A 45-year-old woman presented with supine headache, associated with blurred vision, diplopia, and pulsatile tinnitus. MRI showed diffuse but asymmetric pachymeningeal enhancement, subdural collections, and bilateral transverse sinus junctions narrowing. Spinal MRI revealed trace thoracolumbar epidural fluid. Serum testing demonstrated pancytopenia and features concerning for new diagnosis of hematologic malignancy. With the initial impression of SIH (Bern score of 8), a non-targeted epidural blood patch was performed, but the headache worsened. Subsequent findings of papilledema prompted lumbar puncture, revealing markedly elevated opening and closing pressure (46cmH₂O after 26ml CSF drained). MR venography revealed no cerebral venous thrombosis. Bone marrow biopsy and CSF cytology revealed evidence of Burkitt lymphoma with intrathecal invasion. Despite CSF diversion, the patient succumbed to tumor lysis syndrome and sepsis. This case illustrates how intracranial hypertension secondary to CNS lymphoma, driven by lymphoma-related venous outflow compression, can mimic SIH on imaging, complicating interpretation and clinical decision-making.

This case underscores the importance of careful interpretation of smooth pachymeningeal enhancement. While SIH remains a common cause, atypical features such as asymmetry, lack of spinal longitudinal extradural fluid collection, and clinical discordance should prompt evaluation for alternative diagnoses. Direct CSF pressure measurement and cytologic analysis are critical when imaging and clinical findings diverge. Pattern recognition must be tempered with vigilance for atypical presentations to avoid anchoring bias and ensure appropriate management.