Age / Sex : 20 / F

Chief complaint :

Discussion

Answer:  Osteoblastoma

Findings:

CT

• Osteolytic mass with mineralized matrix and cortical destruction in sacrum


• Wide sclerotic margin

MRI

• Heterogeneous T2 high and T1 low SI with good enhancement


• Peritumoral edema in adjacent bone and soft tissue

Differential Diagnosis:

Osteosarcoma

Ewing’s sarcoma

Chondrosarcoma

Langerhans cell histiocytosis

Discussion:

Osteoblastoma

• 1–2% of all primary bone tumors


• 40% in the spine; 17% of spinal osteoblastomas in the sacrum

Radiography & CT

• Typically, lytic defect larger than 1.5 cm surrounded by a sclerotic rim


• Calcifications, when present, are usually multiple


• May show aggressive feature (e.g. cortical destruction and extension into soft tissue)

MRI

• Nonspecific signal intensity patterns


• May have peritumoral edema in marrow and soft tissue (flare phenomenon)

References:

Llauger J, Palmer J, Amores S, Bagué S, Camins A. Primary tumors of the sacrum: diagnostic imaging. AJR Am J Roentgenol. 2000;174(2):417-24.