Plasmablastic Lymphoma of the Anorectal Region in a Human Immunodeficiency Virus (HIV)-Positive Patient: Integrating Radiologic Findings.

Plasmablastic lymphoma (PBL) is an uncommon and aggressive subtype of diffuse large B-cell lymphoma (DLBCL), strongly linked to immunosuppressed states. Although it most frequently involves the oral cavity, anorectal presentation is exceptionally rare. We describe the case of a 27-year-old male with a recent human immunodeficiency virus (HIV) diagnosis, who presented with a growing perianal mass and rectal bleeding. The lesion progressed despite initial treatment and required surgical management. Imaging revealed a necrotic anal canal mass with soft tissue invasion, and histopathology confirmed the diagnosis of PBL. The patient underwent chemotherapy but ultimately experienced a poor clinical outcome. Due to its rarity and non-specific presentation, anorectal PBL is often misdiagnosed, delaying definitive treatment. Imaging, particularly magnetic resonance imaging (MRI), is essential for evaluating lesion extent and guiding clinical decisions. Despite available therapies, the prognosis remains guarded. This case highlights the importance of considering PBL in the differential diagnosis of atypical anorectal masses in immunosuppressed patients. Early imaging and histopathologic assessment are vital for timely diagnosis and treatment.