MyPACS.net: Radiology Teaching Files > Case 7581402

previously visited BENIGN BONE "TUMOR" IN DISTAL FEMUR
Contributed by: Fritsch & Thompson, Radiologist, Diagnostic Radiology of Houston, Texas, USA.
Patient: 34 year old male
History: 34 year old male with non-traumatic knee pain.
Images:[small]larger

Fig. 1: Sagittal MRI, PD Fat Saturation protocol. Very obvious hyperintense lesion on posterior aspect of distal femur. Note how it is slightly expanding the cortex.

Fig. 2: Lateral knee: I don't see anything...do you???

Fig. 3: Sagittal MRI, T1 protocol. Very obvious hypointense lesion on posterior aspect of distal femur. Note how it is slightly expanding the cortex.

Fig. 4: Coronal MRI, proton density sequence. Do you see the lesion?

Fig. 5: AP Knee: there is a lucency in the distal femur but no correlation on Lateral knee view.

Fig. 6: PD Fat Sat axial images through the lesion.
Findings:

FINDINGS:†††††††††††††††††† MRI examination reveals a well-defined, low-signal T1, high-signal T2 lobulated lesion in the posterior aspect of the distal femoral metaphysis.This lesion shows fluid level on the T2 images with isointense fluid dependent posterior margin.This may represent a resolving simple bone cyst or aneurysmal bone cyst given the patientís age.However, other considerations would be an enchondroma or other cartilaginous-based lesions.The margins of the lesion are well defined.There is mild dorsal expansion of the posterior cortical margin without any disruption, periosteal reaction, or soft tissue mass.The neurovascular bundle which is positioned immediately posterior to the lesion is not related or involved.No other bone abnormalities are identified in the related osseous elements of the knee.

No internal derangement within the knee is identified.There are no meniscal tears.There are no ligament tears.The articular cartilage is well maintained.There is a small effusion with a tiny Bakerís cyst.

CONCLUSIONS:†††††††††††††††††

1.†††††† 1 CM X 2 CM LOBULATED LESION IN THE POSTERIOR ASPECT OF THE DISTAL FEMORAL METAPHYSIS AS OUTLINED ABOVE.THE DIFFERENTIAL DIAGNOSIS AT THIS TIME WOULD BE A CYSTIC ABNORMALITY SUCH AS AN ANEURYSMAL BONE CYST OR A SIMPLE BONE CYST THAT IS RESOLVING.CONSIDERATION SHOULD BE GIVEN ALSO TO CARTILAGE-BASED BENIGN NEOPLASM SUCH AS AN ENCHONDROMA.CLOSE CLINICAL AND RADIOLOGICAL FOLLOW UP ADVISED.NO AGGRESSIVE CHARACTERISTICS AT THIS TIME.

2.†††††† SMALL EFFUSION OF THE KNEE WITH A TINY BAKERíS CYST.

3.†††††† NO MENISCAL TEARS, LIGAMENTOUS DISRUPTION, OR ARTICULAR LESIONS.


Diagnosis: No final bone tumor or tumor-like diagnosis know at this time.

We will update this file if a final biopsy is performed.†

For now we are just watching it. :)
Discussion: This is a nice example of a bone lesion that is clearly seen on MRI but is very difficult to identify on radiographs.  Remember it takes 30% bone destruction before a bone lesion can be visualized.  If the lesion does not involve the cortex, this percentage can be as high as 50%.  In vertebral bodies the estimates have been as high as 75%.

Moral of the story...non-resolving joint pain with negative or equivical radiographs needs to be investigated with MRI.
References: Referring physician:† †Ken Tomlin, DC
Comments:
No comments posted.
Additional Details:

Case Number: 7581402Last Updated: 02-28-2007
Anatomy: Skeletal System   Pathology: Neoplasm
Modality: Conventional Radiograph, MRAccess Level: Readable by all users
Keywords: benigh neoplasm; bone abscess

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