Lipoleiomyoma is a rare variant of uterine smooth muscle tumors composed of a mixture of smooth muscle cells and mature adipose tissue (fat). It accounts for 0.03-0.2% of all uterine leiomyomas. Histologically a benign tumor with no risk of malignant transformation. Typically occurs in peri/postmenopausal women aged 50-70. The diagnostic clue on imaging is detection of macroscopic fat component — fat density on CT (-40 to -120 HU), T1 hyperintense signal with signal loss on fat-suppressed sequences on MRI is pathognomonic. Most cases are asymptomatic and incidentally detected. Symptomatic cases may present with abnormal uterine bleeding or pelvic pressure symptoms. Surgical treatment is generally not required; myomectomy or hysterectomy may be performed in symptomatic cases.
Age Range
40-70
Peak Age
55
Gender
Female predominant
Prevalence
Uncommon
The pathogenesis of lipoleiomyoma is not fully elucidated, but the most widely accepted theory is based on adipose metaplasia of smooth muscle cells within leiomyoma. Mesenchymal stem cells have differentiation potential toward both smooth muscle and adipose tissue lineages. In the postmenopausal period, declining estrogen levels and altered local growth factors (PPAR-gamma activation) trigger metaplastic transformation of smooth muscle cells into adipocytes. This process may also be related to adipogenic differentiation from intratumoral pericytes. An alternative theory proposes clonal expansion of embryonic remnant fat cells within myometrial smooth muscle. From an imaging perspective, mature adipose tissue contains large lipid droplets, and these lipids exhibit short T1 relaxation time on MRI → T1 hyperintense signal forms. On CT, the low X-ray attenuation of fat tissue (low density and low atomic number of lipids) produces negative HU values. On fat-suppressed MRI sequences (STIR or spectral fat-sat), frequency-selective RF pulses selectively suppress fat proton signal → T1 hyperintense areas lose signal, proving fat content.
The signature finding of lipoleiomyoma is signal loss on fat-suppressed sequences of areas showing hyperintense signal isointense with subcutaneous fat on T1-weighted images. This combination is definitive proof of macroscopic fat presence and is pathognomonic for lipoleiomyoma diagnosis. T1 hyperintensity may be seen in hemorrhagic leiomyoma, but signal is preserved with fat suppression — this distinction is critically important in diagnosis.
On T1-weighted images, the fat component of lipoleiomyoma demonstrates prominent hyperintense signal. Depending on fat proportion, the mass may appear entirely hyperintense or exhibit a mixed hypointense-hyperintense pattern with the smooth muscle component. T1 hyperintensity shows similar signal intensity to subcutaneous fat. This finding must be confirmed with fat suppression sequences to distinguish from leiomyoma with hemorrhagic degeneration — signal disappears with fat suppression in lipoleiomyoma while signal is preserved in hemorrhagic leiomyoma.
Report Sentence
Well-defined mass in the myometrium containing areas of hyperintense signal isointense with subcutaneous fat on T1-weighted sequences; consistent with macroscopic fat content and lipoleiomyoma should be considered as the leading diagnosis.
On fat-suppressed T1-weighted sequences (STIR or spectral fat-sat), prominent signal loss is observed in the fat component of lipoleiomyoma. This proves that the hyperintense areas on standard T1 represent true fat. Signal loss may be homogeneous or heterogeneous — depending on fat proportion. This finding is critically important for differentiation from other causes of T1 hyperintensity (hemorrhage, proteinaceous fluid) because only fat protons are selectively suppressed by fat suppression.
Report Sentence
Hyperintense areas detected on T1-weighted sequences demonstrate prominent signal loss on fat-suppressed sequences; this finding proves the presence of macroscopic fat and confirms the diagnosis of lipoleiomyoma.
On T2-weighted images, lipoleiomyoma demonstrates mixed signal intensity. The fat component shows intermediate-to-high signal on T2, while the smooth muscle component remains T2 hypointense like typical leiomyoma. Fibrous component contributes low T2 signal. Consequently, a more heterogeneous T2 appearance is observed compared to homogeneous leiomyoma. The fat-to-muscle ratio determines the degree of T2 heterogeneity.
Report Sentence
Mixed areas of hypointense signal from smooth muscle component and intermediate-to-hyperintense signal from fat component observed in the mass on T2-weighted sequences; this heterogeneous pattern is consistent with lipoleiomyoma.
On non-contrast CT, lipoleiomyoma appears as a well-defined mass containing fat-density areas in the myometrium. Fat component density ranges from -40 to -120 HU. Smooth muscle component appears at soft tissue density (40-60 HU). Fat proportion can vary from 10-90%; in cases with low fat proportion, fat density should be confirmed with ROI measurement. Calcification may accompany. Detection of fat density significantly narrows the diagnosis — fat component in uterine masses is most commonly seen in dermoid followed by lipoleiomyoma.
Report Sentence
Well-defined mass containing fat-density areas (-40 to -120 HU) in the myometrium on non-contrast CT; presence of fat component strongly supports the diagnosis of lipoleiomyoma.
On B-mode ultrasonography, lipoleiomyoma appears as a well-defined, hyperechoic mass in the myometrium. High echogenicity of the fat component creates a bright appearance. Smooth muscle component has lower echogenicity and mixed architecture may show heterogeneous echo pattern. Posterior acoustic shadowing (due to smooth muscle and fibrous component) or mild posterior enhancement may be observed. Fat-containing lesions typically appear hyperechoic on US, but this finding is non-specific — CT or MRI confirmation is required for diagnosis.
Report Sentence
Well-defined hyperechoic mass observed in the myometrium; CT or MRI confirmation is recommended for this appearance that may be consistent with fat content.
On chemical shift sequences, India ink artifact (black rim) is observed at fat-smooth muscle interfaces of lipoleiomyoma. Signal loss lines form at fat-water interfaces on opposed-phase images. This artifact confirms the presence of macroscopic fat-soft tissue boundary. Additionally, intravoxel signal loss may be observed at areas where fat and muscle components mix at the same voxel (microscopic level). India ink artifact is an expected finding in lipoleiomyoma and supports the diagnosis together with fat suppression.
Report Sentence
India ink artifact (black rim) observed at fat-smooth muscle interfaces of the mass on opposed-phase sequences; this finding confirms the presence of macroscopic fat component and is consistent with lipoleiomyoma.
Criteria
Fat component >50% — mass predominantly fat density/signal. Rare variant that may be confused with dermoid and lipoma in diagnosis.
Distinct Features
Mostly negative HU on CT, dominant T1 hyperintensity on MRI. Distinguished from dermoid by myometrial origin and absence of calcification/hair/teeth.
Criteria
Smooth muscle component >50% — mass predominantly leiomyoma-like but containing focal fat foci.
Distinct Features
Predominantly soft tissue density mass with focal negative HU areas on CT. Focal T1 hyperintense foci within T2 hypointense mass on MRI. Distinguished from standard leiomyoma by detection of fat foci.
Criteria
Prominent fibrous component mixed with fat — minimal smooth muscle. Histologically rare variant with coexistence of fibrous tissue and adipose tissue.
Distinct Features
Prominent contrast between T2 hypointense fibrous areas and T1 hyperintense fat areas on MRI. Calcification more frequently accompanies on CT. Fibrous component shows late and slow enhancement on contrast-enhanced MRI.
Distinguishing Feature
Typical leiomyoma does not show fat signal on T1, no signal loss on fat suppression. Negative HU values are not expected on CT. Homogeneous T2 hypointense signal is the classic finding of leiomyoma.
Distinguishing Feature
Dermoid is of ovarian origin, not uterine. May contain hair, teeth, calcification, and sebaceous material. Rokitansky nodule is characteristic. Lipoleiomyoma is of myometrial origin and does not contain these components.
Distinguishing Feature
Leiomyosarcoma does not contain fat component — negative HU values on CT and signal loss on fat suppression on MRI are not expected. Shows necrosis, prominent DWI restriction, and aggressive enhancement pattern.
Distinguishing Feature
Adenomyoma originates from junctional zone and does not contain fat component. Does not show fat signal on T1. Shows hyperintense foci (ectopic endometrial glands) within T2 hypointense mass — different from T1 hyperintensity of lipoleiomyoma.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upLipoleiomyoma is a benign tumor with no risk of malignant transformation. Diagnosis is made when fat component is definitively detected on imaging, and biopsy is not required. No treatment or follow-up is needed in asymptomatic cases. Myomectomy or hysterectomy may be performed in symptomatic cases (bleeding, pressure). Rarely may compress adjacent structures due to size. Prognosis is excellent — no recurrence or metastasis has been reported.
Lipoleiomyoma is a benign tumor and does not require treatment. The presence of fat on imaging is diagnostic. In very rare cases, differential diagnosis from ovarian dermoid or liposarcoma may be needed.