Soft tissue mass — characterisation

ACR AC Soft Tissue Masses; UK soft tissue sarcoma guidelines (2024)

Two studies are both correct starting points, and which one leads is set by the lump rather than by a ranking. Ultrasound triages the superficial palpable lump: confidently benign, or not. A lump that is already deep to fascia, above about 5 cm, growing or painful has passed the referral threshold before anyone scans it, and the right first study is a dedicated soft-tissue mass MRI of the compartment — not a joint MRI, which has the wrong coil, the wrong planes and a field of view built around an articulation. Anything not confidently benign escalates to that MRI and a sarcoma service, not to reassurance.

A palpable soft tissue lump, typically referred from primary care, often described as enlarging.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

Ultrasound musculoskeletal / soft tissue

What we'd amend, and why

Ultrasound is quick, available and settles the large majority of superficial lumps outright — a ganglion, an epidermoid cyst, a typical lipoma, a haematoma or a nerve sheath tumour arising from a visible nerve. It also establishes the two facts that matter most for triage: whether the lesion lies deep to the deep fascia, and whether it is vascular. What it cannot do is exclude sarcoma in an indeterminate lesion, which is why the pathway has an escalation arm.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayany — All patients

Decision support only. Local protocol takes precedence.

Worth asking the referrer (1)

None of these hold the request up. They sharpen the protocol or the plan that follows.

How big is it, is it deep to the fascia, and is it growing?
These three features drive the escalation decision more than any imaging feature does, and they should be stated before the scan rather than inferred after it.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

All patients

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	Ultrasound musculoskeletal / soft tissue Ultrasound musculoskeletal / soft tissue usually appropriate	Ultrasound is quick, available and settles the large majority of superficial lumps outright — a ganglion, an epidermoid cyst, a typical lipoma, a haematoma or a nerve sheath tumour arising from a visible nerve. It also establishes the two facts that matter most for triage: whether the lesion lies deep to the deep fascia, and whether it is vascular. What it cannot do is exclude sarcoma in an indeterminate lesion, which is why the pathway has an escalation arm.
First line	MRI Soft Tissue (Mass Characterisation) MRI soft-tissue mass — characterisation and compartmental mapping usually appropriate	This is the study that characterises the lesion and plans the operation, and it is an equally correct first request — not a second tier — where the lump is already deep to fascia, above about 5 cm, growing or painful, or where ultrasound has reached its limit. It is a different examination from a joint MRI: the study is centred on a skin marker over the palpable lump with a surface coil chosen for that region, the axial plane is set orthogonal to the limb rather than to a joint line, and the field of view must contain the whole lesion, the entire involved compartment, the adjacent joint and the neurovascular bundle, with a large-field-of-view localiser so the surgeon can site it. Booking a knee or shoulder protocol for a lump gives the wrong coil, the wrong planes and a field of view that answers a different question, and it will be repeated. Characterisation rests on the combination of a non-fat-suppressed T1 — the sequence most often omitted, and the one that shows fat, marrow signal and the fat plane against the neurovascular bundle — with a fluid-sensitive T2 or STIR in at least two planes; contrast is added for the indeterminate lesion, with a pre-contrast fat-suppressed T1 in matched geometry so that intrinsic T1-bright haemorrhage is not read as enhancement. The deliverables are the compartment, the relationship to fascia and the distance to the nearest neurovascular structure.
Second line	Limb radiograph Limb radiograph — two orthogonal views	Radiographs are worth adding when the lesion is deep, close to bone, or contains calcification on ultrasound: the pattern of mineralisation distinguishes myositis ossificans, a phlebolith-bearing vascular malformation and a synovial sarcoma, and cortical involvement changes the referral entirely.
Problem solving	CT Extremity / Musculoskeletal CT Extremity — Contrast-Enhanced Soft Tissue	Reserved for the patient who cannot have MRI. CT shows fat and mineralisation and can define the relationship to bone, but its soft-tissue contrast is not sufficient to characterise a mass or to plan sarcoma surgery, so it is a fallback and should be labelled as one.

Ultrasound and soft-tissue mass MRI are both endorsed as a first study, and the lump chooses between them: superficial and probably benign starts with ultrasound, while deep, large, growing or painful goes straight to MRI rather than through an ultrasound that will not settle it.
An unplanned excision of an unrecognised sarcoma contaminates the surgical field and commits the patient to more extensive re-excision. Escalating an indeterminate lump before anyone operates is the single highest-value action in this pathway.

Pitfalls

Reporting an indeterminate lesion as "likely benign" or "probable lipoma". If the appearances are not those of a specific benign entity, the correct output is escalation, and the wording of the report is what determines whether that happens.
Being reassured by a small size in a deep lesion, or by slow growth — well-differentiated sarcomas grow slowly.
Arranging a local biopsy of a possible sarcoma before specialist discussion; a poorly placed tract compromises limb-sparing surgery.
Omitting to say whether the lesion is superficial or deep to the deep fascia, which is one of the features the referral pathway turns on.
Assuming a rapidly enlarging painful lump is a haematoma without a convincing injury; sarcomas bleed and are routinely mistaken for haematomas.
Vetting a lump onto a joint MRI protocol. The coil, the planes and the field of view are all built around an articulation, and a mid-segment mass ends up at the edge of the volume or outside it — the study then has to be repeated before surgery.
Letting the patient into the scanner without the lump marked, and then reporting a study centred on the wrong place as normal.
Cropping the field of view to the lesion alone. Without the whole compartment, the adjacent joint and the neurovascular bundle there is no surgical plan, only a description.
Omitting the pre-contrast fat-suppressed T1 and then calling intrinsic T1-bright haemorrhage or proteinaceous material "enhancement".

Priors — what to pull first

Any previous imaging that includes the region establishes whether the lesion is new or has been stable for years — the most useful single piece of information available.
A history of previous excision at the same site raises recurrence, and previous radiotherapy raises radiation-associated sarcoma.

What makes a good request

Size, depth relative to the deep fascia, and growth are the features that drive escalation. A lump that is large, deep or enlarging warrants specialist assessment even when the imaging looks unremarkable.
The definitive characterisation study is a dedicated soft-tissue mass MRI of the involved compartment, not a joint protocol. The request should name the lump and its location rather than a joint: a knee MRI centred on the joint line with a knee coil will not contain a mid-thigh mass, and a study that does not include the whole compartment, the adjacent joint and the neurovascular bundle has to be repeated before surgery.
Mark the lump with a skin marker before the patient goes into the scanner. An unmarked small or mobile lesion is the commonest reason a study is centred in the wrong place and reported as normal.
Where sarcoma is a genuine consideration, the MRI and any biopsy belong to the sarcoma service, because the biopsy tract has to be placed so that it can be excised with the tumour.
Contrast is not automatic. A lesion that follows fat on every sequence and suppresses completely, or a simple ganglion or cyst, is characterised on unenhanced sequences; gadolinium is added for the indeterminate lesion, for solid versus cystic or necrotic, to identify a biopsy target within a heterogeneous mass, or to look for recurrence in a treated bed.
A radiologically typical lipoma is a diagnosis; "probably a lipoma" in a deep or enlarging lesion is not.

Scoring this once it is done

The classification and risk tools this question ends in.

RECIST 1.1 Tumor Response Choi Criteria for GIST Response Lodwick-Madewell Classification (Lytic Bone Lesion)Bone-RADS (Bone Lesion Scoring)

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

Ultrasound musculoskeletal / soft tissue MRI soft-tissue mass — characterisation and compartmental mapping Limb radiograph — two orthogonal views CT Extremity — Contrast-Enhanced Soft Tissue

Confirm locally

Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.