BSBM-10 PERIVASCULAR-SUBPIAL SPACE METASTASIS (PRISM): BRIDGING THE GAP BETWEEN CNS EXTRAVASCULAR MIGRATORY METASTASIS AND LEPTOMENINGEAL METASTASIS

Abstract Classically, intracranial metastasis has been parsed neuroanatomically into dural, leptomeningeal, parenchymal, or multicompartment disease, with leptomeningeal metastasis (LM) defined by tumor infiltration of the subarachnoid space. LM typically manifests on MR imaging as diffuse leptomeningeal enhancement along the sulci, cisterns, cranial nerves, and/or spinal nerve roots, often accompanied by malignant cells detectable in cerebrospinal fluid (CSF). Increasingly recognized, however, are intermediate or borderline metastatic patterns that exhibit supratentorial focal non-diffuse leptomeningeal enhancement without traditional radiographic or clinical signs of LM, creating diagnostic uncertainty and challenging clinical management decisions. The primary aim of this study is to introduce the concept of perivascular-subpial space metastasis (PRISM), which is the distinctive form of CNS extravascular migratory metastasis (EVMM), through correlative radiographic / histopathologic signatures. We present twelve patients (mean age 59 yrs, range 42–91; 4 males, 8 females) who displayed preoperative imaging features of PRISM and had histopathologic confirmation of metastatic disease. Radiographic features characteristic of PRISM include superficial cortical ribbon-based lesions centered along the sulci, frequently associated with enhancement that was linear, curvilinear, plaque-like, or extended along pial vessels, mimicking LM. Histopathologically, PRISM metastases involve either the perivascular Virchow–Robin compartment, the contiguous subpial space compartment, or both. Primary malignancies included breast (n=4), lung (n=4), melanoma (n=3), and esophageal carcinoma (n=1). Integrated radiopathologic features support the concept of PRISM as an early, pre-LM, phase of CNS metastasis. Recognition of PRISM raises the possibility of early detection, with targeted intervention instituted before irreversible LM occurs. Further studies are warranted to validate the preoperative imaging criteria for PRISM, and to clarify the clinical trajectory, treatment response, and prognostic implications of PRISM.