BACKGROUND: Image-guided percutaneous thermal ablation is a commonly performed therapeutic procedure for various tumors. Thermal ablation is not frequently used in the pelvis as a result of anatomic concerns and the potential risk of nontarget tissue injury.
TECHNIQUE: Percutaneous thermal ablation is a minimally invasive procedure involving special probes inserted through the skin to the target lesion under imaging guidance. Various delivery methods of thermal ablation exist, including radiofrequency ablation, which burns tissue, and cryoablation, which freezes tissue with an ultimate goal to destroy the target tumor while minimizing damage to adjacent structures. Protective measures can be used to provide access and safe treatment delivery such as pyeloperfusion to protect the ureter with the infusion of water using a ureteral stent or hydrodissection to protect adjacent structures by displacing them away with the infusion of water using percutaneously placed needles.
EXPERIENCE: The authors' experience with the technique involves thermal ablation of recurrent pelvic tumor in three patients with various gynecologic malignancies who each had a single focus of pelvic recurrence after surgical resection and radiation treatment. No residual or recurrent disease was seen at the treatment site on follow-up imaging consistent with local tumor control.
CONCLUSION: Thermal ablation of metastatic or recurrent pelvic tumor is technically feasible and should be considered in selected patients with no treatment alternative.
Thermal ablation of metastatic pelvic tumor is technically feasible and should be considered in patients with no treatment alternative.
Department of Radiology, Division of Abdominal Imaging and Intervention, and the Department of Obstetrics and Gynecology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.
Corresponding author: Selim R. Butros, MD, Department of Radiology, Division of Abdominal Imaging and Intervention, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, White 270, Boston, MA 92114; e-mail: firstname.lastname@example.org.
Financial Disclosure The authors did not report any potential conflicts of interest.
Percutaneous thermal ablation is a commonly performed therapeutic procedure in patients with liver, renal, pulmonary, and bone tumors.1–4 Successful results of radiofrequency ablation have been reported for metastatic retroperitoneal lymphadenopathy from a variety of tumors.5–7 Despite its widespread use in solid organs, and in some instances for mediastinal or retroperitoneal metastatic lymphadenopathy, widespread experience with the use of thermal ablation to treat metastatic lesions in the pelvis from gynecologic malignancies does not exist.
Management of pelvic soft tissue or lymph node metastasis in gynecologic malignancies could prove to be a challenge in the postoperative patient in whom dose limits of radiation have been reached and there is poor response to chemotherapy. These patients are usually left with limited treatment options regardless of the response at other sites. In this patient population, alternative means to successfully treat solitary or limited small recurrent or residual disease in the pelvis have the potential to replace systemic therapy and to theoretically improve patient survival. Image-guided thermal ablation is a treatment method that is not frequently entertained as a result of anatomic concerns and the potential risk of nontarget thermal injury to closely located organs in the pelvis such as the sigmoid colon, the bladder, ureters, nerves, and vessels. We describe three cases of successful thermal ablation of metastatic pelvic lymph nodes or tumor with the aid of adjunctive protective measures.
The aim of thermal ablation is to destroy the target neoplastic tissue with a safe surrounding margin, thereby minimizing damage to adjacent tissue. The procedure is considered minimally invasive performed with percutaneously inserted probes (special needles) under guidance of computed tomography (CT) or ultrasonography. Most cases are performed under conscious sedation with use of local anesthesia or under general anesthesia depending on patients' comorbidities, location of the lesion, and expected procedure length among other factors. Subsequent to the procedure, patients are either discharged home the same day or admitted for overnight observation.
Various delivery methods of thermal ablation exist, including radiofrequency ablation, cryoablation, and microwave ablation, among others. The oldest and most widely used technique is radiofrequency ablation, which generates ionic agitation and resistive heating to induce coagulative necrosis in the target tissue through flow of a high-frequency alternating electrical current. To establish this current, the radiofrequency ablation system requires a closed-loop circuit composed of a generator, a needle electrode, the patient, and grounding pads (Fig. 1A and B). Cryoablation on the other hand uses extremely low temperatures to induce cellular death by intracellular ice crystal formation and disruption of the cell membrane. The cryoprobe, a percutaneously inserted special needle, is a closed-loop, high-pressure gas expansion system through which typically argon gas is delivered, rapidly expanding in tissue and forming an ice ball, which can be serially monitored with imaging to ensure sufficient overlap with the target. Both of these modalities have been used in cases presented in this article.
The challenge in performing ablation in the pelvis arises from the difficulty of accessing a lesion deep in the pelvis as a result of multiple overlying structures and a potential higher risk of causing thermal injury to adjacent organs with closely positioned anatomic structures preventing a buffer zone (Fig. 2). Adjunctive maneuvers such as hydrodissection and pyeloperfusion should thus be used with optimal positioning of the patient to protect adjacent anatomic structures during treatment delivery. Hydrodissection is a useful technique to displace usually the bowel, but also various other structures away from tumors targeted for ablation or abscess drainage.8 It implies the creation of artificial ascites before treatment delivery with infusion of 5% dextrose in water through percutaneously placed 19- to 20-gauge needles to create a safe margin around the lesion. Similarly, pyeloperfusion has been used to cool the ureter for ipsilateral renal tumors treated with thermal ablation where the ureter is adjacent to the renal tumor.9 For pyeloperfusion, a ureteral stent is inserted in a retrograde fashion before the procedure. During the procedure, 5% dextrose in water is slowly infused through the stent providing continuous flow within the ureter to minimize the risk of thermal injury from the ablation. Ideal patient positioning is equally important where alternative patient positions such as lateral decubitus or prone could provide a window to access to the target lesion and could displace adjacent structures, thus minimizing thermal injury.
Thermal ablation of recurrent pelvic tumor was successfully performed in three patients with various gynecologic malignancies who each had a single focus of pelvic recurrence after surgical resection and radiation treatment. There was only one other patient who had pelvic recurrence in which the procedure could not be completed as a result of failure of hydrodissection in displacing the tumor from adjacent small bowel loops.
A 64-year-old woman with unresectable International Federation of Gynecology and Obstetrics stage III squamous cell carcinoma of the vulva and fluorodeoxyglucose avid left external iliac metastatic lymphadenopathy was treated with a 6-week course of chemoradiation. Because radiation dose limits to the primary tumor precluded inclusion of the left medial external iliac chain lymph node in the radiation field, the patient was referred for thermal ablation of the lymph node.
Computed tomography-guided radiofrequency ablation was performed from an anterior approach to access the lesion with the patient positioned supine. The lymph node was situated between the sigmoid colon and the iliac muscle, posterior to the left external iliac vein and anterior to the ureter along the left pelvic sidewall (Fig. 3A–B). Hydrodissection with infusion of 180 cc of 5% dextrose in water through two 19-gauge needles was performed to displace the sigmoid colon away from the lymph node. Pyeloperfusion of the left ureter was also performed at the time of the ablation with 5% dextrose in water through a ureteral stent placed before the procedure (Fig. 3C). Two overlapping 12-minute ablations were performed using internally cooled cluster electrodes (Fig. 3D). The patient tolerated the procedure well and had no procedure-related complications. Approximately 1 week after the procedure, she started experiencing mild left lower extremity muscle weakness in the distribution of the left sciatic nerve, which could have been a result of the procedure, the radiation treatment, or both. Follow-up positron emission tomography–CT 1 year after the procedure demonstrated complete absence of fluorodeoxyglucose activity in the lymph node (Fig. 3E).
A 62-year-old woman with International Federation of Gynecology and Obstetrics stage IIB cervical cancer was initially treated with cisplatin and external beam radiation. One year later, she developed central pelvic recurrence in the vaginal apex with no distant or local lymph node metastasis for which she underwent a pelvic exenteration and lymph node dissection. Nine months after the procedure she developed recurrent disease in left inguinal and pelvic inlet lymph nodes, which were hypermetabolic on positron emission tomography–CT scan. She underwent left inguinal lymph node dissection and subsequently was referred for thermal ablation of the inferior mesenteric lymph node, just below the level of the pelvic inlet.
The lesion was closely situated between small bowel loops (Fig. 4A–B). Hydrodissection was used with the insertion of three 20-gauge needles, one superior and two inferior to the lesion, and infusion of approximately 50 cc of 5% dextrose in water diluted with contrast (1 in 20 cc) successfully displacing small bowel loops away from the lesion (Fig. 4C). The patient then underwent a single 10-minute session of radiofrequency ablation of the lesion with an internally cooled single probe (Fig. 4D). The patient had an uncomplicated postprocedural course. Follow-up positron emission tomography–CT 3 months after the procedure demonstrated absence of fluorodeoxyglucose uptake in the lymph node (Fig. 4E). However, residual disease was unfortunately seen in the left inguinal surgical resection bed and subsequently the patient was started on systemic chemotherapy.
A 74-year-old woman was treated with total abdominal hysterectomy and bilateral salpingo-oophorectomy and pelvic and retroperitoneal lymph node dissection for stage IIB, grade 3 endometrial cancer. Subsequently she underwent whole pelvic radiotherapy and vaginal brachytherapy, which was complicated by repeated episodes of small bowel obstruction. Four years later she developed recurrence in her abdominal scar and in a left retroperitoneal lymph node for which she successfully underwent surgical resection and radiofrequency ablation, respectively. The patient was disease-free for 2 years after which she developed an isolated recurrence in a 3.5-cm right pelvic sidewall mass (Fig. 5A). Given the success of previous local treatments, she was referred for thermal ablation of the pelvic recurrence.
Hydrodissection was used with the aid of two 20-gauge needles positioned superior and medial to the lesion to displace the small bowel, which was achieved after the infusion of 1,200 cc of normal saline (Fig. 5B). Two 15-cm cryoprobes were then advanced into the lesion under CT guidance and two cycles of overlapping ablations were performed (Fig. 5C). The patient had an uneventful recovery after the procedure. Up until this date 4 years later, follow-up CT scan does not show residual uptake in the treated region nor does it show any other sites of metastatic disease (Fig. 5D).
In patients with gynecologic malignancies, recurrence of metastatic pelvic tumor is a frequently encountered situation. These patients usually have extensive adhesions and inflammatory changes secondary to previous operations and radiation treatment that frequently precludes repeated surgical operations. In this patient population, it is not uncommon to have completed previous radiation treatments where repeated treatment would be too risky as a result of its toxicity in the adjacent normal structures. In patients with a single residual or recurrent tumor focus, thermal ablation can be used as a minimally invasive treatment alternative. Although the survival benefit of such a procedure remains to be determined, the results of the present cases suggest that thermal ablation may offer local tumor control.
It is critical that the risks and benefits of the procedure are well understood and a combined decision is made with the patient and a multidisciplinary team. Despite anatomical challenges of percutaneous access to the pelvis, and the risk of nontarget thermal injury to vascular structures and various pelvic organs, this procedure is technically feasible by paying close attention to the anatomy and using the described protective techniques. None of our patients had a major complication or recurrence after treatment.
In summary, our current experience shows that when image-guided thermal ablation is combined with adjunct protective procedures, metastatic pelvic tumor can be targeted and treated, providing opportunity to patients where no treatment alternative exists.
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