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 however 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 pia mater. Diagnosis
Screening involves an MRI scan to identify and diagnose tumors in the subarachnoid region of the brain. MRI can make a diagnosis even without an analysis of the cerebrospinal fluid but it can sometimes be difficult to detect because MRI scans cannot always pick up the problem.Diagnosis is most commonly made by lumbar puncture to detect malignant cells in the CSF, although the tests may be negative in roughly 10% of patients. Diagnosis often requires a high index of suspicion and is confirmed by neuroimaging and cerebrospinal fluid analysis.CSF examination is the most useful diagnostic tool for NM. Patients with suspected NM should undergo one or two lumbar punctures, cranial magnetic resonance imaging (MRI), spinal MRI, and a radioisotope CSF flow study to rule out sites of CSF block.
The metastatic tumor cells grow either attached to the pia mater covering the brain and spinal cord or floating unattached to the subarachnoid space. Tumors of diverse origins and hematologic cancers may spread to this space.Some patients can develop a leptomeningeal tumor while receiving chemotherapy for their primary tumor. Pathology
There are three anatomic patterns by which the tumor can spread in the subarachnoid space. More than one pattern may coexist in the same patient.First, there may be plaque-like deposits of cells in the leptomeninges with invasion of Virchow-Robin spaces and, usually, the shedding of tumor cells into the cerebrospinal fluid.Second, there may only be a thin coating of meninges, in some cases with only a single cell layer, but also with shedding of tumor cells into the cerebrospinal fluid. Third, there may be a pattern of nodular deposits of tumor on cranial and spinal nerve roots, frequently without tumor cells being shed into the cerebrospinal fluid.The first and third patterns are common in solid tumors whereas the second occurs most frequently with leukemia and lymphoma. Spinal cord
Neoplastic meningitis (NM) shows diffuse infiltration of tumor cells into the subarachnoid space which may be associated with increased intracranial pressure, signs of meningeal irritation, and damage to the cranial and spinal nerve roots. Pathological feature include:
Circular necrosis of the white matter in the periphery of the spinal cord was also noted which probably resulted from circulatory disturbance secondary to tumor infiltration.