1-2 Cytomorphology: Basic Concepts
Contents
Cell classification by morphology
- Cytology diagnosis depends on the appearance of individual cells usually devoid of architectural detail or extracellular matrix. Because the cells are analyzed at much higher magnification than takes place for histology, you need to shift your focus to details overlooked in histologic exams.
- Nuclear morphology provides information on the level of cellular activity while the cytoplasm provides clues to the cell differentiation or cell type.
- Cell shape will vary in cytology samples depending on how the sample was obtained. Exfoliated cells suspended in liquid fixative often have a round shape. Cells that have been plucked from their tissue either by abrasion (brushing, scraping) or fine needle aspiration may retain their native shape (rectangular glandular cells, polygonal squamous cells).
- Epithelial cells
- The quality of the cytoplasm offers clues as to cell origin: cytoplasm of glandular cells is pale staining with one vacuole or many micro vacuoles containing glandular secretions; squamous cells usually have a more dense, uniformly stained cytoplasm and may show a linear quality surrounding the nucleus. Nuclei are generally “euchromic” that is the chromatin is of a normal intensity. In cytology preparations from women, the inactive X chromosome may be seen as a small dense dot on sitting on the nuclear membrane, known as the Barr body.
- Glandular cells
 |
 |
When single, glandular cells have a rectangular or square shape. The cytoplasm is delicate and the nucleus tends to be round with finely distributed (open or vesicular) chromatin. A small nucleolus may be present. The nucleus tends to be present at the end of cytoplasm nearest the prior attachement to the basement membrane. This site of attachement may appear as a cytoplasmic tail where the cell was detached from the basement membrane.Glandular cells in groups can appear as:
1. Flat sheets with uniform placement of cells in a “honey comb” arrangement similar to a bee hive. By shifting the plane of focus on a glandular sheet, either the mucin-filled cytoplasmic pole or the nuclear pole will be in focus.
 |
 |
|
2. Aligned groups of rectangular columnar cells are said to have a picket fence arrangement. The columnar cells may have a row of cilia attached to a terminal bar at one short end of the cell.
 |
 |
|
3. Clustered groups or three dimensional groups of cells with rounded borders often with visible cytoplasmic vacuoles may be abradedor shed from hyperplastic epithelia. Glandular lumens may be visible.
 |
||
Squamous Cells
4. Squamous cells when single usually appear as flat polygonal cells. The size of squamous cells varies according to the layer of origin within the epithelium and other factors such as hormone stimulation. The Papanicolaou stain differentially colors the cytoplasm according to the stage of keratinization: younger cells appear more blue-green, more fully keratinized cells turn pink and finally appear orange.
 |
 |
The nuclei of the squamous cells vary from larger and round with fine (open) chromatin in less mature cells to pyknotic (dense, dark) and small in superficial cells to a complete absence of nuclei in anucleate squames.
 |
 |
 |
Squamous cells in groups often appear flattened; intercellular junctions can be identified.
 |
||
Mesothelial cells
- These are cuboidal cells that occur in sheets, or when shed in body cavity fluids as rounded cells usually with a dense perinuclear area and paler periphery due to microvilli. When juxtaposed one to another, an intercellular space is visible due to the microvilli.
Mesenchymal cells other than adipocytes often have a spindled or elongate shape. Striations may be seen in skeletal muscle cells
Leukocytes are rounded cells; nuclear shape provides a clue to the cell type: bilobed eosinophils (granules not always obvious), poly lobed neutrophil, reniform shaped macrophage.
Cytoplasmic and extracellular pigment:
- Melanin – brown, dusty to granular on Pap, deep blue with Giemsa
- Hemosiderin – coarsely brown on Pap
- Hematoidin (an intermediate breakdown product of hemoglobin) - yellow
- Bile – deep golden yellow
Morphology of cell response to injury
- Apoptosis
- Necrosis
- Reactive nuclear and cytoplasmic changes:
- Nuclear enlargement B12 deficiency
- Mitoses
- Enlarged nucleoli
- Multinucleation
- Cell enlargement
- Cytoplasmic vacuolization and polychromasia
Cytomorphology of malignancy
Nucleus Multiple nuclear abnormalities occur in malignant cells. No every malignant tumor will show all features and a critical number of features (although there is no magic number) need to be identified before one can say with confidence “this is a malignant cell”. Listed below are the most common changes:
- Nuclear enlargement
- Increased nuclear to cytoplasmic ratio
- Nuclear membrane irregularity
- Chromatin abnormalities: hyperchromasia, coarse irregular chromatin clumping, hypochromasia
- Abnormal nucleoli: excessively large, irregularly shaped, multiple
- Intranuclear inclusions
- Nuclear grooves or creases
- Abnormal mitoses
Cytoplasm and cell arrangement
- Nuclear abnormalities are most critical to the cytologic diagnosis of malignancy, but cytoplasmic and architectural features also occur.
- Depending on the degree of differentiation the malignant cell will vary from near normal in size to extremely large. The malignant cells may vary in size among themselves (anisocytosis).
- Orderly cell arrangement is often lost in malignancy, such as the “drunken honeycomb” pattern seen in ductal carcinoma of the pancreas.
- Loss of cell to cell adhesion often occurs in carcinoma, especially in adenocarcinoma. Paradoxically in some squamous cell carcinomas the malignant squamous cells may be seen in large cohesive groups while abraded normal squamous cells occur as single cells.
- Necrosis (also known as tumor “diathesis”) may be apparent on cytology samples as anuclear cellular debris and fibrin present as a film in the background of smears or as material clinging to cell groups in liquid based cytology preparations.
