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Challenge of the Unknowns—Unknown 1

Diagnosis and Discussion

DIAGNOSIS: Osteochondroma

With a confident diagnosis of osteochondroma, and because of the patients' symptoms, MRI is warranted to fully assess this lesion.

Advanced Imaging Findings:

Axial T1 weighted

Axial T2 weighted

Coronal T1 weighted

Fat saturated image


There is a broad based intracapsular bony excrescence extending from the posteromedial aspect of the right femoral neck showing heterogeneous signal that is isointense with the parent bone marrow. Intact cortex, continuous with the parent bone is noted, except for at the apex of the lesion. Findings are typical of a sessile osteochondroma. There is homogeneous and slightly higher signal surrounding the lesion on the T1 weighted images and very high signal on the T2 and fat suppressed images, representing combined cartilage cap and adjacent fluid that appears to cause a slight pressure erosion of the femoral neck just proximal to the lesion. No definite bursal involvement is noted.

Follow-up and Treatment:

This patient returned to his chiropractor for follow-up care. Because the patient at this point is still skeletally immature, follow-up hip views are recommended to assess for possible increase in size of the lesion. These follow-up views should be taken about every 6 months. Regarding treating the actually lesion itself, surgical removal is the only option. Currently this patient has not elected to have surgery and it being treating conservatively by his chiropractor. If the pain becomes unbearable, due to the proximity of the lesion to sensitive surrounding structures, then surgery will be considered.


Regarding the given differential diagnosis of metastatic disease with associated periosteal reaction, first of all, in this age, metastatic disease is very rare. Second, metastatic disease is not associated with periosteal reactions. Osteosarcoma would be another consideration due to the age range of the patient as well as the apparent erosion. Periosteal reactions are also associated with osteosarcoma, but the bony exostosis does not really have the qualities of a periosteal reaction. Osteomas may produce bony "bumps" on bones, but are virtually exclusive to the skull, most commonly affecting the sinuses. A single osteoma in the proximal femur should not be seriously considered.

The osteochondroma is a primary benign bone tumor with both osseous and cartilaginous components. It forms an excrescence of bone with a hyaline cartilaginous "cap" that extends off the parent bone. This lesion begins due to an abnormality at the growth plate of immature long bones. This fact answers the questions of the age of onset (under 20 years) and location in the bone (metaphyseal) of the osteochondroma. Because it is cells of the growth plate that produce the osteochondroma, when the patient reaches skeletal maturity, the lesion should also stop growing. There are essentially two "types" of osteochondromas based on its morphology, and both are most common in the lower extremity. The types are "sessile" and "pedunculated". Sessile osteochondromas have a broad base and appear as a bump or a hill on the parent bone. Pedunculated osteochondromas have a narrower base than body and appear as a cauliflower or broccoli off the parent bone, but does not have the nutritional value.

Typically these lesions are not painful and are incidental findings, but in some cases, such as this one, irritation to surrounding structures may give rise to symptoms. Although not seen in this case, an adventitious bursa arises not uncommonly. Other complications of osteochondromas are fractures, irritation to surrounding nerves and vessels, and rarely malignant degeneration. This malignant change is rare (about 1%), but an obvious serious possible consequence. Both clinical and radiographic clues will help in this regard. Clinically, ask about change in the quality of pain, and especially a deep, boring type of pain that is not related to movement. Regarding imaging, look for destruction of the cortex and associated soft tissue mass. On MRI, an increase or more importantly persistence of the cartilaginous cap after skeletal maturity is a sign of possible malignancy. A related disorder of multiple osteochondromas is well known and is termed heredity multiple exostoses, HME. Its classic radiographic presentation is bilateral widened femoral necks along with other multiple osteochondromas. It is important to know that this condition has a higher rate of malignancy (up to 20%) and is familial. Therefore close observation as well as examination of family members is recommended. So what about that lucency adjacent to the osteochondroma? This ended up being a pressure type erosion from the cartilaginous cap of the osteochondroma.


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