congenital scrotal anomalies are unusual and include penoscrotal transposition , bifid scrotum , ectopic scrotum , and accessory scrotum ( as ) . among these , as is the least frequent , with only 42 cases reported in the english literature . as is characterized by additional scrotal tissue lacking a testis , besides a normally developed scrotum . various associated anomalies have been reported . in particular , contiguous subcutaneous tumor is the most frequently associated abnormality and is reported to be related to the etiology of as . although prenatal screening techniques have advanced , most reported cases of congenital perineal mass have been identified after birth . a 28-year - old woman was referred to our hospital for the evaluation of a fetal perineal mass at a gestational age of 31 weeks . prenatal ultrasonography and magnetic resonance imaging ( mri ) showed a mass of 1.0  1.2 cm located posterior to the scrotum in a male fetus . 1 ) the likely diagnosis was lipoma and the mass maintained a stable appearance until delivery . the male newborn was delivered vaginally at 38 weeks of gestation and his body weight was 2208 g. there were no specific symptoms after birth . arrowheads indicate a 1.0  1.2 cm mass located posterior to the scrotum . on physical examination , the soft peduncular mass , measuring 2.0 cm in diameter , was attached to a midperineal skin tag . there was also a rugged pigmented swelling on the mass , measuring 0.7 cm in diameter , which resembled the scrotum . the perineal mass showed high signal intensity on t1- and t2- weighted images and the signal intensity was suppressed on fat - suppressed t1-weighted images . mri revealed no associated abnormalities of the intraabdominal organs , musculoskeletal system , or genitourinary system . a. a soft peduncular mass with a rugged and pigmented swelling is located posterior to the normally developed scrotum . c. the mass is attached at the midperineum with a skin tag . the preoperative diagnosis was as with perineal lipoma , and we completely excised the mass under general anesthesia at one month of age . the postoperative course was uneventful , and the patient was discharged on the day after the operation . there was no recurrence or functional sequelae within a follow - up period of six months . a histological examination revealed that the peduncular mass consisted of mature adipose tissue . in this case , it was difficult to distinguish between lipoma and normal adipose tissue pathologically . however , our clinical diagnosis was lipoma because the peduncular mass was separated from normal perineal region by the skin tag . the rugged swelling on the peduncular mass showed smooth muscle fibers in the subcutaneous layer , which represented the tunica dartos . 3 ) the swelling was definitively diagnosed as as . histological examination . b. the peduncular mass smooth muscle fibers in the subcutaneous layer of the rugged swelling represent the tunica dartos . these swellings appear at four weeks of gestation and migrate to the caudal portion after 12 weeks of gestation . abnormal migration or early division of the labioscrotal swellings is possibly related to the etiology of congenital scrotal anomalies . the least frequent congenital scrotal anomaly is as , characterized by additional scrotal tissue without a testis , besides a normally developed scrotum . ( table ) characteristics of accessory scrotum various anomalies associated with as have been reported . in particular , contiguous subcutaneous tumor has a high incidence ( 72.5% ) of association with as . histologically , one case of subcutaneous tumor was lipoblastoma , three cases were hamartoma , and the others were consistent with lipoma . ( table ) it is assumed that the contiguous subcutaneous tumor is related to the etiology of as . sule hypothesized that as develops when intervening mesenchymal tissue ( i.e. , the developing subcutaneous tumor ) disrupts the continuity of the developing caudal labioscrotal swelling . however , the complete etiology of as is not explained by this hypothesis because as can occur with no contiguous tumor . takayasu hypothesized that as develops from the early division and teratoid growth of pluripotential labioscrotal tissue elements . however , two cases associated with skeletal abnormalities were located in the pubic area , and one case was located on the distal penile shaft . our case was detected at a gestational age of 31 weeks , and the other two reported cases were detected at 24 weeks and 32 weeks of gestation . a congenital perineal mass is unusual in itself , and most reported cases have been diagnosed after birth . however , detection is possible with careful prenatal screening . the differential diagnosis of a fetal perineal mass includes lipoma , lipoblastoma , infantile hemangioma , hamartoma , and choristoma . if a fetal perineal mass is detected during the antenatal period , it is important to look for any associated congenital anomalies . the prognoses of surgically treated patients are good , and only one has died , from an associated anomaly before surgery . the reported ages at surgery range from four days to 46 years ( median , nine months ) , and three adult cases are recorded in the literature . our patient was operated upon in the neonatal period because the mass was considered to be excisable without complications and the associated subcutaneous tumor had a low probability of malignancy . although a fetal perineal mass is difficult to diagnose , it can be detected with careful prenatal screening . many ass are associated with contiguous subcutaneous tumors , which are assumed to be related to the etiology of as .
abstractwe report a case of accessory scrotum ( as ) in the perineal region with peduncular lipoma , diagnosed prenatally . 
 a male fetus of 31 weeks gestation was referred to our department with a perineal mass . 
 prenatal ultrasonography and magnetic resonance imaging showed a mass of 1.0  1.2 cm located posterior to the scrotum . 
 no other abnormalities were noted during pregnancy . 
 the patient was delivered vaginally at 38 weeks of gestation . on physical examination , a soft peduncular mass with a rugged and pigmented swelling was located between the normally developed scrotum and the anus . 
 there were no specific symptoms or any other associated congenital anomalies . 
 we completely excised the mass at one month of age . 
 a histological examination revealed lipoma , with tissue suggestive of scrotum , so a definite diagnosis of as was made . as is a rare congenital anomaly of the scrotum . 
 we review the literature .