Lymph node is an essential organ of the human immune system. Lymphadenopathy is a sign noticed when a lymph node increases in size and number or atypical in consistency [1]. The causes of lymphadenopathy are numerous few of them varies from benign reactive lymphoid hyperplasia to malignant diseases and the most common cause is benign lymphadenopathy (90%), including reactive hyperplasia (60%), followed by infectious or inflammatory lymphadenitis (30%). Infectious or inflammatory lymphadenitis includes Kikuchi- Fujimoto disease (KFD), tuberculosis, sarcoidosis, infectious mononucleosis, toxoplasmosis, human immunodeficiency virus infection, cat-scratch disease, drug (phenytoin) reaction, and others [1,2]. Malignant lymphadenopathies only comprise 10% of the cases, which include primary lymphomas (3%), including diffuse large B-cell lymphoma/anaplastic large cell lymphoma, follicular lymphoma (FL), mantle cell lymphoma (MCL), peripheral T-cell lymphoma (PTCL), and Hodgkin’s lymphoma (HL). Metastatic carcinomas account for 7% of cases and include squamous cell carcinoma primarily from oral carcinoma, metastatic papillary thyroid carcinoma, adenocarcinomas primarily from lung or breast, and poorly differentiated squamous cell, small cell, or any primary unknown carcinoma [2]. It is very difficult to diagnose the cause of lymphadenopathy based solely on history, physical examination, or ultrasound alone. Fine needle aspiration cytology (FNAC) is very cost effective and rapid process, therefore,is vastly utilized as a primary diagnostic tool to examine enlarged lymph nodes and to exclude involvement of alternative organs, such as the salivary gland, head, neck, or other subcutaneous masses. It is also a minimally invasive approach that allows fast diagnosis and treatment. There are few complications that have been reported for FNAC, including hemorrhage, nerve damage, and vasovagal reactions in head and neck lymph node procedures [4]. Finally, FNAC is a cost-effective procedure, especially in developing countries. The present study assesses the diagnostic utility of FNAC and evaluates the degree of concordance between cytological interpretation and radiological findings.

Study Design Retrospective cross-sectional study conducted for 8 months in 2 Tertiary care centres of Northern Rajasthan. Sample Size Out of 300 FNAC procedures performed for lymphadenopathy, 210 cases with complete radiological correlation were included. Procedure In all the cases the FNA and USG were performed with patient consent, under aseptic conditions with 23 gauge needle. The superficial and palpable lymph node aspirations were taken blindly and for non palpable and deep lymph nodes, image guidance was taken, mostly by ultrasonography guided FNA. Atleast two air dried and three wet fixed smears were made and stained with Papanicolaou & field stains. Additional smears were made in suspected cases of tuberculosis and stained with Ziehl nelson stain. The smears were reported and classified into 5 different diagnostic categories based on the proposed Sydney system of reporting [5] Diagnostic Categories 1. Non-diagnostic 2. Benign 3. Atypical / Indeterminate 4. Suspicious 5. Malignant Correlation and Statistics Cytology results were compared with radiological findings and available histopathology (n=88). Sensitivity, specificity, PPV, and NPV were calculated following standard diagnostic formulae [4].

Demographic Distribution • Total cases: 210 • Age range: 18–65 years (mean 42 years) • Gender: 59.7% females, 40.3% males Site Distribution • Cervical nodes: 77.6% • Axillary: 13.5% • Submandibular: 12.3% • Others: 10.4% Higher cervical involvement is consistent with previous studies [10,11,15]. Cytological Diagnosis • Benign: 52.3% • Malignant: 30.95% • Indeterminate / atypical: 0.04% • Suspicious: 0.02% • Lymphoma (within malignant): 2.85% • Non-diagnostic: 0.06% FNAC–Radiology Concordance • Benign lesions: 95.2% • Metastatic lesions: 85.9% • Lymphoma: 50% • Atypical cases: 66.6% • All non-diagnostic FNAC cases were correctly interpreted radiologically. Missed Cases Misinterpretation occurred in 10 total cases between both centres. Some lymphomas were mistaken for reactive lymphadenitis, consistent with known diagnostic limitations [12]. Diagnostic Accuracy • Sensitivity: 94% • Specificity: 96% These values are comparable to previously published studies [10–14]. a b Fig.1 (a,b) Reactive hyperplasia showing polymorphous lymphoid cell population with lymphoglandular bodies [40x , 10x]. c d Fig. 2 (c,d )Metastasis and Lymphoma showing pleomorphic immature and mature squamous cells and Lymphoma showing monomorphic lymphoid population[ 40x,10x]. Fig 3.A,B,C,D,E,F Ultrasonographic findings of various lymphadenopathies – A:Benign lymphadenitis,B: Reactive lymphadenitis,C,D :Metastatic lesions , E,F:Lymphoma.

After the successful establishment of Bethesda system for cervical [6] and thyroid cytology [7] and Milan system for salivary gland cytology [8], in 2020 proposal of Sydney system for lymph node was proposed to keep uniform reporting and better communication [9]. The present study showed the diagnostic accuracy of Sydney system in Fine needle aspiration cytology of lymph node pathologies. In the present study, 67.5% (n=131) patients were having cervical lymphadenopathy, both unilateral as well as bilateral. A study by Robert F suggested 55% of lymphadenopathy occurs at head and neck region [15] Similar findings were also suggested by Gupta P et al., Vigilar E et al., [10, 11]. In the present study, L2 category showed more prevalence (77.6%) which could be due to low sample size and also could be due to increased prevalence of tuberculosis in the area where study has been conducted. On the contrary, studies by Gupta P et al., Vigilar E et al., [10,11] showed equal distribution between benign and malignant lesion catagories . On the contrary, in a study by Gupta P et al., 35 cases out of 304 cases 11.51% were found to be malignant [10]. Maximum discordant results (false negative) results were found in category L3, L5 where 3 cases were reported as atypical lymphoid and non lymphoid cells which later were diagnosed as Non Hodgkin’s lymphoma in 6 cases and metastasis from epithelial malignancy in one of the case. Where as in study of Gupta P et al., [10], total 16 cases were discordant in the category L3 .In the category L5, the sub typing of the Non Hodgkin’s lymphoma were followed-up with histopathological examination. Due to lack of other ancillary methods like flowcytometry and cell block preparation, those results could not be correlated. Radiological evaluation played a crucial role in resolving non-diagnostic cases and strengthening the diagnostic impression. Overall, FNAC demonstrated excellent sensitivity and specificity, reinforcing its value in first-line investigation. Variables Present study Gupta P et al[10] Vigilar E et al[11] Cupato A etal[12] Sensitivity 95.23% 79.9% 98.4% 97.9% Specificity 94.11% 98.7% 95.3% 96.2%

FNAC is an effective, rapid,cost effective and minimally invasive technique for evaluating lymphadenopathy. Its diagnostic accuracy is significantly enhanced when combined with radiological assessment. Although challenges persist in diagnosing lymphoma subtypes, FNAC remains vital for patient triage and management. Further research incorporating advanced diagnostic modalities is recommended.

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