IMG-41. Beyond MRI: Differentiating Neurosarcoidosis from Leptomeningeal Metastases through Tissue Diagnosis

Leptomeningeal enhancement on neuroimaging is a radiologic finding with a broad differential, encompassing infectious, inflammatory, and neoplastic etiologies. Sarcoidosis, often termed “the great mimicker,” can present with imaging and cerebrospinal fluid (CSF) findings that can be difficult to distinguish from metastatic disease. In such cases, imaging alone is insufficient for diagnosis. We present two cases of patients with leptomeningeal enhancement and review the workup indicated to differentiate between these two etiologies. Our first case is a 58-year-old woman with a history of chronic myeloid leukemia in remission, who underwent spine magnetic resonance imaging (MRI) for workup of muscle spasms. Imaging showed diffuse leptomeningeal enhancement intracranially and along the spinal cord. Our second case is a 68-year-old female with a history of invasive ductal breast cancer in remission, who had a brain MRI for a first lifetime seizure, also showing leptomeningeal enhancement. Both patients underwent lumbar punctures, where CSF showed elevated protein and pleocytosis. Each patient underwent extensive workup, including inflammatory and rheumatologic serum studies, whole-body computer tomography (CT), Positron Emission Tomography (PET), and biopsy. Our first patient had a PET scan showing diffuse lymphadenopathy. Her lymph node biopsy showed granulomatous lymphadenitis, indicative of sarcoidosis. Our second patient, who had no other evidence of systemic disease or viable biopsy option, thus underwent a leptomeningeal biopsy, which showed metastatic carcinoma with histopathologic features consistent with metastatic disease from a breast primary. These cases illustrate two distinct etiologies of leptomeningeal enhancement that initially can present with similar imaging and overlapping CSF findings yet represent different underlying diagnoses and clinical implications. It is important to consider tissue sampling for definitive diagnosis in these patients to identify more precisely the etiology. Ultimately, differentiating between these diagnostic considerations is critical to determine appropriate treatment options and for discussing prognostication.