endometriosis affects 610% of women in their reproductive years and affects up to 3550% of women with pain or infertility .
urogenital tract is superficially involved in about 1015% of cases but deep endometriosis of the bladder is estimated to be present in 12% of the patients only [ 25 ] bladder endometriosis is frequently accompanied by other forms of pelvic endometriosis .
frequency , urgency , suprapubic pain and dysuria [ 3 , 6 , 7 ] are the most frequent symptoms of bladder endometriosis and a positive correlation between severity of dysuria and lesion diameter has been described .
haematuria seems to be a less frequent symptom in 2035% of patients [ 2 , 3 , 6 ] .
heritability of endometriosis is well known from twin studies for many years , but this concerned mainly the increased risk to develop endometriosis and deep bladder endometriosis was not mentioned [ 811 ] . despite the rare occurrence of bladder endometriosis , a monozygotic twin presented at our clinic with similar complaints and remarkable resemblance in the presentation of disease .
a 33-year - old caucasian woman , g0p0 , was referred to our department for relapse of endometriosis after previous surgery and hormonal treatment elsewhere . although she did not have a relation at the moment , she wanted to preserve fertility .
dysmenorrhoea was acceptable with a levonorgestrel containing iud in situ , but dysuria was increasing .
two years later , a re - excision took place followed by treatment with lhrh analogue for half a year .
recto - vaginal examination revealed an enlarged and somewhat irregular painful uterus without vaginal or rectal involvement .
iud was in situ . at transvaginal ultrasound a round - shaped mass of about 1.5 
there was no haematuria and urine culture was negative . since the placement of the progesterone containing iud a year before , the ca 125 level decreased from 266 to a level varying from 97 to 116  ku / l . ivp showed a dimple in the roof of the bladder and excluded an obstruction of the ureters .
the magnetic resonance imaging ( mri ) scan showed an adenomyotic uterus with one lesion protruding in the backside of the bladder .
the recto - vaginal septum was not involved and ovaries were normal . to plan surgery , an examination under general anaesthesia was scheduled . at cystoscopy , the protruding lesion was seen in the top of the bladder covered with endothelium and well away from the ureters . at laparoscopy
, the bladder attached densely to the adenomyotic uterus and superficial endometriosis was visible at the backside of the uterus .
firm adhesions around an adenomyotic uterus some months later , her monozygotic g0 twin sister presented with dysuria and dyschezia during bleeding periods . as a monozygotic twin sister
, she was heterozygote factor v leiden too without a history of thrombosis or embolism .
she never had child wish and she had a levonorgestrel containing iud 1  year earlier in life .
a firm nodule was palpable at the right sacro - uterine ligament ; the uterus was of normal size and mobility .
mri scan ( fig .  2 ) revealed a normal uterus with a single nodule protruding in the backside of the bladder likewise as her sister . at the backside of the cervix ,
a nodule was seen at exact the same position as seen in her sister ( fig . 
the uterus was normal , but the bladder was attached to the uterus with an implant of endometriosis present at the backside of the cervix comparable to the picture of her sister .
endometriosis nodule protruding in the top of the bladder and a second lesion behind the cervixfig . 
3bladder nodule of patient 1 ( left ) and of patient 2 ( right ) , localised in the roof of the bladder mri scan of patient 2 .
endometriosis nodule protruding in the top of the bladder and a second lesion behind the cervix bladder nodule of patient 1 ( left ) and of patient 2 ( right ) , localised in the roof of the bladder because of the predominant complaint of dysuria , both sisters were planned for laparoscopic excision of the bladder nodule by partial cystectomy and excision of the lesion at the backside of the cervix . after excision
, the bladder was closed with a running suture vicryl 3    0 .
complete closure of the bladder was tested with instillation of 150  ml methylene blue dye solution into the bladder at the end of the procedure .
since the sister with adenomyosis wanted to preserve fertility , her uterus was left in situ .
histology confirmed in both cases an adenomyotic lesion through the bladder wall covered with normal bladder endothelium . at follow - up visit after 6  weeks
, dysuria had disappeared in both . at follow - up so far , the sister with the adenomyosis has some dysmenorrhoea still but bearable without pain medication .
dysmenorrhoea , cyclic dysuria and suprapubic pain are the most frequent reported symptoms related to bladder endometriosis in literature [ 2 , 3 , 6 ] . in both our patients , dysuria was the predominant complaint with dysmenorrhoea as a second complaint .
the dyschezia reported by one of the sisters was probably due to the nodule behind the cervix .
the fact that the endometriotic lesions of both sisters were still covered with urothelium will explain the absence of haematuria .
combination of abdominal , transvaginal and transrectal ultrasound , depending on the complaints , may reveal endometriosis in infrequent sites . in urogenital endometriosis ,
the bladder is the most frequent involved organ and superficial endometriosis of the bladder is often part of more extended endometriosis .
ultrasound may also be used as a first step to exclude obstruction of the ureters .
although a dimple in the bladder was clear , an ivp is not the first choice to diagnose bladder disease . in case of suspicion of obstruction
, however , it may help to localise the place and extent of the obstruction .
mri scanning is more sensitive to diagnose preoperatively the extent of endometriosis especially for retroperitoneal disease and bowel involvement [ 5 , 14 ] .
proposed metaplasia from mullerian remnants , but the histological evidence of mullerian remnants in the urothelium of the bladder has been doubted .
transplantation theory considers the extension of adenomyotic lesions and transport through blood and lymphatic vessels .
finally , post surgery implantation , mainly after caesarean , may be responsible in a part of the cases [ 13 , 16 ] .
both twin sisters of this study had adenomyotic lesions of the bladder but only one of the sisters had further adenomyosis .
bladder endometriosis is frequently accompanied by other forms of endometriosis but bladder endometriosis and ureter endometriosis are not associated [ 4 , 18 ] .
patients with ureter endometriosis usually have more advanced disease [ 5 , 17 , 18 ] .
therefore , the deep endometriosis of the bladder seems to be a different entity within advanced endometriosis .
it is well known that family members of patients with endometriosis have an increased risk to develop endometriosis [ 10 , 19 ] .
the risks between monozygotic twins have been estimated as high as 7587% [ 8 , 9 ] .
however , this concerned the change of endometriosis for relatives and a correlation in severity , but the localization of the endometriosis often differed between the twin pairs and bladder endometriosis was not described .
bladder endometriosis was mentioned neither in the large genome wide linkage study   nor in the genetic studies of bischoff .
the lesions in the bladder and behind the cervix in the monozygotic twin described here were identical and there were no further peritoneal implants .
the development of endometriosis is multi - factorial and the presentation depends on genetic and extrinsic factors .
one of them had fewer complaints , had not been operated on before and had no further adenomyosis .
she never had child wish and the levonorgestrel - releasing iud had been placed about 1  year earlier in her life .
it seems unlikely that the short time difference in the placement of the progesterone containing iud explains the difference in adenomyosis between the sisters .
the iud had not prevented the progression of the bladder and the retro - cervical endometriosis in either of them .
evidence for a beneficial effect of a levonorgestrel - releasing iud is still limited at this moment .
if this may cause extension of the adenomyosis is unlikely , but no other differences between the sisters is available from their medical histories .
inheritance is complex [ 1 , 10 , 19 ] . presumably , different genes may influence the development in different ways as by influencing retrograde menstruation , cell differentiation , hormonal misbalance and by detoxification processes [ 1 , 19 ] .
although this may explain the wide variation in expression of endometriosis , it can not explain differences in our monozygotic twin .
it may have different side effects dependant of the medication chosen . for small lesions and in women near menopause hormonal treatment may be considered . for larger and deeper lesions ( > 5  mm ) surgery
hormonal treatment resulted in temporary relief of symptoms only and previous surgery proved to be inadequate in the first of the twin sisters presented here . in the second sister ,
radical excision of the lesions relieved all her symptoms . especially in younger women , surgical treatment of bladder endometriosis should be first choice treatment .
 it is known for many years that heritability plays a role in the development of endometriosis in many patients . 
 deep endometriosis of the bladder is a rare presentation of the disease and bladder endometriosis was not reported in monozygotic twin studies so far . 
 since monozygotic twins share the same genes , concordance and differences in presentation of endometriosis may help to discriminate between genetic and environmental determinants . 
 the remarkable resemblance in the presentation of bladder endometriosis in this monozygotic twin seems to indicate that genetic factors are of importance in the arising of deep endometriosis in the bladder too . 
Introduction
Case report
Discussion