Localised Kikuchi–Fujimoto Disease With Mediastinal Lymphadenopathy: A Case Initially Mimicking Malignant Lymphoma on Endobronchial Ultrasound‐Guided Transbronchial Needle Aspiration Cytology

Kikuchi–Fujimoto disease (KFD), also known as histiocytic necrotising lymphadenitis, is a benign, self‐limiting disorder that primarily affects young women and is typically characterised by fever and cervical lymphadenopathy. However, isolated mediastinal lymphadenopathy without cervical involvement is rare. We report the case of a 37‐year‐old woman who presented with persistent fever and mediastinal lymphadenopathy. Endobronchial ultrasound‐guided transbronchial needle aspiration (EBUS‐TBNA) cytology of the lymph nodes revealed necrosis and atypical lymphoid cells, highly suggestive of malignant lymphoma. Owing to diagnostic difficulties, video‐assisted thoracoscopic excision was performed to obtain a definitive diagnosis. Histopathological examination confirmed KFD with massive necrosis and histiocytic infiltration. The patient underwent symptomatic treatment and remained under long‐term follow‐up. This case highlights the rarity of mediastinal‐limited KFD and the diagnostic pitfall of EBUS‐TBNA cytology, emphasising that surgical biopsy is critical for an accurate diagnosis when malignancy is suspected in this atypical presentation.