The healing pattern of osteoid osteomas on computed tomography and magnetic resonance imaging after thermocoagulation.
OBJECTIVE
To compare the healing pattern of osteoid osteomas on computed tomography (CT) and magnetic resonance imaging (MRI) after successful and unsuccessful thermocoagulation.


METHODS
Eighty-six patients were examined by CT and 18 patients by dynamic gadolinium-enhanced MRI before and after thermocoagulation for osteoid osteoma. Thermocoagulation was successful in 73% (63/86) and unsuccessful in 27% (23/86) of patients followed by CT. Thermocoagulation was successful in 72% (13/18) of patients followed by MRI. After treatment, the healing of the nidus on CT was evaluated using different healing patterns (complete ossification, minimal nidus rest, decreased size, unchanged size or thermonecrosis). On MRI the presence of reactive changes (joint effusion, "oedema-like" changes of bone marrow and soft tissue oedema) and the delay time (between arterial and nidus enhancement) were assessed and compared before and after thermocoagulation.


RESULTS
Complete ossification or a minimal nidus rest was observed on CT in 58% (16/28) of treatment successes (with > 12 months follow-up), but not in treatment failures. "Oedema-like" changes of bone marrow and/or soft tissue oedema were seen on MR in all patients before thermocoagulation and in all treatment failures. However, residual "oedema-like" changes of bone marrow were also found in 69% (9/13) of treatment successes. An increased delay time was observed in 62% (8/13) of treatment successes and in 1/5 of treatment failures.


CONCLUSIONS
Complete, or almost complete, ossification of the treated nidus on CT correlated with successful treatment. Absence of this ossification pattern, however, did not correlate with treatment failure. CT could not be used to identify the activity of the nidus following treatment. The value of MR parameters to assess residual activity of the nidus was limited in this study.
Vanderschueren
Geert M
GM
Department of Diagnostic Radiology, University Hospital of Ghent, De Pintelaan 185, Ghent 9000, Belgium. geert.vanderschueren@pandora.be
Taminiau
Antoni H M
AH
Obermann
Wim R
WR
van den Berg-Huysmans
Annette A
AA
Bloem
Johan L
JL
van Erkel
Arian R
AR
D001859:Bone Neoplasms / Q000473:pathology / Q000628:therapy*; D004564:Electrocoagulation; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging; D010017:Osteoma, Osteoid / Q000473:pathology / Q000628:therapy*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D014945:Wound Healing