W2L4 - CSF Flashcards
What is CSF
Cerebrospinal fluid (CSF) is formed from circulating blood that is filtered through a complex epithelial organ, the choroid plexus, located within the ventricular system of the brain
This fluid is then distributed within the ventricular system, basal cisterns and subarachnoid space
The normal choroid plexus is a highly selective filter that regulates the chemical consistency and maintains CSF at a constant level
The choroid plexus also regulates the passage of most toxic substances
No blood cells, except for occasional monocytes and lymphocytes cross the choroid plexus, resulting in a highly effective ‘Blood brain barrier’
Normal CSF is generally clear and colourless in appearance
Collection of CSF
Most CSF’s are obtained via a spinal tap/lumber puncture (L3-4 or L4-5)
However, samples can be directly obtained via the cisterna magna and the ventricles of the brain
All CSF’s should be considered ‘urgent’ and prepared ASAP
Because of the low cellularity of CSF sample, the aim is to concentrate the cells received, even if only a 2ml sample has been collected
Cytocentrifugation (c/c) is a simple method which has been utilised by most laboratories
Advantages
- simple to perform
- less time consuming than filters
Disadvantages
- some degree of cell loss
- distortion
Collection of CSF is collected into 4 tubes, what are they for?
Haematology
Cytology
Microbiology
Immunology
Different Colours of CSF and their Causes
A slightly ‘yellow’ CSF may occur when protein content > 10mg/ml
A cloudy CSF occurs when WBC’s exceed 200-300/ml
Problems with CSF Cytology
Usually limited quantity
Cells deteriorate quickly
Primary tumours tend not to exfoliate into CSF
Usually scant cellularity, even when positive
Difficulties in distinguishing lymphocyte variability from leukaemia/lymphoma
Difficulties in differentiating lymphocytes from other small blue cell tumours, esp in children
Specimen Handling
Two very important things to remember above all else:
- Get it to the lab quickly
- less than 30 mins
- fresh, no additives - Spin it gently
- no more than 1000 rpm
- no more than 5min
- too much speed for too long creates “cytospin effect” (cells flatten, distort and break)
- some tumour cells are extremely fragile
Why is CSF Performed in Children
Investigate meningeal disease
Investigate a space occupying lesion
Monitor/stage children with known CNS tumours
Cells of the CNS
Cells of the CNS are typically divided into 2 major categories:
- Cells of neuroectodermal origin:
- neurons
- astrocytes
- oligodendrocytes
- ependymocytes - Cells of mesenchymal origin:
- meninges
- blood vessels
- adipose tissue
- microglia
Histology of the CNS
Extracerebral CSF is contained between 2 epithelial meningeal membranes, the pia (lining the brain) and the arachnoid (lining the dura)
Occasionally cells from the choroid plexus, the pia and the arachnoid may desquamate into the CSF
Any increase in the number of cells in the CSF or any change in glucose or protein levels indicate a pathology
Cytology of CSF
Cellular and acellular components in the absence of disease
In adults: very few lymphocytes and monocytes are observed in CSF
Monocytes appear somewhat larger with a more open indented nucleus and a slightly larger rim of cytoplasm
In neonates; the cell count is higher than in older children
Monocytes are the most prevalent cell type in neonates whereas lymphocytes become more prevalent as children get older
Normal Composition of CSF
Clear, colourless, sterile fluid
No more than 5 cells/mm3 adult (10 cells/mm3 neonate)
A few lymphocytes, occasional monocytes and polymorphs
Blood contamination often seen
May see cells from brain or lining membranes
May see contaminants from other tissues (e.g. cartilage)
Extraneous contaminants
Cytology of Normal Cells in CSF
Cells from the choroid plexus and ependymal cells in CSF is extremely rare
Ependymal cells present as small cuboidal cells often arranged in rows or clusters
Pia arachnoid cells, resemble mesothelial cells and are occasionally interpreted as astrocytes
Elongated cells originate from the meningeal lining
Bone marrow cells may be observed when a spinal tap inadvertently enters the intervertebral cartilage
Squamous cells and anucleated squamous cells are rare and are usually a contaminant from skin
Cytology of Acellular Components in CSF
Corpora amylacea
- transparent spherical proteinaceous structures commonly seen in the brain of the elderly and may mimic psammoma bodies
Powder Crystals
- starch granules from the powder in surgical gloves
- may be mistaken for cryptococcus organisms
Granular amorphous debris
- connective tissue elements
Benign Processes in CSF - Increase in Lymphocytes and Monocytes
A mild increase in cellularity in the number of leukocytes and/or macrophages always reflects a pathological process
An increase in lymphocytes and monocytes may give rise to a chronic inflammatory response
- tuberculous meningitis
- chronic inflammatory process e.g. viral meningitis
Benign Processes in CSF - Increase in PMNs
PMN’s do not usually cross the blood-brain barrier so the increased presence of these is often a result of an acute inflammatory process due to:
- bacterial meningitis (Haemophilus influenzae, pneumococci or other pyogenic organism)
- brain abscess
- early form of viral meningitis
- sometimes a reaction to intrathecal chemotherapy
The appearance of these cells are most likely as a result from damaged blood vessels and capillaries within the brain or meninges
An increase in eosinophils may be a result of a parasitic infection of the CNS or as a result to trauma
