DOI:10.2214/AJR.05.0265
AJR 2006; 186:S322-S326
© American Roentgen Ray Society
Saline-Infused Bipolar Radiofrequency Ablation of High-Risk Spinal and Paraspinal Neoplasms
Xavier Buy1,
Antonio Basile1,2,
Guillame Bierry1,
Juan Cupelli1 and
Afshin Gangi1
1 Department of Radiology B, University Hospital of Strasbourg, Strasbourg,
France.
2 Department of Radiology, Ospedale Ferrarotto, via Citelli, Catania 94125,
Italy.
Received February 16, 2005;
accepted after revision May 9, 2005.
Address correspondence to A. Basile.
Abstract
OBJECTIVE. We present three cases of symptomatic high-risk
metastases involving the vertebral body treated using infused bipolar
radiofrequency ablation either alone or in combination with
vertebroplasty.
CONCLUSION. In our experience, the bipolar technique can reduce the
risk of spinal cord damage in radiofrequency ablation of lesions within 1 cm
of neural structures and involving paravertebral soft tissue.
Keywords: oncology • radiofrequency ablation • spine • vertebroplasty
Introduction
Radiofrequency ablation, either alone or in combination with cementoplasty,
has been shown to be effective in the treatment of refractory pain from spinal
neoplasms [1,
2]. In many series, because of
the hyperthermic cytotoxicity risk of spinal cord injury, lesions within 1 cm
of the spinal cord represent an exclusion criterion
[1,
3,
4]. Furthermore, in many cases
large lesions involve the cortex and soft tissue surrounding vertebral bone.
In these cases, satisfactory ablation of the whole lesion requires that the
radiofrequency needle be repositioned several times to obtain an overlap.
Normal saline (0.9%) infusion has been shown to be effective in enlarging the
area of necrosis during radiofrequency ablation, acting as a liquid electrode
with conductivity 3-5 times greater than that of blood and 12-15 times greater
than that of soft tissues; furthermore, electrical conductivity is increased
even more using a highly concentrated NaCl solution (6-36%)
[5,
6]. Use of a hypertonic saline
infusion in combination with bipolar technique has been attempted in animal
liver and resulted in faster and more extensive ablation and less heat loss
than did monopolar technique. Bipolar technique was first reported in 2003 in
explanted and in vivo livers
[7-9].
It uses one electrode thermally shielded by the opposing second electrode,
which also actively heats nearby tissue. Thus, the heat is trapped between the
two electrodes, obviating diversion of current from the ablation site in any
direction [8,
10,
11]. The aim of this article
is to present three cases of potentially high-risk lesions of the spine (<
1 cm from the spinal cord, with cortical or pedicle invasion) treated with
saline-infused bipolar radiofrequency ablation with or without
vertebroplasty.
Case Report
Case 1
A 49-year-old man with renal cell carcinoma of the left kidney was referred
for palliative treatment of a refractory painful metastasis in L3. CT showed
the lesion to be in the right half of the vertebral body, involving either the
posterior wall or the ipsilateral pedicle
(Fig. 1A). Invasion of soft
tissue around the vertebral body was also noted. The lesion contacted the
spinal cord and dural sac without interposition of the cortex. Once the
patient had given informed consent, we treated the lesion with bipolar
technique through a posterior approach while the patient was prone. Two open,
perfused 18-gauge radiofrequency needles (Berchtold, Medizinelektronik) were
inserted (Fig. 1B). The more
medial needle was less than 1 cm from the spinal cord. While energy was
delivered, hypertonic saline (5.85%) was infused at a rate of 70 mL/hr through
the delivery needle, in accord with our standard protocol. The delivery needle
was the more peripheral needle from the spinal cord, thus obviating delivery
of current to the spine. The radiofrequency power was set at 60 W, and the
lesion was treated for 10 min, in accord with our standard protocol and
suggestions in the literature (Fig.
1C) [8,
11]. On the basis of the Brief
Pain Inventory (BPI, short form), the patient's symptoms were determined to
have improved within 24 hr after the procedure (from 7 degrees before the
procedure to 2 degrees after the procedure). The patient did not experience
radiating pain during the procedure and was neurologically intact when
examined after the procedure.
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Fig. 1A —49-year-old man with renal cell carcinoma of left kidney who was
referred for palliative treatment of refractory painful metastasis in L3.
Axial CT scans show soft-tissue mass involving vertebral body, posterior wall,
and ipsilateral pedicle (A) and same mass with two infused 18-gauge
radiofrequency needles inserted (B).
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Fig. 1B —49-year-old man with renal cell carcinoma of left kidney who was
referred for palliative treatment of refractory painful metastasis in L3.
Axial CT scans show soft-tissue mass involving vertebral body, posterior wall,
and ipsilateral pedicle (A) and same mass with two infused 18-gauge
radiofrequency needles inserted (B).
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Fig. 1C —49-year-old man with renal cell carcinoma of left kidney who was
referred for palliative treatment of refractory painful metastasis in L3.
Posttreatment CT control scan shows air bubbles within treated lesion, a sign
of necrosis.
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Case 2
A 65-year-old man who previously underwent surgery for prostatic cancer was
referred with paresthesia for palliative treatment of a refractory painful
metastasis in T10. Previous CT had shown extensive involvement of both the
vertebral body and the pedicles, with a right paravertebral mass involving the
posterior arc of the ipsilateral rib (Fig.
2A). Signs of medullary compression were observed at the MRI
examination. Once the patient had given informed consent, we treated the
lesion with bipolar technique through a posterior approach while the patient
was prone. Two open, perfused 18-gauge radiofrequency needles (Berchtold) were
inserted into the paravertebral mass (Fig.
2B). The more medial needle was less that 1.5 cm from the spinal
cord. The delivery needle was the more peripheral needle from the spinal cord,
thus obviating delivery of current to the spine. While energy was delivered,
hypertonic saline (5.85%) was infused at a rate of 70 mL/hr through the
delivery needle. The radiofrequency power was set at 60 W, and the lesion was
treated for 10 min, in accord with our standard protocol. Subsequently a
10-gauge vertebroplasty needle was inserted into the vertebral body
(Fig. 2C). Through this needle,
an infused 18-gauge radiofrequency needle was coaxially positioned to reach
the middle of the vertebral body and was connected to the generator for
another 10 min. Once the radiofrequency probe had been retrieved, a normal
vertebroplasty was performed through the 10-gauge needle left in place. On the
basis of the BPI (short form), the patient's symptoms were determined to have
improved within 24 hr after the procedure (from 8 degrees before the procedure
to 2 degrees after the procedure). The neurologic examination immediately
after the procedure had findings identical to those of the previous
examination.
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Fig. 2A —65-year-old man who previously underwent surgery for prostatic
cancer and was referred with paresthesia for palliative treatment of
refractory painful metastasis in T10. CT scan shows extensive involvement of
either vertebral body or pedicles, with right paravertebral mass involving
posterior arc of ipsilateral rib.
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Fig. 2B —65-year-old man who previously underwent surgery for prostatic
cancer and was referred with paresthesia for palliative treatment of
refractory painful metastasis in T10. CT scan shows two infused 18-gauge
radiofrequency needles that were inserted into paravertebral mass under CT and
fluoroscopic guidance.
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Fig. 2C —65-year-old man who previously underwent surgery for prostatic
cancer and was referred with paresthesia for palliative treatment of
refractory painful metastasis in T10. CT scan shows 10-gauge vertebroplasty
needle that was placed into vertebral body between contralateral rib and
pedicle under CT and fluoroscopic guidance, and 18-gauge radiofrequency needle
that was inserted through the 10-gauge needle (arrow).
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Case 3
A 52-year-old man with a history of prostatic carcinoma previously treated
by surgery was referred for palliative treatment of a refractory painful
metastasis in T10. CT showed the lesion to be in the left paravertebral space,
with involvement of the left pedicle and the posterior arc of the ipsilateral
rib (Fig. 3A). The lesion was
laterally contacting the spinal cord and dural sac, without interposition of
the cortex or signs of compression. Once the patient had given informed
consent, we treated the lesion with bipolar technique through a posterior
approach while the patient was prone (Fig.
3B). Two open, perfused 18-gauge radiofrequency needles
(Berchtold) were inserted. While energy was delivered, hypertonic saline
(5.85%) was infused at a rate of 70 mL/hr through the delivery needle. The
delivery needle was the more peripheral needle from the spinal cord, thus
obviating delivery of current to the spine. The radiofrequency power was set
at 60 W, and the lesion was treated for 10 min, in accord with our standard
protocol (Figs. 3C and
3D). On the basis of the BPI
(short form), the patient's symptoms were determined to have improved within
24 hr after the procedure (from 8 degrees before the procedure to 3 degrees
after the procedure). The patient did not experience radiating pain during the
procedure and was neurologically intact when examined after the procedure.
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Fig. 3A —52-year-old man with history of prostatic carcinoma previously
treated by surgery who was referred for palliative treatment of refractory
painful metastasis in T10. CT scan shows left paraspinal soft-tissue lesion,
with involvement of ipsilateral pedicle and posterior arc of ipsilateral
rib.
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Fig. 3B —52-year-old man with history of prostatic carcinoma previously
treated by surgery who was referred for palliative treatment of refractory
painful metastasis in T10. CT scan shows two infused 18-gauge radiofrequency
needles that were inserted through posterior approach with patient prone.
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Fig. 3C —52-year-old man with history of prostatic carcinoma previously
treated by surgery who was referred for palliative treatment of refractory
painful metastasis in T10. Posttreatment CT control scan shows air bubbles
within treated lesion, a sign of necrosis.
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Fig. 3D —52-year-old man with history of prostatic carcinoma previously
treated by surgery who was referred for palliative treatment of refractory
painful metastasis in T10. MR follow-up image shows round-shaped hypointense
area corresponding to ablated tissue.
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Fig. 2D —65-year-old man who previously underwent surgery for prostatic
cancer and was referred with paresthesia for palliative treatment of
refractory painful metastasis in T10. CT and fluoroscopic control image after
radiofrequency plus vertebroplasty shows oval paraspinal necrotic area, with
cement in vertebral body.
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Discussion
Saline infusion and bipolar technique represent two methods to increase the
dimensions of radiofrequency-induced coagulation necrosis. The NaCl injection
increases energy conductivity, limiting tissue carbonization around the
electrodes and thus reducing tissue impedance
[11]. Furthermore, the use of
a hypertonic saline infusion (5.85%) reduces the injected volume of about 40%
(70 mL/hr), preventing the consequences of an unpredictable diffusion of hot
saline (i.e., too great a decrease in impedance, lack of heating, need for
high power). Instillation of large amounts (600 mL/hr) of isotonic saline
during hepatic radiofrequency ablation has been reported to produce
unpredictable burns to distal organ such as stomach and small bowel, likely
related to the diffusion of hot saline
[7]. Use of a highly
concentrated NaCl solution (6-36%)
[5] as a liquid electrode more
effectively enlarges the area of necrosis during radiofrequency ablation, with
conductivity greater than in blood and soft tissues.
Radiofrequency ablation techniques using dual electrodes consist of the
introduction of two probe needles applied in sequential, simultaneous,
alternating, and bipolar modes
[8]. In the last of these
modes, energy is applied to one electrode and the other is used as the return
electrode. In experimental studies, bipolar technique has been found to
produce heat more efficiently at a given current
[8], likely because the flow of
current is concentrated between the electrodes
[11]. Thus, the potential
exists for a more concentrated flow of current between the two electrodes and
a better-defined area of radiofrequency-induced coagulation necrosis, reducing
heat loss and potential damage to adjacent structures. These well-defined oval
lesions that result from bipolar radiofrequency ablation are in contrast to
the two cylindric areas of tissue necrosis that result from the use of two
electrodes in monopolar mode.
There are few reports in the literature describing spinal neoplasms treated
only with radiofrequency ablation; some other cases are found in large series
of bone lesions treated in this way
[5,
12]. Among these articles,
80-95% of patients undergoing radiofrequency ablation of bone metastases
experienced a clinically significant decrease in pain, with the complication
rate ranging from 0% to 6.9%
[2,
12]. Other studies have
advocated that radiofrequency ablation and vertebroplasty be combined for the
management of bone metastases
[13] due to the combination of
the antitumoral effect of heat and the mechanical stabilization of the
vertebral body by the cement injection. Among these studies, the largest
series of spinal metastases treated with radiofrequency ablation was 17 cases
[2]. In that article, Nakatsuka
et al. [2] reported a high
technical and clinical success rate of up to 100%, with 24% of patients with
spinal metastases experiencing neurologic complications. This high
complication rate was likely due to the fact that only three of 17 lesions
were separated from the posterior cortex and pedicles by 3 mm or more
[2]. In most series on either
radiofrequency ablation or radiofrequency plus cementoplasty, lesions within 1
cm of the spinal cord were considered ineligible for treatment. Surely this
exclusion criterion reduces the complication rate; however, it also reduces
the use of radiofrequency ablation in the palliative treatment of patients
with refractory pain that is due to spinal metastases. Callstrom et al.
[12] and Goetz et al.
[4] reported that,
respectively, three of 19 and eight of 94 patients could not be treated
because their lesions were too close to the spinal cord or vital structures.
With the technique that we are reporting, we noted no major complications
related to hyperthermia toxicity of the spinal cord, even in cases with
involvement of the posterior wall and of soft tissue around the vertebral body
with destruction of the cortex. This lack of complications is probably due to
the fact that, as previously described, the flow of current is limited to the
region between the electrodes; thus, the electrode locations almost represent
the limits of the heated tissue. Of course, we used this approach in patients
in end-stage disease, to whom no other options could be offered to increase
their quality of life. In conclusion, although larger series are needed to
confirm our data, our findings suggest that bipolar technique, either alone or
in combination with cementoplasty, reduces the risk of spinal cord damage in
high-risk spinal or paraspinal lesions, increasing the safety of the procedure
and the number of patients eligible to receive such palliative treatment.
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Abstract
Introduction
