Ependymal cells form the ependyma, a specialized lining for the fluid-filled ventricles in the brain and the central canal of the spinal cord. This cellular barrier regulates the exchange of substances between brain tissue and the cerebrospinal fluid (CSF). CSF is a clear liquid that circulates to provide cushioning, nourishment, and waste removal. The appearance of these cells floating within a CSF sample is an unusual finding that suggests a disruption of this barrier, prompting clinical evaluation.
The Normal Role and Location of Ependymal Cells
A primary function of ependymal cells is their role in CSF production. Within the brain’s ventricles, some ependymal cells are modified and combine with capillaries to form a specialized structure called the choroid plexus. This structure is responsible for producing the majority of the CSF by filtering water and specific molecules from the blood. It is estimated that the choroid plexus produces approximately 500 mL of CSF daily.
Once produced, the CSF is not stagnant; it circulates throughout the central nervous system. This movement is aided by the presence of cilia, which are small, hair-like projections on the surface of ependymal cells. The coordinated beating of these cilia helps to propel the CSF through the ventricles and spinal canal. This circulation is important for distributing nutrients and removing waste products.
Causes for Ependymal Cells in Cerebrospinal Fluid
The presence of ependymal cells in cerebrospinal fluid is most commonly an incidental finding related to medical procedures. The process of collecting CSF, known as a lumbar puncture or spinal tap, involves inserting a needle that can inadvertently scrape and dislodge ependymal cells from the lining. This is often referred to as a traumatic tap and is considered a normal artifact of the procedure.
Inflammatory and infectious conditions affecting the central nervous system can also lead to the shedding of ependymal cells. Infections such as meningitis or ventriculitis cause inflammation that can damage the ependymal layer, causing cells to detach and enter the CSF. Severe brain injuries or bleeding, such as a subarachnoid hemorrhage, can also physically disrupt the ependymal lining.
Certain types of tumors that arise from the ependymal cells themselves, known as ependymomas, are another cause. In these cases, malignant cells can break away from the primary tumor and circulate throughout the cerebrospinal fluid. The presence of ependymal cells in the CSF of children, in particular, may raise suspicion for such a tumor. Other conditions, like hydrocephalus, can also disrupt the ependymal lining.
Diagnostic Identification and Analysis
The process of detecting ependymal cells begins with obtaining a sample of cerebrospinal fluid, typically through a lumbar puncture. Once the sample reaches the laboratory, it undergoes cytological examination. Technicians use a machine called a cytocentrifuge to concentrate the cells from the fluid onto a microscope slide.
The prepared slide is then stained with special dyes, which helps to make the different parts of the cells visible under a microscope. A pathologist or laboratory professional examines the slide, looking for any cellular components. Ependymal cells have distinct morphological features that aid in their identification, as they are typically cuboidal to columnar in shape and may be observed in small, cohesive clusters. The potential presence of cilia can also be a distinguishing characteristic.
A challenge in CSF analysis is distinguishing benign ependymal cells from other cell types, especially malignant ones. For example, cells from an ependymoma can look similar to normal ependymal cells, though they may show atypical features. The pathologist must carefully evaluate the cells’ size, shape, and nuclear characteristics to make an accurate identification.
Clinical Significance and Interpretation
The discovery of ependymal cells in a cerebrospinal fluid sample is not a standalone diagnosis. Its meaning is entirely dependent on the broader clinical context, including the patient’s symptoms and the reason for the CSF analysis. The number and appearance of the cells are also important factors in the interpretation of the finding.
In many situations, the presence of a few normal-looking ependymal cells is considered an insignificant and expected consequence of the collection procedure itself. If a lumbar puncture was difficult or resulted in minor local trauma, finding these cells would not typically be a cause for alarm. It is viewed as contamination of the sample.
The implications become more serious when a large number of ependymal cells are found, or if the cells exhibit atypical features. A high count of ependymal cells could suggest the presence of a central nervous system tumor, specifically an ependymoma. This finding acts as a clue that must be pieced together with other diagnostic information, such as imaging studies, to determine its true significance.