الفهرس 
EMBERYOLOGYOnly 14 pages are availabe for public view
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Abstract
The thymus is H shaped gland with variable fusion of the right and left lobes at about the mid portion of the gland. The superior poles are thinner than the inferior poles with connection to the thyroid gland as thyrothymic ligament.
It is an elongated lobulated pinkish yellow structure due to comprising thymic tissue and fat, situated in the antrosuperior mediastinum extending in the midline from the level of the inferior border of the thyroid gland above but occasionally its cranial limit extends over the thyroid gland.
In male, The gland is slightly larger than in female and the left lobe usually reaches somewhat more caudally than the right. Its soft pliable gland that is impressed by the adjacent structures
In the past, substantial progress has been made in understanding the biology of the thymus gland and therefore, the pathology and clinical behavior of thymic tumors.
Tumors of the thymus are classified according to their morphologic features and presumed histogensis. They include tumors arising from thymic epithelial cell called (thymomas), neuroendocrine cells (carcenoid tumors of the thymus), lymphoid cell (malignant non Hodgkins lymphoma and Hodgkins disease) and adipose tissue (thymo lipomas). All other tumors ( myloid and histiocytic) and tumor like lesions (cyst, hyperplasia) are extremely rare.
Myasthenia gravis is an autoimmune disorder of neuromuscular transmission in which antibodies reduce the number of acetylcholine receptors at the neuromuscular junction
Willks recognized this clinical disorder in 1877, and the term myasthenia gravis pseudo paralytica was first used by him.
No effective therapy existed until 1934, when Walker used physostigmine followed by introduction of surgical therapy
Treatment mainly medically by Anticholinesterarses which are the first line of treatment in patient with myasthenia followed by corticosteroids and immunosuppressive drugs. Plasma exchange and human immunoglobulin are used in myasthenic patient who has life threatening signs like respiratory insufficiency and a rapid response to treatment are desired.
7% to 15% of myasthnic patient have thymoma, and in patients with non thymomatous autoimmune myasthenia gravis thymectomy is recommended as an option to increase the probability of symptomatic improvement or remission.
There is a consensus that all adults with generalized symptoms should have thymectomy, particularly if they are younger than 60 years. A small subset of patients with ocular symptoms who fail non operative management or if they have thymoma, some studies report similar result with patients with isolated ocular symptoms. in these patients, thymectomy prevented the progression to the generalized disease.
The timing of surgery, preoperative preparation, anesthetic management and surgical approaches are all controversial.
Further, the trend in therapy is toward earlier surgical intervention.
The best surgical approach to the thymus can be a difficult choice. Apart from biopsy, possible done by mediastinoscopy or anterior mediastinotomy, the only procedure performed on the gland is thymectomy. However, this term can cover different procedures ranging from simply thymectomy (excision of the thymus with its macroscopic capsule) to extended thymectomy (resection of the thymus with exenteration of the anterior mediastinal fat from the lower poles of the thyroid to diaphragm and from one side to the other side from hilum to hilum).