The occurrence of retroperitoneal neoplasms arising independently of the adult urogenital organs has, to date, eluded scientific explanation. Until about 1880, these tumors were diagnosed as sarcoma or pancreatic cyst and dismissed without further consideration or study. Howship, in 1871, had observed a composite tumor possessing certain characteristics similar to dermoid teratomas commonly found in the ovary. In 1889, Bassini described a cystic adenoma morphologically resembling a pseudomucinous cystadenoma of the ovary, and Frank, in 1894, observing a similar tumor, attributed its histogenesis to an accessory ovary. Since 1894, instances of unattached retroperitoneal tumors have been reported in the medical literature, averaging somewhat less than one case a year. Occasionally, authors of these case reports have added to the diversity of histologic features that may be associated with these neoplasms. These now include glomeruli, renal tubules, rete structures, bone, hair, sweat glands, fat, smooth muscle, uterine mucosa and chorion epithelium.
HANSMANN GH, BUDD JW. MASSIVE UNATTACHED RETROPERITONEAL TUMORSAN EXPLANATION OF UNATTACHED RETROPERITONEAL TUMORS BASED ON REMNANTS OF THE EMBRYONIC UROGENITAL APPARATUS. JAMA. 1932;98(1):6–10. doi:10.1001/jama.1932.02730270010002