Expansive lesions of the central nervous system: multiple sclerosis as a rare chameleon

Abstract

Case Presentation: In November 2025, a 25-year-old woman presented to the emergency room with complete severe hemiparesis and motor aphasia that had progressed over 7 days. Magnetic resonance imaging showed a large (6.1 x 4.5 x 3.6 cm) left frontoparietal expansive lesion with incomplete ring enhancement and significant mass effect. She was treated with methylprednisolone pulse therapy and intravenous immunoglobulin. She was discharged with a mild aphasia and hemiparesis and had fully recovered after 8 weeks. Her medical history dates back to 2012, when she had tetraparesis and optic neuritis after a hepatitis A infection. In 2017, she had two new relapses: a complete spinal cord syndrome followed months later by complete left hemiparesis. Serum aquaporin-4 IgG was negative, and magnetic resonance imaging revealed tumefactive lesions in both hemispheres. Due to the urgent need to rule out neoplasia, she underwent a biopsy, which revealed CD68+ histiocytes and axonal preservation, confirming an inflammatory demyelinating nature consistent with tumefactive multiple sclerosis. She was treated with cyclophosphamide pulse therapy. Interferon beta and dimethyl fumarate were used as maintenance treatments, but the patient was non-adherent and lost follow-up in 2020. Discussion: Multiple sclerosis is a chronic, immune-mediated demyelinating disease of the central nervous system, affecting approximately 2.8 million people worldwide. The tumefactive variant is challenging and less common, accounting for 1 to 3 per 1,000 cases of multiple sclerosis. It is defined by the presence of large (>2cm) space-occupying demyelinating lesions that produce mass effect, perilesional edema, and variable contrast-enhancement patterns, often mimicking brain tumors on imaging. Unlike the classical clinical presentations of demyelinating plaques, the tumefactive variant presents with cortical deficits such as hemiparesis and aphasia. Magnetic resonance imaging can help differentiate this disease from other expansive processes. Suggestive features are incomplete ring enhancement, relative sparing of cortical gray matter, and a mass effect that is often mild to moderate. In some cases, a biopsy may be mandatory to establish a definitive diagnosis. The present case is distinguished by its atypical manifestation, the severity of the attacks, and its early onset. Biopsy confirmation was crucial for managing the demyelinating disease and avoiding unnecessary neurosurgical or oncological interventions. Final Comments: This report highlights the challenges in diagnosing and managing atypical forms of multiple sclerosis. The tumefactive presentation, although rare, must be considered in expansive brain lesions with open-ring enhancement, especially in young patients with a history of prior neurological deficits. Brain biopsy remains a fundamental diagnostic tool in cases of radiological uncertainty.