Thymic cyst: a rare cause of cervical cyst in adults

Abstract

Thymic cysts are rare congenital tumors, accounting for 1% of all cervical cystic masses in children. These cysts are extremely rare in adults. We here report the case of a 50-year old female patient with no previous medical history, presenting with anterior basocervical swelling with exertional dyspnea evolving over a period of 2 years. Physical exmination showed anterior soft basocervical swelling measuring 4 * 4cm in diameter that didn't move on swallowing. Cervical ultrasound showed subcutaneous oval cystic formation in the suprasternal notch invading the mediastinum, measuring 4 * 2.5 * 3cm. Cervico-thoracic CT scan showed median cervico-mediastinal hypodense mass in contact with the supra aortic trunks, pressing the thyroid upward and extending to thymic lodge, measuring 46 * 64 * 58mm. Cervicotomy with surgical exploration showed tense well encapsulated cystic mass with yellow citrine content in the thyroid lodge extending to the anterior mediastinum. The mass was completely excised via a cervical approach. Histological examination of the surgical specimen was in favor of thymic cyst. Patient's evolution was favorable without recurrence at 1 year follow-up. The diagnosis of thymic cysts, although rare, should be suspected even in adult patients with cervical or cervico-mediastinal cystic mass. CT scan and MRI, as well as preoperative aspiration citology, are useful but diagnostic confirmation is based on anatomo-pathological examination allowing for the detection of the thymic tissue containing Hassall corpuscles. Treatment is based on surgery with complete excision of the cystic wall, in order to prevent recurrences.