JOURNAL OF ENDOUROLOGYVolume 8, Number 2, 1994Mary Ann Liebert, Inc., Publishers

Laparoscopic Interstitial Contact Laser Ablation ofRenal Lesions: An Experimental Model

M. AMR LOTH, M.B.B.S.,* PETER McCUE, M.D.t and LEONARD G. GOMELLA, M.D.*

ABSTRACT

Tissue ablation with the interstitial Nd:YAG contact laser is a rapidly evolving technique. The urologieapplications of interstitial lasers have not been fully investigated. We developed a model to test the feasibility ofusing interstitial laser energy, administered under laparoscopic guidance, to ablate porcine renal tissue.Utilizing a synthetic sapphire interstitial Nd: YAG contact probe, minimal tissue effects were observed usingtotal energies between 120 and 240 J. At energies of 480 J (8 W/60 seconds), there was predominantlycoagulation necrosis of the renal parenchyma. At 720 J (12 W/60 seconds), there was pronounced tissuevaporization surrounded by a zone of coagulation necrosis approximately 1.5 cm across. This preliminaryinvestigation demonstrates that the interstitial Nd:YAG contact laser probe can be used for both controlledcoagulation necrosis and vaporization of renal parenchymal tissue. This approach may be applicable to thelaparoscopic ablation of small renal lesions in selected patients.

INTRODUCTION

RECENT TECHNOLOGIC ADVANCES have allowedminimally invasive surgery to progress rapidly. Two areas

of widespread interest in urology are laparoscopic surgical pro¬cedures and laser applications. Laparoscopic intervention hasalready been investigated for a variety of renal conditions andhas been pioneered by Clayman and associates.1·2 TheNd:YAG contact laser is ideally suited to laparoscopy becausethe laser energy can be delivered by a flexible fiber, the wave¬

length is well absorbed by tissue, and the contact tip allowsprecise cutting, coagulation, and vaporization with greater pre¬cision and safety than the noncontact Nd:YAG laser.3 Recentdevelopments have demonstrated that contact laser energy can

be delivered as interstitial hyperthermia to heat tissue to thetarget range of 42°C with resulting coagulation necrosis. Heat¬ing tissues to greater than 100°C results in vaporization. Thisinterstitial application of the contact laser has been termed "la-serthermia."4

Incidentally discovered renal cell carcinomas (<3 cm) havepreviously been called "adenomas." It is now recognized that

these adenomas are precursor lesions to the larger renal cellcarcinomas.5 There has been a shift in the management of some

of these smaller lesions from aggressive radical excision to

simple enucleation.6 However, "simple" enucleation still re¬

quires a standard surgical incision. We investigated a minimallyinvasive technique in the porcine kidney model to determine theacute tissue effects of contact Nd:YAG interstitial laser energyadministered under laparoscopic guidance.

MATERIALS AND METHODS

The porcine model was chosen to assess the acute renal tissueeffects and is a standard animal model for laparoscopic urologieprocedures.7 Studies were performed on intact animals main¬tained with general inhalational anesthesia. The animals were

used in laparoscopic surgical training sessions held under Ani¬mal Use and Care Committee-approved guidelines.

Using the transperitoneal approach, the lower pole of thekidney was exposed. The SLT Contact Laser system (Oaks,PA) with a flexible 600-µ quartz fiber (2.2 mm outer diame-

Departments of Urology* and Pathology,t Jefferson Medical College and The Jefferson Cancer Institute, Thomas Jefferson University,Philadelphia, PA

Supported by a grant from Surgical Laser Technologies, Oaks, PA

153

154 LOTFI ET AL.

ter) with coaxial cooling was loaded through a suction-irriga¬tion metal probe to add rigidity to the fiber. A prototype inter¬stitial contact probe of frosted synthetic sapphire measuring 20mm (Fig. 1) was loaded on the fiber and the assembly passedthrough a 5-mm trocar.· The interstitial probe, which has a

conical shape and a slightly blunted tip to allow easy insertioninto tissues without excessive trauma, was inserted to the hub inthe midportion of the lower pole of the renal parenchyma. Atotal of eight kidneys were studied. With the laser set on contin¬uous mode for 60 seconds, two kidneys were treated at each ofthe following energies: 2 W (120 J), 4 W (240 J), 8 W (480 J),and 12 W (720 J). The fiber was then removed and the animalsacrificed. The treated kidneys were examined grossly and his-tologically by routine hematoxylin and eosin staining.

RESULTS

At the lower energies (120 and 240 J), there were no signifi¬cant gross tissue effects. On removal of the probe, minor bleed¬ing was noted from the puncture site. At 240 J, only a verysmall zone (2-3 mm) of coagulation necrosis was apparent on

histologie evaluation. No significant changes were seen at 120J.

At 480 J and 720 J, there was no bleeding from the site duringthe treatment or after the removal of the probe. Gross tissueeffects were observed at an energy of 480 J (Fig. 2). At 720 J,an obvious and progressive zone of tissue blanching could beappreciated (Fig. 3). The histologie changes were more strikingabove 480 J (Fig. 4). At 720 J, a 10-mm zone of coagulationnecrosis surrounding a smaller central area of vaporization withimmediate tissue loss was demonstrated on whole-mount sec¬

tioning (Fig. 5). At 12 W (720 J), a 5-mm zone of vaporizationsurrounded by a 15-mm zone of coagulation necrosis was ob¬served (Fig. 6).

FIG. 2.seconds.

Some deep tissue effect is observed using 8 W/60

light, a laser beam is coherent, monochromatic, focusable, anddirectable. In 1964, Geusic and colleagues announced the de¬velopment of the Nd:YAG laser.9 The first clinically significantapplication of this laser in urology is attributed to Hofstetter andassociates, who in 1978 attempted coagulation of bladder tu¬mors transurethrally.10 The radiant energy of the laser beam can

be absorbed by tissue, where it is transformed into heat energythat produces medical and surgical effects in that tissue. At60°C, irreversible cell damage takes place, with coagulation ofblood vessels. At temperatures above 100°C, the intracellularwater begins to evaporate, causing shrinkage and tissue loss. Ifthe temperature continues to rise, the fluid contents of the tissuewill begin to vaporize in a plume containing charred tissue

DISCUSSION

The emission of a laser beam, first achieved in 1960, is one

of the greatest discoveries of this century.8 Unlike ordinary

FIG. 1. Prototype synthetic sapphire probe for interstitialcontact laser.

PL·

FIG. 3. Gross coagulation necrosis (1.5 cm) surrounds areaof tissue vaporization. This lesion was induced at 720 J (12W/60 seconds).

LAPAROSCOPIC ABLATION OF RENAL LESIONS 155

FIG. 4. Histologie section of porcine kidney treated with 8W/60 seconds (480 J). Small region of vaporization is sur¬rounded by concentric region of coagulation necrosis. (H&E)(X48)

FIG. 6. Histologie examination of tissue in Figure 5 demon¬strating region of central vaporization and zone of coagulationnecrosis. (H&E)(x 120)

components and fluid vapor. A surgical lesion is created sur¬

rounded by a zone of coagulation necrosis. ' '

In 1985, Daikuzono and Joffe introduced a completely new

method of delivering Nd:YAG energy to tissue that has over¬

come many of the limitations encountered with the conven¬

tional noncontact systems.12 Contact laser probes are made of a

synthetic sapphire crystal and, when used in direct contact with

SPECIMEN

FIG. 5. Whole-mount section of porcine kidney treated with720 J demonstrating immediate tissue loss through vaporiza¬tion.

tissue, allow precisely controlled manipulations. By selectingthe appropriate probe and laser power, those investigators were

able to determine the precise spot size and power density and tocontrol the shape and volume of the thermal effect.3

Because òf its optical design, a synthetic sapphire contact

probe diffuses the laser energy from the lateral surface of theprobe and can be used as an interstitial probe. Brown13 initiallyused the Nd:YAG laser for hyperthermia, inserting the barefiber directly into a tumor. However, the high power density atthe distal end of the fiber caused tip damage and tissue vapor¬ization. The burned tissue absorbed the laser energy, and a verylimited amount of tissue was heated. The interstitial contact

probe has a higher melting point and greater tensile strengththan the previously used bare quartz fiber, which ensures ther¬mal and mechanical stability.14

Daikuzono, Joffe, and their associates4·14 reported earlier on

the safety, efficiency, and effectiveness of the interstitial con¬

tact laser technique and coined the term "laserthermia." Theyused a computer-controlled laser system to increase the temper¬ature of the tumor, which was monitored by a thermocoupleinserted into the tumor. Controlled destruction of tissue throughhyperthermia has been attempted with various energy sources,including heated water, electromagnetic energy from radiofre-quency, microwaves, sonic energy from ultrasound, scatteredlight from infrared light, and lasers.14 Hyperthermia destroysboth normal and tumor tissue. Laser energy delivered by fibersinserted into tissue appears to provide an excellent form of localhyperthermia for superficial and deep-seated tumors of clinicalimportance. Early reports of interstitial laser ablation of tissuessuch as liver tumors are beginning to appear in the litera¬ture.15-21 Interstitial laser energy appears to be able to destroytarget tissue and ensure minimal damage to adjacent normaltissue. Subsequent healing of all treated areas so that acceptablefunction and mechanical structure of the organ is maintained atall times also appears to be possible.

The contact Nd:YAG laser is assuming a greater importancein endoscopie and open surgery, allowing coagulation, cutting,and vaporization with greater precision and safety. The abilityto deliver energy in a controlled manner to any tissue accessibleto a single flexible fiber will produce hyperthermia in a rela-

156 LOTFI ET AL.

tively easy and uniform pattern of heat distribution with imme¬diate tissue loss through vaporization at higher energy levels.

In this experimental model, we demonstrated that the intersti¬tial contact laser is capable of inducing coagulation necrosiswith or without significant tissue vaporization in the intactporcine kidney model depending on the energy level. Becausemost incidentally discovered renal adenomas are smaller than 3cm, the combined laparoscopic and interstitial laser ablationwarrants further study. This new technology of laserthermiausing the well-established principle of hyperthermia in the treat¬ment of cancer is expected to expand into many urologie appli¬cations, including renal cell carcinoma, prostate carcinoma,and benign prostatic hyperplasia, as either an adjuvant to or a

possible replacement for other treatment modalities. The lap¬aroscopic, percutaneous, or endoscopie placement of interstitialprobes under radiologie control opens a new area in the tech¬niques of minimally invasive surgery. Further experimental andclinical data are required in these areas.

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Address reprint requests to:Leonard Gomella, M.D.

Dept. of UrologyJefferson Medical College

1025 Walnut St.Philadelphia, PA 19107