IRF4 and Hodgkins lymphoma: The histopathological diagnosis of CNS‐HL is identical to that of systemic HL and reliant on identification of Hodgkin and Reed–Sternberg cells (expressing CD15, CD30, and multiple myeloma oncogene 1 [MUM1] with variable expression of B‐cell antigens) on a typical non‐neoplastic background comprising small lymphocytes, plasma cells, macrophages, and eosinophils.18, 24