cytology laboratories in large centers treating cancer patients occasionally come across meningeal carcinomatosis or neoplastic meningitis ( nm ) , in which there is diffuse seeding of the csf by metastatic carcinoma cells . detection of exfoliated malignant cells in csf due to the meningeal carcinomatosis may sometimes be the first diagnostic clue in patients with diverse neurological symptoms . while csf cytology is highly specific ( > 95% ) in detection of cancer cells in addition , the detection of metastatic carcinoma cells in csf of patients suffering from an extracranial carcinoma also has important therapeutic and prognostic implications . nm is a clinically important condition and numerous reports on cytology are available in literature ; however , mostly from early 80s and late 90s . the central nervous system ( cns ) is becoming a more common site of involvement as cancer patients live longer due to improvements in systemic therapies and advancement in neuroimaging studies . moreover , many chemotherapeutic agents do not cross the blood brain barrier , leaving the cns / meninges as a potential tumor hideout . this is increasing the importance of effective detection methods of cancer cells in the csf as early management can increase the therapeutic benefit . there are three methods to detect nm , which include clinical signs and symptoms , magnetic resonance imaging ( mri ) of the brain and spine and csf cytology . mri sensitivity and specificity vary with the type of primary cancer with a detection rate of nm in fewer than 50% of patients . on the other hand , csf cytology has a high specificity ( > 95% ) but associated with less sensitivity . this retrospective study was undertaken to evaluate the utility of csf cytopathology for the diagnosis of metastatic malignancies and to describe cytomorphologic features of various tumors , which help in diagnosis of nm . this study was a retrospective analysis of all csf samples , obtained by spinal tap exclusively and received in the cytopathology laboratory over a period of 20 years from january 1993 to june 2012 . in most cases , csf samples were processed by cytocentrifugation technique ( cytospin ) and stained by papanicolaou and may grunwald giemsa ( mgg ) stains . in nine cases , immunostaining with cytokeratin ( ck ) ( thermo scientific , ca , usa ) and epithelial membrane antigen ( ema ) ( thermo scientific , ca , usa ) was carried out in four cases . all cases reported positive and suspicious for metastatic carcinoma cells were included in the study . clinically , these patients presented with neurologic deficits and thus were subjected to csf cytologic examination . imaging details such as mri features were not available due to the retrospective nature of the study . slides were reviewed by four cytopathologists ( gs , srm , vki , dj ) and classified based on the consensus into negative , positive and suspicious categories ; when multiple csf samples had been examined for a patient , the highest category of cytologic classification was selected . a total of 15,430 csf samples were evaluated during the study period of 20 years . three hundred thirty five of these specimens from 292 patients were positive or suspicious for malignant non - lymphoreticular tumors , whereas 755 specimens from 548 patients were positive or suspicious for lymphoreticular tumors [ tables 1 and 2 ] . non - lymphoreticular neoplasms detected by cytologic examination of csf lymphoreticular neoplasms detected by cytologic examination of csf the most common non - lymphoreticular tumors were primary cns neoplasms ( 72.9% ) followed by metastatic carcinomas ( 22.6% ) . the most common lymphoreticular tumors were all ( 60.2% ) followed by non - hodgkins lymphomas ( 29.1% ) . 36 ( 54.6% ) patients had already been diagnosed with systemic malignancy whereas 45.4% of the cases presented with neurological symptoms . in the former , the most common primary was breast ( 28.7% ) followed by ovary ( 6% ) and lung ( 4.5% ) [ table 3 ] . types of metastatic tumors in csf cytology the age of patients with nm ranged from 22 years to 79 years with a mean of 50.5 years . there were 22 males and 44 females ( m : f ratio of 1:2 ) . csf smears of patients with metastasis from breast carcinoma were highly cellular [ figure 1a ] . the tumor cells were arranged mainly singly [ figure 1b ] , although an occasional small cohesive cluster of tumor cells could be seen in most samples . a cell in cell appearance with one cancer cell engulfing an adjacent cancer cell ( cellular cannibalism ) was seen in most of the cases [ figure 1d ] . the cells contained central nuclei with a moderate amount of dense cytoplasm with only occasional cell showing fine peripheral vacuolation [ figure 1e ] . prominent eosinophilic nucleoli most often multiple were seen in all cases [ figure 1f ] . cerebrospinal fluid cytospin preparation from a case of carcinoma breast shows highly cellular smear ( a ) with largely dyscohesive atypical cells ( b ) ; frequent multinucleation ( c ) and cellular cannibalism is evident ( d ) . individual cells show fine cytoplasmic vacuolations ( e ) and prominent nucleoli ( f ) . ( a : may grunwaldgiemsa , 200 , b : pap , 400 , c - f : pap , 400 ) the cellularity of cytospin csf preparation was high with an abundance of cell clusters , which in the majority of cases exhibited papillary pattern [ figure 2a ] . case of carcinoma ovary shows tight papillary clusters ( a : pap , 400 ) and cytoplasmic vacuolation ( b : may grunwaldgiemsa , 400 ) singly lying cells with high nuclear cytoplasmic ratio and hyperchromatic nuclei were seen [ figure 3a ] . intracytoplasmic coarse black granular pigment was identified in a significant number of tumor cells as well as within histiocytes , which failed to stain with iron ( prussian blue ) stain [ figure 3b ] and positive for melanin bleach stain . cytospin preparation of csf of a case of melanoma displays large atypical cell with high nuclear cytoplasmic ratio present within hemorrhagic background ; coarse black pigment is seen in the cytoplasm of an adjacent degenerated cell ( a : may grunwaldgiemsa , 400 ) . increase cellularity of singly lying atypical cells is observed in majority of cases of unknown primary site of cancer ( c : pap , 400 ) lung ( 4 ) , stomach ( 2 ) , gallbladder ( 1 ) , prostate ( 1 ) and neurondocrine carcinoma ( 1 ) : no specific features were identified due to a small number of cases . the tumor cells mainly showed a dyscohesive pattern with singly lying cells having moderate cytoplasm . one case each of tonsillar carcinoma and papillary carcinoma of thyroid could not be analyzed due to poor staining and cellular preservation . the tumor cells were present singly in a majority ( 25 ) of the cases [ figure 3c ] . the site of primary was suggested based on subtle morphologic features ; however , no follow - up could be obtained and exact primary remained unknown . the tumor cells had moderate cytoplasm and centrally placed nuclei showing mild to moderate nuclear pleomorphism . this pattern was largely seen in metastatic breast and lung carcinoma [ figure 4a ] . a case of adenocarcinoma of lung shows singly lying cells with pleomorphic nuclei ( a : pap , 400 ) . milipore membrane filtration preparation shows a cluster of atypical cells from another case of pulmonary adenocarcinoma ( b : pap , 400 ) . immunocytochemistry for cytokeartin shows strong cytoplasmic positivity in a case of ovarian carcinoma ( c ) pattern ii consisted of large cells with abundant cytoplasm with frequent cell groupings and clusters . pattern iii was characterized by the presence of necrotic debris , inflammatory background with a few tumor fragments . few lung carcinomas , melanomas and cases of unknown primary showed pattern iii [ figure 4b ] . immunocytochemistry ( icc ) for ck and ema was performed in 4 cases of breast ( 2 ) and ovarian ( 2 ) carcinoma . in other cases , icc could not be carried out due to either scanty cellularity or a limited number of diagnostic slides . further icc for diagnosis of primary site could also not be attempted in any of the cases as the quantity of csf sample obtained was always limited . csf smears of patients with metastasis from breast carcinoma were highly cellular [ figure 1a ] . the tumor cells were arranged mainly singly [ figure 1b ] , although an occasional small cohesive cluster of tumor cells could be seen in most samples . a cell in cell appearance with one cancer cell engulfing an adjacent cancer cell ( cellular cannibalism ) was seen in most of the cases [ figure 1d ] . the cells contained central nuclei with a moderate amount of dense cytoplasm with only occasional cell showing fine peripheral vacuolation [ figure 1e ] . prominent eosinophilic nucleoli most often multiple were seen in all cases [ figure 1f ] . cerebrospinal fluid cytospin preparation from a case of carcinoma breast shows highly cellular smear ( a ) with largely dyscohesive atypical cells ( b ) ; frequent multinucleation ( c ) and cellular cannibalism is evident ( d ) . individual cells show fine cytoplasmic vacuolations ( e ) and prominent nucleoli ( f ) . ( a : may grunwaldgiemsa , 200 , b : pap , 400 , c - f : pap , 400 ) the cellularity of cytospin csf preparation was high with an abundance of cell clusters , which in the majority of cases exhibited papillary pattern [ figure 2a ] . case of carcinoma ovary shows tight papillary clusters ( a : pap , 400 ) and cytoplasmic vacuolation ( b : may grunwaldgiemsa , 400 ) singly lying cells with high nuclear cytoplasmic ratio and hyperchromatic nuclei were seen [ figure 3a ] . intracytoplasmic coarse black granular pigment was identified in a significant number of tumor cells as well as within histiocytes , which failed to stain with iron ( prussian blue ) stain [ figure 3b ] and positive for melanin bleach stain . cytospin preparation of csf of a case of melanoma displays large atypical cell with high nuclear cytoplasmic ratio present within hemorrhagic background ; coarse black pigment is seen in the cytoplasm of an adjacent degenerated cell ( a : may grunwaldgiemsa , 400 ) . increase cellularity of singly lying atypical cells is observed in majority of cases of unknown primary site of cancer ( c : pap , 400 ) lung ( 4 ) , stomach ( 2 ) , gallbladder ( 1 ) , prostate ( 1 ) and neurondocrine carcinoma ( 1 ) : no specific features were identified due to a small number of cases . the tumor cells mainly showed a dyscohesive pattern with singly lying cells having moderate cytoplasm . one case each of tonsillar carcinoma and papillary carcinoma of thyroid could not be analyzed due to poor staining and cellular preservation . the tumor cells were present singly in a majority ( 25 ) of the cases [ figure 3c ] . the site of primary was suggested based on subtle morphologic features ; however , no follow - up could be obtained and exact primary remained unknown . the tumor cells had moderate cytoplasm and centrally placed nuclei showing mild to moderate nuclear pleomorphism . this pattern was largely seen in metastatic breast and lung carcinoma [ figure 4a ] . a case of adenocarcinoma of lung shows singly lying cells with pleomorphic nuclei ( a : pap , 400 ) . milipore membrane filtration preparation shows a cluster of atypical cells from another case of pulmonary adenocarcinoma ( b : pap , 400 ) . immunocytochemistry for cytokeartin shows strong cytoplasmic positivity in a case of ovarian carcinoma ( c ) pattern ii consisted of large cells with abundant cytoplasm with frequent cell groupings and clusters . marked cytoplasmic vacuolation was a frequent finding in this group [ figure 2b ] . pattern iii was characterized by the presence of necrotic debris , inflammatory background with a few tumor fragments . few lung carcinomas , melanomas and cases of unknown primary showed pattern iii [ figure 4b ] . immunocytochemistry ( icc ) for ck and ema was performed in 4 cases of breast ( 2 ) and ovarian ( 2 ) carcinoma . in other cases , icc could not be carried out due to either scanty cellularity or a limited number of diagnostic slides . further icc for diagnosis of primary site could also not be attempted in any of the cases as the quantity of csf sample obtained was always limited . leptomeningeal metastasis is a serious complication of cancer that occurs in 5 - 10% of patients with solid tumors and is observed most commonly in patients with breast cancer , lung cancer or melanoma . nearly , 20% of patients with neurological symptoms and signs are found to have meningeal carcinomatosis at autopsy . tumor cells reach the leptomeninges by hematogenous spread or by direct extension from lesions and are then disseminated throughout the nervous system by the flow of the csf . unfortunately , false negative results are common . it has been suggested that false negative results can be minimized by withdrawing more csf for cytologic analysis , processing the csf specimen immediately and repeating the procedure if the initial cytology is negative . although there are ancillary markers or techniques available , which are helpful in detection of csf dissemination such as csf levels of protein , glucose and tumor markers or contrast - enhanced mri , none of these have shown a definite increase in the diagnostic yield compared to the cytological examination . mri plays an important confirmatory role and can demonstrate involved sites , even in cytology negative cases . however , almost similar character of enhancement in the presence of infective , inflammatory or neoplastic process is the reason for the restricted specificity of mri . on comparative analysis , mri is found to have equal sensitivity to csf cytology , but suffers from lesser specificity . several reports in the literature deal with a comparison of various techniques . in our experience , smears made by cytospin cytocentrifuge technique and one slide each stained by papanicolaou and mgg technique gives the maximum information . filter membrane preparation may be reserved for cases with low yield or diagnostic problems . in our laboratory , we use filter membrane preparation for the diagnosis of primary cns neoplasms where low yield is expected ; however , this method suffers from the drawbacks of exhaustion of complete fluid ; hence , further ancillary studies can not be carried out . thin monolayer technology has been suggested as an appropriate diagnostic method for metastatic tumors in csf . a number of large series have described the statistical information regarding the prevalence of various primary carcinoma sites , which cause nm . few studies have documented the morphologic peculiarities of carcinoma cells found in the csf depending on the primary sites . the diagnosis of meningeal involvement is relatively easy when the patient has a history of carcinoma . patients with neurological signs and symptoms of nm without any known primary site are more difficult to diagnose on cytology unless there is a high index of suspicion . similar to several previous reports , the most common sites were breast , lung , stomach and melanoma . we did not come across any squamous cell carcinoma , which is considered a rare diagnosis in csf cytology . cns metastases occur in approximately 35% of patients with breast cancer , which is associated with poor survival and only 50% of patients with leptomeningeal carcinomatosis are diagnosed . morphologic analysis of breast carcinoma patients was characterized by the presence of singly scattered isolated cells with minimal aggregation . this pattern was without characteristics of the original tumor architecture and signifies extensive involvement of the subarachnoid space . in contrast to earlier reports , characteristic indian file pattern was not conspicuous in our cases . ovarian cancer does not commonly involve the nervous system . leptomeningeal metastasis is an even rarer complication of ovarian cancer with only a handful cases reported in the literature . we have identified four cases of ovarian carcinoma in the present series with characteristic cytomorphologic features . ovarian malignancies showed largely grouping of cells with papillary architecture ( pattern ii ) and prominent cytoplasmic vacuolation , which was degenerative in nature . pattern iii was characterized by the presence of necrotic material with a few large tumor fragments and the presence of an inflammatory background , which may represent intraparenchymal metastasis ; however , it could not be correlated with imaging studies . we have identified the same pattern in lung carcinomas , melanomas and cases of unknown primary malignancies . although , exact site of primary was not identified due to either lack of follow - up or early demise of the patient due to disseminated malignancy , report of positive cytology helped the clinician in the overall management and prognostication of patient . multidisciplinary therapy , such as radiation and chemotherapy can improve quality - of - life in patients of meningeal metastasis . role of icc in diagnosis of nm is limited and is of minor help in the problem of false negative cytology . combined use of conventional cytology and icc leads to a slight increase of sensitivity in detecting malignant cells compared with cytology alone . an overview of research tools in the field of csf cancer detection reveals a variety of technologies that can be used to understand the biology of metastatic cancer . methods currently under investigation include new icc methods and flow cytometry for detection of cells . in addition , polymerase chain reaction , fluorescence in situ hybridization and mass spectrometry are being tested for assessment of the non - cellular biomarkers in csf . in primary cns neoplasms ( ependymoma   retinoblastoma , medulloblastoma   and pineoblastomas ) , the malignant cells appear in groups of cells , which seldom allow for the histological identification of the original tumor . however , age of the patient , known diagnosis , high nuclear cytoplasmic ratio and nuclear molding were helpful features to distinguish these from carcinoma cells . in these cases , the csf cytology is useful only for confirmation of the presence of malignant cells and has no role in histological definition . leukemia and lymphoma cells retain original characteristics of the tumor and the severity of the disease is not reflected necessarily in the csf cellularity , which may vary from scanty to elevated . a positive csf cytology result , especially in cases of metastatic non - lymphoreticular neoplasms therefore , an attempt must be made to differentiate primary cns neoplasms from metastatic tumors on the basis of cytomorphology of tumor cells . identification of the type of metastatic neoplasm facilitates the detection of the site of the primary neoplasm in such cases . this study presents cases of nm diagnosed over a period of 20 years at a tertiary care referral center ; however , limited by follow - up information of cases , in which primary site of malignancy remained unknown . cytologic examination of csf is an important modality to diagnose meningeal involvement by the systemic malignancies . there are cytomorphologic clues by which this condition is diagnosed and site of primary cancer may be identified . srm and vki contributed in the design of study , acquisition of data , analysis and interpretation of data . dj has been involved in drafting the manuscript , revising it critically for important intellectual content , analysis and interpretation of data . all authors take the responsibility of maintaining relevant documentation of records , slides and other data of cases used in this study on archival material as per the institutional policy . to ensure the integrity and highest quality of cytojournal publications , the review process of this manuscript was conducted under a double - blind mode ( authors are blinded for reviewers and vice versa ) through automatic online system