A review of both the pathology and oncology databases at a tertiary referral centre for orthopaedic oncology was performed for patients with talar lesions.
histology and imaging features were recorded where available.
The site within the talus,
involvement of subchondral bone,
marrow and soft tissue oedema and fluid-fluid levels were recorded.
One hundred and twenty one patients with talar lesions were identified on our institutions databases with histopathological confirmation.
Patients with normal or nonspecific findings on histopathology were excluded.
Seventy-five patients with true talar lesions were included in this cohort.
Forty-three (57.3%) patients were male and 32 (42.7%) patients were female.
Mean age of patients in our cohort was 29.5 years,
with a range of 1-71 years.
The histology of talar lesions in our patient cohort is detailed in Fig. 2.
Primary bone tumours were histologically-proven in 60 (80.0%) patients.
The majority of primary bone tumours identified were benign (56 (93.3%) patients).
Two metastatic lesions,
including metastatic endometrial carcinoma and metastatic breast carcinoma,
were identified in our patient cohort.
The remaining 13 lesions included infectious,
inflammatory and degenerative conditions.
Chondroblastoma was the most common lesion of the talus,
accounting for 31% of lesions,
followed by osteoid osteoma (16%).
Histopathology data is detailed by patient age in tables 1 and 2.
In patients under 30 years,
primary bone tumours accounted for 97.7% of lesions,
with chondroblastoma and osteoid osteoma accounting for 62.8% of lesions (table 1). There was one malignant lesion (2.4%),
with one Ewing sarcoma identified in a 10 year old female patient.
In patients over the age of 30 years,
primary bone tumours accounted for 78.1% of lesions,
the range of tumours was broad (table 2).
Five (15.6%) malignant lesions were identified.
Table 1: Histopathology of talar lesions in patients <30 years (n=43).
Histopathology of talar lesions in patients <30 years (n=43)
Aneurysmal Bone Cyst
Giant Cell Tumour
Benign Fibrous Histiocytoma
Table 2: Histopathology of talar lesions in patients >30 years (n=32).
Histopathology of talar lesions in patients >30 years (n=32)
|Giant Cell Tumour
|Spindle Cell Sarcoma
|Aneurysmal Bone Cyst
Twenty-five patients had magnetic resonance imaging (MRI) available for review.
Based on a literature review and imaging features observed in our patient cohort,
a proposed algorithm for differential diagnosis of talar lesions is detailed in Fig. 3.
The imaging features of some of the lesions observed in our patient cohort will be reviewed:
Chondroblastoma is a rare benign cartilaginous neoplasm which accounts for less than 1% of all primary bone tumours1,
with a clear male predominance.
Lesions in the foot occur in a slightly older age group (mean 25.5 years),
in contrast to lesions in other locations2.
A minority occur in skeletally immature patients2.
The talus is an unusual but classic site for chondroblastoma.
Treatment is with either detailed curettage and bone grafting or radiofrequency ablation for selected lesions.
Radiographic features (Fig. 4):
- Well-defined lytic lesion with a thin sclerotic margin.
- Expansile lesion with thinning of the subarticular bone.
- Punctate mineralised matrix seen in 40-60% of cases3.4.
- Moderate to significantly increased lesion uptake.
- Better delineates its relationship to the articular surface and presence of endosteal scalloping and periosteal reaction.
- Punctate mineralised matrix seen up to 93%5.
low to intermediate signal intensity on both T1 and T2-weighted imaging (Fig. 5 and Fig. 6).
- Lobular internal architecture with fine lobular margins.
- Best delineates perilesional oedema (seen in 40-77% of lesions).
- Secondary aneurysmal bone cyst seen in more than 30% of cases2 (Fig. 7).
First reported by Jaffe in 1935,
an osteoid osteoma (OO) is a benign osteoblastic bone tumour which typically measures less than 1 cm in size6.
The talus is the fourth most common site for OO,
accounting for 2-10% of cases7,8.
Talar OO occur in the neck in 97% of cases9.
The majority of lesions in the foot are intramedullary or subperiosteal where periosteal reaction is minimal or absent10.
Radiographic features (Fig. 8):
- Depends on the location of the lesion.
- Intra-cortical OO demonstrate a radiolucent nidus,
1.5-2cm in dimension,
with variable central mineralisation and prominent reactive sclerosis and cortical thickening.
- Intramedullary OO demonstrate less adjacent sclerosis and cortical thickening
- Subperiosteal OO demonstrate cortical erosion with minimal associated sclerosis,
typically along the neck of the talus.
- Joint effusion of talo-crural joint.
- Increased uptake on blood flow,
blood pool and delayed phases.
- “Double density” sign can be seen where moderate uptake is seen in the surrounding reactive areas and greater uptake at the site of the nidus.
- Superior to MRI.
- Demonstrates low attenuation nidus with focal central calcification and peri-nidal sclerosis (Fig. 9).
MRI (Fig. 10 and Fig. 11):
- Marrow and perilesional oedema seen.
- Can miss diagnosis in 33-35% of cases11-12.
Histologically similar to OO,
this a rare neoplasm,
representing approximately 3% of benign bone tumours13.
The foot and ankle is affected with relative frequency,
with more than 20% of osteoblastomas occurring here.
The talus is the most commonly affected bone,
often at the junction of the dorsal neck and body14,15.
Surgical excision and curettage are often the treatment of choice,
radiofrequency ablation is a useful treatment option in selected cases.
Radiographic features (Fig. 12):
- Well-circumscribed lytic lesion with or without a sclerotic rim,
larger than 1.5-2cm.
- Perilesional sclerosis not typical.
- Matrix mineralisation seen in approximately 50%,
- Regional osteoporosis in approximately 50% of cases15.
- More commonly intra-medullary.
- Intense uptake.
- “Double density” sign.
CT (Fig. 13):
- Best demonstrates tumour location,
soft tissue extension and matrix mineralisation.
- Matrix mineralisation can be osteoid or simulate chondroid matrix.
MRI (Fig. 14):
- Low to intermediate signal on T1-weighted imaging,
intermediate to high signal on T2-weighted imaging.
- Surrounding oedema is less marked than with OO.
- 10-15% of cases can be associated with secondary aneurysmal bone cyst15.
Aneurysmal Bone Cyst
Aneurysmal bone cyst (ABC) is an expansile collection of blood-filled cavities and typically affects patients younger than 20 years.
It is considered primary in 65-99% of cases and secondary in 1-35% of cases16-19.
Giant cell tumour,
osteoblastoma and chondroblastoma are common lesions with secondary ABC.
12% of primary ABC affect the foot and ankle and the talus is rarely involved.
Radiographic features (Fig. 15):
- Partially well-circumscribed,
expansile lytic lesion with or without a sclerotic rim.
- Increased peripheral uptake (“doughnut sign”).
- Demonstrates internal septations with multiple fluid levels.
- Cortex may be interrupted.
MRI (Fig. 16):
- Lobulated mass with varied signal intensities between cavities.
- Fluid-fluid levels best demonstrated on T2-weighted imaging.
- Thin peripheral and septal enhancement in primary ABC.
- Solid enhancing components in secondary ABC20.
Giant Cell Tumour
Giant cell tumour (GCT) is a benign,
locally aggressive tumour characterised by sheets of neoplastic,
ovoid mononuclear stromal cells interspersed with uniformly distributed large,
osteoclast-like giant cells.
GCT rarely presents in the foot with an incidence of 1-2%21,22.
The tarsal bones are most frequently affected21,22.
- Lytic expansile lesion with remodelling and thinning of cortex.
- Involves subarticular bone.
CT (Fig. 17):
- Geographic lytic lesions without matrix mineralisation.
MRI (Fig. 18 and Fig. 19):
- Heterogenous low to intermediate signal intensity on T1 and T2-weighted imaging.
- Secondary ABC can be seen in up to 14% of cases23.
Malignant bone tumours of the foot and ankle are extremely rare.
Osteosarcoma is the most common malignant bone tumour,
only 4% of osteosarcomas arise in this location.
The mean age of presentation is later in than osteosarcoma in general (4thdecade)24.
Osteosarcoma in the foot and ankle is more likely to be of a lower histological grade24,25.
Radiographic features (Fig. 20):
- Typically a sclerotic lesion with amorphous osteoid matrix mineralisation,
ill-defined borders and cortical erosion.
- Less commonly lytic or mixed lytic and sclerotic.
Bone scintigraphy (Fig. 21):
- Marked uptake on all three phases.
- Used to assess for distant metastases.
- Demonstrates osteoid matrix mineralisation.
MRI (Fig. 22 and Fig. 23):
- More accurately defines the extent of tumour.
- Intermediate signal intensity on T1 and T2-weighted imaging.
Ewing sarcoma is the second most common malignant bone tumour in the foot and ankle.
It is an aggressive,
malignant round blue cell tumour.
- Lytic permeative lesion with aggressive periosteal reaction and associated soft tissue mass.
- Reactive medullary sclerosis can mimic osteosarcoma and benign conditions such as stress fracture and avascular necrosis.
- Similar to radiographic findings.
- Intermediate signal intensity on T1-weighted imaging; intermediate to high signal intensity on T2-weighted imaging.
- Better evaluates soft tissue component.
Chondrosarcoma is a malignant tumour with pure hyaline cartilage differentiation.
Approximately 1-3% of all chondrosarcomas occur in the hand and foot26,27.
Chondrosarcoma can arise in a pre-existing benign cartilaginous lesion,
including enchondroma and osteochondroma.
- Mixed lytic and sclerotic lesion.
- Chondroid matrix mineralisation.
- Endosteal scalloping with cortical destruction and soft tissue extension common28.
- Intense increased uptake.
- Can be useful in differentiating low grade chondrosarcoma from enchondroma.
- Better demonstrates radiographic findings.
- Matrix mineralisation best visualised on CT.
- Lobulated mass with low signal intensity on T1-weighted imaging and high signal intensity on T2-weighted imaging.
- Matrix mineralisation seen as low signal on all pulse sequences.
Metastases to the foot and ankle are uncommon,
with a reported incidence of 0.01%.
The talus is the fourth most common bone involved29.
The most common primary malignancies with metastasis to the foot include genito-urinary,
breast and colorectal carcinoma.
Radiographic features (Fig. 24):
- Similar to other skeletal metastases in the axial and proximal appendicular skeleton.
sclerotic or mixed lytic and sclerotic lesions.
- Increased uptake.
- Used to assess for solitary or multifocal disease.
- Mimics radiographic findings.
MRI (Fig. 25 and Fig. 26):
- Generally low to intermediate signal intensity on T1-weighted imaging and high signal intensity on fluid-sensitive sequences.