DOI:10.2214/AJR.06.0641
AJR 2007; 188:1044-1046
© American Roentgen Ray Society
CT-Guided Percutaneous Radiofrequency Ablation of Spleen: A Preliminary Study
Toshiyuki Matsuoka1,
Akira Yamamoto,
Tomohisa Okuma,
Yoshimasa Oyama,
Kenji Nakamura and
Yuichi Inoue
1 All authors: Department of Radiology, Osaka City University Graduate School of
Medicine, 1-4-3 Asahi-machi, Abeno-ku, Osaka 545-8585, Japan.
Received May 14, 2006;
accepted after revision August 18, 2006.
Address correspondence to T. Matsuoka
(tmatsuoka{at}msic.med.osaka-cu.ac.jp).
Abstract
OBJECTIVE. The objective of our study was to evaluate the technical
feasibility, safety, and changes of platelet counts of CT-guided percutaneous
radiofrequency ablation of normal spleen in a porcine model.
CONCLUSION. It is feasible and safe to perform CT-guided
percutaneous radiofrequency ablation of the spleen in a pig. Although further
study is still required in clinical applications, this method can be a
minimally invasive and effective therapeutic technique in patients with
hypersplenism.
Keywords: animal studies • interventional radiology • percutaneous ablation • radiofrequency ablation • spleen
Introduction
Partial splenic embolization is used as an interventional treatment
of hypersplenism [1,
2]. The aim of partial splenic
embolization is to create infarction and shrink the spleen. However, serious
complications have been reported
[2,
3]. Radiofrequency ablation
(RFA) has been performed for tumors of various organs as a minimally invasive
treatment [4]. Thermal
coagulative necrosis induced by radiofrequency energy can reduce the
parenchyma of organs. Thus, RFA could be an effective therapeutic technique,
with fewer complications, for hypersplenism. Although experimental and
clinical studies regarding RFA of the spleen under laparoscopy and laparotomy
have been reported
[5-7],
there have been few reports of percutaneous RFA. We performed CT-guided RFA of
normal spleen in animal models to evaluate the technical feasibility, safety,
and changes in platelet count, and the results are reported here.
Materials and Methods
Animal Models and Ablation Procedures
Five domestic pigs (17-21 kg) were used, and this study was approved by the
animal experimentation committee of Osaka City University.
For all procedures, anesthesia was induced with midazolam (40 mg/kg).
Pentobarbital sodium (50-150 mg) was used to maintain anesthesia. We used a
radiofrequency 2,000 generator system and 17-gauge LeVeen Needle Electrode
(Boston Scientific) that has eight retractable hooks with a diameter of 2 cm.
Two ground pads were placed on both thighs of the animals. After anesthesia,
one pig was placed in the right lateral position on a CT table (ProSpeed, GE
Healthcare) (Fig. 1A). The
probe was percutaneously inserted into the splenic parenchyma and tins were
deployed under CT guidance with care not to penetrate the spleen. Ablation was
performed at three points per animal so that they did not overlap each other.
The emission power was initially set at 30 W and was increased by 10 W every
minute. The maximum output did not exceed 50 W. Radiofrequency output was
applied until the generator automatically stopped due to the increased
impedance caused by tissue dehydration.
CT Observation and Laboratory Data
A contrast-enhanced CT scan (2.0 mL/kg of 300 mg I/mL, [iopamidol]
Iopamiron, Nihon Schering) was obtained immediately after ablation using a
5-mm collimation. Complications such as hemorrhage and thermal injury of the
bowel were monitored by CT. Splenic size and ablated volume were measured on
CT films. Blood samples were collected before and 2, 4, and 8 weeks after the
procedure. The number of platelets was counted.
Results
RFA
In all pigs, the puncture was easy and successful. Confirmation by CT
enabled the probe to be placed at an appropriate position in the splenic
parenchyma to prevent damage to other organs
(Fig. 1B). Tissue coagulation
was achieved in between 2 minutes 24 seconds and 8 minutes 45 seconds (mean, 3
minutes 49 seconds). All procedures were performed without awakening the pigs.
The CT images showed that 10.5-18.9% (mean, 14.5%) of the spleen was ablated
(Fig. 1C). No hematoma was
observed on CT in all punctures. After RFA, all pigs were well fed. Vomiting,
anorexia, and significant body weight loss were not observed.
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Fig. 1C —Radiofrequency ablation performed under CT guidance. Ablation was
performed at three points per animal. Contrast-enhanced CT image obtained
immediately after procedure shows no hematoma.
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|
Platelet Count
Platelet numbers before the procedure were 149,000-394,000/mm3
(mean, 236,000/mm3). Counting platelet numbers was difficult at 2
weeks in pig 2, at 4 weeks in pig 3, and at 2 and 8 weeks in pig 4 because of
coagulation of the sampling blood. Therefore, those numbers were excluded from
the data. The platelet count showed a mild increase at 2 and 4 weeks
postprocedure (mean, 125% at 2 weeks, 119% at 4 weeks) that was not durable at
8 weeks (mean, 91% at 8 weeks) (Fig.
2).
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Fig. 2 —Graph shows numbers of platelets at 2, 4, and 8 weeks for all pigs
as a percentage of the count before radiofrequency ablation. Platelet count
showed mild increase at 2 and 4 weeks and declined at 8 weeks. RFA =
radiofrequency ablation.
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Discussion
Hypersplenism is caused by various disorders and induces pancytopenia,
which increases the risk of bleeding and infection. Surgical splenectomy is a
reliable treatment of hypersplenism; however, a high incidence of portal
thrombosis, up to 25% after surgery, is reported
[8]. Partial splenic
embolization is performed as an effective technique in patients with
hypersplenism from idiopathic portal hypertension, liver cirrhosis, and
hematologic disorders such as paroxysmal nocturnal hemoglobinuria and
ß-thalassemia [1,
2].
Because thrombocytopenia is a problem, particularly in surgical cases,
puncture procedures such as needle biopsy, and interferon therapy for
hepatitis C, partial splenic embolization is often performed before such
treatments. Partial splenic embolization is less invasive than surgical
splenectomy. However, there is a technical problem in that it is difficult to
determine the embolized volume from the angiogram. Although it is preferable
to infarct 75-80% of the spleen volume
[2], the infarction area
sometimes is too wide or too small. Furthermore, serious complications of
partial splenic embolization such as severe pain that requires opioid
analgetics, splenic abscess, and splenic rupture have been reported
[3].
RFA has been performed for many kinds of malignant and benign tumors
[4]. A few reports have shown
the feasibility and safety of RFA of the spleen in experimental studies
[5,
6]. In each study, RFA was
performed under laparotomy or laparoscopically. Initial clinical reports
showed the effectiveness of RFA in the management of hypersplenism
[7]. The RFA needles were
inserted through the skin during surgery or under a celoscope in the reports.
However, the method of approach to the spleen in that study was not mentioned
in detail. Since RFA is expected to be a minimally invasive method, a
percutaneous approach is necessary so that RFA for hypersplenism can be widely
accepted. For this reason, we conducted percutaneous RFA using CT guidance to
evaluate the technical feasibility and safety. Changes in the platelet count
were also examined.
Monitoring CT images was useful to confirm the location of the electrodes
and the positional relationship between bowel and spleen. It was easy to
determine the ablation site to avoid thermal damage to the bowel close to the
spleen and to prevent pneumothorax and hemorrhage caused by penetrating
through lung parenchyma and large vessels. The percutaneous RFA procedure was
conducted safely. Although there was a fear of hematoma occurring, it was not
observed in any of the punctures on CT images. In laparoscopic RFA, bleeding
has been reported immediately after insertion of the needles into the spleen.
This bleeding ceased soon after insertion
[6]. This bleeding is thought
to occur because thermal coagulation of RFA has the potential of hemostasis.
CT guidance would be helpful in clinical cases to avoid complications related
to the procedure.
It is difficult to evaluate pain and abscess in animal models. Judging from
appetite and behavior after awakening from the anesthesia through 8 weeks
later, there were no major complications in the animals' condition. There was
no morbidity or mortality in our study, similar to the experimental study and
clinical cases in which laparotomic or laparoscopic RFA was performed.
Although the ablated volume was small (mean, 14.5% of whole spleen), a 25%
increase in platelet counts compared with before RFA was achieved in the
second week after RFA. In partial splenic embolization, the objective is to
infarct 75-80% of the spleen
[2]. Normal spleen in pigs is
thin, and possible sites of ablation were limited in this study. In a clinical
report on splenic RFA under laparotomy, significant improvements in platelet
counts compared with those before RFA were achieved by 20-43% ablation of the
spleen volume [7]. Splenomegaly
occurs in patients with hypersplenism. Because percutaneous puncture of
enlarged spleen would be easier and a larger volume could be ablated, a
greater increase in the platelet counts is expected in clinical
applications.
In conclusion, it is feasible and safe to perform CT-guided percutaneous
RFA of the spleen in a pig. Although further study is still required in
clinical applications, this method can be a minimally invasive and effective
therapeutic technique in patients with hypersplenism.
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Abstract
Introduction
