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Vetfractuur politieagent elleboog
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The case
A 40-year-old man referred by his GP for a palpable swelling over the elbow, query soft-tissue tumour. Imaging showed no mass. Instead there was a focal discontinuity in the subcutaneous fat with an overlying skin depression — a subcutaneous fat fracture, not a neoplasm. The clinical "lump" was the rim of normal fat bordering a focal defect, giving the false impression of a mass.
Why this case matters
A referral for "rule out tumour" primes you to look for a mass. The diagnosis here is the absence of one plus a subtle finding: a cleft through the fat. Recognising it turns an anxious oncological work-up into a benign, self-limiting post-traumatic injury. A fat fracture is a rare and rarely-considered diagnosis after trauma, so it is easy to over-call as tumour or miss entirely.
Anatomy you must name
- Dermis / overlying skin — intact, no discoloration; the depression is the visible sign
- Subcutaneous fat lobules and their fibrous septa — the fractured layer; blunt force distorts the organised septa and disrupts the adipose architecture
- Superficial (fascial) plane vs deep muscular fascia — the injury sits *above* the deep fascia
- Intact underlying myofascial plane and muscle — confirming the process is confined to subcutaneous fat is what excludes deeper pathology
- At the elbow: relate the defect to the olecranon and rule out olecranon bursa pathology
Classifications
No formal grading exists. Frame it as the post-traumatic subcutaneous fat injury spectrum:
- Fat contusion — echogenic oedematous fat, fluid clefts, no discrete defect (acute)
- Fat fracture — a discrete hypoechoic cleavage plane/defect through the fat → skin depression; classically described as a physical sign mimicking tendon rupture
- Fat necrosis — later; oval anechoic areas of lobular liquefaction, or on MRI a globular T1-hyperintense component with a laminar stellate fibrous (T1/T2-low, STIR-high) component that evolves over time
- Post-traumatic pseudolipoma — the opposite morphology: a non-encapsulated bulge of fat with thickened stacked septa; female predominance
The clinical decision
The question the referrer actually needs answered is "is this a tumour?" — so the report must do two things:
1. State positively that there is no soft-tissue mass, no vascularised nodule, no infiltration.
2. Attribute the palpable/visible abnormality to a focal subcutaneous fat defect with skin depression, in keeping with a fat fracture given the trauma history.
That combination lets the clinician reassure and manage conservatively rather than escalate.
Protocol & reporting checklist
Ultrasound is the first-line and usually sufficient tool (high-frequency linear probe, long- and short-axis, plus power Doppler).
Look for and report:
- A hypoechoic defect or cleavage plane through the subcutaneous fat
- Intact overlying skin and intact underlying myofascial plane / muscle
- No significant power-Doppler hyperemia (argues against tumour, abscess, active inflammation)
- No discrete solid mass and no oval anechoic liquefaction pools (which would suggest fat necrosis)
Reserve MRI for equivocal cases or persistent deformity — it maps the fatty defect, asymmetry vs the contralateral side, and any fibrous/non-fatty component.
Pitfalls
- The rim of preserved fat around the defect palpates as a "lump." Don't let the referral word "tumour" anchor you into finding a mass that isn't there.
- Doppler hyperemia or a solid nodule is NOT a fat fracture — reconsider abscess, fat necrosis, or true neoplasm.
- Differential still matters: fat necrosis (liquefaction pools), subcutaneous panniculitis, and subcutaneous abscess can mimic it — the trauma history and the clean, avascular cleft are the discriminators.
- Absent trauma history doesn't exclude it (repetitive minor trauma counts), but a clear inciting injury greatly supports the diagnosis.
- Don't reflexively recommend biopsy of a benign post-traumatic fat defect.
Management implication
Conservative management is first-line: reassurance, avoiding re-injury, progressive rehabilitation. Return to baseline can be slow and there's a recurrence risk with further trauma. Surgery — excision/liposuction, sometimes with fat transfer for contour — is reserved for persistent pain or a chronic cosmetic deformity. The radiologist's confident benign call is what keeps this in the conservative lane.
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