The thymus gland consists predominantly of epithelial cells and lymphocytes. When precursor leukocyte cells reach the thymus, they differentiate into T-lymphocytes. Thymoma is a neoplasm which originates within the epithelial cells of the thymus. This neoplasm constitutes 25% of all mediastinal tumors, therefore it is considered as the most common neoplasm of the anterior mediastinum. About one-third of patients with thymoma are asymptomatic. Another one-third present with local symptoms such as cough, chest pain, shortness of breath, hoarseness and trouble swallowing that indicate the spread of the tumor to the surrounding structures. The remaining one-third show systemic symptoms related to myasthenia gravis, such as muscle weakness. Thymoma can be classified into four stages that proper treatment can be done according to them. Stage-I represents the tumor within the thymus gland only. Stage-II occurs when the tumor spreads to the surrounding tissues. If the tumor invades the nearby organs, thymoma will be considered as stage-III thymoma. Finally, stage-IV describes the condition of deep spreading of tumor to other body parts. Males and females are equally affected. Mostly, thymoma occurs in the fourth and fifth decades of life. Radiography is the basic diagnostic tool for thymoma. Usually, surgical removal of the affected parts of the thymus gland (thymomectomy) is the best choice for treatment.
Rajab and Issa (2004) described a 43-year old Yemeni woman, and married for 22 years, presented with typical invasive malignant thymoma. Six months earlier, she had developed a cough and chest pain. CT scan revealed an anterior lobulated mediastinal tumor and she was advised surgery. The fat plane between the vessels and the tumor was obliterated in places suggestive of invasive nature of the tumor. Operative findings showed that the tumor invaded the pericardium and it was extending on the right side invading the upper lobe of the right lung beyond the right phrenic nerve. On the left side it was just reaching the phrenic nerve. Superiorly, the tumor was invading and adherent to the bronchiocephalic vein. Several enlarged lymph nodes were also seen in the soft tissues around the tumor. Surgery procedures included sternotomy, resection of a thymoma, and wedge resection of the right upper lobe en block with the tumor. Histopathology report described a partially encapsulated thymic tumor composed of a mixed population of epithelial cells and a large number of lymphocytes. The tumor was separated by thick bands of fibrocollagenous tissue, which were infiltrated by neoplastic epithelial cells.
[Rajab KE, Issa AA. Invasive malignant thymoma in early pregnancy. J Bahrain Med Soc. 2004; 16(2):78-81.]