On the left an illustration of the most common sclerotic bone tumors and tumor-like lesions.

In the right column the most common sclerotic bone tumors and tumor-like lesions in different age-groups.

Fibrous dysplasia and eosinophilic granuloma more commonly present as osteolytic lesions, but they can be sclerotic.
Notice that many benign osteolytic lesions that are frequently seen in younger age groups may heal and appear as sclerotic lesions in the middle aged group.

Infection is seen in all ages.

A more general approach to sclerotic bone lesions is to use the mnemonic I VINDICATE, which means ...I clear myself from accusation.
It is a universal differential diagnostic approach to any lesion.

Key facts

• Typical presentation: central lesion in metaphysis or diaphysis with a well defined serpentiginous border.
• Bone infarcts resemble cartilaginous tumors.

The term bone infarct or osteonecrosis is used for lesions in the diaphysis or metaphysis. If the osteonecrosis is located in the epiphysis, the term avascular osteonecrosis is used.
On the left typical bone infarcts.

On MR imaging bone infarcts are characterized by irregulair serpentiginous margins with low signal intensity on both T1 and T2 WI and with intermediate to high fat signal in the center part.

Differentiating a bone infarct from an enchondroma or low-grade chondrosarcoma on plain film can be difficult or even impossible.
Cartilaginous tumors in particular chondrosarcoma may show endosteal scalloping, while a bone infarct does not.
Chrondroid tumors are more frequent than bone infarcts.

A bone island, also known as enostosis, is a benign lesion consisting of well-differentiated mature bone tissue within the medullary cavity.
It is frequently encountered as a coincidental finding and can be found in any bone.

The image on the left shows a calcified lesion in the proximal tibia without suspicious features.
This could very well be an enchondroma.
There were other features that favored the diagnosis of a low-grade chondrosarcoma like a positive bone scan and endosteal scalloping of the cortical bone on an MRI (not shown).
A chondrosarcoma was diagnosed at biopsy.

On the left two other lesions in different patients that proved to be chondrosarcoma.
The sclerotic lesion in the humeral head could very well be a benign enchondroma based on the imaging findings.
Symptoms are usually absent, however, in adult patients with a chondroid lesion in a long bone, particularly of larger size, always consider low-grade chondrosarcoma.

On the left barely visible on the radiograph the typical calcifications in the chondroid matrix of an enchondroma.
Notice how easily MRI depicts these lesions. Enchondroma is a fairly common benign cartilaginaous lesion which may present as an entirely lytic lesion (without any calcifications), a dense calcified lesion or a mixed appearance (lytic with rings-and-arcs of calcifications or popcorn-like calcifications). Enchondromas are frequently encountered as coincidental findings, particularly in adult patiens (MRI of the knee, staging carcinoma using bone scintigrapy etc).

On the left a 20 year old patient with a sclerotic expansile lesion in the clavicle.
Notice that there are also some small areas of ill-defined osteolysis.
In an older patient one should first consider an osteoblastic metastasis.
If the patient had fever and a proper clinical setting, osteomyelitis would be in the differential diagnosis.

FD is often purely lytic, but may have a groundglass appearance as the matrix calcifies.
Ossifications or calcifications can be present in variable amounts.

On the left a well-defined mixed sclerotic-lytic lesion of the left iliac bone.
The diagnosis was fibrous dysplasia.
DD: old SBC.

Osteoblastic or sclerotic metastases must be included in the differential diagnosis of any sclerotic bone lesion in a patient > 40 years.
These metastases most commonly originate from prostate and breast cancer and less frequently from lung cancer, lymphoma or carcinoid.

On the left images of a patient with prostate cancer.
Notice the numerous predominantly osteoblastic metastases.

On the left images of a patient with breast cancer.
There is an osteoblastic metastasis, which presents as a subtle sclerotic lesion in the humerus metaphysis.

Osteoblastic metastases (2)
On the left a radiograph of the pelvis with a barely visible osteoblastic metastasis in the left iliac bone (blue arrow).
Notice that CT depicts these lesions far better (red arrows).

On the left CT-images of a patient with prostate cancer.
Notice the numerous ill-defined osteoblastic metastases.

Osteochondroma is a bony protrusion covered by a cartilaginous cap.
Growth of the osteochondroma takes place in the cap, corresponding with normal enchondral growth at the growth plates.
Accordingly, growth of osteochondromas is allowed until a patient reaches adulthood.
Growth of osteochondromas at adult ages (characterized by a thick cartilaginous cap (high SI on T2 weighted MR images) should raise the suspicion of progression to a chondrosarcoma.
Osteochondroma usually presents as an incidental finding, or in the form of a syndrome with multiple osteochondromas.

Osteoid osteoma is a benign bone lesion with a small nidus surrounded by a zone of reactive sclerosis.
In the case on the left the reactive sclerosis is the most obvious finding on the X-ray.
CT scan is very helpful in detecting the nidus and differentiating osteoid osteoma from other sclerotic lesions like osteoblastoma, osteomyelitis, arthritis, stress fracture and enostosis.
The case on the left shows reactive sclerosis with a nidus that is barely visible on the radiograph (blue arrow), but clearly visible on the CT (red arrows).

Osteoid osteoma is a small (up to 1.5 cm) osteolytic lesion, with or without central calcification.
Location is usually cortical/eccentric, sometimes subperiosteal or even intra-articular.
Most common sites of origin include the femur, tibia, spine (posterior), hands and feet.
The lesion is characterized by extensive reactive sclerosis with cortical thickening.
CT is optimal to appreciate the nidus.
MRI also may detect the nidus, combined with abundant bone marrow and/or soft tissue edema. In the long bones, differential diagnosis may include reactive processes like stress fracture or cortical abcess.
Because of this differential diagnosis, it is important to be informed about the history of the patient, pattern of complaints and biochemical values.

Osteoid osteoma (2)
In most cases of osteoid osteoma the radiographic appearance is determined by the reactive sclerosis.
In some cases however the osteolytic nidus can be visible on the radiograph (figure).

key facts

• Osteoma, similarly consists of densely compact bony tissue. These lesions predominantly occur in the (outer table of the) neurocranium or in a paranasal sinus. Sometimes, an osteoma is present along the surface of a flat or tubular bone. Osteoma may mimic a heavily ossified fibrous dysplasia.

On the left an image of a patient with chronic osteomyelitis.
Centrally there is an ill-defined osteolytic area.
The major part of the lesion consists of reactive sclerotic.

Key facts

• Most common primary malignant bone tumor.
• 50% around the knee.
• Presentation: pain, mass, pathologic fracture.
• Sclerosis is present from either tumor new bone formation or reactive sclerosis.
• Plain films typically reveal lesions with moth-eaten or permeative pattern of the transition zone with irregular cortical destruction and an interrupted periosteal reaction with soft tissue extension.
• A periosteal reaction known as Codman's triangle appears as tumor elevates periosteum from underlying bone. Cortical soft tissue extension may produce radiating spicules of bone called sunray appearance.

  Osteosarcoma (osteogenic sarcoma) is the 2nd most common primary bone tumor and is highly malignant. It is most common among people aged 10 to 25, although it can occur at any age. Osteosarcoma produces malignant osteoid (immature bone) from tumor bone cells. The bone formation dictates the radiographic pictures. When abudant bony tumor matrix is lacking, the osteosarcoma may be of the telangiectatic subtype (which sometimes may mimic aneurysmal bone cyst!), or the differential diagnosis includes Ewings sarcoma or lymphoma, particularly when a large soft tissue mass is present. In older patients, also chondrosarcoma can be in the differential diagnosis. Osteosarcoma usually develops around the knee (distal femur more often than proximal tibia) or in other long bones (like proximal humerus), particularly the metaphyseal-diaphyseal area, and may metastasize, usually to lung or other bones. Pain and swelling are the usual symptoms. Findings on imaging studies vary and may include sclerotic and/or lytic features. Diagnosis requires biopsy, which shoud always be performed after imaging Patients need a chest x-ray and CT to rule out or detect lung metastases and a bone scan to detect bone metastases. MR imaging is the optimal modality for loco-regional staging. An imaging protocol should at least include T1-weighted TSE series in two perpendicular directions for assessment of the intraosseous extent and relationship to joint(s) nearby, and axial T2-WI with FS, for assessment of the soft-tissue extension and relationship to important neurovascular structures. Longitudinal imaging of an entire long bone is strongly advocated to rule skip metastases. After administratipn of i.v. contrast, T1-weighted series are repeated in two directions with FS. Treatment is a combination of chemotherapy and surgery. Use of (neo-)adjuvant chemotherapy increases survival from < 20% to > 65% at 5 yr. Chemotherapy usually begins before any surgery. The goal of neoadjuvant chemotherapy is to eliminate occult distant micrometastases, and to cause tumor volume reduction, in order to make limb-salvage surgery possible. As such, more than 80% of patients can be treated with limb-sparing surgery without decreasing long-term survival rate. The role of imaging during and after neoadjuvant chemotherapy is to assess the rate of response. IN particular, significant reduction of tumor vascularization and perfusion is a strong indicator of good response. Increase in tumor volume strongly suggests poor response, however, volume decrease does not necessarily indicate favourable response. Continuation of (adjuvant) chemotherapy after surgery is usually necessary. If there is nearly complete tumor necrosis (about 99%) from preoperative chemotherapy, 5-yr survival rate is > 90%. Low-grade intraosseous osteosarcoma is a very rare variant of osteosarcoma,which may however have a benign radiographic appearance and therefore can be confused with, for instance,, fibrous dysplasia. Surface osteosarcomas have their origin on the surface of bone and grow primarily into the surrounding soft tissues, but may also infiltrate into the bone marrow. Among these, the parosteal (or juxtacortical) osteosarcoma is the most frequently encountered variant, most commonly on the posterior side of the distal meta-diaphysis of the femur.

Osteosarcoma (2)
On the left images of an osteosarcoma in the right femur.
It is barely visible, but an agressive periostitis is seen (arrow).
Continue with the MR-images.

The MR images show a large tumor mass infiltrating a large portion of the distal femur and extending through the cortex.

Stress fractures occur in normal (fatigue fractures) or metabolically weakened (insufficiency fractures) bones. Usually stress fractures are easy to recognize ...... Uncommonly it can be difficult to differentiate a stress fracture from a pathologic fracture, that occurs at the site of a bone tumor (7).

Uncommonly it can be difficult to differentiate a stress fracture from a pathologic fracture, that occurs at the site of a bone tumor (7).

• Stress fractures