Microwave ablation was used to treat epiphyseal osteoid osteomas in 7 patients. All patients experienced complete pain relief within 1 week of the procedure and had no complications, except for 1 patient who experienced back pain for 2 months. MRI scans after treatment showed ablation areas averaging 21 x 12 x 14 mm. The study demonstrated that microwave ablation can safely and effectively treat epiphyseal osteoid osteomas with a single needle insertion and without complications. However, more research with larger patient groups is still needed to validate these promising initial results.

1. CLINICAL INVESTIGATION
The Use of Microwaves Ablation in the Treatment of Epiphyseal
Osteoid Osteomas
Antonio Basile • Giovanni Failla • Angelo Reforgiato • Giovanni Scavone •
Elena Mundo • Martina Messina • Giuseppe Caltabiano • Francesco Arena •
Viola Ricceri • Antonio Scavone • Salvatore Masala
Received: 2 July 2013 / Accepted: 22 July 2013
Ó Springer Science+Business Media New York and the Cardiovascular and Interventional Radiological Society of Europe (CIRSE) 2013
Abstract
Objective This study was designed to demonstrate the
feasibility and the reliability of microwave ablation
(MWA) of epiphyseal osteoid osteomas (OO).
Materials and Methods From February to November
2012, 7 patients (4 males and 3 females; age range
16–30 years) with epiphyseal OOs were treated with
MWA. The treatment was performed with 16 G antennas
with a power of 20 W for 2 min. The OOs were approa-
ched by using coaxial needles inserted with hammer or
with automatic drill. All patients underwent spinal anaes-
thesia, with posttreatment 6–8 h observation before dis-
charging. We treated epiphyseal OOs placed away from
nervous and vascular nontarget structures, located in:
femoral head (n = 2), femoral lesser trochanter (n = 2),
femoral neck (n = 2), and proximal tibial epiphysis
(n = 1). CT was used to visualize the nidus and to insert
the needle for thermal ablation and for postprocedure
control. Technical success was considered the positioning
of the antenna in the nidus, while the efficacy of treatment
was clinically evaluated as the complete remission of pain
after the procedure by using the visual analogue score
(VAS). Follow-up was performed by using VAS score
1 day, 1 week, and 1, 3, and 6 months after the procedure,
whereas MRI examination was performed immediately
after the procedure, at 1 month, and in any case of recur-
rence. Complications were also recorded.
Results All patients experienced resolution of the symp-
tomatology (VAS = 0) in *1 week until the last follow-
up, with residual VAS 2 points occurring only from 1 to
7 days after the procedure. No intraprocedural complication
was noted, whereas one patient had back pain for 2 months
after the procedure, likely due to spinal analgesic injection.
Conclusions In our experience, MWA can be safely
performed with excellent results without complications in
selected cases of epiphyseal OOs; however, the clinical
significance of this report is limited because there were
only few patients included in this study. Thus, these data
must be confirmed by further and larger studies.
Keywords Osteoid osteoma Á Radiofrequency
ablation Á Microwaves ablation
Radiofrequency ablation (RFA) is considered the less
invasive technique for the treatment of osteoid osteomas
(OOs), a small benign bone neoplasm, often with a diam-
eter of 1 cm [1, 2]. For decades, surgery represented the
standard therapy for such lesions. The use of RFA was
described for the first time in 1989, and the first results
were published in 1992 [3]. Today, this minimally invasive
procedure is widely available, safe, and effective for neo-
plasms located in the liver, kidney, lung, and also for both
A. Basile Á G. Failla Á A. Reforgiato Á G. Scavone Á E. Mundo Á
M. Messina Á G. Caltabiano Á F. Arena Á V. Ricceri Á
A. Scavone
Department of Diagnostic and Interventional Radiology,
Garibaldi Centro Hospital, Piazza Santa Maria del Gesu`,
95124 Catania, Italy
A. Basile (&)
Via Trieste 14, 95127 Catania, Italy
e-mail: antodoc@yahoo.com
G. Failla
Department of Radiology, Policlinico Vittorio Emanuele, Via
Santa Sofia 22, 95100 Catania, Italy
S. Masala
Department of Diagnostic Imaging and Interventional
Radiology, Molecular Imaging and Radiotheraphy, Policlinico
Universitario Tor Vergata, 00133 Rome, Italy
123
Cardiovasc Intervent Radiol
DOI 10.1007/s00270-013-0722-z

2. primary and secondary bone tumours [4–6]. Also, laser
ablation has been used for OOs in particularly risky loca-
tions, such as spinal [7]. The clinical success of RFA of
OOs rates are in the range of 55–100 % for initial success
[8, 9] and 88.8–100 % if reablation is considered [8]. Its
clinical success has been reported to range from 67 to 96 %
with a recurrence rate from 5 to 10 % [2, 3, 10, 11].
With the same technique and the same coaxial intro-
duction systems, it is possible to insert microwaves
antennas in place of radiofrequency needles. Microwave
ablation (MWA) induces cellular death trough coagulation
necrosis caused by high intratumoral temperature, this is
produced by the agitation of water molecules exposed to
the electromagnetic field; these characteristic can overtake
major limitations of RFA related to incomplete nidus
ablation [4]. The purpose of our case series was to dem-
onstrate the feasibility and the reliability of treatment with
MWA of epiphyseal OOs.
Materials and Methods
From February 2012 to November 2012, 7 patients (4
males and 3 females; age range 16–39 years; age range
from 16 to 30 years, respectively) underwent CT-guided
MWA of epiphyseal OOs. All patients had been referred
for treatment if they had both clinical and radiological
features of OO and if lesions were located in the long bone
epiphysis, thus away from nervous and vascular nontarget
structures. All patients had never been treated. The lesions
were located in: femoral head (n = 2), lesser femoral tro-
chanter (n = 2), femoral neck (n = 2), and proximal tibial
epiphysis (n = 1) (Figs. 1, 2A–D). The lesion diameter
ranged from 4 to 11 mm (Table 1). All patients had
increasing pain during the night with a mean pretreatment
visual analogue score (VAS = 2) during the day (range
0–5) and VAS = 6 (range 4–7) during the night. Six
patients needed pain medication during the night, whereas
only one also during the day.
Patients were informed of alternative treatments,
including the option of medical management. Informed
consent was obtained in all cases. All patients underwent
spinal anaesthesia and deep sedation for pain relief under
the anaesthesiologist guidance. CT (Optima, GE Health-
care, USA) was used to visualize the nidus and to insert the
needle for thermal ablation and for postprocedure control.
Interventional radiologists examined CT images and mul-
tiplanar reconstruction to identify the nidus and to plan
needles trajectory. The guiding CT protocol refers to 4/8
continuous slices of 1-mm thickness with low kV (100) and
mA (50) to reduce the radiation exposure, parallel to the
needle trajectory. For the OOs located in the lesser tro-
chanter, the lesions were approached by drilling from the
lateral portion of the bone to give more support to the
needle and not get out from the cortex.
Fig. 1 Patient 1: magnetic resonance imaging (A), showing a femoral OO (arrow) not well seen at coronal and axial CT scans (B, C arrows),
treated with MW antenna (D)
A. Basile et al.: The use of MWA in the treatment of epiphyseal OO
123

3. The OOs were approached by using coaxial needles
(Bonopty, Radix, Sweden) inserted manually or with
hammer or automatic drill (Oncontrol Power Driver,
Vidacare, Shavano Park, TX, USA). An antenna of 16 G
(HS, Aprilia, Italy) was introduced to ensure that the
antenna active tip of 2 cm was kept inside the bone
Fig. 2 Patient 2: lesser trocanteric OO with thick osteosclerotic rim:
A coronal and B axial CT scans, treated with MWA, 16-gauge
(Amica, HS, Italy) 20 W 9 2 min; D posttreatment CT scan; E MRI
performed after the procedure, STIR axial sequence, coronal T1 turbo
spin echo. F, G Axial T1 turbo spin echo weighted shows post-
ablation signal intensity of the bone tissue. ROI region of interest was
positioned to measure the surface area of the ablation zone (D, E) and
three dimensions were obtained (F, G)
A. Basile et al.: The use of MWA in the treatment of epiphyseal OO
123

4. trajectory. The applicator we used has to be inserted in the
bone for at least 2 cm, which correspond to the antenna
length, to avoid heating tissues outside the bone.
The treatment was performed by connecting the antenna
to the generator (HS, Aprilia, Italy) with a power of 20 W
for 2 min as suggested by manufacturer. After removal of
the needle system, CT scan was performed to evaluate
ablation area and identify possible complications. All
patients underwent spinal anaesthesia, with posttreatment
6–8 h observation before discharge.
Technical success was considered the positioning of the
antenna in the nidus, while the efficacy of treatment was
clinically evaluated as the complete remission of pain after
the procedure by using the (VAS 1 without medication)
obtained by outpatient visit or telephone interview. Follow-
up was performed by using VAS score at 1 day, 1 week,
and 1, 3, and 6 months after the procedure while MRI
examination was performed immediately after the proce-
dure, after 1 month, and in any case of recurrence. MRI
was performed with a 1.5-T imager (Philips, Ingenia 1.5T).
The imaging protocols included: multiplanar T1-weighted,
T2-weighted, and STIR sequences. No contrast medium
was administered, even if contrast enhancement is known
to be a predictor of recurrence.
The imaging parameters used were: repetition time
480–670 ms, echo time 20 ms for T1-weighted sequences;
repetition time 2,400–4,120 ms, echo time 90 ms for T2-
weighted sequences; repetition time 4,104 ms, inversion
time 140 ms, echo time 30 ms for STIR sequences; a
18–22 cm FOV, 4–5 mm section thickness with a 0.4- to
0.5-mm interslice gap, 284–512 9 246–512 matrix and 1-2
NEX. Complications also were recorded.
Results
All patients experienced resolution of the symptomatology
(VAS 1 without medication) until the last follow-up,
with residual VAS 2 points occurring only from 1 to
7 days after the procedure. Follow-up time ranged from 5
to 13 months (Table 1). No intraprocedural complication
was noted, whereas one patient (no. 2) had back pain for
2 months after the procedure, likely due to spinal analgesic
injection.
MR images showed the nidus as hypointense area in T1-
weighted sequences and hyperintense area in long TR
sequences in all of the cases (n = 7); the surrounding bone
marrow was inhomogeneously hyperintense in long TR
sequences in all cases (n = 7) and in three cases the same
signal was detected along the needle pathway; hyperintense
signal of the adjacent soft tissue was detected in three cases in
long TR sequences (Fig. 2E–H); intra-articular effusionof the
hip was revealed in both lesions located in the femoral neck.
We measured approximately the ablation area at
1-month MR follow-up, and we had a mean of 21 9 12 9
14-mm3
ablation area (Table 1).
Discussion
The reduction and elimination of pain caused by OO is the
goal of the treatment. The recurrence rate for RFA has been
reported to be from 5 to 10 % [1, 3, 11]. In a recent article
[12], the authors stated that treatment failure can occur
more frequently in lesions treated with only one needle
position, especially but not exclusively when needle
placement was inaccurate, missing the nidus ablation, or
when lesions were large. The use of only one needle
position is the most important independent parameter that
is associated with an increased risk for treatment failure in
lesions of all sizes. The main problem related to the one
needle insertion is the relative inadequate ablation area;
multiple needle insertions lead to a time-spending proce-
dure with an increasing radiation exposure especially for
young patients, because the operator has to insert the
needle and give energy, thus replaces the needle and gives
Table 1 Summary of patient population
Patient Age
(years)/
gender
Pretreatment VAS
(d = day) (n = night)
Lesion
location
Maximum
diameter
(mm)
Follow-up
(months)
Last
follow-up
VAS
Ablation area
measured at
1 month MR (mm3
)
1 22/m d = 1 n = 6 (needing medication) Femoral neck 4 13 0 21 9 13 9 13
2 30/m d = 2 n = 6 (needing medication) Lesser trocanter 11 10 0 22 9 11 9 13
3 16/f d = 0, n = 7 (needing medication) Femoral head 6 9 0 24 9 12 9 15
4 29/f d = 4, n = 7 (needing medication) Femoral neck 8 8 1 20 9 13 9 14
5 18/m d = 1 n = 6 (needing medication) Proximal tibial epiphysis 4 8 0 21 9 13 9 15
6 16/f d = 5 (needing medication)
n = 7 (needing medication)
Lesser trocanter 10 7 1 19 9 11 9 13
7 18/m d = 1 n = 4 Femoral head 8 5 0 22 9 14 9 16
A. Basile et al.: The use of MWA in the treatment of epiphyseal OO
123

5. again energy. The insufficient ablation area also can be
related to the impossibility to achieve the needed temper-
ature for sufficient time due to problems in current mod-
ulation or to high impedance inside the OO [13].
Many studies have assessed the use of MW for the
ablation of lesions located in liver, lungs, kidneys, or
adrenal gland and in treatment of cystic masses, such as
adrenal metastasis, and in these cases are valid options for
RF ablation [14].
MWA induces cellular death trough coagulation necro-
sis caused by high intratumoral temperature produced by
the agitation of water molecules exposed to the electro-
magnetic field. For the supramentioned reasons, micro-
waves are insensitive to impedance thus provide deeper
penetration and more successful heating resulting in larger
ablation areas [4, 14].
The characteristic of MWA could overtake the limitation
of RFA for OOs, due to the need for multiple needle inser-
tions and to inadequate ablation area also potentially related
to high impedance and low thermal conduction present in
these lesions. MWA is in fact able to produce faster heating,
higher intralesional temperature, and bigger ablation area
even with only one needle insertion, potentially even if not
precisely located in the centre of the nidus [4].
Until now, there is no experience in the literature with
treatment of OOs with microwaves likely because of the
risk of nontarget damage in small lesions. Benign bone
lesions and especially OOs often are *1 cm and require
short ablation zones that many systems are not capable to
generate. Today, with modulating energy and time we are
able to produce smaller ablation areas, thus it is feasible to
use them to treat OOs away from nontarget neurological
structures.
Some authors [14] have established that the use of MW
is more advantageous in tissue with high impedance, such
as bone, because higher impedance reduces energy depo-
sition from current RF generators, which, in turn, leads to a
smaller temperature increase and potentially increased
treatment failure rates.
In our preliminary experience to evaluate the feasibility
of MWA for epiphyseal OOs, we chose lesions located
away from neurological structures. Furthermore, we had to
choose a needle trajectory of at least 2 cm inside bone, as
suggested by manufacturer, warranting that the 2-cm tip of
the antennas was ‘‘insulated by bone tissue.’’ This technical
precaution limits the use of MWA, because many OOs do
not allow for 2-cm bone coverage, for example, those
periosteal or subperiosteal. For these reasons, we enrolled
for this study only epiphyseal OOs. Potentially, with MWA
we do not need to put the antenna in the long axis of the
lesion and we do not need multiple insertions, because we
can achieve an effective ablation of the entire lesion
exploiting its ability to create a larger area of necrosis.
Furthermore, theoretically MW antennas do not need to be
perfectly in the centre of the nidus, such as for RFA, and
this could be helpful in cases of not perfectly viewable
lesions or for lesions with a thick osteosclerosis difficult to
over cross. In our series, we also had an approximate
ablation area very similar in every case (Table 1). Our
study has some major limitations, in particular the small
group of patients.
Whilst this would need to be confirmed by larger and
prospective, randomized trials, our data suggest that MWA
of OOs can be considered a feasible alternative to RFA in
selected cases, potentially overtaking the limitations of the
latter method, in particular that related to the incomplete
nidus ablation secondary to the high intralesional imped-
ance or to the necessity of multiple needle insertion.
In our experience, MWA can be performed with
excellent results without complications in selected cases, in
particular those located in the epiphyses of long bones,
because in that location we are likely away from vascular
or neurological nontarget structures. Furthermore, we have
several possible bone accesses trajectories, ensuring that
the 2-cm active tip of the antenna is kept inside the bone.
Conflict of interest None
References
1. Rosenthal DI, Hornicek FJ, Torriani M et al (2003) Osteoid
osteoma: percutaneous treatment with radiofrequency energy.
Radiology 229(1):171–175
2. Kjar RA, Powell GJ, Schilcht SM et al (2006) Percutaneous
radiofrequency ablation for osteoid osteoma: experience with a
new treatment. Med J Aust 184:563–565
3. Gangi A, Tsoumakidou G, Buy X et al (2010) Quality
improvement guidelines for bone tumour management. Cardio-
vasc Intervent Radiol 33:706–713
4. Lubner MG, Brace CL, Hinshaw JL et al (2010) Microwave
tumor ablation: mechanism of action, clinical results, and devi-
ces. J Vasc Interv Radiol 21(8 Suppl):S192–S203
5. Motamedi D, Learch TJ, Ishimitsu DN et al (2009) Thermal
ablation of osteoid osteoma: overview and step-by-step guide.
Radiographics 29(7):2127–2141
6. Gangi A, Basile A, Buy X et al (2005) Radiofrequency and laser
ablation of spinal lesions. Semin Ultrasound CT MR 26(2):89–97
7. Gangi A, Alizadeh H, Wong L et al (2007) Osteoid osteoma:
percutaneous laser ablation and follow-up in 114 patients. Radi-
ology 242:293–301
8. Mahnken AH, Bruners P, Delbru¨ck H et al (2011) Radiofre-
quency ablation of osteoid osteoma: initial experience with a new
monopolar ablation device. Cardiovasc Intervent Radiol 34:
579–584
9. Mastrantuono D, Martorano D, Verna V et al (2005) Osteoid
osteoma: our experience using radio-frequency (RF) treatment.
Radiol Med (Torino) 109:220–228
10. Rehnitza C, Sprengela SD, Lehnerb B et al (2012) CT-guided
radiofrequency ablation of osteoid osteoma and osteoblastoma:
clinical success and long-term follow-up in 77 patients. Eur J
Radiol 81(11):3426–3434
A. Basile et al.: The use of MWA in the treatment of epiphyseal OO
123

6. 11. Rosenthal DI, Springfield DS, Gebhardt MC et al (1995) Osteoid
osteoma: percutaneous radio-frequency ablation. Radiology
197:451–454
12. Vanderschueren GM, Taminiau AHM, Obermann WR et al
(2004) Osteoid osteoma: factors for increased risk of unsuc-
cessful thermal coagulation. Radiology 233:757–762
13. Pinto CI, Taminiau AHM, Vanderschueren GM et al (2002)
Technical considerations in CT-guided radiofrequency thermal
ablation of osteoid osteoma: tricks of the trade. AJR Am J
Roentgenol 179:1633–1642
14. Brace CL, Hinshaw JL, Laeseke PF et al (2009) Pulmonary
thermal ablation: comparison of radiofrequency and microwave
devices by using gross pathologic and CT findings in a swine
model. Radiology 251(3):705–711
A. Basile et al.: The use of MWA in the treatment of epiphyseal OO
123