endometriosis is defined as the presence of ectopic , functional endometrial tissue outside the endometrium and myometrium and affects approximately 10 - 15% women in the reproductive age - group . endometriosis can occur at intra- and extrapelvic locations with abdominal wall as a site in 0.5 - 1% cases of pelvic endometriosis . although it is fairly diagnosed on an adequate biopsy specimen , based on the presence of any two of the three histological components , including endometrial glands , stroma and macrophages , a challenge occurs of diagnosing endometriosis on a fine needle aspiration cytology ( fnac ) that at times , becomes the first diagnostic modality in such cases , especially when the available clinical details are limited and some of the cytological features are atypical . cutaneous endometriosis is a recognized diagnostic pitfall on cytological smears . in a documented series of 10 cases of abdominal endometriosis , diagnosed by fnac , herein , we present a case of cutaneous endometriosis occurring in the abdomen , mimicking adenocarcinoma on fnac . this was a case report of a 33-year - old , non - obese , asian , lady physician , p1 , a0 sustained a minor scald over her right inguinal region . the scald was adjacent , but not involving the right lateral aspect of her 3-year - old pfannenstiel incision scar . the wound completely re - epithelialized within 10 days , leaving behind slight skin discoloration . clinically , the swelling was superficial to abdominal muscles and measured 2 cm ; was non - tender , non - inflammatory , firm and mobile . the patients serum tumor marker levels , including celomic antigen ( ca ) 125 , carcino embryogenic antigen and ca 19.9 were within the normal range . her abdominal and pelvic ultrasonogram revealed a 3 cm sized subcutaneous , hypoechoic , solid mass with scattered internal echoes . magnetic resonance imaging ( mri ) showed a heterogeneous subcutaneous soft tissue mass measuring 3 cm  2.5 cm  2 cm . the lesion was hypointense on plain t1-weighed images , hyperintense on t2-weighed and short inversion time recovery axial images . post - contrast t1-weighed images showed heterogeneous enhancement within the lesion [ figure 1 ] . magnetic resonance imaging findings . ( a ) short inversion time recovery axial image showing hyperintense lesion in area of surgical scar ( arrow ) . ( b ) post - contrast t1-weighed sagittal view showing heterogeneous enhancement within the lesion ( arrow ) on review , hematoxylin and eosin ( h and e ) , as well as giemsa stained smears were hypercellular and revealed epithelial cells in groups and glandular architecture , imperceptibly admixed with numerous , relatively smaller , short spindly cells . epithelial cells exhibited mild to focally , moderate nuclear enlargement . interspersed were metaplastic cells against a hemorrhagic background [ figure 2 ] . whereas the initial diagnosis offered was a metastatic adenocarcinoma , on review , endometriosis was suggested . ( a ) hypercellular smear showing glandular cells ( arrows ) intimately admixed with short spindle shaped stromal cells ( h and e , 200 ) . ( b ) glands with smooth contours , stromal cells and blood vessels ( h and e , 200 ) . ( d ) higher magnification displaying epithelial cells exhibiting nuclear enlargement and discernible nucleoli ( giemsa , 400 ) incisional biopsy revealed fibrocollagenous tissue and few glands exhibiting focal nuclear atypia that was interpreted as dysplasia . excision specimen measured 5.5 cm  4.5 cm  2.5 cm with an overlying skin that showed a linear scar . on serial sectioning , a firm nodule was identified in the subcutaneous region measuring 1.3 cm  0.5 cm  0.4 cm . conventional h and e stained microsections showed glandular structures , exhibiting focal dilatation , surrounded by stromal cells , indicative of endometrial tissue with focal inflammation and metaplasia . epithelial cells exhibited focal atypia . however , there was insufficient atypia to label it as an adenocarcinoma . immunohistochemically , the glands were diffusely positive for estrogen receptor and progesterone receptor while the stroma was diffusely positive for cd10 . ( a ) initial biopsy revealing a gland within stroma exhibiting atypia ( h and e , 200 ) . ( b ) excision specimen displaying variable dilated endometrial glands with interspersed stroma ( h and e , 100 ) . ( c ) focal atypia within endometrial gland ( h and e , 400 ) . ( d ) diffuse estrogen receptor positivity within glands and stroma ( diaminobenzidine ( dab ) , 400 ) . ( e ) diffuse cd10 positivity highlighting the stroma ( dab 400 ) post - surgery , patient is on gonadotropin releasing hormone analogues ; is currently free of disease since 12 months and is on follow - up . the patients serum tumor marker levels , including celomic antigen ( ca ) 125 , carcino embryogenic antigen and ca 19.9 were within the normal range . her abdominal and pelvic ultrasonogram revealed a 3 cm sized subcutaneous , hypoechoic , solid mass with scattered internal echoes . magnetic resonance imaging ( mri ) showed a heterogeneous subcutaneous soft tissue mass measuring 3 cm  2.5 cm  2 cm . the lesion was hypointense on plain t1-weighed images , hyperintense on t2-weighed and short inversion time recovery axial images . post - contrast t1-weighed images showed heterogeneous enhancement within the lesion [ figure 1 ] . magnetic resonance imaging findings . ( a ) short inversion time recovery axial image showing hyperintense lesion in area of surgical scar ( arrow ) . ( b ) post - contrast t1-weighed sagittal view showing heterogeneous enhancement within the lesion ( arrow ) on review , hematoxylin and eosin ( h and e ) , as well as giemsa stained smears were hypercellular and revealed epithelial cells in groups and glandular architecture , imperceptibly admixed with numerous , relatively smaller , short spindly cells . epithelial cells exhibited mild to focally , moderate nuclear enlargement . interspersed were metaplastic cells against a hemorrhagic background [ figure 2 ] . whereas the initial diagnosis offered was a metastatic adenocarcinoma , on review , endometriosis was suggested . ( a ) hypercellular smear showing glandular cells ( arrows ) intimately admixed with short spindle shaped stromal cells ( h and e , 200 ) . ( b ) glands with smooth contours , stromal cells and blood vessels ( h and e , 200 ) . ( d ) higher magnification displaying epithelial cells exhibiting nuclear enlargement and discernible nucleoli ( giemsa , 400 ) incisional biopsy revealed fibrocollagenous tissue and few glands exhibiting focal nuclear atypia that was interpreted as dysplasia . excision specimen measured 5.5 cm  4.5 cm  2.5 cm with an overlying skin that showed a linear scar . on serial sectioning , a firm nodule was identified in the subcutaneous region measuring 1.3 cm  0.5 cm  0.4 cm . conventional h and e stained microsections showed glandular structures , exhibiting focal dilatation , surrounded by stromal cells , indicative of endometrial tissue with focal inflammation and metaplasia . epithelial cells exhibited focal atypia . however , there was insufficient atypia to label it as an adenocarcinoma . immunohistochemically , the glands were diffusely positive for estrogen receptor and progesterone receptor while the stroma was diffusely positive for cd10 . ( a ) initial biopsy revealing a gland within stroma exhibiting atypia ( h and e , 200 ) . ( b ) excision specimen displaying variable dilated endometrial glands with interspersed stroma ( h and e , 100 ) . ( c ) focal atypia within endometrial gland ( h and e , 400 ) . ( d ) diffuse estrogen receptor positivity within glands and stroma ( diaminobenzidine ( dab ) , 400 ) . ( e ) diffuse cd10 positivity highlighting the stroma ( dab 400 ) post - surgery , patient is on gonadotropin releasing hormone analogues ; is currently free of disease since 12 months and is on follow - up . most cases of cutaneous endometriosis have been known to have occurred in the surgical scars . the incidence of endometriosis associated with cesarean incisions has been reported to be up to 1% ( most commonly , 0.03 - 0.4% ) . the imaging features in such cases are non - specific , except for site and extent of the lesion that can be accurately delineated by mri , as noted in the present case . whereas the definite diagnosis of cutaneous endometriosis is made on a sizable biopsy , there is documentation on cytomorphological features of cutaneous endometriosis , considering fnac , in view of being a relatively safe , inexpensive and non - invasive procedure in present time 's forms as one of the first tests for diagnosis and triage of such cases . while most of these studies have addressed prospective or retrospective analysis of cytopathological spectrum of endometriosis , only rarely diagnostic challenge , in terms of cases suspected with malignancy , has been addressed . in the present case , presence of cytological atypia led to an erroneous initial diagnosis of a metastatic adenocarcinoma and on the subsequent biopsy , glandular dysplasia was suspected . there was no history relating to appearance or increase in size of the swelling with menstrual cycle that otherwise , is a suggestive clinical history in such cases . after the access of the history of an earlier cesarean section scar , endometriosis was considered that was confirmed on wide - excision . the present case is one of the few displaying atypia and metaplasia in endometriosis that constituted as a diagnostic pitfall . while atypia should not delude a cytopathologist from consideration of endometriosis , it should be documented and such cases may be followed up . only 21.3% of cases of malignant transformation of endometriosis occur at extragonadal pelvic sites and 4% in laparotomy scars . with regards to pathogenesis , two proposed theories of scar endometriosis include hematogenous , lymphatic or direct implantation of endometrial tissue through surgical manipulation , or regurgitation of menstrual blood during menstruation and primitive pluripotent mesenchymal cells undergoing endometrial differentiation and metaplasia . therapeutically , wide excision is the treatment of choice in such cases . our patient is presently free of disease since a year and is on follow - up . to sum up , fnac is a safe and effective tool for identification of endometriosis and can obviate the need for diagnostic surgical procedures . moreover , it can save the patient from undergoing radical treatment . clinical history and careful interpretation of cytopathological features are necessary for developing an index of suspicion for correct identification of endometriosis over an adenocarcinoma on fnac . atypia within the glandular epithelium of endometrioid lesions should be documented and such patients should possibly be followed - up after a wide - excision of their lesion .
scar endometriosis can be a diagnostic challenge in fine - needle aspiration cytology ( fnac ) smears that at times , is the first diagnostic modality in such cases . 
 the challenge is amplified when the clinical details are limited and cytopathological features reveal nuclear atypia . a 33-year - old lady presented with an abdominal swelling that she noticed after she met with a scald . 
 clinically , the swelling was located lateral to her 3-year - old pfannenstiel incision scar . 
 the initial diagnosis on fnac was metastatic adenocarcinoma . on review , 
 smears were hypercellular , comprising epithelial cells in groups and focally , regular glandular arrangements , imperceptibly admixed with numerous , relatively smaller , short spindly cells . 
 epithelial cells exhibited mild to focally , moderate nuclear enlargement / atypia . 
 subsequent biopsy and excision revealed endometrial glands exhibiting focal nuclear atypia with adjacent stroma . 
 diagnosis of endometriosis was offered . 
 the results were reinforced with positive estrogen receptor staining in the glands and stroma , along with cd10 positivity in the stroma . 
 the patient was recommended gonadotropin releasing hormone analogs and is presently free of disease a year after her diagnosis . 
 fnac can be a pitfall in the diagnosis of endometriosis . 
 correct diagnosis has significant therapeutic implications . 
 although presence of atypia in such cases should not delude the diagnosing cytopathologist for consideration of endometriosis , it should be documented . 
 the value of clinical history in such cases can not be overemphasized .