Acute Superior Vena Cava Obstruction Mimicking Aortic Dissection: A Case of Primary Mediastinal Large B-cell Lymphoma.

Superior vena cava (SVC) obstruction typically presents with facial swelling, upper-limb edema, and dyspnea due to impaired venous drainage from the upper body. Acute presentations are uncommon and may differ markedly from the classic clinical picture. We report the case of a 27-year-old woman who presented with sudden back pain radiating to the chest. This was accompanied by coldness, numbness, and discoloration of the left upper limb, initially raising concern for acute aortic dissection. A CT aortogram excluded arterial pathology. However, it revealed a large anterior mediastinal mass compressing the SVC, consistent with acute SVC obstruction. Laboratory evaluation showed elevated lactate dehydrogenase and CA-125 levels. Histopathological examination confirmed a diagnosis of primary mediastinal large B-cell lymphoma. The patient experienced rapid symptomatic improvement following corticosteroid therapy. Subsequent treatment with R-CHOP chemotherapy (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone) resulted in a marked clinical and radiological response. This case highlights an atypical, pain-dominant presentation of acute SVC obstruction mimicking acute aortic dissection. It emphasizes the importance of considering venous etiologies early to avoid diagnostic delay in patients presenting with acute chest pain and limb vascular abnormalities.