A Rare Case of Primary Bone Lymphoma Masquerading as Langerhans Cell Histiocytosis

Anaplastic Large Cell Lymphoma (ALCL) is an uncommon type of Non Hodgkin Lymphoma (NHL). It commonly arises in lymph nodes and can also involve extranodal sites such as the skin, soft tissues, lungs, bones, and liver. Here, a case of Anaplastic Lymphoma Kinase (ALK)-positive ALCL in a 17-year-old male patient who presented with swelling in the frontal and occipital bones is presented. The patient was clinically and radiologically diagnosed with Langerhans Cell Histiocytosis (LCH), and excision of the occipital lesion was performed. Preoperatively, lymphoma was not considered a differential diagnosis. Detailed histopathological examination, immunohistochemistry, and Positron Emission Tomography (PET) scan confirmed the diagnosis of primary bone ALK-positive ALCL. This T-cell NHL is composed of large lymphoid cells with abundant cytoplasm and pleomorphic horseshoe or kidney-shaped nuclei, with characteristic ALK and CD30 positivity. An isolated presentation of ALCL as a primary lesion in the bone is extremely rare. Clinicians and pathologists should be aware of this rare presentation, as prompt diagnosis and proper treatment can lead to favourable outcomes.