Radiologic and pathologic correlation of leptomeningeal metastasis presenting as a circumscribed comedo-like bulky mass with minimal brain parenchymal invasion: A case report

Abstract

Bulky, mass-like leptomeningeal metastasis is rare. In radiology and surgery, it mimics an extra-axial mass and can be mistaken for meningioma. When reported pathologically as metastasis, it can be mistaken for parenchymal brain tumors, potentially delaying appropriate CSF-directed therapy. We report a unique case in which leptomeningeal disease presented as an extra-axial lesion embedded in the cortex with a comedo-like protruding surface. Recognizing this imaging and intraoperative appearance may be important, as differentiating leptomeningeal from parenchymal metastases could alter prognosis and help guide treatment decisions, including consideration of CSF-directed treatments, such as intrathecal chemotherapy or craniospinal irradiation, rather than relying on focal radiosurgery alone. Although anecdotal, this report underscores the need for heightened diagnostic awareness and warrants the need for further study to determine whether this feature reliably indicates leptomeningeal disease and meaningfully influences patient management.