Describing a Bone Tumour Radiograph

What the pattern is. A focal abnormality of bone density on a plain radiograph: lytic, sclerotic or mixed. The task in the viva is not to name it in the first sentence but to build a description that constrains the differential to two or three possibilities, and then to state whether the lesion is aggressive.

Confirming the finding is genuine. A true lesion is present on both views, so reproduce it on the orthogonal view before describing anything, and exclude the mimics:

• Overlying soft tissue or bowel gas projecting as a lucency
• Normal anatomical lucencies: the pseudocyst of the humeral head, Ward's triangle in the femoral neck, the greater trochanteric trabecular void, the calcaneal neutral triangle. All are trabecular rather than destructive and none involves the cortex
• Nutrient foramen and vascular channels: thin, oblique, cortically based lines with sclerotic walls
• Healing fracture and stress fracture: a linear sclerotic band with solid periosteal reaction, often at a classic site (proximal femur, tibial diaphysis, second metatarsal). A stress fracture with florid periosteum is the classic false-positive for osteosarcoma
• Osteomyelitis and Brodie abscess: the great impersonator of both benign and malignant lesions; a penumbra sign (T1 hyperintense rim on MRI) supports abscess
• Bone infarct: a serpiginous sclerotic border enclosing normal-density marrow, which separates it from a chondroid lesion, where the rings-and-arcs lie inside

View larger

View larger

The exact words to use out loud. Recite in this fixed order:

1. "This is a radiograph of the [bone], [AP/lateral], in a patient stated to be [age]."
2. "There is a [lytic / sclerotic / mixed] lesion measuring approximately [x] cm."
3. "It lies in the [epiphysis / metaphysis / diaphysis], [centrally / eccentrically / cortically / juxtacortically / surface]."
4. "The zone of transition is [narrow / wide]; the margin is [sclerotic / well-defined non-sclerotic / moth-eaten / permeative] — Lodwick grade [IA / IB / IC / II / III]."
5. "There is [no matrix / chondroid rings-and-arcs / cloud-like osteoid / ground-glass fibrous] mineralisation."
6. "The cortex is [intact / thinned and expanded / breached]."
7. "There is [no / solid / lamellated / spiculated / Codman triangle] periosteal reaction."
8. "There is [no] associated soft tissue mass."
9. "Overall these features are [non-aggressive / indeterminate / aggressive]. My differential is..."

Lodwick grading, verbatim. IA and IB are essentially benign; IC onwards is indeterminate to aggressive.

• IA: geographic with a sclerotic rim
• IB: geographic, well defined, without sclerosis
• IC: geographic with an ill-defined margin
• II: moth-eaten
• III: permeative

What the grade is worth. Lodwick's grades express rate of growth, not histology, and he proposed them to decide which lesions need a biopsy and which can safely be followed. Caracciolo and colleagues applied a three-grade modification to 183 lesions and correlated it with the final pathology, which puts numbers on that judgement:

Where it stops helping. The system is powerful at the two ends and decides nothing in the middle. That is the honest thing to say in a viva: an ill-defined geographic margin is not a "probably benign" finding to be watched, it is a genuinely indeterminate one, and it is the grade at which the description stops answering the question and the next investigation has to. Two observers also agree on a Lodwick grade less than 40 per cent of the time, and seniority does not help (Willenbring, in the evidence base), so the weight of the description lies in the findings you name, with the grade offered as shorthand.

The description chooses the next test. Whenever tissue is going to be needed, the sequence is always radiograph, then MRI of the whole involved bone, then staging CT of the chest, then biopsy performed by or in discussion with the treating sarcoma surgeon. Haematoma, oedema and tract seeding from a biopsy corrupt MRI staging, which is why the biopsy comes last.

No further imaging. The classic "don't touch" lesions are diagnosed on the radiograph alone: non-ossifying fibroma, fibrous cortical defect, bone island, cortical desmoid (the avulsive cortical irregularity of the distal medial femur), a simple bone cyst in the proximal humerus of a child and an asymptomatic small enchondroma in a phalanx. Cortical desmoid, fibrous cortical defect, bone island and healing fracture callus can all look alarming; their discriminators are a classic site and lack of progression, and biopsy is harmful and unnecessary. Reassure and discharge, with an interval radiograph only if symptoms change.

Orthogonal and comparison radiographs. Two views of the whole bone including both joints confirm the lesion is real, define the true zone of transition and identify a second lesion. Old films are the single most valuable investigation: an unchanged lesion over two years is effectively benign.

CT. Best for cortical detail, matrix mineralisation and the nidus of osteoid osteoma (thin slices, less than 1 mm), and it changes management by confirming chondroid versus osteoid matrix when the radiograph is ambiguous. CT also assesses pathological fracture risk and stages the chest in any suspected sarcoma.

View larger

MRI of the whole involved bone. The staging test for any indeterminate or aggressive lesion: marrow extent, skip lesions, soft tissue mass, joint and neurovascular involvement, fluid-fluid levels. It must be done before biopsy, and it changes management by determining resection margins and detecting the skip metastases that alter the operation.

View larger

Bone scintigraphy or whole-body MRI. For polyostotic disease and metastatic screening; a positive screen converts a solitary-lesion plan into palliative or systemic treatment. Myeloma is often scan-negative, so use whole-body low-dose CT or whole-body MRI instead.

Bloods and biochemistry before biopsy. They diagnose myeloma and brown tumour without a scalpel and prevent an unnecessary biopsy:

• FBC, ESR/CRP
• Calcium, phosphate, ALP, PTH
• Serum and urine electrophoresis with free light chains
• PSA in men

Biopsy, last and by the treating unit. An image-guided core through a tract that can be excised with the definitive specimen, planned by the sarcoma surgeon: never transverse, never through more than one compartment, never through neurovascular planes. A misplaced tract can cost the limb.

Related pages. Apply the description to a site: Predicting a Bone Tumour by Age is step 1 of the algorithm in its own right, and Diaphyseal Bone Lesion works the hardest longitudinal location.

Each row gives the age and setting, the feature that discriminates the cause from its neighbours, and what confirms it. The next section is how a description arrives at a row.

Interrogate the lesion in a fixed order. Each question removes part of the table above, and age goes first because it does the most work.

Age. Age alone removes roughly half the list and should be the first sentence of your differential.

• Under 5: metastatic neuroblastoma, leukaemia, LCH, osteomyelitis
• 5-25: osteosarcoma, Ewing, simple cyst, ABC, NOF, chondroblastoma, osteoid osteoma
• 25-40: giant cell tumour, enchondroma, fibrous dysplasia
• Over 40: metastasis, myeloma, chondrosarcoma, lymphoma

Solitary or multiple. A solitary lytic lesion changes to a metastatic or polyostotic differential the moment a second is found, so always ask for the whole bone and consider a skeletal screen; fibrous dysplasia, enchondromatosis, LCH and metastases are all frequently multiple. Multiple lesions over 40 mean metastasis, myeloma or brown tumours, and the next step becomes biochemistry and staging CT rather than biopsy. Multiple in a child means LCH, leukaemia, neuroblastoma metastases or osteomyelitis, and multiple with a growth-plate distribution suggests enchondromatosis or hereditary multiple exostoses.

Where in the bone. The longitudinal site names the shortlist and the transverse position ranks it.

• Epiphysis, mature skeleton: giant cell tumour, then clear cell chondrosarcoma and infection
• Epiphysis, child: chondroblastoma
• Metaphysis: the vast majority, among them osteosarcoma, simple cyst, ABC and NOF
• Diaphysis: Ewing, lymphoma, LCH, osteoid osteoma, adamantinoma (anterior tibial cortex)

Transversely, eccentric favours NOF, giant cell tumour and ABC; central favours simple cyst, enchondroma and fibrous dysplasia; surface lesions are osteochondroma and parosteal osteosarcoma.

Zone of transition and margin. A narrow zone with a sclerotic rim (Lodwick IA) is a slow, benign process: the lesion has been there long enough for bone to wall it off. An ill-defined, moth-eaten or permeative margin (Lodwick IC to III) is fast growth, which means sarcoma, infection, lymphoma, myeloma or metastasis. This single feature is the strongest predictor of aggressiveness and should be stated explicitly, with the grade read off the Caracciolo table above.

Matrix. Matrix names the tissue of origin; absent matrix excludes nothing.

• Rings-and-arcs or popcorn calcification is chondroid: enchondroma, chondroblastoma, chondrosarcoma
• Fluffy, cloud-like, amorphous density is osteoid: osteosarcoma, osteoblastoma, bone island
• Ground glass is fibrous dysplasia
• No matrix at all keeps giant cell tumour, simple cyst, ABC, myeloma and metastasis in play

Cortex, periosteum and soft tissue mass. An intact, expanded cortex with solid periosteal reaction says slow. A cortical breach with spiculated or interrupted periosteum (Codman triangle, sunburst, onion-skin) and an extraosseous soft tissue mass says aggressive, and the soft tissue mass is the discriminator that should trigger urgent sarcoma referral regardless of the rest of the description.

Why the periosteum is never the diagnosis. Codman triangle and sunburst indicate rate of growth. Osteomyelitis, Ewing sarcoma, osteosarcoma and even eosinophilic granuloma in a child can all produce an aggressive-looking periosteum, so say "aggressive periosteal reaction" and then use age, site and matrix to narrow it.

Systemic features and bloods. Fever with a raised CRP and WCC pushes towards osteomyelitis or Ewing. Weight loss, a smoking history or a known primary pushes towards metastasis; anaemia, renal impairment and a raised ESR push towards myeloma. Raised calcium with subperiosteal resorption means hyperparathyroidism, and the lesion is a brown tumour that needs a corrected calcium, not a biopsy.