Age / Sex : 17 / M

Intramedullary osteoid osteoma

Discussion

Findings:

1) Plain radiograph

- Anteroposterior
radiograph demonstrates cortical thickening and medullary sclerosis in the distal
metaphysis and diaphysis of the right femur.

2) CT

- Axial CT image
demonstrates an intramedullary lytic lesion with medullary and cortical sclerosis
of the femur.

3) MR

- Coronal T1-weighted
pre-contrast and fat-saturated post-contrast MR images show a tumor nidus
associated with extensive bone marrow, and extra-osseous edema involving the distal
metaphysis, diaphysis and epiphysis of the right femur.

Differential Diagnosis:

Intramedullary osteoid osteoma

Diagnosis: Intramedullary osteoid osteoma

Discussion:

Osteoid osteoma is a common benign bone lesion in the pediatric
and young adult populations. Males are more commonly affected at a 1.6-4 ratio.
Long bones are the most common location for these lesions with the majority
occurring in the lower extremity. Presenting symptoms in children are often
pain, which is worse at night and relieved with salicylates, and a noticeable
limp.

The
location of these lesions within the bone may vary. The classic and most common
location is within the cortex. The frequency of cortical and subperiosteal
osteoid osteomas peaks in the second decade, but the frequency of the
intramedullary forms peaks in the first decade. The unusual intramedullary
localization may also present a diagnostic challenge because the typical radiographic
lesion located within the cortex of a long bone, with a central lucent zone
(i.e., nidus), and sclerosis of the surrounding bone tissue may be absent.

CT
scans generally show a small, hypodense nidus surrounded by reactive sclerosis,
when localized in the cortical or subperiosteal bone. MR imaging can barely detect
the nidus, and the intramedullary soft tissue changes may produce a
misleadingly aggressive appearance. Typically, an intermediate signal is seen
on T1-weighted images, and a high-intensity signal is seen on T2-weighted images.
A low-intensity signal within the nidus on T2 images suggests calcification.

References:

1. Halanski MA,
Mann DC. Case report: unusual tibia intramedullary osteoid osteoma in a
two-year-old. Iowa Orthop J 2007;25:66–8.

2.
Falappa P, Garganese MC, Crocoli A, Toniolo RM, Lembo A, Marconi F, et al.
Particular imaging features and customized thermal ablation treatment for
intramedullary osteoid osteoma in pediatric patients. Skeletal Radiol
2011;40:1523-30