similar to the surrounding normal thyroid tissue. Hot or warm nodules were historically thought to be benign; therefore, they did not require further evaluation for malignancy.
CT scanning and MRI can be used to evaluate soft-tissue extension of large or suspicious thyroid masses into the neck, trachea, or esophagus and to assess metastases to the cervical lymph nodes.
TSH assay is useful in the evaluation of solitary thyroid nodules. A low serum TSH value suggests an autonomously functioning nodule, which typically is benign. However, malignant disease cannot be ruled out on the basis of low or high TSH levels.
Other thyroid function tests are usually not necessary in the initial workup. Serum thyroglobulin measurements are not helpful diagnostically because they are elevated in most benign thyroid conditions.
Elevated serum calcitonin levels are highly suggestive of MTC. Serum calcitonin measurement, which was once the mainstay in the diagnosis of FMTC, has been replaced by sensitive polymerase chain reaction (PCR) assays for germline mutations in the RET proto-oncogene.
FNAB is the most important diagnostic tool in evaluating thyroid nodules and should be the first intervention. The technique is inexpensive and easy to perform, and it causes few complications, The 4 results from FNAB are benign disease, malignant disease,suspecious for diagnosis, and nondiagnostic, 69% of FNAB results were benign, 4% were malignant, 10% were indeterminate, and 17% were nondiagnostic. Their false-positive rate was 2.9%, and their false-negative rate was 5.2%. Sensitivity and specificity were 83% and 92%, respectively
PTC has aproperity to invade lymphatics but less likely blood vessels, however FTC spread mostly by angioinvasion and haematogenous spread.in MTC early spread to regional lymph nodes is common, but in ATC spread mainly to bone , brain , and lung which is likely to be presented at the time of diagnosis in about 50% of patients.
Treatment of cancer thyroid is mainly surgical, Total thyroidectomy is the main treatment of DTC and is recommended for tumors > 1cm however Hemithyroidectomy may be considered for small (< 1cm), low risk, unifocal, intrathyroid tumors in the absence of prior head and neck radiation and cervical nodal metastasis
Total thyroidectomy with prophylactic or therapeutic central neck dissection (level VI) is considered the standard of care for all patients with medullary thyroid cancer, as they don’t concentrate radioactive iodine , also exclusion and treatment of pheochromocytoma should be done in patients with FMTC .
In ATC most patients have advanced disease at the time of diagnosis, surgery is often not indicated and it is mainly palliative and is associated with high risk of complications however, if the tumor appears to be localized to the thyroid total thyroidectomy is recommended, often in conjunction with postoperative adjuvant radiotherapy or combined-modality therapy. Surgical debulking may provide symptomatic relief for patients with very large tumors and significant airway compression.
Prophylactic unilateral or bilateral central neck dissection may be considered in clinically( N0 )disease, especially for advanced primary tumors (T3 or T4) When lateral cervical lymph nodes have biopsy-proven disease, therapeutic central and lateral compartment neck dissection should be performed .
Therapeutic compartmental lateral neck dissection should be attempted for patients with minimal or no distant metastasis, In the presence of distant metastasis or advanced local disease, less aggressive neck surgery that preserves speech and swallowing function may be appropriate .
RAI ablation is indicated for large (>4 cm) tumors, known distant metastasis, and/or gross extrathyroid extension however RAI ablation may be considered for moderate-size (1-4 cm) tumors that are node positive; grossly multifocal; aggressive, based on histology; and high risk, based on patient factors (age >45y, history of head and neck radiation, family history of thyroid cancer), but RAI not recommended for small (< 1 cm), solitary tumors or multifocal tumors when all foci are < 1 cm.
RAI is equally effective when used with thyroid hormone withdrawal or with recombinant human thyroid-stimulating hormone (rh-TSH) stimulation , Primary combined radiotherapy and chemotherapy is advised for locally advanced, unresectable disease
Most studies use a doxorubicin-based regimen, such as doxorubicin 20 mg once weekly given prior to the first radiotherapy session, Doxorubicin has also been given concurrently with radiation therapy as a radiosensitizer then Consider surgical resection for patients who have a good response to treatment
Thyroid replacement therapy (standard dosing with thyroxine replacement) should be initiated postoperatively with the goal of maintaining euthyroidism
Prognosis is related to age , sex and stage of the disease, it is better in female patients and in patients younger than 40 years, DTC has agood prognosis but ATC has the worst prognosis , thyroid lymphoma also has arelatively good prognosis as it is alocalised disease.