acute megakaryoblastic leukemia ( aml m7 ) is a rare hematological malignancy accounting for less than 5% of all cases of acute myeloid leukemia .
aml m7 accounts for 7 to 10% of all cases of childhood aml but less than 1% of aml cases in adults .
diagnosis is primarily based on bone marrow examination including both bone marrow aspiration and biopsy .
there are only occasional case reports discussing the morphological features suggestive of megakaryocytic leukemia in extramedullary location on cytological smears .
we report here a case of aml m7 presenting with cervical lymphadenopathy , emphasizing the cytological clues which may help in suspecting such a case on fine needle aspiration cytology ( fnac ) and cerebrospinal fluid .
this is also the first report describing the morphology of aml m7 in cerebrospinal fluid .
a 25-year - old male patient was treated with surgical excision for a mediastinal mixed germ cell tumor , the components of which included teratoma , embryonal carcinoma , and choriocarcinoma .
subsequently he was administered four cycles of bep ( bleomycin , etoposide , and carboplatin ) and two cycles of etoposide and carboplatin in 2009 .
six months after completing the treatment , he presented with complaints of easy fatigability and generalized weakness . on examination ,
a clinical diagnosis of recurrent metastatic germ cell tumor was considered . a routine hemogram revealed hemoglobin of 6 g / dl .
there was pancytopenia with a total leukocyte count of 3000/l and a platelet count of 20,000/l .
the touch preparation showed few poorly preserved blasts , morphology of which was not clear .
the decalcified sections of the biopsy were initially stained with hematoxylin and eosin stain and showed partial replacement of normal marrow by blasts .
the blasts had scant to moderate cytoplasm with one to three prominent nucleoli , a few of them were binucleate and a few megakaryocytes showing multinucleation were also seen .
on immunohistochemistry , the blasts were negative for myeloperoxidase ( 1:150 dilution , 59a5 clone , novocastra , new castle , united kingdom ) and leukocyte common antigen ( 1:100 dilution , rp2/18 and rp2/22 clone , novocastra , new castle , united kingdom ) , but positive for cd 61 ( 1:100 dilution , 2f2 clone , novocastra , new castle , united kingdom ) [ figures 1a  d ] . based on these findings , a diagnosis of acute megakaryoblastic leukemia was made and the patient was treated for the same with daunorubicin and cytarabin .
however , six months later , the patient developed a single large cervical lymph node measuring 44 cm . a fine needle aspiration ( fna )
the smears were fixed in 95% ethyl alcohol for papanicolaou stain and immunocytochemistry , and air dried for may - grunewald giemsa ( mgg ) staining .
there is partial replacement of normal marrow with blasts ( h and e , 100 ) ; ( b ) the blasts have scant to moderate cytoplasm with prominent nucleoli ( h and e , 400 ) ; ( c ) occasional multinucleated dysplastic megakaryocyte was also noted ( arrow ) ( h and e , 400 ) ; ( d ) blasts showing strong cytoplasmic positivity cd 61 , ihc ( 400 ) : microscopic examination of the aspiration smears revealed numerous blasts which varied in size from two to three times the size of mature lymphocytes .
they had scant to moderate granular cytoplasm , fine chromatin , and single or multiple prominent nucleoli .
some of the blasts had a notch in the nuclear membrane ; many had nuclear indentations and folds [ figure 2a ] .
interestingly at places , they were present in small clumps which on low power examination mimicked marrow particles as seen in smears prepared from bone marrow aspirate . within this population ,
there were cells which had single nucleus , but with the nucleus showing lobations , indentations and folds , some being horseshoe shaped [ figures 3a  c ] .
bi to multinucleated cells reminiscent of megakaryocytes were also noted [ figures 3d  f ] .
in addition , many anucleate pale blue staining masses were seen in the background , possibly representing shredded and clumped cytoplasmic fragments or giant platelets [ figure 2b ] .
immunocytochemistry showed the blasts to be negative for mpo , but positive for cd61 and cd34 ( 1:100 dilution , qbend 10 clone , dako , glostrup , denmark ) , thus confirming the diagnosis of extramedullary leukemic deposit of aml m7 [ figure 2c ] .
( a ) blasts varying in size from medium to large , having scant to moderate granular cytoplasm , fine nuclear chromatin and single to multiple prominent nucleoli .
occasional larger cells , having abundant cytoplasm and lobated nuclei ( arrow ) papanicolaou ( 200 ) ; ( b ) anucleate pale blue shredded cytoplasmic fragments in the background demonstrated better in low cellularity areas mgg ( 400 ) ; ( c ) blasts immunopositive for cd 61 icc ( 400 ) ; ( d ) bi and multinucleate forms on cytocentrifuge preparation of the csf specimen ; ( inset ) binucleate cell mimicking megakaryocyte mgg ( 400 )
( a ) large cell with moderate amount of granular cytoplasm and a single nucleus showing multiple lobations papanicolaou ( 400 ) ; ( b ) cell having horse shoe shaped nucleus and dusky cytoplasm mgg ( 400 ) ; ( c ) another cell showing nuclear indentation and early lobulation mgg ( 400 ) ; ( d , e , f ) multinucleated cells with abundant cytoplasm and nuclear lobations resembling immature megakaryocytes mgg ( 400 ) a cytocentrifuge preparation ( cytospin 4 , thermo scientific , san diego , usa ) of the csf specimen stained with mgg showed many blasts with scant to moderate granular cytoplasm , irregular nuclear margins , fine granular chromatin , and prominent nucleoli .
there were binucleate forms ( micromegakaryocytes ) and multinucleate forms ( immature megakaryocytes ) [ figure 2d ] .
microscopic examination of the aspiration smears revealed numerous blasts which varied in size from two to three times the size of mature lymphocytes .
they had scant to moderate granular cytoplasm , fine chromatin , and single or multiple prominent nucleoli .
some of the blasts had a notch in the nuclear membrane ; many had nuclear indentations and folds [ figure 2a ] .
interestingly at places , they were present in small clumps which on low power examination mimicked marrow particles as seen in smears prepared from bone marrow aspirate . within this population ,
there were cells which had single nucleus , but with the nucleus showing lobations , indentations and folds , some being horseshoe shaped [ figures 3a  c ] .
bi to multinucleated cells reminiscent of megakaryocytes were also noted [ figures 3d  f ] .
in addition , many anucleate pale blue staining masses were seen in the background , possibly representing shredded and clumped cytoplasmic fragments or giant platelets [ figure 2b ] .
immunocytochemistry showed the blasts to be negative for mpo , but positive for cd61 and cd34 ( 1:100 dilution , qbend 10 clone , dako , glostrup , denmark ) , thus confirming the diagnosis of extramedullary leukemic deposit of aml m7 [ figure 2c ] .
( a ) blasts varying in size from medium to large , having scant to moderate granular cytoplasm , fine nuclear chromatin and single to multiple prominent nucleoli .
occasional larger cells , having abundant cytoplasm and lobated nuclei ( arrow ) papanicolaou ( 200 ) ; ( b ) anucleate pale blue shredded cytoplasmic fragments in the background demonstrated better in low cellularity areas mgg ( 400 ) ; ( c ) blasts immunopositive for cd 61 icc ( 400 ) ; ( d ) bi and multinucleate forms on cytocentrifuge preparation of the csf specimen ; ( inset ) binucleate cell mimicking megakaryocyte mgg ( 400 ) ( a ) large cell with moderate amount of granular cytoplasm and a single nucleus showing multiple lobations papanicolaou ( 400 ) ; ( b ) cell having horse shoe shaped nucleus and dusky cytoplasm mgg ( 400 ) ; ( c ) another cell showing nuclear indentation and early lobulation mgg ( 400 ) ; ( d , e , f ) multinucleated cells with abundant cytoplasm and nuclear lobations resembling immature megakaryocytes mgg ( 400 ) a cytocentrifuge preparation ( cytospin 4 , thermo scientific , san diego , usa ) of the csf specimen stained with mgg showed many blasts with scant to moderate granular cytoplasm , irregular nuclear margins , fine granular chromatin , and prominent nucleoli .
there were binucleate forms ( micromegakaryocytes ) and multinucleate forms ( immature megakaryocytes ) [ figure 2d ] .
extramedullary leukemic deposits often have to be differentiated clinically from infections and carcinomas for which fnac is an important diagnostic tool .
there are only a few studies describing the morphological features of acute leukemia on fna smears , most of them being case reports.[521 ] however , of these , only one report discusses in detail the cytological features indicative of megakaryoblastic differentiation .
we report the morphological features in a case of aml m7 with involvement of cervical lymphnode and cerebrospinal fluid .
on fnac , granulocytic sarcomas can be classified into blastic , immature , and maturing forms of leukemias , based on the proportion of blasts to the more differentiating granulocytic cells . blasts from aml m7 typically show more abundant cytoplasm with a relatively lower nuclear to cytoplasmic ratio than what is seen in other subtypes of leukemia .
presence of blasts of varying sizes including both small and large blasts , focal clumping of blasts forming small groups may also indicate the possibility of megakaryocytic differentiation .
micromegakaryocytes in the form of large cells with single but multilobated nuclei , and/or bi or multinucleated cells having dusky cytoplasm or megakaryocytes along with dispersed giant platelets in the background may also be seen .
although monoblasts also show nuclear membrane folds and indentations along with scant to moderate cytoplasm similar to megakaryocytes , they lack other features like multinucleation , multilobation , cytoplasmic shredding , micromegakaryocytes , and giant platelets .
promyelocytes and promyeloblasts also show nuclear convolutions and low nucleo - cytoplasmic ratio , although some might have auer rods .
kumar pv described many faggot cells ( promyelocytes showing many auer rods ) in a case of granulocytic sarcoma diagnosed by fnac .
auer rods are however not seen in cases of aml m7 . in the study by suh et al
, auer rods were not seen in any of 27 cases of granulocytic sarcomas included in their study .
another common differential is extramedullary hematopoiesis , especially when a deposit is characterized by presence of more maturing myeloid forms . a clinical history of myeloproliferative disorder or myelophthisic anemia , the presence of cells of erythroid lineage and also myeloid precursors besides megakaryoblasts can aid in making a correct diagnosis .
metastatic carcinoma , when poorly differentiated , is an important differential diagnosis for aml m7 due to the presence of grouping of blasts , more abundant cytoplasm and large size of the blasts .
poorly differentiated carcinoma may , however , have a suggestive clinical history . additionally , the tumor cells in carcinoma have coarser chromatin are more monomorphic and are cytokeratin positive on immunocytochemistry .
multinucleated giant cells , if present , will have more bizarre hyperchromatic nuclei with or without prominent nucleoli in contrast to megakaryoblasts . in the case under discussion
since there was a history of a mediastinal germ cell tumor , metastasis from the same may also be considered as a differential both clinically as well as on morphological assessment . of the germ cell tumors ,
seminoma especially shares some morphological features with leukemia / lymphoma infiltration as it is characterized by a hypercellular cytologic preparation with cells dispersed singly as well as in loosely dyscohesive clusters .
nuclei are round to oval with thin nuclear membrane , vesicular chromatin , and prominent one central nucleolus or two to three smaller nucleoli .
in contrast to megakaryoblastic leukemia which shows a more polymorphic population of cells of variable sizes with multinucleation and multilobation , multinucleated cells are usually absent in seminoma except for occasional  syncytiotrophoblast - like  cells .
also background in the latter may have necrotic debris along with variable numbers of lymphocytes , plasma cells , and epithelioid histiocytes .
a characteristic  tigroid  background may be noted on romanowsky stains . in comparison ,
however , some cases may be difficult to further characterize , in which case immunocytochemistry may be used .
seminoma cells are immunopositive for cd117 , placental - like alkaline phosphatase ( plap ) , and sometimes for cytokeratin , all of which are negative in a case of megakaryoblastic leukemia except for cd117 which may be focally positive .
smears in the former show mitotically active , markedly atypical cells arranged as glandular and papillary 3-dimensional structures .
aspirates from choriocarcinoma show an admixture of multinucleated syncytiotrophoblasts and the mononuclear cytotrophoblasts in a background of hemorrhage and necrosis .
although syncytiotrophoblasts may be misinterpreted for megakaryoblasts , they are much larger with more abundant cytoplasm , several pleomorphic nuclei and lack nuclear lobations .
the tumor cells are mostly epithelioid - cell type , dispersed singly , having abundant cytoplasm ; marked anisokaryosis , bi- and multinucleation are common .
cytoplasmic melanin pigment , present only in a minority , is beyond doubt the most diagnostic .
confirmation in a case of amelanotic melanoma may be done with the aid of monoclonal antibodies for s-100 and hmb-45 . in morphologically ambiguous cases ,
a panel of antibodies including lca , mpo , cd33 , cd34 , cd61 , cd43 , tdt , factor viii , cd117 , plap , s-100 , hmb-45 , and cytokeratin should help in arriving at the diagnosis .
suh and coauthors have used flow cytometry on their fna material to characterize their cases of granulocytic sarcomas .
farray et al . also have described a case of megakaryoblastic leukemia involving pleural cavity ; they did not give detailed morphological description of the blasts though they performed a flow cytometry on pleural effusion fluid .
in the cerebrospinal fluid sample evaluated in the present case , blasts , micromegakaryocytes and cells resembling megakaryocytes could all be identified as seen in the aspiration smears .
this is the first report describing the finer cytomorphological features suggestive of megakaryoblastic differentiation on both aspiration and effusion smears .
the features highlighted here may be of help in diagnosis and subtyping of extramedullary leukemic deposits of aml m7 , especially in the event of a dry bone marrow tap , which is a common problem .
all authors of this article declare that we qualify for authorship as defined by icmje .
all authors are responsible for the conception of this study , participated in its design and coordination , and helped to draft the manuscript .
as this is a case report without patient identifiers , approval from institutional review board ( irb ) is not required at our institution .
to ensure integrity and highest quality of cytojournal publications , the review process of this manuscript was conducted under a double blind model(authors are blinded for reviewers and reviewers are blinded for authors)through automatic online system .
 extramedullary deposits may be the presenting feature of acute myeloid leukemia . 
 an early and accurate diagnosis on cytology will aid in correct patient management . 
 this is especially true for patients with acute megakaryoblastic leukemia ( aml m7 ) , where bone marrow aspiration may yield only a dry tap . 
 while cytomorphological features of myeloid sarcoma of other types are well recognized due to its rarity , there are only two case reports discussing the morphological details of megakaryoblastic differentiation on aspiration cytology . 
 we present the case of a 25-year - old patient with extramedullary involvement of lymph node and cerebrospinal fluid by aml m7 , describing in detail , the morphological features on aspiration as well as exfoliative cytology . 
INTRODUCTION
CASE REPORT
Cytomorphologic features
DISCUSSION
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