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

Discussion

Answer: chondroblastoma with aneurysmal bone cyst change.

Findings:

 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

Discussion:

• 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.

References:

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.