EP14.02 CLIVAL DIFFUSE LARGE B-CELL LYMPHOMA AS AN UNCOMMON INITIAL PRESENTATION: A DIAGNOSTIC CHALLENGE AT THE SKULL BASE

Abstract BACKGROUND Clival involvement by primary or secondary diffuse large B-cell lymphoma (DLBCL) is extremely rare and may mimic other skull base tumors such as chordomas or metastases. Due to its anatomical location, lesions in this area may initially present with cranial neuropathies, often delaying diagnosis and treatment. MATERIAL AND METHODS We report the case of a 43-year-old woman with no prior medical history who presented with binocular diplopia due to right sixth cranial nerve palsy, in the absence of systemic symptoms. Brain magnetic resonance imaging (MRI) revealed a right-predominant clival infiltrative lesion extending ventrally and caudally into the petrous apex and Meckel’s cave, with mild T2 hyperintensity, heterogeneous enhancement, absent bone remodeling, and involvement of cranial nerves V, VI, IX, X, and XI. Although chordoma was initially suspected, the atypical imaging features prompted further evaluation. FDG-PET revealed multifocal hypermetabolic lesions in the pancreas, spleen, pelvic lymph nodes, iliac/gluteal muscles, and subcutaneous tissue, with lytic bone involvement in the iliac crest and clivus. Laboratory tests showed mild leukopenia, elevated LDH (1270 U/L), and negative tumor markers (CA 19-9, CEA, β-hCG, CA-125). Cerebrospinal fluid (CSF) analysis and flow cytometry were negative for malignancy. A trans-sphenoidal biopsy was performed following tumor board discussion. Histopathological analysis confirmed DLBCL of non-germinal center phenotype RESULTS The disease was staged as Ann Arbor IV-A, with high-risk International Prognosis Index (IPI). Despite no CSF involvement, craniospinal radiotherapy, systemic chemotherapy (polatuzumab vedotin, rituximab, cyclophosphamide, doxorubicin) and intrathecal chemotherapy (cytarabine/methotrexate) were administered. At six months, the patient is clinically stable with neurologic improvement and complete metabolic response. CONCLUSION Secondary clival lymphoma is rare and may mimic other skull base tumors. Distinctive imaging features should raise suspicion. A multidisciplinary management is essential for timely diagnosis and treatment.