Uterine adenomyoma is a benign mass formed by the invasion of the myometrium by endometrial cells. Adenomyoma is a focal part of the related diffuse condition called adenomyosis. Treatment may be surgical (excision of the mass alone, or hysterectomy for women who do not wish to become pregnant), or medical by administration of gonadotropin-releasing hormone agonists.
Uterine adenomyoma is a collection of endometrial glands, which are bordered by two consecutive layers of cells, the first derived from endometrial stroma and the second, outermost one, formed by leiomyomatous smooth muscle cells. Adenomyoma is believed to develop with endometrial glandular and stromal cells invading the myometrium . Adenomyosis is defined in a similar way, but it affects a larger region of the uterus. Adenomyoma is regarded by some as a focal region within the larger area of adenomyosis, and by others as a different version of the condition. Adenomyoma may be difficult to distinguish from uterine fibroids.
Adenomyoma is not a frequent uterine lesion. Of the samples obtained by hysterectomy, twenty percent show evidence of adenomyosis, but the solid focal forms, i.e. adenomyomas, are rare , and the cystic forms even more so. Adenomyomas are usually firm , but can sometimes be soft. Most identified adenomyomas are in the corpus of the uterus  . In one study close to 50% of the patients with adenomyomas also had fibroids . Adenomyomas may be polypoid, - as was the case in an older woman treated with tamoxifen for breast cancer - or may present as cystic lesions, either adult or juvenile type  . Decidualization of adenomyomas has also been observed in a pregnant woman .
The most frequent symptoms are abnormal vaginal bleeding , chronic pelvic pain, and dyspareunia . Serious cases may lead to infertility. Cystic forms of adenomyoma are characterized by severe dysmenorrhea  . These symptoms also accompany other conditions that can coexist with adenomyomas, such as uterine fibroids and endometriosis .
Clinical diagnosis is not feasible since the symptoms are not specific. Adenomyomas are characterized histologically. Histopathologic examination of biopsies reveals lesions consisting of glands and cysts surrounded by endometrial epithelium, stroma, and smooth muscle cells. Distinguishing adenomyoma from atypical polypoid adenomyoma or adenosarcoma may be problematic . An adenomyoma invaded by lymphocytes has been described that structurally resembled a lymphoma, and might have been misdiagnosed as such .
A suspicion of adenomyosis (including adenomyomas) is usually first followed up by ultrasound techniques. Transabdominal sonography has a sensitivity of only 32.5%– 63%  and is not regarded as a dependable method , but transvaginal sonography shows higher accuracy in diagnosis . According to some sources , transvaginal sonography can be as sensitive as magnetic resonance (MR) imaging. A hysterosalpingogram can detect the expansion of diverticula into the myometrium . Computed tomography cannot satisfactorily diagnose adenomyosis, or differentiate it from fibroids.
Changes in the thickness of the endometrium-myometrium junctional zone are characteristic of both diffuse and focal forms of adenomyosis. The thickness of the junctional zone can be examined by both two- or three dimensional transvaginal ultrasound or by MR imaging; a junctional zone thicker than 12 mm indicates adenomyosis. Adenomyoma, situated in the myometrium, has a round shape and low signal intensity on T2 weighted MR imaging, but often with small regions of high intensity .