Adenomyoma is the focal form of adenomyosis — a well or ill-defined focal mass within the myometrium containing ectopic endometrial glands and stroma. Unlike diffuse adenomyosis, it is a localized lesion and may be confused with leiomyoma. It typically occurs in premenopausal women (age 30-50) and presents with dysmenorrhea and menorrhagia. On imaging, it appears as an ill-defined, predominantly T2 hypointense heterogeneous mass within the myometrium — small cystic areas within it (T2 hyperintense foci corresponding to ectopic endometrial glands) are critical findings for diagnosis. Differentiation from leiomyoma directly affects treatment planning.
Age Range
30-55
Peak Age
43
Gender
Female predominant
Prevalence
Common
Adenomyoma forms when endometrial glands and stroma invade from the endometrial-myometrial junction (junctional zone) deep into the myometrium. This invasion concentrates locally forming a focal mass — unlike diffuse adenomyosis, it is confined to a limited area. Ectopic endometrial glands respond to hormonal cycles — bleeding and inflammation occur during menstruation. This repetitive micro-hemorrhage and inflammation causes reactive smooth muscle hypertrophy and fibrosis in surrounding myometrium — this is why it appears hypointense on T2. Blood and secretions accumulating in ectopic glands form small cystic areas — these appear as T2 hyperintense foci and are the diagnostic signature finding of adenomyoma. T1 hyperintense foci reflect hemorrhagic products (methemoglobin) within glands. Unlike leiomyoma, adenomyoma is uncapsulated and does not form a clear boundary with surrounding myometrium — this difference manifests as absence of 'pseudocapsule' on MRI.
The signature finding of adenomyoma is the presence of small (1-5 mm) T2 hyperintense cystic foci within a T2 hypointense myometrial mass. These foci represent fluid accumulation in ectopic endometrial glands. The 'bright spots on dark background' pattern is the pathognomonic finding distinguishing adenomyoma from leiomyoma (homogeneous T2 hypointense, no cystic foci). These foci may also be focally hyperintense on T1 (hemorrhagic products), further strengthening the diagnosis.
Ill-defined, predominantly hypointense focal mass within myometrium on T2-weighted images — containing small T2 hyperintense cystic foci (1-5 mm). Cystic foci correspond to ectopic endometrial glands and are the diagnostic signature finding of adenomyoma. Mass borders show gradual transition with surrounding myometrium — the sharp border and hypointense pseudocapsule seen in leiomyoma are absent. Junctional zone disruption or thickening may accompany.
Report Sentence
Ill-defined, T2 hypointense focal mass within the myometrium containing small T2 hyperintense cystic foci; consistent with focal adenomyosis (adenomyoma).
Focal hyperintense foci within the mass on T1-weighted images — corresponding to hemorrhagic products (methemoglobin) in ectopic endometrial glands. This finding reflects the subacute stage of blood accumulating in ectopic glands during menstrual cycle. T1 hyperintense foci should be evaluated especially on fat-suppressed T1 sequences — remaining hyperintense after fat suppression confirms hemorrhagic content.
Report Sentence
Focal hyperintense foci within the mass on T1-weighted images, consistent with hemorrhagic products in ectopic endometrial glands.
Adenomyoma shows mild-moderate heterogeneous enhancement on contrast-enhanced MRI — less enhancement than leiomyoma. Cystic foci show no enhancement. Mass borders remain indistinct in contrast phase — gradual transition with surrounding myometrium is observed. Leiomyoma is more clearly demarcated in contrast phase due to its pseudocapsule.
Report Sentence
Mild-moderate heterogeneous enhancement of the myometrial mass on contrast-enhanced MRI without enhancement in cystic foci; consistent with adenomyoma.
Ill-defined, heterogeneous echogenicity focal mass within myometrium on transvaginal US. Not clearly separated from surrounding myometrium by a sharp border — different from the sharp boundary in leiomyoma. Small anechoic cystic areas (1-5 mm) may be seen within the mass — corresponding to ectopic endometrial glands. Accompanying myometrial heterogeneity suggests a diffuse adenomyosis component.
Report Sentence
Ill-defined focal mass with heterogeneous echogenicity within the myometrium containing small cystic foci; consistent with adenomyoma.
Adenomyoma does not show significant diffusion restriction on DWI — ADC values are generally similar to or mildly lower than normal myometrium. Cystic foci may appear hyperintense on DWI due to T2 shine-through effect but ADC values are high. Significant diffusion restriction suggests malignant lesions such as leiomyosarcoma or endometrial stromal sarcoma and plays a critical role in differential diagnosis.
Report Sentence
No significant diffusion restriction in the myometrial mass on DWI with preserved ADC values; consistent with benign adenomyoma.
Mild-moderate diffuse vascularity within adenomyoma on Doppler US — similar vascular pattern to surrounding myometrium. Peripheral ring vascularity seen in leiomyoma is absent. Feeding arterial vessel pattern differs from leiomyoma — adenomyoma shows diffuse, leiomyoma shows peripheral pattern.
Report Sentence
Diffuse vascularity in the myometrial mass on Doppler US without peripheral ring pattern; finding favoring adenomyoma.
Criteria
Ill-defined focal mass within myometrium — T2 hyperintense cystic foci on T2 hypointense background. Uncapsulated. Most common type. Recognized with high confidence on MRI.
Distinct Features
Classic MRI findings, ill-defined border, prominent cystic foci, most common type
Criteria
Dominant large cystic area (>10 mm) within adenomyoma — formed by excessive fluid accumulation in ectopic endometrial glands. Rare. Appears as a large T2 hyperintense cystic lesion within myometrial mass on MRI. May present with severe dysmenorrhea in young women. May require surgical excision or marsupialization.
Distinct Features
Large dominant cyst (>10mm), rare, severe dysmenorrhea, in young women, surgery may be needed
Criteria
Rare adenomyoma variant presenting as polypoid mass in endometrial cavity — containing atypical glandular architecture and myomatous stroma. Unlike typical adenomyoma, originates from endometrial cavity. Carries premalignant potential (8-12% endometrial carcinoma association). Occurs in young women and fertility-preserving treatment may be considered.
Distinct Features
Polypoid in endometrial cavity, atypical glandular architecture, premalignant potential, in young women, fertility can be preserved
Distinguishing Feature
Leiomyoma is a well-defined, T2 hypointense homogeneous solid mass with pseudocapsule — no T2 hyperintense cystic foci within (except degeneration). Adenomyoma is ill-defined, without pseudocapsule, containing small T2 hyperintense cystic foci (ectopic glands). Pseudocapsule presence and absence of T2 hyperintense foci favor leiomyoma; ill-defined border and cystic foci favor adenomyoma.
Distinguishing Feature
Diffuse adenomyosis is characterized by widespread myometrial thickening and diffuse >12 mm junctional zone thickening. Adenomyoma forms a focal mass. T2 hyperintense cystic foci may be seen in both but diffuse adenomyosis shows widespread distribution while adenomyoma shows localized clustering.
Distinguishing Feature
Leiomyosarcoma is a rapidly growing, markedly heterogeneous malignant myometrial mass with extensive necrosis areas showing diffusion restriction (ADC <1.0 x 10^-3). Adenomyoma is a slowly growing benign lesion without significant diffusion restriction. Rapid size increase, prominent necrosis and low ADC values are distinguishing findings favoring leiomyosarcoma.
Distinguishing Feature
Endometrial stromal sarcoma is a malignant tumor invading from endometrium into myometrium showing worm-like extensions and vascular invasion. Adenomyoma is a benign focal mass without vascular invasion. In stromal sarcoma, parametrial spread and venous invasion (ligament/ovarian vein) are distinguishing findings.
Urgency
routineManagement
medicalBiopsy
Not NeededFollow-up
12-monthAdenomyoma is a benign lesion and symptom control can be achieved with medical therapy (GnRH analogs, progestins, levonorgestrel IUS). Hysterectomy is curative in symptomatic patients with completed fertility. In fertility-preserving approach, focal excision (adenomyomectomy) can be performed but complete excision is more difficult than myomectomy due to ill-defined borders. Accurate diagnosis with MRI directly affects treatment planning — leiomyoma is easily removed by myomectomy while adenomyoma requires different surgical approach due to absence of capsule. In atypical polypoid adenomyoma variant, close follow-up or hysterectomy should be considered due to malignancy risk.
Differentiating adenomyoma from leiomyoma is important for surgical planning. Unlike leiomyoma, recurrence after myomectomy is higher. Hormonal therapy (GnRH agonists) can be used for symptom control. Hysterectomy is the definitive treatment for patients who have completed fertility.