Paravertebral extramedullary haematopoiesis revealing previously unrecognised hereditary xerocytosis.

Extramedullary haematopoiesis (EMH) is a rare cause of posterior mediastinal masses, often linked to chronic anaemia. A man in his late 60s with recurrent biliary disease was referred for evaluation of posterior mediastinal masses incidentally found during hospitalisation for choledocholithiasis. Imaging and biopsy revealed paravertebral EMH. Laboratory testing showed compensated haemolytic anaemia with stomatocytes, elevated eosin-5-maleimide binding, decreased erythrocyte osmotic fragility, and a PIEZO1 mutation (p.K2323T), leading to diagnosis of hereditary xerocytosis (HX). Family screening revealed the same condition in his son. HX, a rare congenital haemolytic anaemia, often remains undiagnosed due to mild symptoms and subtle findings. This case highlights HX as a unifying cause of recurrent biliary disease and posterior mediastinal EMH, emphasising the importance of recognising this rare condition to avoid inappropriate interventions such as splenectomy.