CSF cytopathology

CSF cytopathology is a subset of CNS cytopathology, which is a subset of cytopathology.

This article deal only with cerebrospinal fluid (CSF) cytopathology. An introduction to cytopathology is in the cytopathology article.

All CSF specimens get triaged at UHN as:

1. They are small specimens ~ usually 1-10 ml.
2. The procedure to obtain them is non-trivial, i.e. not pleasant for the patient and not risk free.
3. Lymphoma is a common malignancy of malignancies found in the CSF.

All CSF specimens are stat.

Normal

• Paucicellular.

Gobs of anuclear material:

• Protein vs. white mater.

Bark-like flaky material:

• Contaminant.

Fluffy/smudged large cells (~2-3x RBC dia.) with an indistinct nucleus:

• Degenerated white cells.
  • Should prompt a comment about "degeneration", if the population is dominant.

Routine processing

• Cytospin - if no abnormality at triage.
  • The cellularity of the cytospin will appear to be increased (artifact).

Acute bacterial meningitis

• Neutrophils; none should be present normally.
  • If the tap is traumatic (i.e. fibrin is present) the finding may be uninterpretable.

Viral meningitis

• Polymorphous population of lymphocytes.

Mollaret's meningitis

General:

• Rare aseptic meningitis.
• Suspected to be caused by HSV1 and HSV2.

Clinical:

• Recurrent meningismus, headache, +/-fever.

Histology:

• Mollaret cells - described as monocytoid cells (look like monocytes - but do not phagocytose), and large endothelial cells.
  • Features - large cells with: abundant cytoplasm, footprint-shaped" nucleus.
  • Mollaret cells not pathognomonic.
• Mixed population of inflammatory cells (PMNs, monocytes, plasma cells, lymphocytes); usually lymphocyte predominant.

Image:

• Mollaret cells (cmaj.ca).

CNS lymphoma

Histology:

• Too many cells - key feature.
  • Not diagnostic... but should raise suspicion.
• Single cells (as typical of lymphoma/leukemia).
• Large lymphocytes - >2x RBC diameter.
• +/-Nuclear atypia.
  • Radial segmentation - a completely cleaved nucleus/quasi-binucleation.

Notes:

• Massive karyorrhexis (nuclear fragmentation) is suggestive of lymphoma - not common.

CNS fungal infections

• Cryptococcus is the most common.

Cryptococcus infection

• Immunocompromised host.

Microscopic appearance:

• Yeast:
  • Round/ovoid 5-15 micrometres.
  • Thick mucopolysacchardie capsule + refractile centre.
    • "Target-like" shape/"bull's eye" appearance.
  • "Tear drop-shapped" budding pattern (useful to differentiate from Blastomyces, Histoplasma).

Images:

• Cryptococcus in lung FNA - Field stain (WC).
• Crytococcosis - mucicarmine stain (WC).
• Crytococcosis - methenamine silver stain (WC).

Main article: Microorganisms

Non-lymphoid neoplasm

• Non-lymphoid neoplasms are rarely found in the CSF.

Astrocytoma:

• May vaguely resemble a neuroendocrine tumour:
  • Small cell clusters.
  • Nuclear moulding.
  • Cells somewhat larger than small cell carcinoma.
  • Scant cytoplasm.

See also

• CNS cytopathology.
• Cytopathology.
• Basics.
• Neuropathology.