Distal Femur Intramedullary Lesion

Multiple Choice: During Dr. Liz Buchanan’s bone tumors portion of our Mystery to Mastery Longitudinal Course, a 54YO with knee pain underwent AP and lateral radiograph evaluations—revealing a lucent intramedullary lesion in the distal femur, filled with ring- and arc-shaped internal mineralization.

  • T1: Well-demarcated hypointense lesion with small foci isointense to fat.
  • STIR: Predominantly hyperintense with low-signal intralesional foci matching the mineralized cartilage matrix.
  • Post-Contrast: Shows diffuse septal enhancement sans perilesional edema or enhancement.

Final Answer? Enchondroma. Chondroid calcifications occur in ~95% of long bone enchondromas (though enchondromas of the hands and feet may lack calcification).

  • While endosteal scalloping can occur in benign enchondromas, full cortical breakthrough or soft-tissue extension strongly indicates malignant transformation to chondrosarcoma.

Final Test: 10 minutes following IV gadolinium administration, the patient developed coughing, dyspnea, mild desaturation, and expiratory wheezing without facial/tongue swelling or hoarseness.

  • Diagnosis: Acute bronchospasm contrast reaction.
  • Treatment: Administer supplemental oxygen and an albuterol inhaler.
  • Protocol: Reserve epinephrine for laryngeal edema (evidenced by tongue/facial swelling or hoarseness) or for bronchospasm that is severe or non-responsive to albuterol.

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