What is the role of imprint cytology in diagnosing respiratory conditions, such as lung cancer, in adults with respiratory symptoms and a history of smoking or exposure to carcinogens?

Imprint Cytology in Respiratory Medicine

Imprint cytology of bronchoscopic biopsy specimens is a valuable adjunctive technique that significantly improves diagnostic yield for lung cancer, increasing sensitivity from approximately 77% to 85% when combined with histopathology, and provides rapid preliminary diagnosis while awaiting formal histopathology results.

Diagnostic Performance and Clinical Utility

Enhanced Diagnostic Accuracy

• Imprint cytology combined with histopathology increases the diagnostic rate of bronchoscopy from 76.9% to 84.8% (P<0.0001), representing a statistically significant improvement in detecting peripheral lung cancers 1

• The technique demonstrates high sensitivity (84.9%) and specificity (72.4%) when compared to histopathology as the gold standard, with diagnostic accuracy reaching 98.08% in some studies 2, 3

• No false-positive results have been reported with imprint cytology, making it a reliable technique when positive results are obtained 2, 4

Optimal Sampling Strategy

The evidence supports a multimodal cytological approach during bronchoscopy:

• Imprint smears of biopsy specimens should be prepared immediately after tissue collection, before placing the specimen in formalin 1, 2

• Rinse fluid cytology of the biopsy forceps adds additional diagnostic value, increasing sensitivity to 83.7% (P<0.0001) 1

• Combining both imprint cytology and rinse fluid examination achieves the highest diagnostic rate of 86.2% (P<0.0001) 1

• The rinse fluid technique involves placing bronchial biopsies initially in balanced salt solution, then removing visible tissue fragments for histopathology while sending the rinse fluid for cytological examination 4

Clinical Advantages

Rapid preliminary diagnosis is a key benefit:

• Imprint smears can be stained with Leishman-Giemsa cocktail or Papanicolaou stain and evaluated quickly, providing preliminary results while awaiting formal histopathology 3

• In 4.8% of malignant cases, bronchial biopsy rinse fluid cytology provides the only positive diagnostic result, making it essential for maximizing diagnostic yield 4

Cost-effectiveness and efficiency:

• The technique neither prolongs the bronchoscopy procedure nor increases costs, as it utilizes material that would otherwise be discarded 4

• Agreement with histological results reaches 81.8%, providing reliable preliminary information for clinical decision-making 4

Integration with Broader Diagnostic Algorithm

Context Within Lung Cancer Diagnosis

While imprint cytology is valuable, it must be understood within the broader diagnostic framework established by the American College of Chest Physicians:

• Sputum cytology remains the least invasive initial diagnostic method for suspected lung cancer, with pooled sensitivity of 66% and specificity of 99%, though it is particularly useful for central lesions (71% sensitivity) versus peripheral lesions (49% sensitivity) 5

• Bronchoscopy is recommended for central lesions to confirm diagnosis, with further testing required if results are non-diagnostic 5

• For peripheral lung nodules requiring tissue diagnosis, radial endobronchial ultrasound or electromagnetic navigation should be used as adjuncts to conventional bronchoscopy 5

Important Caveats

Tissue adequacy considerations:

• While cytology (including imprint cytology) reliably diagnoses non-small cell lung cancer, adequate tissue should be obtained to accurately define histologic type and perform molecular analysis for treatment planning 5

• This is critical because modern lung cancer treatment increasingly depends on molecular profiling for targeted therapies

Institutional factors:

• The diagnostic accuracy of cytological techniques, including imprint cytology, depends on institutional expertise in specimen collection, processing, and interpretation 5

• Centers without established cytology programs may experience lower sensitivity than reported in studies from specialized institutions 5

Practical Implementation

Recommended technique during bronchoscopy:

1. Obtain bronchial biopsy specimens under fluoroscopic guidance for peripheral lesions 1
2. Immediately prepare imprint smears by gently touching the biopsy specimen to glass slides before fixation 2, 3
3. Place the biopsy specimen in balanced salt solution temporarily 4
4. Collect rinse fluid from biopsy forceps and brushes for cytological examination 1
5. Remove visible tissue fragments and place in formalin for histopathology 4
6. Submit rinse fluid for cytological examination 1, 4

Staining and interpretation:

• Imprint smears should be stained with both Leishman-Giemsa and Papanicolaou stains for optimal cellular detail 3
• Cytological examination should be performed by experienced cytopathologists to maximize diagnostic accuracy 2