Chest wall lipoma is an encapsulated benign soft tissue tumor composed of mature adipose tissue and is the most common benign soft tissue mass of the chest wall. It can be located within subcutaneous fat, between muscles (intermuscular), or within muscle (intramuscular). It generally occurs between ages 40-60 and affects both sexes equally. Imaging findings are highly characteristic: fat density on CT (-50 to -150 HU) and T1 hyperintense signal with complete signal loss on fat suppression are pathognomonic findings. Lesions show homogeneous fat content, are surrounded by a thin capsule, and show no enhancement after contrast. Size is typically 1-10 cm but giant lipomas (>10 cm) have been reported. Chest wall lipomas may occasionally extend through the intercostal space into the intrapleural space (dumbbell lipoma) — entering the differential of pleural lesions. Symptoms are generally cosmetic concern or local mass effect. Risk of malignant transformation is practically nonexistent; however, liposarcoma should always be considered in the differential.
Age Range
30-70
Peak Age
50
Gender
Equal
Prevalence
Common
Lipomas are encapsulated benign neoplasms composed of mature adipocytes (fat cells). Histologically, they are indistinguishable from normal fat tissue — but their encapsulation by a thin fibrous capsule and growth independent of surrounding fat tissue is diagnostic. Genetically, HMGA2 gene rearrangements at 12q14-15 are the most commonly detected anomaly. Lipoma cells have low metabolic activity with practically no mitotic activity — this is the basis for low FDG uptake on PET-CT. Mature adipocytes contain a single large fat droplet and most of the cell cytoplasm consists of triglycerides. This triglyceride content determines imaging characteristics: low attenuation on CT (fat density), short T1 relaxation time on MRI (T1 hyperintense), and chemical shift effect (fat-water frequency difference). Signal loss on fat suppression sequences is based on elimination of fat proton signal through selective RF pulse or inversion targeting the chemical shift frequency of fat. The thin fibrous capsule forms the boundary of the lipoma from surrounding normal fat tissue and appears as a thin hypodense/hypointense line on imaging. Intramuscular lipomas may infiltrate between muscle fibers — in this case the capsule may be incomplete and muscle fibers traverse through the lesion (infiltration pattern). Dumbbell lipomas extend through anatomic weakness of the intercostal space, showing extension both external to the chest wall and into the pleural space.
The combination of homogeneous fat density on CT (-50 to -150 HU) and T1 hyperintense signal with complete signal loss on fat suppression on MRI is pathognomonic for lipoma. Homogeneous fat signal without solid components confirms the lesion consists of mature adipose tissue, allowing definitive diagnosis without biopsy.
On non-contrast CT, chest wall lipomas appear as well-defined, oval or lobulated masses showing homogeneous fat density (-50 to -150 HU). No solid components, calcifications, or soft tissue density areas are present within the lesion. The thin fibrous capsule may sometimes be visible as a thin line but generally remains at the resolution limit. In subcutaneous lipomas, detection of the thin capsule is important for delineating the boundary with surrounding fat tissue. In intramuscular lipomas, muscle fibers traversing through the lesion may create linear bands of soft tissue density — this is a normal finding and should not be confused with aggressive lesion.
Report Sentence
A well-defined encapsulated mass measuring ___ x ___ cm with homogeneous fat density (-___ HU) is seen in the chest wall, consistent with lipoma.
On T1-weighted MRI sequences, lipoma shows homogeneous hyperintense signal isointense with subcutaneous fat. Signal intensity is identical to normal subcutaneous fat — this is the most reliable MRI finding to confirm mature adipocyte content. A thin hypointense capsule surrounds the lesion, forming its boundary from normal fat tissue. In intramuscular lipomas, linear low-signal bands may be seen within T1 hyperintense fat signal — these represent normal muscle fibers traversing through the lesion. Any T1 hypointense solid nodule or thick septation should raise concern for atypical lipomatous tumor (well-differentiated liposarcoma).
Report Sentence
A mass showing homogeneous hyperintense signal isointense with subcutaneous fat on T1-weighted sequences is seen, consistent with lipoma.
On fat suppression sequences (STIR, spectral fat-sat, Dixon fat image), lipoma shows complete signal loss — confirming that the lesion consists entirely of mature fat tissue. This finding is the most reliable MRI technique for definitively proving fat content in T1 hyperintense lesions. Dixon technique generates separate fat and water images — lipoma appears bright on fat image and loses signal on water image. On STIR, inversion time is set according to fat T1 → fat signal is suppressed at null point → lipoma loses signal. Any residual signal (areas not fully suppressed) indicates non-adipose tissue content and raises suspicion for liposarcoma.
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The mass shows homogeneous signal loss on fat suppression sequences, confirming pure fat content.
On T2-weighted sequences, lipoma shows intermediate-high signal — isointense with subcutaneous fat. T2 signal is not as distinctly bright as T1 but is distinguishable from water and muscle signal. On STIR, the lipoma completely loses signal because fat is suppressed — this difference between STIR and T2 has diagnostic value. Any high-signal non-adipose solid component on T2 raises liposarcoma in the differential. The capsule appears as a thin hypointense line on T2 — due to the short T2 of fibrous tissue.
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The mass shows signal isointense with subcutaneous fat on T2, with complete signal loss on STIR.
On contrast-enhanced CT, lipoma shows no enhancement — the lesion maintains the same fat density as on non-contrast images. This finding reflects low vascularity and absence of actively proliferating tissue. Any enhancing solid component or septal thickening after contrast should raise suspicion for atypical lipomatous tumor (well-differentiated liposarcoma). The thin capsule may show minimal enhancement but this is clinically insignificant. In dumbbell lipomas, intercostal vessels traversing through the lesion may be visible — these should not be confused with tumoral enhancement.
Report Sentence
The mass shows no enhancement on contrast-enhanced CT, consistent with benign lipoma.
In superficially located chest wall lipomas, US shows an isoechoic-hyperechoic, oval, well-defined, homogeneous mass. The lesion is compressible with probe pressure. A thin hyperechoic capsule may be visible. Boundary determination can be difficult as the lesion echogenicity is similar to surrounding fat tissue — careful assessment with linear probe is needed. Intramuscular lipomas are more easily identified as hyperechoic areas within muscle. No vascularity is seen on Doppler or minimal peripheral vascularity may be present.
Report Sentence
An isoechoic-hyperechoic, compressible, avascular mass is seen on US, consistent with subcutaneous lipoma.
Criteria
Location within subcutaneous fat; most common form; easily palpable
Distinct Features
Easy assessment with US; may blend with surrounding fat on CT/MRI — capsule detection important; easy surgical excision
Criteria
Location within muscle; muscle fibers traverse through lesion; capsule may be incomplete
Distinct Features
Linear hypointense muscle bands within T1 hyperintense fat on MRI; may require wider surgical excision; atypical lipomatous tumor differential more important; infiltrative growth pattern
Criteria
Extension through intercostal space with both extrathoracic and intrathoracic components; dumbbell-shaped morphology
Distinct Features
Enters differential of pleural lesions; intercostal neurovascular bundle relationship important; multiplanar MRI essential for preoperative surgical planning; intercostal widening visualized on CT
Distinguishing Feature
Liposarcoma: Non-adipose solid components (T2 hyperintense, enhancing nodules), thick septa (>2 mm), areas not suppressed on fat saturation. Lipoma: Homogeneous fat signal, thin septa, complete fat suppression, no enhancement
Distinguishing Feature
Desmoid tumor: Low-heterogeneous T2 signal (fibrous tissue), enhancement present, infiltrative margins, no signal loss on fat suppression. Lipoma: T1 hyperintense fat signal, complete loss on fat suppression, no enhancement
Distinguishing Feature
Hematoma: High density in acute/subacute phase (50-70 HU), T1 hyperintense (metHb) but no signal loss on fat suppression, trauma history. Lipoma: Homogeneous fat density (-50 to -150 HU), complete loss on fat suppression
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upLipomas with typical imaging features (homogeneous fat density/signal, complete loss on fat suppression, no enhancement, no solid components) are considered definitively diagnosed and require no biopsy or follow-up. Surgical excision is curative for symptomatic lesions (pain, cosmetic). In large (>10 cm) or deeply located lesions and when any atypical features are present (non-adipose component, enhancement, thick septa), further evaluation (MRI) and biopsy are recommended — atypical lipomatous tumor/well-differentiated liposarcoma must be excluded.
Lipomas are benign tumors with no risk of malignant transformation. They generally require no treatment. Surgical excision may be performed for symptomatic or cosmetically concerning lesions. For large (>10 cm), deep-seated, or rapidly growing lesions, well-differentiated liposarcoma (atypical lipomatous tumor) should be excluded — MRI or biopsy is recommended. Thick septa, nodular components, or enhancement should prompt consideration of liposarcoma.