Omental lipoma is a benign mesenchymal tumor developing within the greater or lesser omentum. It consists of mature fat cells and is an encapsulated, well-defined mass. Omental lipomas are rare and usually asymptomatic, detected incidentally. They can reach large sizes (>10 cm) and cause abdominal pain or bowel obstruction through mass effect. On CT, a well-defined mass of homogeneous fat density (-80 to -120 HU) is diagnostic. In the presence of thin septa or minimal soft tissue component, liposarcoma should be considered in the differential. Surgical excision is performed in symptomatic cases.
Age Range
30-70
Peak Age
55
Gender
Equal
Prevalence
Uncommon
Omental lipoma arises from clonal proliferation of mature adipocytes originating from mesenchymal stem cells within the omentum. Genetically, HMGA2 gene rearrangement at chromosome region 12q13-15 is frequently detected; this gene regulates fat cell differentiation and proliferation. The tumor is a slow-growing, well-vascularized, encapsulated mass. The capsule consists of a thin fibrous band separating the tumor from surrounding normal omental fat. Homogeneous fat density on CT reflects the tumor being composed almost entirely of mature adipocytes — low electron density of lipid droplets causes low X-ray attenuation. Lipomas do not undergo malignant transformation; however, in the presence of thick septa (>2 mm), nodular soft tissue components, or enhancing areas within fat density, well-differentiated liposarcoma should be considered — liposarcoma has MDM2 gene amplification and shows more aggressive biological behavior unlike lipoma.
Well-defined, encapsulated mass of homogeneous fat density (-80 to -120 HU) on CT — diagnostic for lipoma in the absence of soft tissue component or enhancement.
Well-defined, oval or lobulated mass of homogeneous fat density (-80 to -120 HU) in the omentum on non-contrast CT. No soft tissue density, calcification or enhancement is seen within the mass. Thin septa (<2 mm) may be present but do not enhance. Mass size can vary from 1 cm to 30 cm.
Report Sentence
Well-defined mass of homogeneous fat density in the omentum is observed, consistent with omental lipoma.
No enhancement in the lipoma after contrast — mass maintains fat density. Minimal enhancement may be seen in thin septa or capsule but no solid enhancing component is present. Absence of enhancement strengthens the diagnosis of benign lipoma; presence of enhancing solid component increases liposarcoma suspicion.
Report Sentence
No enhancement in the mass after contrast is observed, consistent with benign lipoma.
Homogeneous hyperintense signal on T1-weighted images — isointense with subcutaneous fat. Homogeneous signal loss on fat-suppressed sequences (STIR, fat-sat) — confirms bulk fat content. Chemical shift artifact may be seen at mass margins. Fat signal is also seen on T2 (intermediate to high signal).
Report Sentence
The mass shows T1 hyperintensity with homogeneous signal loss on fat-suppressed sequences, confirming macroscopic fat content; consistent with omental lipoma.
Homogeneous hyperechoic or isoechoic (with surrounding fat) well-defined oval mass on B-mode US. Mass may be compressible and shows no posterior acoustic shadow. Thin hypoechoic capsule may be visible. Minimal or no vascularity on Doppler.
Report Sentence
Homogeneous hyperechoic, well-defined mass in the omental area is observed, consistent with omental lipoma.
No intravoxel signal drop on opposed-phase in chemical shift imaging — lipoma contains macroscopic fat, not intracellular microscopic fat. India ink artifact may be seen at mass-tissue interface but no signal loss within the mass. This finding is also important in evaluating liposarcoma.
Report Sentence
No intravoxel signal drop within the mass on chemical shift imaging, confirming macroscopic fat content and consistent with lipoma diagnosis.
Thin, smooth-contoured fibrous capsule surrounding the mass. Capsule thickness is usually <2 mm and may show minimal enhancement. Capsule presence clearly separates the mass from surrounding omental fat and provides a well-defined appearance. Thick or irregular capsule should raise concern for liposarcoma.
Report Sentence
Thin fibrous capsule surrounding the mass is observed, consistent with well-defined benign lipoma.
Criteria
Homogeneous fat density, thin capsule, no soft tissue component
Distinct Features
Diagnosis definitive — no follow-up or biopsy needed; excision if symptomatic
Criteria
Size >10 cm; homogeneous fat density preserved but liposarcoma exclusion may be needed due to size
Distinct Features
Mass effect and bowel displacement; size alone is not an indicator of malignancy — lipoma if no soft tissue component
Criteria
Thin fibrous septa within fat density (fibrolipoma) or small vascular structures (angiolipoma)
Distinct Features
Mildly heterogeneous appearance; enhancement minimal; septa thickness (<2 mm) and enhancement pattern critical for differentiating from liposarcoma
Distinguishing Feature
Liposarcoma shows thick septa (>2 mm), solid enhancing nodular components and heterogeneous density; these are absent in lipoma
Distinguishing Feature
Omental lymphangioma shows cystic structures of water density; lipoma shows homogeneous fat density
Distinguishing Feature
Mesenteric panniculitis shows diffuse fat infiltration and fat ring sign; lipoma is a well-defined focal mass
Distinguishing Feature
Omental infarction shows density increase within fat (-40 to -80 HU) and inflammatory halo; lipoma density is homogeneously -80 to -120 HU
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upOmental lipoma is a benign tumor and CT diagnosis is definitive — biopsy is not needed. No treatment or follow-up is needed in asymptomatic cases. Surgical excision is performed in symptomatic cases (mass effect, pain, bowel obstruction). In the presence of homogeneous fat density, thin capsule and absence of enhancement, liposarcoma risk is negligible.
Omental lipomas are benign lesions that generally require no treatment. Absence of soft tissue component should be confirmed to exclude liposarcoma. Surgical resection can be performed for symptomatic or growing lesions.