leptomeningeal

Leptomeningeal is an anatomical term referring to the leptomeninges, the inner two meninges of the central nervous system: the arachnoid mater and the pia mater. These membranes envelop the brain and spinal cord and create the subarachnoid space, which contains cerebrospinal fluid and the pial blood vessels.

The pia mater closely follows the contours of the brain and spinal cord, dipping into sulci and surrounding vessels, while the arachnoid mater forms a largely avascular barrier and a web-like sheet between the subarachnoid space and the dura mater. Arachnoid granulations protrude into the dural sinuses to facilitate CSF drainage into the venous system.

Clinical relevance arises when the leptomeninges are involved in disease. Leptomeningeal disease, or leptomeningeal carcinomatosis, occurs when malignant cells disseminate to the CSF and meninges from cancers such as breast, lung, or melanoma. Infectious and inflammatory processes—such as bacterial, viral, fungal meningitis and granulomatous diseases—can also affect the leptomeninges, producing meningeal symptoms and CSF abnormalities.

Diagnosis commonly involves magnetic resonance imaging with gadolinium to detect meningeal enhancement and lumbar puncture for cerebrospinal fluid analysis. CSF studies may show pleocytosis, elevated protein, or low glucose, and cytology or flow cytometry can identify malignant cells. Management is cause-dependent and may include intrathecal chemotherapy, systemic therapies with adequate CNS penetration, craniospinal irradiation, and corticosteroids to reduce inflammation and edema. Prognosis varies with the underlying etiology and timeliness of treatment, with leptomeningeal involvement often signaling a complex or advanced disease state in cancer patients.