Current technology ideally works best for tumor size less than 3.5 cm. Tumors between 3.5 and 4.5 cm will likely require additional probes and run a greater risk of incomplete ablation or complication when laparoscopically ablated and in general is not recommended for cryotherapy, although these larger tumors may be reasonable for a percutaneous approach depending on the clinical situation. For therapeutic ablation, patients should have an absence of local and systemic dissemination on magnetic resonance imaging (MRI) or computed tomography (CT), although palliative treatment may be offered under appropriate conditions.
In addition to routine preoperative assessment, a recent high-quality, dual-phase renal CT or MRI delineating exact tumor dimensions and location is imperative. Mechanical bowel preparation may be recommended to decompress the intestines. Patients also receive a dose of a broad-spectrum cephalosporin.
Cryosurgery is an ablative technology and, as such, can be used via an open surgical, percutaneous, or laparoscopic (transperitoneal, retroperitoneal, or hand-assisted) approach. The transperitoneal, pure laparoscopic approach and the percutaneous image-guided technique will sequentially be illustrated.
Temperatures within the iceball vary and represent a gradient from extremely cold (approximately –180°C) adjacent to the thermal shaft of the cryoprobe to 0°C at the outside edge of the iceball. An isotherm is a temperature zone colder than a specific cutoff temperature characterizing that temperature gradient (e.g., 0°C, −20°C, and −40°C isotherms). Approximately 2–3 mm inside the outer edge of the iceball begins the <−15° to −20° C isotherm, at which point temperatures become cold enough to be considered lethal to some cells. It is generally accepted that the <−40°C isotherm is sufficient for complete cellular destruction; however, in vitro studies have suggested that cellular death can occur at different temperatures depending on the type of tumor. Fig. 29.1 provides an example of iceball dimensions according to the desired isotherm achieved.
Laparoscopic Renal Cryoablation
The instruments used in this procedure include argon-based (with or without helium) cryotherapy unit with cryoprobes and thermocouples, intraoperative ultrasonography, laparoscopic ports and instruments, needle biopsy gun, and hemostatic agents.
Procedure ( )
Position: The patient is positioned in an approximately 60-degree modified lateral position, pressure points are padded and protected, and is well secured to the table. The table can be rotated during the procedure (should be tested before draping) to achieve further lateral positioning. The patient should be centered toward the edge of the table facing the surgeon, tumor side up. General anesthesia is used.
Port placement: Typically three laparoscopic ports are used: a 5-mm port in the midline epigastrium, a 5- or 12-mm camera port at the umbilicus and a 12-mm port in the lower quadrant on the side of the tumor ( Fig. 29.2 ). Alternatively, the three ports can be placed at the lateral border of the rectus muscle beginning 2 cm below the costal margin (the superior port usually serves as the camera port), evenly spaced with a hand’s-width between each port. With either port configuration, one must use a 12-mm port to allow access of the laparoscopic ultrasound probe. An assistant port (usually 5-mm) can be added per the surgeon’s discretion. A 5-mm liver retractor is used when appropriate. A pneumoperitoneum is created.
Mobilization: The overall principle is to mobilize sufficient tissue to (1) allow exposure of the tumor and (2) to place the cryoprobes perpendicular to the tumor, rather than obliquely. The rib cage is usually the limiting anatomic factor that challenges perpendicular probe placement, especially for upper-pole tumors. Anatomically, for many patients, the upper pole lies beneath the costal margin whereas the lower pole is unencumbered by the rib cage ( Fig. 29.2 ). Therefore, the amount of mobilization will depend on being able to ideally attain perpendicular cryoprobe access to the tumor. As an example, for an anterior, lower-pole tumor, minimal mobilization is needed to both expose the tumor and to directly access it with the cryoprobe(s) ( Fig. 29.3A ). For posterior or upper-pole tumors, more extensive mobilization may be necessary. For example, upper-pole tumors will usually require greater mobilization to pull the kidney inferiorly below the rib cage, to prevent oblique cryoprobe placement into the tumor ( Fig. 29.3B ). Retracting the upper pole beyond the rib cage can be accomplished by placing additional retractors or using a hand-assist device to pull the kidney inferiorly.
When mobilizing the kidney, the line of Toldt is incised only to the extent it need be to attain access to the tumor. For left-sided upper-pole tumors, the spleen should be sufficiently mobilized to prevent inadvertent traction injury due to pulling on the lienorenal and lienocolic ligaments. The colon is reflected medially by incising the renocolic ligament. Hilar control is not necessary for cryosurgery. During the freezing phase, the ultrasound probe is placed perpendicular to the cryoneedles on the underside of the kidney ( Fig. 29.4 ). Therefore, for anterior tumors, it may be necessary to mobilize an area posterior to the kidney to allow for subsequent placement of the ultrasound probe.
The tumor dimensions and location should already be known based on a recent preoperative CT or MRI scan. For endophytic lesions, it may be necessary to locate the tumor solely using ultrasound guidance in contrast to exophytic tumors that can be visually identified. The location of endophytic tumors can be verified by frozen-section biopsy. Once the tumor is identified, the Gerota fascia adjacent to the neoplasm is incised and the renal surface exposed. The perirenal fat overlying the tumor is removed, placed in a laparoscopic entrapment bag and sent for histologic evaluation. The renal surface is scanned with the laparoscopic ultrasound probe to define the exact dimensions of the lesion, its relationship to the calyceal system and vascular structures, and the presence of any satellite lesion(s). An x-ray detectable sponge can be temporarily placed through a 12-mm port to either provide a field around the tumor or to protect other vital structures, such as bowel, from adhering to the ice probe during the freezing phase. The sponge can also retract and protect the ureter when treating medial, lower pole lesions.
Cryoprobes: Based on the size of the lesion, the number of cryoprobes needed to ablate the tumor must be determined. For very small lesions, it may be possible to use a single cryoprobe for ablation. For larger lesions, triangulation of the probes may provide sufficient ice overlap to encompass the tumor ( Fig. 29.5 ). For even larger lesions, cryosurgeons may use a four-probe “square” or “box” configuration placed around the perimeter of the tumor, or a five- to six-probe pentagon/hexagon probe placement. It is important to consult with the manufacturer about the size of the ice generated and the isotherm data for a particular product when determining the number of cryoprobes or the positioning/configuration of probes needed to achieve cell kill. However, the principal remains the same: to ensure the tumor remains engulfed in a lethal isotherm and that adjacent ice balls overlap sufficiently to attain a lethal isotherm between ice balls in the target zone. If a single cryoprobe is used, it is placed in the center of the tumor with sufficient depth to achieve an adequate deep parenchymal margin. For instructive purposes, this chapter will illustrate a more complex multiprobe configuration. Fig. 29.6A depicts three cryoprobes properly spaced apart so that there are even colder temperatures achieved where adjacent ice balls overlap. In contrast, Fig. 29.6B demonstrates that if adjacent cryoprobes are spaced too far apart, then one may have “warm pockets” called the “variable freeze zone” where two adjacent ice balls do not overlap sufficiently to provide lethal temperatures.