Contrast-enhanced MRI predicts local recurrence of osteoid osteoma after radiofrequency ablation

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1 bs_bs_banner Journal of Medical Imaging and Radiation Oncology 56 (2012) RADIOLOGY ORIGINAL ARTICLE Contrast-enhanced MRI predicts local recurrence of osteoid osteoma after radiofrequency ablation Andreas H Mahnken, 1,2 Philipp Bruners, 1,2 Heide Delbrück, 3 Rolf W Günther 1 and Cedric Plumhans 1 1 Department of Diagnostic and Interventional Radiology, 2 Applied Medical Engineering, Helmholtz Institute, and 3 Department of Orthopedic Surgery, RWTH Aachen, Aachen, Germany AH Mahnken MD MBA MME; P Bruners MD; H Delbrück MD; RW Günther MD; C Plumhans MD. Correspondence Professor Andreas H Mahnken, Department of Diagnostic and Interventional Radiology, University Hospital, RWTH Aachen University, Pauwelsstrasse 30, D Aachen, Germany. andreas.mahnken@rwth-aachen.de Conflict of interest: There is no conflict of interest to report. Submitted 25 March 2012; accepted 3 May /j x Abstract Introduction: Osteoid osteoma is a painful benign tumour, which is commonly treated by radiofrequency ablation (RFA). The goal of this study is to assess the value of contrast-enhanced magnetic resonance imaging (MRI) for predicting clinical success after RFA of osteoid osteoma. Methods: Twenty consecutive patients (14 male, 6 female; mean age years) suffering from osteoid osteoma underwent unenhanced and contrast-enhanced T1-weighted MRI the day after RFA. Post-interventional contrast enhancement of the nidus was analyzed by comparing signal-to-noise ratios (SNR) of the nidus before and after contrast administration. The SNR between pre- and post-contrast scans was computed. Results: There were no significant differences in SNR between pre- and post-contrast scans in the area of ablation (P = ), while the SNR exceeded one in four patients, indicating residual contrast enhancement. In three of these patients clinical symptoms recurred, requiring re-ablation, while one patient remained free from symptoms during follow-up. In patients with a pre- and post-contrast SNR of 1.18 no local recurrence was observed. Conclusions: Contrast enhancement on T1-weighted MRI imaging seems to be predictive of clinically unsuccessful RFA in osteoid osteoma. Patients with a SNR increase of 20% after contrast administration might be considered for re-ablation to avoid symptomatic tumour recurrence. Key words: intervention; magnetic resonance imaging; musculoskeletal imaging; non-vascular interventional radiology. Introduction Osteoid osteomas are painful bone lesions representing approximately 12% of all benign bone tumours. 1 First described in 1935 by Jaffé, 2 osteoid osteomas affect men twice as often as women with a predilection of 5 to 25 years. It is most commonly seen in long bones such as femur and tibia, but may occur in all parts of the skeleton. 1 Osteoid osteomas respond well to nonsteroidal anti-inflammatory drugs (NSAIDs) especially salicylates. 3 Despite its benign character and the availability of effective drugs, osteoid osteomas typically require invasive treatment due to persistent pain or intolerance to long-term NSAID consumption. For decades orthopaedic surgery has been the method of choice for treating osteoid osteoma. Introduced in 1992, 4 radiofrequency ablation (RFA) emerged as an alternative to resection. 5 7 Determination of treatment success relies on clinical assessment and resolution of clinical symptoms. Unlike in resection where pathology defines complete or incomplete resection, there is no early confirmation of clinically successful minimally invasive treatment using imaging. Therefore, we sought a simple imaging test to achieve this goal. While there are reports on the appearance of osteoid osteoma after RFA, 8,9 thereisnodataonthe predictive value of magnetic resonance imaging (MRI) regarding the success of treatment. While the nidus of untreated osteoid osteomas is known to show a distinct contrast enhancement on T1-weighted MRI, 10,11 there is Journal of Medical Imaging and Radiation Oncology 2012 The Royal Australian and New Zealand College of Radiologists 617

2 AH Mahnken et al. a lack of contrast enhancement in the nidus after ablation, while a peripheral zone should show a rim-like hyperenhancement. 9 From these data we hypothesized that a lack of contrast enhancement of the entire nidus on T1-weighted MR images should correspond to complete ablation. The goal of this study was to quantitatively assess if the lack of contrast enhancement on T1-weighted MR images early after the procedure is predictive of clinically successful ablation in osteoid osteoma. Materials and methods Twenty consecutive patients (14 male; 6 female, mean age years) with osteoid osteoma were included in this study. The study was approved by the local institutional review board and written informed consent was obtained from all patients or their legal guardians. Diagnosis of osteoid osteoma was based on typical symptoms with nocturnal pain, decline of pain after oral administration of 500 mg acetylic salicylic acid and presence of a typical lesion indicative of osteoid osteoma on conventional radiography and computed tomography (CT). Lesions were located in the femur (n = 12), the tibia (n = 3), the fibula (n = 2), the humerus (n = 1), the os ilium (n = 1) and the cervical spine (n = 1). Mean nidus diameter was 6 2 (4 12) mm. Percutaneous, CT-guided RFA was performed under general anaesthesia. Immediately before the procedure was started a single dose of 15 mg/kg body weight clindamycin (Sobelin; Pfizer, Karlsruhe, Germany) was administered intravenously. First a unenhanced spiral CT scan was performed to localize the nidus and to determine the most appropriate access route. For CT guidance either a 4-slice CT scanner (VolumeZoom; Siemens, Forchheim, Germany) or a 64-slice dual source CT scanner (Definition; Siemens, Forchheim, Germany) were used. After a small skin incision was made an 11-gauge drill (OsteoSite; Cook, Bloomington, IN, USA) was introduced through a 9-F introducer sheath (Pinnacle Introducer; Terumo, Tokyo, Japan) and manually advanced into the nidus. After removing the drill an 18-gauge bipolar RF probe with an active tip of 9 mm (CelonProSurge micro; Celon, Teltow, Germany) was placed in the lesion through the sheath. Application of energy was started at 2 W and subsequently increased by 1 W every 3 min to a maximum of 5 W. If a resistance of 900 ohm was reached the probe was rotated by approximately 30 and the procedure was repeated. After removal of the probe 2 ml of bupivacaine (Bupivacaine RPR 0.25%; DeltaSelect, Dreieich, Germany) was injected into the lesion to alleviate post-procedural pain. Thereafter the sheath was removed, and an adhesive tape was applied. All patients underwent MRI the day after the procedure (Fig. 1). MRI was performed with a 1.5T scanner (Gyroscan Intera; Philips Medical Systems, Best, the Netherlands). A T1-weighted spin echo sequence before and immediately after i.v. administration of 0.2 ml/kg bodyweight gadopentate dimeglumine (Magnevist; Bayer- Schering, Berlin, Germany) was applied. Depending on the lesion location an axial or coronal slice orientation was chosen. Additional subtraction images were computed from pre- and post-contrast images. Sequence parameters were as follows: slice thickness 3 mm without interslice gap, field-of-view mm, TR ms, TE ms, matrix Images were independently read by two radiologists and differences were resolved by consensus. The size of tumour a b c Fig. 1. Post-interventional MRI in a 14-year-old boy. The T1-weighted MR images before (a) and after contrast administration (b) show a lack of contrast enhancement in the nidus indicating complete ablation (signal-to-noise ratio = 0.78). There is a typical rim-like contrast enhancement around the area of ablation, which is particularly well seen on subtraction images (c; arrows). 618 Journal of Medical Imaging and Radiation Oncology 2012 The Royal Australian and New Zealand College of Radiologists

3 MRI after RFA of osteoid osteoma nidus was noted and images were assessed for residual contrast enhancement in the nidus. For quantitative analysis a region of interest was placed in the nidus and in the air to evaluate the signal of noise before and after contrast administration. The signal-to-noise ratios (SNR) of the nidus before and after intravenous contrast medium application were calculated. Thereafter SNRpost contrast the SNR ratio =, which describes the SNRpre contrast percentage signal change between pre- and postcontrast MR images was computed. 12 A SNR 1.0 indicated a lack of contrast enhancement, while SNR >1.0 signified residual contrast enhancement. All patients underwent a clinical examination the day after the procedure prior to discharge from hospital. Four to 6 weeks after the procedure all patients were seen in the outpatient clinic of the department of orthopaedic surgery. At the end of the follow-up period structured telephone interviews were conducted by a physician to determine long-term outcome. Patients were asked about their general condition, appearance of the puncture site, current medications and any subsequent procedures. The outcome was defined as clinically successful, if the patient was free of pain without taking medication and if no subsequent procedures were performed during the follow-up period. Quantitative data are given as mean standard deviation. Pre- and post-contrast SNR was compared using paired two-sided t-tests. Receiver operating characteristic (ROC) analysis was performed to identify a cut-off value of the SNR for predicting local recurrence. A P-value < 0.05 was considered statistically significant. All statistics were computed with MedCalc Version (MedCalc Software, Mariakerke, Belgium). Results All procedures were completed and considered technically successful. Mean duration of energy deposition was min and a mean of kj was applied. No complications occurred, and all patients were discharged from hospital the day after the procedure. Mean follow-up was (48 83) months. On visual assessment of the MR images residual contrast enhancement in the area of the nidus was identified in two patients (Fig. 2). Both were free from pain at the outpatient visit 4 6 weeks after the procedure, but developed recurrent symptoms at 4 and 22 months. Both were scheduled for re-intervention, which were performed 4 and 24 months after the initial procedure. Thereafter both patients remained free from symptoms during a follow-up period of 56 and 62 months. In all other patients no residual contrast enhancement was detected on visual assessment of MR images. Quantitative evaluation did not show significant differences in SNR between pre- and post-contrast scans (P = ). In four patients, however, SNR >1 ( ) were found, indicating residual contrast enhancement after ablation. The highest SNR corresponded to the visually seen areas of residual contrast enhancement, while in two more patients residual contrast enhancement was only identified by means of elevated SNR. SNR were markedly higher in case of visible contrast enhancement with 2.42 and 3.11, when compared with the two patients where residual contrast enhancement was only detected by elevated SNR of 1.18 and One of these patients developed recurrent symptoms 34 months after the initial procedure and underwent re-ablation. Thereafter she stayed free from symptoms during the entire followup period of 55 months. ROC analysis identified a a b c Fig. 2. Post-interventional MRI in an 8-year-old girl. The T1-weighted MR images before (a) and after contrast administration (b) as well as the corresponding subtraction image (c) clearly depict a localized area of residual contrast enhancement inside the nidus (arrow), directly on the margin of the hypointense ablation zone. This finding is indicative of incomplete ablation (signal-to-noise ratio = 3.11). Four months after the initial procedure she underwent re-ablation for recurrent symptoms. Journal of Medical Imaging and Radiation Oncology 2012 The Royal Australian and New Zealand College of Radiologists 619

4 AH Mahnken et al. SNR threshold of 1.18 for predicting recurrent osteoid osteoma. Discussion Percutaneous RFA using different devices has emerged as an accepted first-line procedure for treating osteoid osteoma. 5 7 With an initial failure rate of about 13%, but a secondary success rate of 95% percutaneous RFA is an effective treatment in osteoid osteoma, 13 but there is a strong demand for the early prediction of incomplete ablation and early recurrence of symptoms. Although the typical post-interventional MRI features have been described previously, 8,9 there is no data on the predictive value of post-interventional imaging. While previous studies focused on the imaging appearance and their changes over time, the goal of this study was to establish a simple approach for the early prediction of clinical success of treatment. Because the nidus of osteoid osteomas is hypervascularized T1-weighted contrastenhanced images during arterial phase were reported to provide the best sensitivity for diagnosing vital osteoid osteoma. 10 In order to minimize susceptibility artefacts after using metallic bone drills and ablation a robust T1-weighted spin echo sequence was used. The approach proved feasible and robust in clinical routine practice. The findings indicate that a non-vital nidus can be presumed if there is no contrast enhancement in the nidus with a SNR 1. An increase in signal intensity of about 20% after administration of contrast material appears to go along with clinical success while further signal increase appears to be related to symptomatic incomplete ablation or recurrent tumour. Therefore, early post-interventional contrast enhancement seems to be predictive for the need of further treatment. Interestingly the lesion which stayed clinically silent for almost 3 years presented only with slight residual contrast enhancement, while the lesion with early recurrence of symptoms presented the most distinct contrast enhancement of the nidus with an SNR of Although the number of observations with residual tumour is very low, one may assume that the asymptomatic interval in patients with recurrent osteoid osteoma is related to the extent of residual contrast enhancement in the lesions nidus. Moreover, lesions with residual contrast enhancement and an SNR of 1.2 might be considered for early re-ablation to prevent symptomatic tumour recurrence. Although lesion conspicuity is known to be best during arterial phase, there is a distinct contrast enhancement of the nidus for much longer than 150s. 10 Thus, images may either be acquired by scanning directly after contrast injection or by using dynamic perfusion scans. For the sake of simplicity in clinical routine practice we preferred the first approach. However, even under these simple conditions a smooth workflow between manual contrast media administration and beginning of data acquisition is mandatory. Otherwise the washout period of the nidus will be measured limiting the diagnostic value. Nevertheless, the simple approach proved robust and predictive. The results also indicate the need for a quantitative assessment as only mild changes in signal intensity might be missed by visual assessment. This could be overcome by using additional subtraction images. The latter, however, may be misinterpreted due to motion artefacts. 14 Therefore, a quantitative analysis was preferred. There are some limitations to this study. Firstly, only a very basic imaging protocol utilizing only T1-weighted images was used and there were no images with fat saturation as they are commonly used for assessing osteoid osteoma However, this proved predictive and appears to be suitable for clinical decision making. Moreover, it was very time effective with an average total scan duration of less than 7 min for pre- and post-contrast scans. Secondly, there were only few patients with local recurrences. With a primary clinical success rates in the range of 67% to 100% large numbers of patients need to be examined, 13 warranting further studies on the predictive value of post-interventional MRI after local ablation of osteoid osteoma. Finally, this study focused on the predictive value of early post-interventional MRI, and there is no information on the predictive value of MRI during mid- or long-term follow-up. Conclusion In conclusion, the SNR as determined in the nidus of the lesions from unenhanced and contrast-enhanced T1-weighted MRI early after RFA of osteoid osteoma appears to be predictive of symptomatic local tumour recurrence. In case of more than 20% increase in SNR after intravenous contrast administration, local tumour recurrence should be anticipated and early re-ablation might be considered to avoid symptomatic lesion recurrence. References 1. Greenspan A. Benign bone-forming lesions: osteoma, osteoid osteoma and osteoblastoma. Clinical, imaging, pathologic and differential considerations. Skeletal Radiol 1993; 22: Jaffé HL. Osteoid osteoma: a benign osteoblastic tumor composed of osteoid and atypical bone. Arch Surg 1935; 31: Kreisl JS, Simon MA. Medical management compared with operative treatment for osteoid-osteoma. J Bone Joint Surg Am 1992; 74: Rosenthal DI, Alexander A, Rosenberg AE, Springfield D. Ablation of osteoid osteomas with percutaneously placed electrode: a new procedure. Radiology 1992; 183: Mahnken HA, Tacke JA, Wildberger JE, Günther RW. Radiofrequency ablation of osteoid osteoma: initial 620 Journal of Medical Imaging and Radiation Oncology 2012 The Royal Australian and New Zealand College of Radiologists

5 MRI after RFA of osteoid osteoma results with bipolar ablation device. J Vasc Interv Radiol 2006; 17: Rimondi E, Bianchi G, Malaguti MC et al. Radiofrequency thermoablation of primary non-spinal osteoid osteoma: optimization of the procedure. Eur Radiol 2005; 15: Vanderschueren GM, Taminiau AHM, Obermann WR, Bloem JL. Osteoid osteoma: clinical results with thermocoagulation. Radiology 2002; 224: Cantwell CP, Kerr J, O Byrne J, Eustace S. MRI features after radiofrequency ablation of osteoid osteoma with cooled probes and impedance-control energy delivery. AJR Am J Roentgenol 2006; 186: Lee MH, Ahn JM, Chung HW et al. Osteoid osteoma treated with percutaneous radiofrequency ablation: MR imaging follow-up. Eur J Radiol 2007; 64: Liu PT, Chivers FS, Roberts CC, Schultz CJ, Beauchamp CP. Imaging of osteoid osteoma with dynamic gadolinium-enhanced MR imaging. Radiology 2003; 227: Zampa V, Bargellini I, Ortori S, Faggioni L, Cioni R, Bartolozzi C. Osteoid osteoma in atypical locations: the added value of dynamic gadolinium-enhanced MR imaging. Eur J Radiol 2009; 71: Grimm J, Mueller-Huelsbeck S, Mueller M, Egbers HJ, Brinkmann G, Heller M. Evaluation of hydroxyapatite implants in vertebral bodies and extremities by contrast-enhanced magnetic resonance imaging. Arch Orthop Trauma Surg 2001; 121: Bruners P, Penzkofer T, Günther RW, Mahnken A. Percutaneous radiofrequency ablation of osteoid osteomas: technique and results. Rofo 2009; 181: [German]. 14. Lee VS, Flyer MA, Weinreb JC, Krinsky GA, Rofsky NM. Image subtraction in gadolinium-enhanced MR imaging. AJR Am J Roentgenol 1996; 167: Journal of Medical Imaging and Radiation Oncology 2012 The Royal Australian and New Zealand College of Radiologists 621