signet ring cell lymphoma ( srcl ) are proliferations of malignant lymphoid cells containing cytoplasmic inclusions or vacuoles that displace the nucleus , imparting it a  signet ring  appearance . it is a rare morphological variant of non - hodgkin lymphoma ( nhl ) , which can be confused with other more common tumors such as signet ring cell carcinomas , especially in cytological preparations and bone marrow biopsies . though originally described as a variant of follicular lymphoma the signet cell appearance in these cases may be due to cytoplasmic accumulation of immunoglobulin ( ig ) or vacuoles derived from multivesicular bodies ( mvbs ) , however these morphological features in lymphomas are very rare and prompted us to report one such case where immunofluorescence ( if ) helped us to demonstrate igg in the cytoplasm of these cells . we have not come across any other instance in literature where if was used for this purpose in srcl . a 60-year - old male presented with a 2-month history of pain and fullness in the abdomen , breathlessness , and weight loss . on palpation , left supraclavicular and cervical lymphadenopathy was revealed . a single , large , firm lump with nodular surface was felt in the umbilical region . radiological investigations showed bilateral plural effusion and ascitis with extensive para - aortic , retroperitoneal , celiac , portal and mesenteric nodal masses . fine needle aspiration smears of cervical lymph node predominantly revealed a monotonous population of medium sized lymphoid cells with scanty to moderate cytoplasm and cleaved and noncleaved nuclei showing inconspicuous nucleoli . scattered among these were larger cells with prominent cytoplasmic vacuoles and a typical signet ring cell morphology with eccentrically placed flattened or crescentic nuclei . ( a ) fine needle aspiration smear show lymphoid population admixed with signet ring cells ( arrow , leishman stain , 400 ) . ( c ) pleural fluid show lymphocytes , mesothelial cells ( arrowhead ) , and signet ring cells ( arrow , h&e , 400 ) . inset shows hbme1 cytoplasmic positivity in mesothelial cells ( arrowhead ) , with negative staining in signet ring cells ( arrow , immunocytochemical stain , 400 ) . ( d ) histology highlighting the follicular architecture ( h&e , 40 ) the histochemical stains for mucin ( periodic acid schiff and mucicarmine ) were negative . to demonstrate ig in the cytoplasm of these cells , if technique was used . we re - aspirated the cervical lymph nodes , and cell suspensions were prepared in phosphate buffer saline ( pbs ) in two test tubes . from the first tube , the cells were washed twice and the smears were prepared from the deposit . from the second tube , the cell pellate was transferred to frozen section medium and cell block was prepared . the smears and cell block sections both were stained for igg and igm using the direct if technique . to our surprise , the signet ring cells gave brilliant fluorescence for igg antibody [ figure 1b ] . no reaction could be seen with the igm antibody . the if was better demonstrated on direct smears rather than sections . pleural fluid cytology also showed typical signet ring cells in addition to lymphocytes and mesothelial cells . these signet ring cells showed negativity for the mesothelial marker hbme1on immunocytochemistry [ figure 1c ] . the lymph node biopsy showed classical follicular lymphoma with some diffuse areas [ figure 1d ] . the signet ring cells were seen mostly in diffuse areas and interfollicular areas [ figure 2a , arrow ] . there were no plasmacytoid cells , cells with eosinophilic russel body - like inclusions or large blast cells . ( a ) histology show inter follicular area showing signet ring cells ( arrow h&e , 400 ) . ( d ) cd 20 positivity ( cd20 , 400 ) immunohistochemistry demonstrated positivity for cd 10 , cd 20 , cd 45 , and negative for t - cell markers such as cd 3 and cd 5 , as well as pan - cytokeratin [ figure 2b  d ] . bone marrow biopsy sections also showed presence of signet ring cells . considering the secreting nature of the neoplastic cells , the pleural fluid and serum in consideration of all these findings , a final diagnosis of b - cell follicular lymphoma grade i signet ring cell type ( stage iv ) was offered . however , subsequently , various workers described similar morphology in t - cell , immunoblastic , burkitt - like , malt - type , and small and large cell lymphomas . the nature of the vacuoles or cytoplasmic inclusion is yet under debate , and may be igg ( in centrocytic lymphoma ) or igm , forming russel body - like eosinophilic globules ( immunoblastic and large cell lymphoma ) or membrane bound spaces derived from multivesicular bodies ( em observation ) especially in t - cell srcl . however , the morphology is rare and may cause confusion in diagnosis in certain situations . in the metastatic lesions and extranodal sites such as the skin , bone marrow , stomach , thyroid , salivary gland and ovary primary suspicion may be of adenocarcinoma , melanoma or liposarcoma . in addition to negative stains for mucin , the absence of clumping of cells and the fact that in most secondary deposits the aspirations smears are mostly entirely neoplastic epithelial cells , rarely having a predominantly lymphoid background , are helpful pointers for differential diagnosis . except in cases with russell body - like inclusions , where igm could be unequivocally demonstrated , the immunocytochemical staining for igg has not always been convincing even in b cell lymphomas . in this context , the if technique using fresh washed cytological smears may be rewarding , as in our case . incidentally , there are no previous reports on the use of if for demonstration of igg in srcl . further proof of the secretary nature of the neoplastic cells in our case was available by demonstration of monoclonal band in gamma region on electrophoresis of serum and pleural fluid . we could distinguish neoplastic cells because of the absence of mesothelial markers [ figure 1c , inset ] . recently one large case series of srcl comprising seven cases with predominant emphasis on cytological features was published . the authors of the case series emphasized distinguishing features of srcl from melanoma , adenocarcinoma , liposarcoma as well as benign histiocytic proliferations . our aim of presenting this case is to review the awareness of this rare lymphoma among the pathologists to give due consideration for avoiding inappropriate investigations and treatment . our new innovative immunofluorescence technique on fine needle aspiration samples can be utilized as a rapid tool to demonstrate immunoglobulins in these cells in conjunction with the histochemical stains .