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An animation showing two micrographs in different planes of focus of a cytopathology specimen with serous carcinoma. (WC)
Granulomatous inflammation in the hilum of lung. Diff-Quik stain.

Cytopathology, often called cytology, is the study of pathologic changes in cells.

Specimen types include exfoliated cervical cytology (Pap tests), urine, body cavity fluids (pleural, pericardial, and peritoneal), cerebrospinal fluid, and fine needle aspirations from any body site, among others (see detail articles section). These are often collected by minimally invasive means.

Cytologic preparation methods usually include viewing single cells or small clusters of cells on slides, in contrast to surgical biopsy specimens that usually include larger pieces of tissue, with tissue architecture. In some institutions, small tissue biopsies such as core needle biopsies may also be assigned to the cytology service.

It is often divided into gynecologic and non-gynecologic. Gynecologic in this context usually refers to Pap test specimens, i.e. uterine cervix, vaginal vault; other gynecologic specimens are considered non-gynecologic.

Slide-marking conventions

Conventions are important for facilitating communication between various team members.

Common conventions:[1]

  • The slide is placed with the label on the right hand side.
  • "Marks-of-interest", e.g. dots, are place above the field of interest (when viewed through a microscope - that does not correct for image inversion).
    • Microscopes used for surgical pathology, generally, do not correct for image inversion.
      • The "marks-of-interest" appear below the field of interest when the slide is viewed with the naked eye.


  • Dot - region of interest.
  • Inverted "V" - transformation zone (in cervical cytology specimen).
  • Inverted "Y" - benign finding.


  • Image inversion in the microscope comes about as light travels in a straight line.
  • Marks should draw attention to the best examples of the highest grade lesion present.
    • More than 7 marks on slide is generally considered excessive.

Dictums of cytopathology

  • Malignant cells are malignant because they have malignant features.
  • Benign cells are benign because they lack malignant features and have benign features.


  • Cells lacking malignant features are not malignant.
  • Cells lacking benign features are not malignant.

Cytologic features of malignancy

Cytologic features of malignancy:

  1. High nuclear-to-cytoplasmic ratio.
  2. Nuclear membrane irregularities.
    • Notches/sharp discontinuities.
  3. Chromatin abnormalities.
    • Clumped chromatin, esp. differences between quadrants of a nucleus.
    • Chromatin clumping at the nuclear membrane (chromatin margination).
  4. Hyperchromatic nucleus (when compared to other cells).
  5. Nuclear pleomorphism (comparison of neighbouring cells).
    • Def'n: variable staining, shape, and size.


  • Not all features of malignancy will be present in one cell.[2]

Cell types

WG's cell typing guide:[3]

Cell type Nucleus location Nucleus shape Cytoplasm Chromatin Nucleoli Other Architecture
Squamous Center Oval/Spindle Solid/dense Coarse Absent Squamous pearls, streaming Streaming
Eccentric Oval Vacuoles Fine Present Columnar Acini (glandular structures), (true) papillae
Neuroendocrine Center (?) Oval Fine granules (neuroendocrine
granules - seen on Romanowsky
type stains)
Reticulated "stippled" Absent Perinuclear blue bodies
(not seen in lymphoid cells)
Clusters, may appear dyscohesive
Lymphoid Eccentric Oval Very scant, basophilic Coarse Usually absent Lymphoglandular bodies,
Single cells
Germ cell Central/variable Oval Variable Variable (?), present in seminoma Tigroid background
in seminoma
(Romanowsky stains)
Usu. in clusters
Mesenchymal Central Spindle (?) Fine (?) Absent Variable Clusters, streaming

The big list of hole-y cells

  1. Large Golgi apparatus.
    • May be seen in melanoma.
  2. Phagocytic vacuole
    • Contains foreign material.
  3. Fat.
    • Usually small.
  4. Glycogen.
  5. Mucin.
  6. Hydropic.


  • The last two are the most important.


Hydropic vacuoles and secretory vacuoles:[4]

Contents Distorts nucleus Significance Classic description
Hydropic vacuole empty (clear) less common dying cell diamond engagement ring
Secretory vacuole "globs" of stuff (usu. pink) more common secretory cell/consider adenocarcinoma signet ring


  • Size the vacuole is not discriminative.[5]
  • Nuclear distortion (by the vacuole) is probably the strongest indicator the vacuole is secretory.

Subtyping adenocarcinoma

Adenocarcinoma can be subtyped:[6]

Architecture Group borders Group cellular/nuclear pleomorphism Vacuoles (cytoplasmic) Nucleoli Other
Serous carcinoma Micropapillae Knobby Marked size variation, +/-second benign pop. Hydropic Large, red Psammoma bodies
Gastric (signet ring) carcinoma Single cells, groups Community border (?) Limited, cells uniform, +/-second benign pop. Mucin Usu. inconspicuous -
Breast ductal carcinoma Clusters (tubular) Community border Limited, cells uniform, +/-second benign pop. Mucin Inconspicuous/small -
Adenocarcinoma not otherwise specified (NOS) 3-D clusters Community border Limited, malignant cells uniform, +/-second benign pop. Mucin Inconspicuous/small -
Mesothelioma (see Note 1) Clusters (usu. large), single cells Knobby border Usu. uniform size, one cell population Hydropic Often large Intercellular windows,
cytoplasmic blebs

Note 1:

  • Mesothelioma is a type of carcinoma,[7] yet is not an adenocarcinoma; it is added to the table to make the point that it is similar to adenocarcinoma.
    • Mesothelioma arises from the mesothelium, a type of epithelium. Carcinomas are epithelial derived malignant tumours (by definition).


There are two standard stains:

  1. Papanicolaou stain (Pap stain).
    • Is a modified H&E stain.
    • Done on alcohol-fixed material.
  2. Romanowsky stain.
    • Many variants exist.
    • Used on air-dried specimens; air-dried cells are much larger, it is easier to see the nuclear detail.


  • Carnoy's solution (ethanol, glacial acetic acid) - used to lyze RBCs to get rid of 'em.

Further details are in the main article on staining.


  • Jörundsson et al. compare the types of stains.[8]
  • Romanowsky type staining is uncommon in the Canadian cytopathology community and not on FRCPC exams.

Pap stain


  • Blue = nucleus, basophilic cytoplasm.
  • Pink = cytoplasm.
  • Orange = keratin.

DDx of orange:

  1. Keratin.
  2. Dying/dead cell.
  3. Center of cluster effect/diffusion effect.
    • The center of large clumps of cells are often artifactually pink/orange, as the eosin (a small molecule) get there but the azure (a large molecule) does not.

Romanowsky stains


  • Diff-Quik.
  • Field's stain.
  • May-Grünwald-Giemsa.
  • Wright stain.

Interpretation (Romanowsky stain):[10]

  • Red - RBCs, eosinophil granules, neuroendocrine granules.[11]
  • Blue (basophilic) - lymphocyte cytoplasm.
  • Purple - nuclear chromatin, neutrophil granules, platelets.


  • May have air-drying artifact.
    • Usually on slide periphery.
    • Appearance: white holes.
      • Air-drying may mimic the appearance of nuclear pseudoinclusions.
  • Cells tend to be larger than on Pap stain.

Adequacy of specimens

Standards are lacking for most types of specimens. A generally accepted standard is established only for cervical cytology specimens.


Standards at one large centre for non-gyne specimens:[12]

  • Breast: >= 6 cell groups (6 cells/cluster).
  • Thyroid: >= 20 cell cluster (20 cells/cluster).
  • Urine: >=50 urothelial cells.
  • Sputum: >= 10 pulmonary macrophages.


There is a generally accepted standard for cervical (liquid-based) cytology specimens:[13]

  • >5000 squamous cells/slide, if no abnormality is present.
    • If abnormal cells are present, any number of cells is acceptable.
      • This works-out to approx. 4 cells/HPF.
        • Where: HPF = area seen at 400X with an eye piece diameter is ~22 mm.
      • 10 HPFs are counted and a table is used to see whether the sample is adequate.


  • The standard for conventional pap smears is: 8000-12000 squamous cells/slide.[14]

Transformation zone (TZ)

The presence of the TZ should be commented on:[15]

  • An adequate TZ is 10 cells - endocervical cells or squamous metaplastic cells (per Bethesda).

Difficulties in obtaining a TZ may arise in the following populations:

  • Pregnant (endocervical canal not sampled).
  • Menopausal.
  • Young nulliparous.

Principles of FNA


  • Fine needle aspiration of superficial lesions may be performed by pathologists or other clinicians
  • Fine needle aspiration of deep-seated lesions may be performed by interventional radiologists under imaging guidance
  • Endobronchial ultrasound may be used by pulmonologists and thoracic surgeons to access pulmonary lesions, while endoscopic ultrasound may be used by gastroenterologists to access GI tract or pancreatic lesions
  • Fine needle aspiration is an oxymoron.[16]
    • One does not really aspirate.


  • Use a small needle - 22-25 gauge.
  • Use minimal suction - aspiration per se is not the key; the sample is obtained by coring.
  • Use minimal back and forth angulation - it destroys blood vessels


  • Popularized by the Swedes.[18]

Triage of specimens

At some large centres the specimens are triaged. This is an uncommon practise in the world of cytopathology.


  • Smear.
  • Fancy (automated) thin layer preparations:
    • Cytospin - centrifuged onto slide.
    • ThinPrep - centrifuged onto filter then onto slide.
  • Smear + IHC.
  • Cell block. + IHC.

Triage of cytopathology specimens:

Triage of specimens
Morphologic analysis
Rest to morphology

Management (liquid):

  • Lymphoid:
    • Fresh:
      • Flow cytometry (FC) or laser scanning cytometry (LSC) if sufficient.
      • Additional preps (i.e. CytoSpin) not usually useful.
    • Fixed:
      • Minimal material: smear + immunostains.
      • Abundant material: cell block + immunostains.
  • Non-lymphoid:
    • Cell block immunostains.
  • Unknown:
    • Minimal material: smear + immunostains, possibly cell block + immunostains.
    • Abundant material: cell block + immunostains and flow cytometry.

Management (solid/clot):

  • Cell block +/- immunostains.


  • It may be hard to diagnose large B cell lymphoma from LSC; thus, a cell block is useful if you have the material.[19]
  • Abundant macrophages cause problems with LSC.[20]
  • It is not worthwhile to do LSC if there is a scant amount of lymphoid tissue present in the specimen.[21]
  • LSC is (usually) not done on CSF specimens with less than 7 mL of volume.[22]

Number of cells for LSC - calculation


-- number of cells needed.
-- volume of sample.
-- est. volume of rapid assessment (RA).
-- est. rapid assessment (RA) area.
-- area with 20x obj. on microscope with 18 mm eye piece.


Application of rule

  1. Count cells in one field (on the microscope with the 18 mm eye piece) at 20x.
  2. Divide 167.36 cells ml by the volume of the sample.
  3. If the cell count in (1) is greater than the number of cells in (2) there are enough cells for a full panel.


Cost Cells required Fixation Disadvantages/problems
Smear Minimal ~$5/slide 1+ Air dry/alcohol Layering of cells
CytoSpin Expensive 50 ? Expensive
ThinPrep (liquid-based cytology) Expensive ~$35/slide; intermediate
for several slides
300-400 Always alcohol (methanol) Filter damage at edge of prep.
Sure-Path (liquid-based cytology) - see Note 1 Expensive (?) 300-400 (?) Always alcohol (ethanol) (?)
Cell block Expensive >500 Usually formalin Expensive, loss of cells large,
truncation artifact in FISH
Laser scanning
Expensive ~50,000 for full B cell panel + minimal T cell panel - see Note 2 None Tissue needs to be fresh

Note 1:

  • Sure-Path (from TriPath) is not used at many teaching centres (in Ontario) as it has some short coming for non-gyne specimens vis-a-vis ThinPrep (from Cytyc).[23]
    • It is used by the private labs in Ontario and seems to be better for Pap tests.
  • A comparison between SurePath and ThinPrep/experience from one lab in the USA is here:

Note 2 - see lymphoma article for detailed description of markers:

  • The typical "full" panel is:
    • B-cell markers: CD10, CD19, CD20, CD23, FMC7, Kappa, Lambda.
    • T-Cell markers: CD3, CD5, CD4, CD8, CD7, CD2.
    • NK-Cell markers: CD56, CD16.
    • Miscellaneous markers: CD11c, CD14.

Notes (general):

  • CytoSpin used for CSF specimens.

Cytologic features

Large clusters

  • Large clusters - fibrin (junk) vs. other:
    • Small (~1/10 of RBC diameter) ovoid, purple staining (on Field stain) = platelets.
      • If you see platelets think fibrin.


  • Blobs of acellular material.
  • No nucleus or pyknosis of nucleus.
  • Disrupted/frayed cellular membrane.
  • Orangeophilic material (orange material) - on Pap stained material.


Cytology (six features):[24]

  1. Foamy/bubbly cytoplasm, abundant - low power.
  2. Epithelioid morphology - cell borders near indistinct - key feature.
  3. "Footprint" pattern nuclei/bean-shaped nuclei - key feature.
    • Macrophages usu. have an ovoid nucleus.
  4. +/-Nucleoli, small.
  5. +/-Fibrosis.
  6. +/-Palisading at edge.


  • Granulomas are not always nice and round, as in non-cytology specimens.



Detail articles

Details are dealt with in separate articles.

Gynecologic cytopathology

Gynecologic cytopathology is the origins of cytopathology and still a large part of cytopathology practise. It is deal with in separate article.

CNS cytopathology

The above article deals with CNS cytopathology, i.e. lumbar puncture specimens.

Pulmonary cytopathology

The above article deals with pulmonary cytopathology, i.e. FNA specimens and sputum specimens.

Fluid from mesothelial-lined space cytopathology

The above article deals with cytopathology specimens from spaces lined with mesothelium.

Urine cytopathology

The above article deals with urine cytopathology.

Thyroid cytopathology

The above article deals with thyroid cytopathology.

Head & neck cytopathology

The above article deals with head and neck cytopathology, excluding thyroid cytopathology.

Breast cytopathology

The above article deals with breast cytopathology.

Gastrointestinal cytopathology

The above article deals with gastrointestinal cytopathology.

Kidney cytopathology

Grab bag of stuff

The following is a grab bag of stuff that is:

  • Not covered in the above articles.
  • Something that applies to multiple sites (e.g. melanoma).






  • Mixed population of cells:
    • Epithelial cells.
      • Circular nuclei with well seen micronucleoli (seen at ~10X objective).
      • +/-Nuclear membrane invaginations.
    • Mature Lymphocytes.

DDx (pitfalls):

  • Lymphoproliferative disorder (when epithelial component sparse).
  • Carcinoma (when lymphoid population small).
    • Should not have nuclear features of malignancy.


  • May have necrosis.
  • Should not mistake for granuloma... as nuclei of epithelial cells round not oval.


Benign ovarian cyst




  • Benign epithelial cells - often ciliated.
  • Macrophages.
  • +/-Rare squamous cells.


Sign out

Ovarian Cyst, Left, Fine Needle Aspiration: 
- Compatible with cyst contents; consisting of macrophages, small groups of ciliated cells and rare squamous cells. 
- Low cellularity. 
- NEGATIVE for atypia and NEGATIVE for malignancy. 

Germ cell tumours



Classic scenario:

  • Retroperitoneal lymph node enlargement and testicular mass.



  • +/-"Corners" in the nuclear membrane.
  • Cells cohesive.
  • Central nucleus.
  • Clear cytoplasm - may be stripped.
  • Background with "viscous" or "tigroid" appearance on (air dried) Romanowsky type stains - key feature.
    • Tigroid = striped or spotted appearance.[28]
      • Related to the presence of glycogen.
    • Tigroid pattern not seen on Pap stain.
    • Not always seen.
  • +/-Small mature lymphocytes (common).
  • +/-Granulomas.


Crystals in fluids

The above article covers gout, pseudogout and urine crystals.


Malignant melanoma

Classic features:

  1. Loosely cohesive cells and single cells.
  2. Mixure of epithelioid cells and spindle cells.
  3. Malignant cells have:
    • Prominent red nucleolus.
    • Pigmented cytoplasm - key feature (often not pigmented).
    • Pigment may only be present in macrophages
    • Occasional large binucleated cells (bug-eyed monster cell).
      • Nuclei are often at opposite poles of the cell, i.e. the nuclei are as far apart as possible ("divorce cells").[30]
    • Intranuclear inclusions.
  4. Pigmented macrophages (useful feature - but less specific for melanoma than pigment in malignant looking cells).


  1. Large nucleolus - may vaguely resemble adenocarcinoma.
    • Prominent red nucleolus common in: serous carcinoma.
  2. The classic appearance of melanoma without pigment is closest to adenocarcinoma (which may have red nucleoli, large cells, abundant cytoplasm, occasional binucleation).
    • Differentiating morphologic features: adenocarcinoma - 3-D clusters of cells, no spindle-shaped cells.
  3. Bug-eyed monster cells - may vaguely resemble Reed-Sternberg cells (RSCs) which are diagnostic of Hodgkin's lymphoma (HL).
    • RSCs do not have the granular cytoplasm typical of melanoma.
    • Nuclei usually adjacent, i.e. not at opposite poles of the cell.
    • Background of melanoma different than HL.


Bone marrow/vertebrae


  1. One should see three lineages:
    • Megakaryocytes.
      • Large cells ~ 5-10X RBC.
      • Eccentric nuclei.
    • Erythrocyte precursor.
      • Central nucleus.
      • Chromatin - granular.
      • One should see ejected nuclei of the same size.
    • Granulocytes.
  2. Fat.
    • May be seen in a lymph node.


  • Megakaryocytes - reduced post-bone marrow transplant.

Short DDx:

Soft tissue lesions

Nodular fasciitis


  • Rapid growth - need clinical.



  • Tissue culture-like appearance - key feature.
  • Myxoid background.
  • Moderate nuclear pleomorphism.




  • Bent fish hook-like nuclei - key feature.
  • Variable cellularity (Antoni A = cellular, Antoni B = paucicellular).

Solitary fibrous tumour



  • Spindle cells with oval nuclei.
  • Wire-like lamellar collagen.


  • CD34 +ve.
  • BCL2 +ve.
  • CD99 +ve.

See also


  1. UHN Screening process. PCY50001.08.
  2. WG. 19 February 2010.
  3. WG. 6 January 2010.
  4. SM. 5 January 2010.
  5. SB. 27 January 2010.
  6. SM. 16 May 2008.
  7. URL: Accessed on: March 18, 2010.
  9. Horobin RW, Walter KJ (1987). "Understanding Romanowsky staining. I: The Romanowsky-Giemsa effect in blood smears". Histochemistry 86 (3): 331–6. PMID 2437082.
  10. Horobin RW, Walter KJ (1987). "Understanding Romanowsky staining. I: The Romanowsky-Giemsa effect in blood smears". Histochemistry 86 (3): 331–6. PMID 2437082.
  11. Sapino A, Papotti M, Pietribiasi F, Bussolati G (September 1998). "Diagnostic cytological features of neuroendocrine differentiated carcinoma of the breast". Virchows Arch. 433 (3): 217–22.
  12. UHN PCY50001.08 P.11.
  13. UHN PCY50001.08 P.10.
  14. GR. 4 February 2010.
  15. GR. 4 February 2010.
  16. SB. 11 January 2010.
  17. SB. 11 January 2010.
  18. Diamantis A, Magiorkinis E, Koutselini H (2009). "Fine-needle aspiration (FNA) biopsy: historical aspects". Folia Histochem. Cytobiol. 47 (2): 191–7. doi:10.2478/v10042-009-0027-x. PMID 19995703.
  19. WG. 16 February 2010.
  20. SB. March 8, 2010.
  21. SB. March 8, 2010.
  22. SB. March 11, 2010.
  23. SM. January 2010.
  24. GS. 26 January 2010.
  26. 26.0 26.1 URL: Accessed on: 9 April 2012.
  27. FNAC PP.203-4.
  28. URL: Accessed on: January 4, 2010.
  29. URL: Accessed on: 10 April 2012.
  30. GS. 24 February 2010.
  31. SB. 25 January 2010.

External links