Weekly Case

Title : Case 624

Age / Sex : 17 / F

Chief complaint : Incidentally noted osteolytic lesion in right distal femur

What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : Joon-Yong, Jung, Seoul St. Mary’s Hospital, The Catholic University of Korea


Answer: chondroblastoma with aneurysmal bone cyst change.



 About  2.3cm sized well-circumscribed mass at epiphysis of right medial femoral condyle.
 - Mild reactive BM edema

- No definite periosteal reaction.
 - Internal fluid-fluid level.
 - Probable, solid component appeared as low SI on T2 weighted image at the non-dependent portion of the mass


Differential Diagnosis:

 Giant cell tumor with aneurysmal bone cyst change.

 Primary aneurysmal bone cyst



  • Epidemiology : young patients (< 20 years old), male predilection

  • Clinical presentation : non-specific and may include joint pain, muscle wasting, tenderness, and swelling/local mass

  • Location : long bone (>75%), epiphyseal origin

  • Radiographic finding : geographic lytic lesion with sclerotic margin in majority (90%), chondroid matrix (30~50%)

  • MR finding

  • Inhomogenously high SI mass on fluid-sensitive sequence and low SI on T1WI

  • No distinct soft tissue mass

  • No cortical breakthrough

  • Smooth, thick periosteal reaction if present

  • High signal on fluid-sensitive sequences in adjacent cortex, marrow, and soft tissue in majority of cases

  • Secondary aneurysmal bone cyst can be seen


  • In the majority of cases, distinguishing the primary ABC from the secondary ABC was possible based on characteristic features, including age of the patient at diagnosis and the tumor location.




  1. Radiology 1994; 190:467-474. Chondroblastoma: Classic and Confusing Appearance at MR Imaging.

  2. ONCOLOGY LETTERS 13: 2290-2296, 2017. Diagnosing and discriminating between primary and secondary aneurysmal bone cysts.


Correct Answer
Total applicants 29 Correct answers 8
Name Institution
김지은 서울대학교병원, 전문의
김기욱 국군대전병원, 전문의
윤유성 순천향대 부천병원, 전문의
이진영 전문의
이승은 전문의
김창현 365병원, 전문의
한유비 병무청, 전문의
김보람 전문의
Semi-Correct Answer
Total applicants 29 Semi-Correct answers 4
조은경 새움병원, 전문의
손상욱 군의관, 전문의
이준영 전공의
최형인 국군수도병원, 전문의