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endometriosis was first described by rokitansky in 1860 and was defined as the presence of proliferation of endometrium outside the uterine cavity , commonest site being the pelvis .
it is a common gynecological condition that affects up to 22% of all women , 8 - 15% of women of reproductive age and 6% of premenopausal women .
deposits of endometriosis occur frequently anywhere in the pelvis including vulva , vagina , cervix , ovaries , pelvic peritoneum , and less commonly ( 12% ) in the extrapelvic sites including intestinal tract , urinary tract , peritoneum , omentum , lung , thoracic cage , surgical scars , abdominal wall , inguinal region and umbilicus .
the majority of the reported cases occurred in gynecologically induced abdominal or pelvic scars , including hysterectomy , episiotomy , cesarean section and laparoscopy.[27 ] few cases of spontaneous umbilical endometriosis have been reported .
a 38-year - old woman presented with a history of slowly growing blackish nodule over the umbilicus of 3 years duration .
the nodule was 2  1.5  1 cm in size , soft to firm in consistency , brown to black in color , was tender on palpation and was non - reducible [ figure 1a ] .
ultrasound abdomen showed multiple uterine intramural fibroids and ultrasound of the nodule showed well - defined anechoic area at the umbilicus .
as a number of benign and malignant lesions come into clinical differential diagnosis , fine needle aspiration cytology ( fnac ) was advised as the first line of investigation .
the smears were stained with papanicolaou ( pap ) and may - grnwald - giemsa ( mgg ) stain .
aspirate revealed a moderately cellular smear comprising strips and sheets of endometrial epithelial cells with crowded nuclei and scanty cytoplasm [ figure 1b and c ] .
aspirated specimen also included degenerated red blood cells and hemosiderin laden macrophages [ figure 1d ] .
( b ) microphotograph showing strips and sheets of endometrial epithelial cells and stromal cells in the background ( pap , 100 ) .
( c ) microphotograph showing crowded nuclei and scanty cytoplasm ( pap , 400 ) .
( d ) microphotograph showing endometrial cells and hemosiderin laden macrophage ( arrow ) ( mgg , 100 ) microphotograph showing endometrial glands and stroma ( h and e , 100 )
aspirate revealed a moderately cellular smear comprising strips and sheets of endometrial epithelial cells with crowded nuclei and scanty cytoplasm [ figure 1b and c ] .
aspirated specimen also included degenerated red blood cells and hemosiderin laden macrophages [ figure 1d ] .
( b ) microphotograph showing strips and sheets of endometrial epithelial cells and stromal cells in the background ( pap , 100 ) .
( c ) microphotograph showing crowded nuclei and scanty cytoplasm ( pap , 400 ) .
( d ) microphotograph showing endometrial cells and hemosiderin laden macrophage ( arrow ) ( mgg , 100 ) microphotograph showing endometrial glands and stroma ( h and e , 100 )
primary ( spontaneous ) umbilical endometriosis was first described by villar in 1886 and represents about 0.5 - 1% of all cases of extragenital endometriosis.[810 ] endometriosis involving the abdominal wall is termed as cutaneous endometriosis and is commonly associated with surgical scars . clinically , the lesions appear as firm nodules varying in size from a few millimeters to centimeters .
the pathogenesis of endometriosis has been a topic under constant debate during the last decade .
sampson hypothesized in 1920s that endometriosis resulted from retrograde menstruation through the fallopian tube into the pelvis .
however , several other theories exist for the development of endometriosis , including coelomic metaplasia , direct spread , iatrogenic dissemination , and lymphatic or hematogenous spread .
the theory of lymphatic and hematogenous transplantation is favored in the case of umbilical endometriosis with coexisting pelvic endometriosis .
however , it is believed that the disease might arise through metaplasia of urachus remnants in case of isolated umbilical endometriosis .
those patients commonly present with a brownish or bluish painful umbilical nodule , as noted in our patient .
a slow - growing umbilical mass associated with cyclical pain during menstruation and brown color gives a picture clinically characteristic of cutaneous endometriosis .
however , only 75% of patients have their symptoms associated with the menstrual cycle . because characteristic symptoms are not always present
so , when a mass develops at the umbilicus , the possibility of endometrioma must be kept in mind although it may be mistaken for suture granuloma , lipoma , abscess , cyst hernia , and nonmalignant melanocytic tumors .
the cytology smears are generally cellular with epithelial and stromal fragments admixed with hemorrhage and hemosiderin laden macrophages.[57 ] the cytologic features of cutaneous and subcutaneous endometriosis are related to cyclic hormonal changes . in proliferative phase ,
the epithelial cells form cohesive sheets of uniform , small cells with scant cytoplasm , round to oval nuclei with bland chromatin and occasional non - atypical mitotic figures . during secretory phase ,
the cells show a gradual increase of the cellular size and microvacuolation is observed . in the same way
, the stromal cells reveal more abundant cytoplasm as the hormonal cycle progresses and may undergo pre - decidual changes showing an epithelioid appearance that can cause diagnostic difficulties . also , in the second phase of the cycle , a prominent vascular network may be observed closely associated with the stromal fragment . the background is generally sanguineous and contains a variable proportion of lymphocytes , neutrophils and histiocytes .
the mesenchymal component is scant , with small fragments of adipose tissue and fibrous tissue with a different grade of collagenisation representing the tissue where the ectopic endometrium is set .
fnac smears can be hemorrhagic , showing only a few macrophages and inflammatory cells in which case endometriosis may be missed .
if only endometrial stroma is picked up , it could be mistaken for a stromal neoplasm .
if nuclear atypia is seen , the mass should be excised and evaluated to rule out malignancy .
the imaging modalities are nonspecific , but are useful in determining the extent of the disease and planning of operative resection , especially in large and recurrent lesions . due to the typical cyclical pain and clear - cut cytomorphological features , cytological diagnosis of umbilical endometriosis was rendered without any difficulty in this patient .
thus , fnac is a fast and accurate method to make the diagnosis before surgery , avoiding errors in approach of the umbilical nodules .
primary ( spontaneous ) umbilical endometriosis is very rare with an estimated incidence of 0.5 - 1% of all patients with endometrial ectopia . 
 endometriosis is a common gynecological condition , the pelvis being the most common site of the disease . 
 extrapelvic site is less common and even more difficult to diagnose due to the extreme variability in presentation . a 38-year - old woman presented with a blackish nodule over the umbilicus of 3 years duration . 
 fine needle aspiration cytology of the lesion showed cells in clusters and sheets with background of scant stromal fragment , hemosiderin laden macrophages and rbcs , leading to a suggestion of umbilical endometriosis . 
 histopathological examination of the excised lesion confirmed the same .