CNS cytopathology

CNS cytopathology is a subset of neuropathology and cytopathology.

An introduction to cytopathology is in the cytopathology article. Cerebrospinal (CSF) specimens are dealt with in a separate article called CSF cytopathology.

Technique

Smears (really squash preps) are common in neuropathology. Here are some tips for getting a good smear:

1. Sampling is key -- choose 3-4 small pieces of tissue from different areas of the tissue (if there are different colours, get some of each).
2. Keep pieces small (easier to smear).
3. Avoid air drying (place into formal alcohol immediately upon smearing).

Basic approach

CNS cytology

Tumour

Non-tumour

Glial

Non-glial

Infectious

Non-infectious

	Glial	Non-glial
Stranding (cytoplasmic)	thin - cannot be seen at low power (2.5x obj.), true cytoplasmic processes	thick - can be seen at low power (2.5x obj.), artifact of smearing
Edge of cluster	smooth/non-distinct	sharp

Glial vs non-glial:

• Glial has cytoplasmic processes/cytoplasmic strands (stringy processes) ~ 1 micrometer thick.
  • They cannot be seen well at low power.
  • Cotton candy-like appearance.
  • Images:
    • Stringy processes - glial tumour (msdlatinamerica.com).
    • Glial tumour mimicing a carcinoma (msdlatinamerica.com).

Gliosis vs. neoplasm:

• Gliosis - uniform, pink
• Astrocytoma - irregular, coarse clumps of pink fibrillary material

High grade vs. low-grade:

• Markers of high grade glioma:

1. Mitoses (can see these in smear)
2. Necrosis (can also see in smears)

Notes:

• Crush artifact (in smear preparation) can mimic glial processes.
  • Crush artifact vs. real glial processes:
    • No glial processes run perpendicular to the direction of smear.
    • Glial processes may branch.
    • Crushed/elongated nuclei are present in artifactual processes.

Meningioma

Most meningiomas smear rather well, the only exception being ones that are densely fibrous.

• Key features of meningioma smears:

1. Single cells or small groups of epithelioid cells with distinct cytoplasmic 'flags' (cytoplasm usually abundant)
2. Round nuclei with vesicular chromatin and unapparent or small nucleoli
3. Visible actin striations / stress filaments in cells (seen as pink straight lines)

• 

  HE smear of a meningioma displaying typical whorl formations (WC/jensflorian)

Metastatic carcinoma

Typically has a 'cannonball' appearance -- with small, highly cohesive clusters of epithelioid cells.

Main article: Metastasis

• Squamous cell carcinoma (ouhsc.edu).
• Adenocarcinoma (ouhsc.edu).
• Small cell carcinoma (ouhsc.edu).

Metastatic melanoma

• Occasionally large bi- or multinucleated cells
• Discohesive cells
• Large nucleoli
• Pigmented tumor cells
• Accompanied by tumor infiltrating lymphocytes

• 

  Melanoma smear prep (H&E)

• 

Metastatic lymphoma

• Small round and blue cells

Glial tumors

• Elongated cell processes
• Cohesive growth
• Often attached to vasculature

• 

  Pilocytic astrocytoma smear preparation (H&E)

Things that don't smear well

Cohesive tumours:

• Neurofibroma.
• Schwannoma.
• Subependymoma
• Abscess (because of fibrous capsule)
• Metastasis.

Things that smear well

Dyscohesive tumours:

• Lymphoma.
• Pituitary adenoma.
• Oligodendroglioma.
• Astrocytoma.
• Normal brain.

See also

• Neuropathology.
• Neurohistology.
• CNS tumours.

External links

• Diagnostic neuropathology smears (msdlatinamerica.com).