Presentation
Referred for CT of the knee due to persistent pain despite an unremarkable plain x-ray.
Patient Data
- rounded ill-defined lytic lesion within the medial femoral condyle
- small knee joint effusion
- Baker cyst
- no acute fracture
- increased blood pool and osteoblastic activity demonstrated in the lytic medial femoral condyle lesion
- foci of increased tracer uptake in the anterior left 2nd-4th ribs indicative of increased osteoblastic activity (given the alignment of these foci of uptake, they were thought to be more likely due to fracture rather than metastases)
The lesion in the medial femoral condyle is:
- T1 hypointense, T2 mildly hyperintense
- expansile; breaching the anterior and lateral cortex
- heterogeneously gadolinium enhancing
Small knee joint effusion.
The lesion was also noted to have grown in size since the CT (performed one month prior).
- poorly defined spiculated mass lesion located medially within the right upper lobe of lung, suspicious for primary lung carcinoma
- smaller peripheral nodule in the peripheral right upper lobe
- mediastinal lymphadenopathy
- upper lobe predominant centrilobular and paraseptal emphysema
- cortical lesions within the left anterior upper ribs correlating to the bone scan findings
CT imaging of the abdomen and pelvis was unremarkable.
Case Discussion
Given the knee pain, the patient in this case underwent resection of the distal femoral lesion and total knee replacement. Histopathological examination confirmed that the lesion in the medial femoral condyle was a metastasis from lung squamous cell carcinoma.
This case demonstrates an uncommon presentation of metastasis to the distal femur from primary lung carcinoma. A distal bone metastasis is more likely to be from a lung primary tumor, since a lung tumor can directly enter the pulmonary venous system, flowing through into the systemic arterial circulation.
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