A previously healthy 17-year-old girl presented at the emergency department with acute pain in the left popliteal fossa with 4 hours of evolution, which woke her from sleep. She also mentioned paresthesias in the painful area. Fever, recent injuries, strenuous exercise, consumption of any medication or tobacco use were denied.
On presentation, she was hemodynamically stable and afebrile, walking with a limp. Palpation of the left popliteal fossa revealed tenderness and movement maneuvers showed pain with knee extension and flexion; the remaining physical examination did not reveal any significant abnormality, namely, any cutaneous findings.
A complementary study showed normal blood count, normal renal and liver function, negative C-reactive protein, normal lactate dehydrogenase and normal erythrocyte sedimentation rate (9 mm/h). The coagulation profile and D-dimer test were within the reference range.
A vascular surgeon performed a doppler ultra-sound and ruled out vascular pathology. She was observed by an orthopedist, who prescribed a left leg X-ray. This exam revealed a radiotransparent multiloculated bone lesion with a sclerotic rim located in the distal femur, without associated periosteal reaction, cortical breach or associated soft tissue mass (Figures 1 and 2).
This lesion was diagnosed as a small non-ossifying fibroma, which was considered an imaging finding, not related to the patient’s complaints. Since the physical examination was normal and the complementary study did not reveal abnormal findings, the patient was discharged with symptomatic treatment. To follow the evolution of the non-ossifying fibroma, she was referred to an orthopedic consultation.
Figure 1. Conventional X-ray, anterior view of the left leg.
Figure 2. Lateral view of the left leg.
What is the diagnosis?