Cell Block in Cytology

Cell Block

• A method of preparing cytologic material to obtain diagnostic information in addition to that obtained from cytology slides.
• Allows for easier performance of special stains, immunohistochemistry, and examination of histological structure.
• Acquisition of tissue for cell block can increase diagnostic sensitivity and specificity.

Cell Block Preparation Methods

• Clot and Scrape method
• Formalin or Alcohol vapor method
• BBC fixative method
• Cell block pellet alcohol fixation
• Cell block pellet formalin fixation
• Plasma thrombin method
• Collodion method
• Cellient automated system
• Histogel method

Cell Block Methods

BBC Cell Block Fixative Method

• Uses a needle to rinse the specimen in 1 mL of BBC Cyto-Cell Block.
• Fix in a non-coated tube.
• Invert the tube onto appropriate filter paper.
• Scrape tissue on the paper into a small area.
• Process routinely in the histopathology laboratory.

Plasma Thrombin Method

• Centrifugation of the cell suspension.
• Add plasma and thrombin.
• Mix and allow the mixture to sit for a few minutes until a soft ball forms.
• Place the mass into an appropriately labeled cassette.
• Process in fixative and submit for processing as tissue.

Collodion Bag Cell Block

• Concentrates the cells for a more adequate cell block preparation in a collodion bag.
• Preparation of collodion bag tubes.
• Pipette specimen into collodion bag.
• Centrifuge and pipette off supernatant.
• Assemble the edge of the collodion bag on the lip of the tube.
• Lift the bag from the tube and tie with cotton string.
• Place the remaining bag in a tissue cassette and process in neutral buffered formalin.

Histogel Method

• Used for cytology specimens with a predominance of individually scattered cells.
• Concentrates the cells of interest along the plane parallel to the cutting surface of the cell block.
• Can be used for cell block preparations of cervical ThinPreps.

Tissue Coagulum Clot Method

• Allows a clot to form in the lumen of the fine needle aspiration tip.
• The clot is then transferred directly to formalin for fixation.
• Prevents the loss of diagnostic material.

Cell Block Advantages

• Slides are more readily interpretable by histopathologists.
• Availability of a block facilitates more sections.
• Important residual material is salvaged which is generally not available in cytology smears.
• Loose cells, cell aggregates, and microscopic tissue fragments are easily recoverable.
• Concentrated in a small area of the slide, making examination less time-consuming.
• Allows for special stains, immunocytochemistry, and molecular analysis.

Cell Block Limitations

• Takes longer time compared to routine smears.
• Sparse cellularity.
• Distortion artifacts.

Clinical Applications

• Diagnostic accuracy of routine smears for malignancy ranges from 50-80% with a false negative rate of about 25%.
• Cell block preparation can improve diagnostic accuracy.
• Identification of primary site of malignancy can be enhanced with the use of cell block technique.
• Histologic patterns of cancer can be readily identified on a cell block.
• Psammoma bodies, granulation tissue, cholesterol clefts, microorganisms, fragments of collagenous stroma, and hyperplastic mesothelium can be identified.
• Fluid samples or tissue fragments can be preserved in a refrigerator for 72 hours before processing in cell blocks.

Immunohistochemistry and Molecular Analysis

• IHC on cell blocks are comparable to that of surgical specimens.
• Microarray technique, molecular tests like FISH, and in situ PCR can be performed.
• Electron microscopy can be performed.
• CBs are the preferred choice for IHC as they are comparable with surgical biopsies.

Organ-Specific Applications

• Breast: CB is considered suitable for hormone receptors and Her-2/neu analysis.
• Lung: CBs can be prepared from EBUS-TBNA samples and subjected to a panel of antibodies.
• Deep Seated Abdominal organs: CB with on-site cytopathological evaluation of direct FNA smears can increase diagnostic yield.
• Thyroid: CBs have a minimal role due to low cellularity.
• Lymphocytic Effusion: CBs can be used for microarray construction.