SECTION EDITOR: C. DOUGLAS PHILLIPS, MD
Diagnosis: Cervicomediastinal thymic cyst
Cervicomediastinal thymic cysts are rare congenital neck masses. Embryologically, the thymus develops from the ventral aspect of the third branchial pouch during the sixth week of fetal life along with the inferior parathyroid gland. It further descends along the thymopharyngeal tract and occupies its place in the superior mediastinum by 12 weeks. At birth, it weighs approximately 13 g, reaching its absolute size at puberty. Later in adult life, it is replaced by fibrofatty tissue. It acts as a secretory organ in cell-mediated immunity. T lymphocytes derived from the bone marrow undergo differentiation in the thymus gland.
Radiology Quiz Case 3: Diagnosis. Arch Otolaryngol Head Neck Surg. 2011;137(7):721-722. doi:10.1001/archoto.2011.97-b