Langerhans Cell Histiocytosis and Erdheim-Chester Disease: A Case Report of Atypical Imaging Overlap

Histiocytoses are rare disorders characterized by abnormal proliferation of histiocytic cells in tissues and organs. They have a broad clinical spectrum and are traditionally categorized as Langerhans cell histiocytosis (LCH) and non-Langerhans cell histiocytosis (N-LCH), but recent evidence highlights a molecular and clinical overlap between LCH and a type of N-LCH known as Erdheim-Chester disease (ECD). While both disorders have distinct features, up to 20% of ECD patients may present with concurrent LCH lesions. Overlap between LCH and ECD is increasingly recognized, but reports of imaging of this phenomenon are scarce. Here, we present a rare case of directly contiguous LCH and ECD lesions in a 69-year-old woman and discuss the radiologic and histopathologic findings as well as the classification of these findings within the revised histiocytosis system.