Background: Cystic lesions in mediastinum are rare (10-27%). They are believed to originate as a result of developmental anomalies of the foregut.  Generally found in young adults (average age, 31 years).

Case Description: Clinical presentation: 55 year old female presented with dry cough for 6 months, breathlessness for 3 months, progressively increasing for past 10 days presented as a acute emergency in the casualty. Radiological imaging revealed a non-enhancing cystic lesion at the upper two third of right hemithorax. Thoracotomy was performed and intra-operatively a multiloculated encapsulated tumor adherent to lung and lateral aspect of trachea, containing straw colored fluid was noted. Cyst was removed in piecemeal and exact origin was not made out.

Gross: specimen was received in multiple fragments with grey white external surface and irregularly thickened yellowish cut surface.

Microscopy: showed a thick fibrocollagenous wall discontinuously lined by single layer of ciliated coloumnar epithelium with abundant inflammatory infiltrate of foamy histiocytes, lymphocytes and  spindle cells- fibroblastic proliferation, lung parenchymal attachment with no evidence of peripheral thymic tissue  hence diagnosed as Branchial cyst.

Discussion: Branchial cleft cysts are located on the lateral side of neck, mediastinum is involved if it arises from fifth to sixth cleft. Theoretically, the existence of fifth or sixth branchial cleft and its anomalies in mediastinum are possible in humans.

Conclusion: Branchial cyst in mediastinum is rare with only 3 cases being reported in the literature till now. The key to uncover the mystery of Mediastinal cyst is only by histological means. 

Keywords: Branchial cyst, Mediastinal cyst.

Dr D. Pushpalatha