Primary Splenic Follicular Lymphoma Presenting As Isolated Splenomegaly: A Case Report

Follicular lymphoma (FL) is an indolent B-cell lymphoma that usually presents with lymph node enlargement; primary splenic involvement without nodal disease is exceedingly rare. We describe a woman in her late 60s with three months of early satiety, abdominal distension, and weight loss. Examination revealed massive splenomegaly without lymphadenopathy. Laboratory tests were largely normal aside from mild thrombocytopenia. Imaging positron emission tomography/computed tomography (PET/CT) demonstrated an fluorodeoxyglucose (FDG)-avid enlarged spleen with no other lesions. Bone marrow biopsy showed a benign-appearing lymphoid aggregate, and a definitive diagnosis could not be reached. The patient subsequently underwent splenectomy, and histopathology with immunohistochemistry confirmed WHO grade 2 FL confined to the spleen (Ann Arbor stage I). She was started on rituximab therapy and remains in remission on maintenance treatment. This case highlights the diagnostic challenge of isolated splenomegaly and underscores the importance of splenectomy for both diagnosis and cytoreduction when noninvasive tests are inconclusive. Rituximab immunotherapy can achieve disease control in low-tumor-burden FL, though vigilant long-term follow-up is required.