We report a case of mediastinal abscess formation following endoscopic ultrasound-guided tissue acquisition (EUS-TA) performed for the diagnosis of mediastinal lymphadenopathy. A 50-year-old man, who had undergone surgery for lung cancer and received adjuvant chemotherapy, presented two months after completing chemotherapy with subcarinal lymph node enlargement on computed tomography (CT) and fluorodeoxyglucose (FDG) uptake on positron emission tomography (PET)-CT. The size of the lymph node increased more than twofold over the following month, as revealed by evaluation with EUS. EUS-TA was then performed, confirming lymph node metastasis from lung cancer. Six days later, contrast-enhanced CT revealed a hypodense lesion with marginal enhancement surrounding the punctured lymph node, leading to the diagnosis of a mediastinal abscess. The patient’s clinical condition improved with conservative treatment using intravenous antibiotics. The abscess formation was primarily outside the lymph node, suggesting that the puncture needle may have inoculated bacteria into a poorly vascularized area. The patient’s immunocompromised state following chemotherapy and the inadequate blood supply within the rapidly enlarging lymph node likely contributed to the abscess formation. Mediastinal abscess formation following EUS-TA for lymphadenopathy is rare, and current guidelines do not recommend prophylactic antibiotics. However, as demonstrated in this case, endoscopists may encounter this complication when multiple risk factors are present.
