What are the current practices in cytopathology for disease diagnosis?

Current Cytopathology Practice for Disease Diagnosis

Modern cytopathology practice emphasizes rapid onsite evaluation, multiple preparation techniques, and integration with molecular testing to maximize diagnostic accuracy while minimizing invasive procedures.

Core Diagnostic Applications

Current cytopathology serves three primary clinical functions:

• Differential diagnosis between neoplastic and reactive processes, particularly for plasma cell disorders, lymphoproliferative diseases, and solid tumors 1
• Intraoperative consultation for immediate surgical decision-making, especially in neurosurgery and endoscopic procedures 1
• Minimal residual disease detection and treatment monitoring in hematologic malignancies 1, 2

Specimen Preparation Techniques

Multiple Preparation Methods

Pathologists should routinely employ multiple cytology preparation types on each specimen, as each provides complementary diagnostic information 1:

• Touch/imprint preparations: Used on all tissue samples regardless of size; excellent for detecting cellular dyscohesion in inflammatory processes, hematologic disorders, pituitary adenomas, germinomas, and metastatic tumors 1
• Smear/squash preparations: Best for demonstrating tissue architecture, distinguishing glial from non-glial lesions, and identifying specific features like papillary structures, rosettes, and microvascular proliferation 1
• Scrape preparations: Essential for firm, fibrous, bony, or calcified samples that cut poorly for frozen section 1

Staining Protocols

Two complementary staining approaches are standard 1:

• Air-dried smears with Diff-Quik staining: Provides rapid results (minutes), excellent for immediate onsite evaluation, preserves cytoplasmic features 1
• Alcohol-fixed smears with H&E or Papanicolaou staining: Preserves superior nuclear detail, allows direct comparison with frozen sections 1

When tissue quantity permits, both staining methods should be performed as they reveal different diagnostic features 1.

Rapid Onsite Evaluation (ROSE)

Impact on Diagnostic Yield

The presence of an onsite cytopathologist during procedures significantly improves outcomes 1:

• Reduces inadequate samples from 12.6% to 1% 1
• Increases diagnostic sensitivity from 78.2% to 96.2% 1
• Decreases the number of needle passes required 1
• Reduces procedure duration 1

Alternatives When ROSE Unavailable

When onsite cytopathology is not accessible, specific compensatory strategies are recommended 1:

• Perform at least 3 passes on lymph nodes and 6-7 passes on pancreatic masses 1
• Dedicate one pass specifically for cell block preparation to enable immunohistochemical staining and flow cytometry 1
• Use larger gauge needles (19G) or reverse-beveled needles to obtain histologic cores, achieving >90% diagnostic accuracy 1
• Train cytotechnicians or endosonographers in basic cytopathology for adequacy assessment 1

Cell Block and Advanced Processing

Cell Block Preparation

Cell block preparation is mandatory when special studies may be required 1:

• Specimen placed in liquid media, spun into pellet, formalin-fixed, paraffin-embedded, and sectioned 1
• Enables immunohistochemical staining, flow cytometry, and molecular testing 1
• Essential for cases requiring clonality assessment or phenotypic characterization 1

Liquid-Based Cytology

Automated liquid-based methods (ThinPrep, SurePath) provide 1:

• High cell preservation and uniform monolayer dispersion 1
• Reduced technical artifacts compared to manual preparation 1

Caution: Cannot provide immediate assessment unless specimen is split; may cause loss of background mucin critical for diagnosing mucin-producing tumors 1.

Flow Cytometry Integration

Essential Markers and Panels

For plasma cell identification and enumeration, CD38, CD138, and CD45 must all be included in at least one tube, with primary gating based on CD38 vs. CD138 expression 1, 2, 3:

• Minimal panel for abnormal plasma cells: CD19 and CD56 1, 2
• Preferred comprehensive panel: CD20, CD117, CD28, CD27, CD81, and cytoplasmic kappa/lambda light chains 1, 2, 3

Diagnostic Sensitivity

Flow cytometry detects neoplastic cells at 0.01% of leukocytes when acquiring ≥1,000 total events with minimum 100 neoplastic plasma cell events 3.

CSF Cytology Practices

Diagnostic Yield Optimization

For suspected leptomeningeal metastases, collect ≥5-10 mL CSF and process within 30 minutes to prevent cellular degradation 1:

• First lumbar puncture has 50-90% sensitivity 1
• Second lumbar puncture recommended if initial result negative or equivocal 1
• Ventricular or cisternal collection may improve yield when lumbar sampling is negative with intracranial-only enhancement 1

Diagnostic Categories

The field is moving toward standardized reporting systems 1:

• Atypical urothelial cells of undetermined significance (repeat cytology) 1
• Atypical urothelial cells, cannot rule out high-grade carcinoma (requires endoscopic evaluation) 1

Molecular Testing Integration

Cytopathology now serves as the primary platform for precision oncology, with cytopathologists responsible for appropriate specimen triaging and molecular test allocation 4, 5:

• Molecular testing complements but does not replace visual cytopathology interpretation 6
• Small cytology samples provide sufficient material for next-generation sequencing and targeted mutation analysis 4, 5
• Proper specimen handling and triaging by cytopathologists is critical for successful molecular testing 5

Common Pitfalls to Avoid

• Inadequate sample volume: Ensure sufficient CSF (≥5-10 mL) and multiple tissue passes when ROSE unavailable 1
• Delayed processing: Process CSF within 30 minutes; cellular degradation causes false negatives 1
• Single preparation technique: Always use multiple cytology preparation types for complementary information 1
• Ignoring specimen adequacy: Verify presence of normal marrow elements in follow-up samples, especially when assessing minimal residual disease 1
• Insufficient flow cytometry events: Acquire ≥1,000 total events for adequate sensitivity 3
• Inadequate antibody panels: Use comprehensive panels to distinguish normal from neoplastic cells 1, 2