A rare case of ectopic laterocervical thymoma.

The ectopic cervical thymoma is a rare site for a thymus neoplasm. It is frequently confused with cyst or with later neck mass of uncertain diagnosis until a histological diagnosis is made. Thymic neoplasms normally arise in the mediastinum, causing signs and symptoms of compression of the adjacent structures. Although rare, malignant thymomas may develop from an ectopic thymus, situated in the thyroid gland (Miyauchi et al., 1985; Matsuura et al., 2004), the neck (Yan et al., 2010; Yao et al., 2010; Jung et al., 1999), the lungs (Myers et al., 2007), and the heart (Miller et al., 2005). It is thought to be caused by the persistence of embryological organ portions along its route of physiological descent from the neck into the mediastinum during embryological development. The incidence of ectopic thymoma is around 4%. The thymus is a lympho-epithelial organ that is the centre of the development and maturation of the T lymphocytes. It develops from the ventral portion of the third and fourth pharyngeal pouches and by the sixth week of gestation it descends into the anterior mediastinum. It has a lobular structure with an external or cortical portion, richly populated by immature T cells, thymocyte and an internal medullary part.