Serous effusions imply that accumulation of fluid is in excess of the normal expected amount in the serous cavities.¹ Accumulation of fluid other than blood in the body cavities is broadly described as ‘effusion’.² The transudates are clear, straw-coloured fluids that do not clot and have low specific gravity (<1.010) and low protein content (<3 g/dl). The exudates are turbid or cloudy and have relatively high protein content (>3 g/dl) and high specific gravity (>1.015).³

The pathophysiology of serous effusion is governed by the disruption of Starling’s forces, which normally maintain a dynamic equilibrium between the capillary bed and the interstitial space.⁴ In malignant effusions, a combination of these factors is often present, as tumor cells not only block lymphatic outlets but also secrete vascular endothelial growth factors (VEGF) that significantly enhance vascular leakiness.⁵

Causes of Serous Effusions⁶

Serous effusions present a spectrum of neoplastic and non-neoplastic conditions, either local or systemic.⁷. Thus, understanding the relative frequency and underlying mechanisms of serous effusions is essential for accurate interpretation and clinical correlation.

Diagnostic cytopathology is a rapid, inexpensive and simple diagnostic tool. Cytological examination is imperative to identiy non-inflammatory, inflammatory (acute or chronic) and Neoplastic aetiopathogenesis of effusion. The presence of malignant cells in the effusion is almost always indicative of metastatic tumours, as primary malignancies arising from the mesothelial cell lining are rare. In case of primary malignancy the tumour cells are usually found to be numerous and in clusters. A positive effusion for malignant cells is an important prognostic indicator in oncologic patients.⁸ Sensitivity of cytological diagnosis of  effusions for malignancy is 40-60%.⁹

Aspiration of serous cavities is a simple and relatively non-invasive technique to achieve diagnosis.¹⁰ Thoracentesis is a commonly performed diagnostic and therapeutic procedure for removing fluid from the pleural space; by removing fluid, it helps alleviate symptoms like dyspnoea and provides crucial diagnostic information regarding the underlying cause of pleural fluid accumulation.¹¹  Adequate volume, timely fixation, and appropriate preparation techniques significantly influence diagnostic yield. Errors at the pre-analytical and analytical stages, such as delayed processing or improper fixation, may lead to cellular degeneration and compromise diagnostic yield.¹²

The conventional smear (CS) technique has long been the standard and most widely used method for the cytological evaluation of serous effusions in most laboratories worldwide.¹³ Cytocentrifugation is preferred as it is less tedious and quicker than the membrane filtration, but at times it may cause cellular distortion. The cell block technique is a pivotal procedure of examining the body fluids. The procedure in toto along with concomitant use of conventional smears has shown an added advantage in making an accurate diagnosis. It is a technique of cell concentration without compromising the cellular content and preserving the tissue architecture. Preparation of cell block from the effusion sediment is desirable and is being frequently and increasingly requested by the clinician.^{14, 15} Further, the effectiveness of the cell block lies in the availability of the diagnostic material for the further histological examination, histochemistry and IHC studies for a better classification of the tumour and for the identification of infectious causes by using microbiologic stains.¹⁶  Clinicians should be aware of the high variability in diagnostic sensitivity by primary tumour type as well as the potential reasons for false-negative cytology results.¹⁷

In view of the wide spectrum of etiologies underlying serous effusions and the inherent diagnostic challenges associated with their evaluation, the present study was undertaken to assess the diagnostic yield and clinical utility of effusion cytology.

AIMS AND OBJECTIVES

The present study was undertaken to evaluate and compare the diagnostic efficacy of conventional cytological smears and cell block tissue sections in detecting malignancies in serous effusions. The objectives include comparing morphological findings in various serous effusions, assessing the individual diagnostic efficacy of conventional fluid cytosmear and cell block techniques and comparing the findings with other similar studies.

MATERIAL AND METHODS

This hospital-based, prospective cross-sectional study on 103 samples was conducted at the Department of Pathology, Jawaharlal Nehru Medical College and Associated Group of Hospitals, Ajmer (Rajasthan), from June 2024 to May 2025. The study was approved by the institutional ethical committee. All the fresh serous effusions samples (ascitic and pleural effusions) sent by various departments of the hospital were included and scanty fluid samples and deteriorated samples were excluded. The clinical information including age, sex, history, provisional diagnosis were noted. After routine physical examination of the effusion sample (colour, appearance) it was divided into two test tubes (5 ml each) for conventional cytology and cell block preparation.  Contents from first test tube was transferred to a centrifugation tube and centrifuged at 1500 RPM for 5 minutes. Two thin smears was prepared from the sediment. One slide was wet fixed in 95% ethanol and stained with Haematoxylin and Eosin stain¹⁸ and the second one was air dried and stained with May-Grunwald Giemsa (MGG)¹⁰ stain.

Standard Operative Procedure For Cell Block [Plasma – Thromboplastin Method]⁹ : The cell block preparation involves enmeshing cellular material in a clot. A 5 ml serous fluid sample is centrifuged at 2000 rpm for 10 minutes, and the supernatant is discarded. The sediment is mixed with plasma and thrombin, allowed to form a soft ball, and then placed in filter paper and fixed for processing.

Tissue Processing For Histopathological Study: Prepared cell block was subjected to routine tissue processing. Then 3–5-micron sections were cut from paraffin embedded blocks. These sections were routinely stained with Harris Haematoxylin & Eosin stain¹⁹ and was examined for presence of malignancy, histological type, and grade. Special stains (Periodic acid -Schiff stain / Mucicarmine) was used wherever found necessary. Quality of smears and cell blocks was assessed according to Mair’s criteria.²⁰

Scoring system according to Mair’s criteria²⁰

0 to 2 points scores was given to individual smear/ cell blocks based on each of the above criteria, and the final score was calculated by adding the scores of four criteria.

Qualitative grouping of smears and cell blocks⁹

The cytological smears and block sections were examined separately for quality, cellularity, architectural patterns and morphology (cytoplasmic and nuclear details) to render a diagnosis for each case, and the findings was compared. Cytomorphological features were studied to identify the malignancy. Yield for malignancy was calculated by both methods. Diagnostic yield of both conventional smear and cell block method for diagnosing malignancy was calculated.

Statistical Analysis: Statistical analysis was done using computer software (SPSS Trial version 23 and primer). Qualitative data was expressed in proportions and percentages and the quantitative data was expressed as mean and standard deviations. The appropriate test of significance was applied. 5% probability was considered as statistically significant i.e. p<0.05.

RESULTS

Table 1 : Age Wise Distribution of Cases

Table 2 : Sex Wise Distribution of Cases

Table 3 : Comparative Quality Evaluation of Conventional Smear and Cell Block Cytology (According to Mair’s Criteria)

Table 4 : Descriptive Statistic for each of the Four Parameters of Conventional Smear and Cell Block Cytology

Table 5 : Diagnostic Scores of Conventional Smear and Cell Block Sections

Table 6 : Comparison of Cytological Diagnosis on Conventional Smear and Cell Block Study

Table 7 : Comparison of Cytological Diagnosis in Pleural and Ascitic Fluid

DISCUSSION

The present study aimed to prospectively evaluate and compare the diagnostic efficacy of Conventional Smear (CS) versus Cell Block (CB) techniques on 103 serous effusion samples and to contextualize these findings within the existing body of literature.

In this study, serous effusions were most frequently observed in patients in the 41-50 years (23.30%) and 61-70 years (21.36%) age groups. The findings of the present study align closely with Bansode S et al. (2015)²¹, Padmavathi A et al. (2016)²² and Dehariya C et al. (2020)²³. This suggests that while the overall age trend remains stable over time, the most significant concentration of cases in this study occurred in the fifth decade of life. This consistency across studies underscores that the diagnostic challenge of evaluating serous effusions is most pertinent to patients over 40 years.

The gender distribution in the Present Study indicates a notable male predominance, with a male-to-female ratio of approximately 1.86:1. These findings align most closely with the study by Bansode S et al. (2015)²¹, which reported a higher male-to-female ratio of 2:1., Dehariya C et al. (2020)²³ and Chandan RH et al. (2021)^58/24 observed 1.06:1 and 1.08:1 respectively.

Comparison of Morphological Quality of Conventional Smear and Cell Block

This study found that the CB method was statistically superior to CS in three of the four parameters (P<0.0001 for all):

The present study confirms that the cell block (CB) technique significantly enhances diagnostic yield, achieving a 2.91% absolute increase in malignancy detection and a 100% resolution of "suspicious" cases. This improvement aligns with findings by Dey S et al. (2017) [22% additional yield of malignancy by CB over CS (48% vs.26%)]²⁷, who similarly resolved suspicious smears using CB. While the additional yield in this study is more conservative than the 11.94% to 19.23% reported by Dehariya C et al. (2020)²³, Chandan RH et al. (2021)²⁴ (Increased malignancy detection in both pleural (7 to 12 cases) and ascitic fluids (8 to 15 cases) and Datta P et al. (2020)²⁸ (19.23% additional yield of malignancy by CB over CS (37.5% vs. 18.27%), it supports the consistent trend of increased sensitivity also noted by Grandhi B et al. (2014)²⁶ (Increased malignancy detection in both pleural (7 to 12 cases) and ascitic fluids (8 to 15 cases). Overall, the results reinforce the role of CB in providing definitive diagnoses and reducing diagnostic ambiguity.

CONCLUSION

Cell block technique demonstrated superior morphological preservation and improved diagnostic yield compared with conventional smear cytology. By employing tissue-processing principles, the cell block acts as a "mini-biopsy." It inherently concentrates exfoliated cells, eliminates obscuring hemorrhagic and proteinaceous backgrounds, and crucially preserves three-dimensional cellular architecture and spatial arrangements. These morphological enhancements directly translate to superior diagnostic yield.

The most significant clinical advantage of the cell block method is its ability to bridge the diagnostic gap between cytology and histology. By converting ambiguous, "suspicious" cytological smears into definitive benign or malignant diagnoses, the cell block prevents unnecessary diagnostic delays, reduces the need for subsequent invasive surgical procedures (such as pleural or peritoneal biopsies), and facilitates the immediate initiation of targeted patient management. Furthermore, cell block may facilitate ancillary techniques such as immuno-histochemistry and molecular studies.

ACKNOWLEDGEMENT

The authors wish to acknowledge the Department of Pathology, JLN Medical College Ajmer for its support and opportunity. The authors also wish to acknowledge Dr. Shailendra Vashistha (Assistant Professor, Transplant Immunology – HLA Lab, Department of IHTM, GMC, Kota) and the VAssist Research team (www.thevassist.com) for their contribution in journal selection and manuscript submission process.

Conflict of interest: None

Source of funding: Nil

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