Neoplastic meningitis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Sujit Routray, M.D. [2]

Pathogenesis

Neoplastic meningitis refers to the spread of malignant cells through the cerebrospinal fluid space. These cells can be originated both in primary CNS tumors (e.g. drop-metastases), as well as from distant tumors that have metastasized (hematogenous spread).

From primary cancer to the meninges

• Neoplastic meningitis is a secondary cancer meaning that it is the result of neoplastic cells that have metastasized from a primary cancer site. These cancers develop an enzyme that is able to break down blood vessels at a microscopic level. These cells enter the blood vessels and travel across the body. Once the brain is reached, they break down the blood brain barrier to enter the cerebrospinal fluid (CSF). The cancerous cells seed and disseminate into the leptomeninges which are composed of the arachnoid and the pia. The CSF continues to carry neoplastic cells through the brain tracts and spreads the cancerous cells.
• Since neoplastic meningitis is a result of primary cancer metastasis and can develop from primary brain tumors or parenchymal metastasis when tumor cells are lodged in small central nervous system (CNS) vasculature, causing local ischemia and vessel damage which result in tumor spillage into the Virchow-Robin spaces and providing access to the subarachnoid space.

Invasion routes

• Hematogenous spread occurs either through the venous plexus of Batson or by arterial dissemination. This occurs with arterioles as a result of tumor cells being lodged in vessels that feed the meninges and later causing leakage into the meninges and CSF. This same situation also appears with spinal arteries where leakage of tumor cells is into the nerve roots. Tumor cells may also seed the choroid plexus, where CSF is produced, and ultimately gaining direct access to the CSF. Seeding of the choroid plexus is most common in patients with third and lateral ventricular hydrocephalus.
• Venous spread may occur when intra-abdominal or thoracic pressure increases and venous flow is retrograde which then allows the tumor cells in the systemic venous system to enter the vertebral venous system.
• Centripetal migration from systemic tumors along perineural, invasion of nerve space, or perivascular spaces. Malignant cells can migrate along spinal or cranial nerve (epineurium-perineurium), invade the subpial space, travel along blood vessels into the endoneurial space, or invade the nerve parenchyma.
• Often, the infiltration happens at the base of the brain, dorsal surface, and especially at the cauda equina which is largely due to the effect of gravity. Once in the CSF, malignant cells can extend along the membrane surfaces or spread freely in the CSF and attach to other locations. These cells have the ability to penetrate the pial membrane and invade the spinal cord and cranial nerves.

Infiltration to spinal cord

• Infiltration from the subarachnoid space into the spinal cord occurs primarily along the perivascular tissues that surround blood vessels at the brain entrance. Infiltration from the anterior median fissure, a 3mm deep furrow on the anterior side of the spinal cord, to the anterior horn of the spinal cord, the ventral grey matter of the spinal cord, is found along the central artery. Direct infiltration of the nerve roots is also observed, mostly from the dorsal roots (the afferent sensory root of the spinal nerve) than the ventral roots (the efferent motor root of a spinal nerve).
• With mild infiltration, tumor cells are found diffusely in the subarachnoid space from the cervical to sacral levels. In some cases, there are no differences between spine levels. Infiltration from the subarachnoid space into the spinal cord occurs mainly along the perivascular space of the white matter. However, in some cases, direct infiltration into the spinal cord parenchyma is found together with destruction of the piamater.

Microscopic pathology

The microscopic pathology of neoplastic meningitis may vary according to the primary cancer involved. Generally, on microscopic histopathological analysis, neoplastic meningitis is characterized by large, hyperchromatic cells.

Gallery

<gallery> Image:Micropathologyneoplastic meningitis image 1.PNG|_{Light microscopy pictures of the cytological specimen of cerebrospinal fluid obtained from patient 1: (a) hematoxylin and eosin staining of the hypercellular sample, with large, hyperchromatic cells associated with erythrocytes; (b) atypical cells stained with Melan-A, a melanoma-specific marker; (c) Schmorl staining confirmed the presence of melanin (blue granular stain) in the cytoplasm; magnification, 20x.}

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References

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