Spot Diagnosis

Chondromyxoid fibroma

This is an uncommon lesion that occurs most commonly in the proximal tibia or distal femur. The lesion is commonly seen in the 2nd and 3rd decades and presents as an expansile lesion with trabeculations, located in the metaphysis, extending into the diaphysis and sometimes the epiphysis. It is commonly mistaken for other tumors that present with trabeculations and expansion, such as aneurysmal bone cyst, giant cell tumor, desmoplastic fibroma and hemangioma.

Scapular osteochondroma

This 32-years old man complained of a small lump in the mid thoracic wall posteriorly, for many years. He had an episode of pain and tenderness and underwent an imaging series.

The plain radiographs (Figs. 1, 2) were able to demonstrate the bony projection / exostosis only on the tangential view (Fig. 2). The MRI showed continuity of the lesion with the scapular marrow, with a thin cartilage cap (Figs. 3, 4). The CT scan showed the lesion well (Fig. 5).

In flat bones, especially, depiction of lesions often requires manipulation of x-ray parameters to the best of our ability and even then, it may be difficult to visualize the lesion. In such situations, CT and / or MRI become primary diagnostic tools and help depict these lesions better.

Osteochondroma

This was a 33-years old man with a swelling over the upper leg. He was known to have an osteochondroma, but due to a perceived increase in size, he came for renewed imaging. The plain radiographs (Figs. 1, 2) show a well-defined bony outgrowth from the fibular metaphysis with a well-defined outer rim. The MRI shows a well-defined, thin cartilage cap (Fig. 3) and a typical appearance of central marrow, which communicates with the fibular marrow (Figs. 3, 4). There is no altered signal, abnormal thickening of the cartilage cap or any other sign to suggest malignancy.

Even on gross specimens, osteochondromas pretty much resemble their radiologic appearances. Though they are usually of no consequence, osteochondromas can cause local problems or undergo malignant transformation.

Transpedicular biopsy for central body tuberculosis

This 21 years old man had backache. The MRI showed a focal lesion involving the L3 vertebral body. The clinico-radiologic profile was suggestive of tuberculosis, but the orthopedic surgeon wanted to be sure.

The lesion (Fig. 1 arrow) was biopsied using a transpedicular approach. An 11G needle was introduced through the pedicle into the body (Figs. 2-4) and through it, an 18G gun was passed to obtain the biopsies (Figs. 5,6).

The diagnosis of tuberculosis was confirmed on the biopsy.

Chondroblastoma - femoral head

This was a 20-years old lady with a well-defined osteolytic lesion in the left femoral head (Fig. 1). Just as with the earlier examples in the tibia and humerus, this was a characteristic epiphyseal lesion. An MRI was performed, which showed a speckled appearance on the STIR (Fig. 2) and T2W (Fig. 3) images with intense enhancement and reactive synovial enhancement as well (Fig. 5).

In countries where tuberculosis is endemic, this may be considered as a differential diagnosis in the event of a less well-defined zone of transition and the presence of a significant amount of soft tissue or abscess formation.

Biopsy of a vertebral lesion - tuberculosis

This 36-years old man had back pain. His MRI had shown a lesion in the L2 vertebral body. The assumption was of tuberculosis, but the findings were not pathognomic. A CT guided biopsy was advised. The CT scan shows an osteolytic lesion with sclerosis with minimal adjacent soft tissue. Instead of biopsying the soft tissue, it was felt that the best thing would be to go through the sclerotic bone into the osteolytic lesion - this was done and the biopsy material obtained was proven to be tuberculosis.

Chondroblastoma

This 24-years old man had pain in the left shoulder. The plain radiograph (Fig. 1) showed a well-defined osteolytic lesion with septae in the humeral epiphysis, with a narrow zone of transition. This appearance is consistent with a chondroblastoma. The MRI (Figs. 2, 3) showed a lesion with fluid-fluid levels. Such levels are common in aneurysmal bone cysts (ABC).

ABC transformation in a chondroblastoma is not uncommon and the presence of fluid-fluid levels should not prevent us from making a diagnosis of a chondroblastoma.

You can also see the other examples of a chondroblastoma in the tibial epiphysis and femoral head.

Multiple osteolytic lesions - metastases from signet cell carcinoma - stomach

This 56-years old man, with mild bone pain, but otherwise well-preserved and asymptomatic, was found to have extensive osteolytic lesions on MRI and plain radiographs. A biopsy was attempted at another hospital, but was inconclusive.

Using a Cook 18G co-axial gun canula system, biopsies were obtained from two sesions, one in the sacrum and one in the ilium. There was clear fluid obtained from both lesions, so the walls of both lesions were biopsied.

The eventual diagnosis was of metastases from signet cell carcinoma, probably from the stomach - a gastric mass was found on endoscopy.

Chondroblastoma

This was a 20-years old man who had severe knee pain. The plain radiograph (Fig. 1) showed a well-defined osteolytic lesion in the epiphysis with a sclerotic rim and a central matrix of increased density. No significant surrounding sclerosis was seen.

An epiphyseal lesion such as this most commonly is a chondroblastoma, which it turned out to be on excision. Though an osteoid osteoma may present in this manner, the epiphyseal location and the lack of other findings go against this diagnosis. Often, these lesions do not have a chondroid matrix and appear to be purely osteolytic.

You can also see the other examples in the humeral and femoral heads.

Enchondroma - long bone, not always straightforward

We saw a classic enchondroma the last week, but all cartilage tumors are not always as straight-forward.

This young patient had mild pain in the leg and a plain radiograph (Figs. 1, 2) showed a mildly expansile, trabeculated lesion with a narrow zone of transition in the proximal tibial diaphysis, with a smaller lesion more superiorly in the metaphysis. The MRI (Figs. 3, 4) showed a lobulated lesion with septae, an appearance highly suggestive of a chondroid tumor. Another lesion was seen more superiorly (Fig. 5). This combination of the plain radiographic appearance and the MRI morphology suggested an enchondroma.

Due to the multifocality and the pain, a biopsy was performed. The pathologist was not able to differentiate between a low-grade chondrosarcoma and an enchondroma. The patient is on follow-up.