Salivary gland lipoma is the most common mesenchymal tumor of the parotid gland but accounts for only 0.6-4.4% of all parotid tumors. It is a benign tumor composed of mature adipocytes. It most commonly occurs in the superficial lobe of the parotid gland. Peak incidence is between 40-60 years, slightly more common in males. Clinically presents as a slowly growing, soft, painless, mobile mass. Lipoma variants include classic lipoma, fibrolipoma, myxoid lipoma, intramuscular lipoma, and pleomorphic lipoma. Must be distinguished from lipomatous atrophy (age-related fat infiltration of the gland). Malignant transformation (liposarcoma) is extremely rare. Diagnosis on imaging is usually definitive — homogeneous mass with fat signal/density is pathognomonic.
Age Range
40-70
Peak Age
55
Gender
Male predominant
Prevalence
Rare
The imaging findings of lipoma are based on the tumor being entirely composed of mature adipocytes. The cytoplasm of adipocytes is filled with triglycerides (fat) and this fat content produces characteristic signal/density features on all imaging modalities. On MRI, fat has short T1 relaxation time (due to efficient dipole-dipole interactions of protons in methylene chains) and produces bright signal on T1. On T2, fat shows intermediate-to-high signal. Suppression of fat signal on fat-suppressed sequences (STIR or chemical shift-based) confirms the diagnosis — if the mass loses signal on fat suppression, it contains fat. On CT, the low density of fat (-50 to -150 HU) is characteristic and clearly separates from soft tissue density. On US, echogenicity of lipoma varies relative to surrounding salivary gland parenchyma but is generally isoechoic to mildly hyperechoic and homogeneous. Well-developed fibrous capsule creates smooth margins.
The pathognomonic MRI finding of lipoma is T1 hyperintense signal and complete signal loss on fat-suppressed sequences. The combination of these two findings confirms fat content and verifies the diagnosis without need for additional imaging.
On T1-weighted sequences, lipoma shows markedly hyperintense signal isointense with subcutaneous fat. This finding is the most characteristic MRI finding of lipoma. The mass has a homogeneous signal pattern — internal heterogeneity suggests non-lipoma pathologies. Capsule may be seen as thin hypointense rim on T1. No or minimal enhancement on post-contrast series.
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A well-defined homogeneous mass showing hyperintense signal isointense with subcutaneous fat on T1-weighted sequences is identified in the parotid gland; consistent with lipoma.
On fat-suppressed T2 sequences (STIR or spectral fat saturation), lipoma shows complete signal loss — this finding confirms fat content and verifies the diagnosis. Without fat suppression, lipoma shows intermediate-to-high T2 signal. In Dixon technique, water-fat separation shows lipoma bright on fat maps and dark on water maps. India ink artifact (chemical shift artifact) may be seen at the lipoma-normal tissue boundary on opposed-phase imaging.
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The lesion demonstrates complete signal loss on fat-suppressed sequences; this finding confirms that the mass content is fat and verifies the diagnosis of lipoma.
On non-contrast CT, lipoma appears as a homogeneous, well-defined mass of fat density (-50 to -150 HU). This density value is pathognomonic and a definitive criterion for distinguishing from other parotid tumors. Thin fibrous septa may be seen but the mass has homogeneous fat density. No enhancement. Thin capsule may be observed.
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A homogeneous, well-defined mass of fat density (mean [value] HU) is identified in the parotid gland; consistent with lipoma.
On B-mode US, lipoma generally appears as an isoechoic or mildly hyperechoic, homogeneous, well-defined, compressible mass relative to surrounding parotid parenchyma. Thin echogenic capsule may be observed. Posterior acoustic change is generally absent. No or minimal internal vascularity on Doppler. US diagnosis is not as definitive as CT and MRI because echogenicity alone cannot confirm fat content.
Report Sentence
A well-defined, homogeneous, compressible, isoechoic mass is identified in the parotid gland; lipoma is considered and CT or MRI is recommended for diagnostic confirmation.
On DWI, lipoma does not show diffusion restriction — ADC values are high. Fat tissue may show variable signal on DWI (T2 shine-through or fat suppression effect). ADC value reflects the free water content and adipocyte size of fat.
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The lesion does not demonstrate diffusion restriction on DWI; consistent with a fat-containing benign lesion.
Criteria
Entirely composed of mature adipocytes, homogeneous fat signal/density.
Distinct Features
Homogeneous fat signal, no enhancement, thin capsule.
Criteria
Fibrous septa or fibrous component within fat tissue.
Distinct Features
Thin fibrous septa T1/T2 hypointense, septa may enhance, fat component loses signal on fat suppression but septa retain signal.
Criteria
Age-related replacement of gland parenchyma with fat. Diffuse change, not focal mass.
Distinct Features
Diffuse fat infiltration, no focal mass, no capsule, bilateral symmetric. In lipoma, focal encapsulated mass.
Distinguishing Feature
Pleomorphic adenoma is T1 hypointense (no fat signal), markedly T2 hyperintense (myxoid), no signal loss on fat suppression. Lipoma is T1 hyperintense (fat signal), complete signal loss on fat suppression.
Distinguishing Feature
Warthin is cystic-solid mixed, soft tissue density (30-50 HU). Lipoma is fat density (-50 to -150 HU). CT density difference provides definitive differentiation.
Distinguishing Feature
Schwannoma is T2 hyperintense, target sign, fusiform, shows enhancement, no fat signal. Lipoma shows fat signal, no enhancement.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
Görüntülemede tanı kesin ise biyopsi gereksizdir. Asemptomatik lipomlar takip edilebilir. Cerrahi endikasyon: kozmetik sorun, boyut artışı, kompresyon semptomları. Süperfisiyal parotidektomi büyük tümörlerde.Salivary gland lipoma is a benign tumor that can be definitively diagnosed on imaging. In the presence of typical imaging findings (T1 hyperintensity + signal loss on fat suppression or fat density on CT), biopsy is unnecessary. Small asymptomatic lipomas can be followed with clinical follow-up. Surgery is performed for lipomas causing cosmetic concerns or showing size increase. Transformation of lipoma to liposarcoma is extremely rare; when heterogeneous structure, enhancing solid component, or thick septa are detected, well-differentiated liposarcoma must be excluded. Differentiation from lipomatous atrophy is made by presence of focal mass and capsule.
Surgical excision is the treatment option. Malignant transformation is not expected.