Comparison of thermal injury zones in loop electrical and laser cervical excisional conization Michael S. Baggish, MD, Faith Barash, MD, Yvonne Noel, MD, and Marlon Brooks, MD Syracuse, New York Thirty cervical conization specimens obtained by thin-loop electric excision were compared with 30 carbon dioxide laser excisional cone specimens. Zones of thermal artifact were measured with a precise stage micrometer technique calibrated to a Zeiss standard. The mean depth of coagulation at the ectocervical margin measured 0.187 and 0.164 mm for thin loop and laser, respectively. Thermal artifact at the endocervical margin was greater with electric loop (0.295 mm) than with superpulsed carbon dioxide laser (0.137 mm). The zones of thermal injury induced by both electric loop and laser made no significant impact on the interpretation of margin adequacy. (AM J OBSTET GVNECOL 1992;166:545-8.) Key words: Loop electric conization, carbon dioxide laser, thermal injury From the Department of Obstetrics and Gynecology, State University of New York Health Science Center at Syracwe and Crouse Irving Memorial Hospital. R eceivedf01' publication March 15,1991 ; revised June 27, 1991; accepted July 15, 1991. Reprint requests: Michael S. Baggish, MD, Department of Obstetrics and Gynecology, Ravenswood Hospital Medical Center, 4550 N. Winchester, Suite 3633, Chicago, JL 60640. 6/1 /32446 Recent reports of large-l oo p diathermy to perform outpatient conization for the treatment of cervical in- traepithelial neoplasia have appeared in the peer re- view literature. H This method of excision combines the advantages of simplicity, hemost asis, and the retrieval of a pathologic specimen with economy. The latter may be exem plified by considering that women who have Fig. 1. A, Ectocervical margin of loop electric cone specimen. Slage micromeler is al igned perpen- dicularly with specimen. (Original magnification x 40.) B, Zone of lhermal injury can be divided into small zone of carbonization and desiccated-coagulated zone benealh. (Original magnificalion x 100.) 545 Comparison of thermal injury zones in loop electrical and laser cervical excisional conization Michael S. Baggish, MD, Faith Barash, MD, Yvonne Noel, MD, and Marlon Brooks, MD Syracuse, New York Thirty cervical conization specimens obtained by thin-loop electric excision were compared with 30 carbon dioxide laser excisional cone specimens. Zones of thermal artifact were measured with a precise stage micrometer technique calibrated to a Zeiss standard. The mean depth of coagulation at the ectocervical margin measured 0.187 and 0.164 mm for thin loop and laser, respectively. Thermal artifact at the endocervical margin was greater with electric loop (0.295 mm) than with superpulsed carbon dioxide laser (0.137 mm). The zones of thermal injury induced by both electric loop and laser made no significant impact on the interpretation of margin adequacy. (AM J OSSTET GVNECOL 1992;166:545-8.) Key words: Loop electric conization, carbon dioxide laser, thermal injury From the Department of Obstetrics and Gynecology. State University of New York Health Science Center at Syracuse and Crouse Iroing Memorial Hospital. Received for publication March 15, 1991; revised June 27. 1991; accepted July 15, 1991. Reprint requests: Michael S. Baggish, MD, Department of Obstetrics and Gynecology, Ravenswood Hospital Medical Center, 4550 N. Winchester, Suite 3633, Chicago, /L 60640. 6/1 /32446 Recent reports of large-loop diathermy to perform outpatient conization for the treatment of cervical in- traepithelial neoplasia have appeared in the peer re- view literature.1-4 This method of excision combines the advantages of simplicity, hemostasis, and the retrieval of a pathologic specimen with economy. The latter may be exemplified by considering that women who have Fig. 1. A, Ectocervical margin of loop electric cone specimen. Stage micrometer is aligned perpen- dicularly with specimen. (Original magnification X 40.) B, Zone of thermal injury can be divided into small zone of carbonization and desiccated-coagulated zone beneath. (Original magnification x 100.) 545
Transcript
Comparison of thermal injury zones in loop electrical and laser cervical excisional conization
Michael S. Baggish, MD, Faith Barash, MD, Yvonne Noel, MD, and Marlon Brooks, MD
Syracuse, New York
Thirty cervical conization specimens obtained by thin-loop electric excision were compared with 30 carbon dioxide laser excisional cone specimens. Zones of thermal artifact were measured with a precise stage micrometer technique calibrated to a Zeiss standard. The mean depth of coagulation at the ectocervical margin measured 0.187 and 0.164 mm for thin loop and laser, respectively. Thermal artifact at the endocervical margin was greater with electric loop (0.295 mm) than with superpulsed carbon dioxide laser (0.137 mm). The zones of thermal injury induced by both electric loop and laser made no significant impact on the interpretation of margin adequacy. (AM J OBSTET GVNECOL 1992;166:545-8.)
Key words: Loop electric conization, carbon dioxide laser, thermal injury
From the Department of Obstetrics and Gynecology, State University of New York Health Science Center at Syracwe and Crouse Irving Memorial Hospital. Receivedf01' publication March 15,1991; revised June 27, 1991; accepted July 15, 1991. Reprint requests: Michael S. Baggish, MD, Department of Obstetrics and Gynecology, Ravenswood Hospital Medical Center, 4550 N. Winchester, Suite 3633, Chicago, JL 60640. 6/1 /32446
Recent reports of large-loop diathermy to perform outpatient conization for the treatment of cervical intraepithelial neoplasia have appeared in the peer review literature. H This method of excision combines the
advantages of simplicity, hemostasis, and the retrieval of a pathologic specimen with economy. The latter may be exemplified by considering that women who have
Fig. 1. A, Ectocervical margin of loop electric cone specimen. Slage micromeler is aligned perpendicularly with specimen. (Original magnification x 40.) B, Zone of lhermal injury can be divided into small zone of carbonization and desiccated-coagulated zone benealh. (Original magnificalion x 100.)
545
Comparison of thermal injury zones in loop electrical and laser cervical excisional conization
Michael S. Baggish, MD, Faith Barash, MD, Yvonne Noel, MD, and Marlon Brooks, MD
Syracuse, New York
Thirty cervical conization specimens obtained by thin-loop electric excision were compared with 30 carbon dioxide laser excisional cone specimens. Zones of thermal artifact were measured with a precise stage micrometer technique calibrated to a Zeiss standard. The mean depth of coagulation at the ectocervical margin measured 0.187 and 0.164 mm for thin loop and laser, respectively. Thermal artifact at the endocervical margin was greater with electric loop (0.295 mm) than with superpulsed carbon dioxide laser (0.137 mm). The zones of thermal injury induced by both electric loop and laser made no significant impact on the interpretation of margin adequacy. (AM J OSSTET GVNECOL 1992;166:545-8.)
Key words: Loop electric conization, carbon dioxide laser, thermal injury
From the Department of Obstetrics and Gynecology. State University of New York Health Science Center at Syracuse and Crouse Iroing Memorial Hospital. Received for publication March 15, 1991; revised June 27. 1991; accepted July 15, 1991. Reprint requests: Michael S. Baggish, MD, Department of Obstetrics and Gynecology, Ravenswood Hospital Medical Center, 4550 N. Winchester, Suite 3633, Chicago, /L 60640. 6/1 /32446
Recent reports of large-loop diathermy to perform outpatient conization for the treatment of cervical intraepithelial neoplasia have appeared in the peer review literature.1-4 This method of excision combines the advantages of simplicity, hemostasis, and the retrieval of a pathologic specimen with economy. The latter may be exemplified by considering that women who have
Fig. 1. A, Ectocervical margin of loop electric cone specimen. Stage micrometer is aligned perpendicularly with specimen. (Original magnification X 40.) B, Zone of thermal injury can be divided into small zone of carbonization and desiccated-coagulated zone beneath. (Original magnification x 100.)
545
546 Baggish et al.
Fig. 2. Total zone of thermal injury measures 0.230 mm. (Original magnification x 200.)
been screened cytologically may undergo a colposcopic examination with accurate identification of the abnormal transformation zone followed by loop electric excisional conization, which provides both histologic diagnosis and therapy in one sitting. Although this therapeutic program at first appears to be ideal, certain concerns should be considered. The histologic quality of the specimen, particularly at the resection margins, is vitally important to determine whether all the disease has been removed and to determine the severity of disease. If thermal artifact makes this determination impossible, then this alone would constitute a major disadvantage of the technique. In the last decade the carbon dioxide laser became an accepted alternative to knife conization because of its precision and hemostatic benefits and because it eliminated the need for sutures. The literature contains descriptions of large numbers of laser conization operations whose specimens showed highly acceptable margins and demonstrated a slight degree of thermal injury to neighboring tissue.5
.7 This
article concerns itself with prospectively comparing and accurately quantitating the zones of irreversible thermal injury created by the loop electric cone and the carbon dioxide laser cone.
Material and methods
Thirty loop electric excisional conization specimens were obtained from women with cytologic and col poscopically directed biopsy evidence of cervical intraepithelial neoplasia. Another 30 excisional conization samples emanated from women with cervical intraepithelial neoplasia diagnosed in the outpatient depart-
February 1992 Am J Obslel Gynecol
Table I. Mean depth of thermal injury in excisional conization
Technique
Loop electric Carbon dioxide laser
Ectocervical margin (mm)
0.187 0.164
Endocervical margin (mm)
0.295 0.137
ment who underwent laser excisional conization. Both laser and electric loop excisions were performed by M.S.B. or one of the pelvic surgery fellow coauthors. All cone specimens were fixed in formalin, cut, blocked, sectioned, and stained with hematoxylin and eosin.
The specimens were examined by M.S.B. with an Olympus Vanox T Photomicroscope (Olympus, Newtown, Pa.) equipped with a built-in stage micrometer and floating stage. Before the sections were examined, the stage micrometer was calibrated to a I mm standard (Carl Zeiss, Thornwood, N.Y. ) subdivided into 0.01 mm segments. The calibration was made with X 4 and X 10 objectives. Margins were measured by orienting the stage to effect a perpendicular measurement, initiating the measurement at the outer carbonized zone and finishing at the beginning of normal stromal or epithelial tissue. Three measurements were performed for each section and averaged. A total of 1200 sections were studied.
An ERBE model 450 (ERBE, USA, Mission Viejo, Calif.) or a Valley Lab Force 2 (Boulder, Colo.) highfrequency (350-750 kHz), low-voltage electrosurgical generator with a 400 W rated output at 350 n resistance with automatic voltage regulation during cutting was used for all loop excisions. Five predetermined settings were available with the Erbe unit. The Valley Lab unit was set to deliver 50 W of power. A setting that used a four fifths cut to one fifth coagulation blend was used (setting 200 to 500 V) for the 30 conizations performed with this equipment. The loops used to perform the conizations ranged from 15 to 10 mm in height (measured from the top of the loop to the insulated Y connection of the probe yolk). The wire electrodes measured 0.2 mm in diameter. Conizations were performed by placing the loop perpendicularly to the cervix at either the 12 or 6 o'clock position with approximately a 3 mm margin around the atypical transformation zone, activating the cutting button on the handle of the probe, and allowing the wire to cut into the cervix to the desired depth. Next the loop was swept across the base of the tissue with very slight pressure while the cutting button was depressed, i.e., allowing the speed of the vaporization to determine the velocity of the sweep and subsequent finishing scoop action of the operator's hand.
A Lasersonics model 500 Z (Heraeus Lasersonics, Milpitas, Calif.) carbon dioxide laser rated at 60 W power and equipped with a micromanipulator was cou-
546 Baggish et al.
Fig. 2. Total zone of thermal injury measures 0.230 mm. (Original magnification x 200.)
been screened cytologically may undergo a colposcopic examination with accurate identification of the abnormal transformation zone followed by loop electric excisional conization, which provides both histologic diagnosis and therapy in one sitting. Although this therapeutic program at first appears to be ideal, certain concerns should be considered. The histologic quality of the specimen, particularly at the resection margins, is vitally important to determine whether all the disease has been removed and to determine the severity of disease. If thermal artifact makes this determination impossible, then this alone would constitute a major disadvantage of the technique. In the last decade the carbon dioxide laser became an accepted alternative to knife conization because of its precision and hemostatic benefits and because it eliminated the need for sutures. The literature contains descriptions of large numbers of laser conization operations whose specimens showed highly acceptable margins and demonstrated a slight degree of thermal injury to neighboring tissue.5
.7 This
article concerns itself with prospectively comparing and accurately quantitating the zones of irreversible thermal injury created by the loop electric cone and the carbon dioxide laser cone.
Material and methods Thirty loop electric excisional conization specimens
were obtained from women with cytologic and col poscopically directed biopsy evidence of cervical intraepithelial neoplasia. Another 30 excisional conization samples emanated from women with cervical intraepithelial neoplasia diagnosed in the outpatient depart-
February 1992 Am J Obstet Gynecol
Table I. Mean depth of thermal injury in excisional conization
Technique
Loop electric Carbon dioxide laser
Ectocervical margin (mm)
0.187 0.164
Endocervical margin (mm)
0.295 0.137
ment who underwent laser excisional conization. Both laser and electric loop excisions were performed by M.S.B. or one of the pelvic surgery fellow coauthors. All cone specimens were fixed in formalin, cut, blocked, sectioned, and stained with hematoxylin and eosin.
The specimens were examined by M.S.B. with an Olympus Vanox T Photomicroscope (Olympus, Newtown, Pa.) equipped with a built-in stage micrometer and floating stage. Before the sections were examined, the stage micrometer was calibrated to a 1 mm standard (Carl Zeiss, Thornwood, N.Y. ) subdivided into 0.01 mm segments. The calibration was made with X 4 and X 10 objectives. Margins were measured by orienting the stage to effect a perpendicular measurement, initiating the measurement at the outer carbonized zone and finishing at the beginning of normal stromal or epithelial tissue. Three measurements were performed for each section and averaged. A total of 1200 sections were studied.
An ERBE model 450 (ERBE, USA, Mission Viejo, Calif.) or a Valley Lab Force 2 (Boulder, Colo.) highfrequency (350-750 kHz), low-voltage electrosurgical generator with a 400 W rated output at 350 n resistance with automatic voltage regulation during cutting was used for all loop excisions. Five predetermined settings were available with the Erbe unit. The Valley Lab unit was set to deliver 50 W of power. A setting that used a four fifths cut to one fifth coagulation blend was used (setting 200 to 500 V) for the 30 conizations performed with this equipment. The loops used to perform the conizations ranged from 15 to 10 mm in height (measured from the top of the loop to the insulated Y connection of the probe yolk). The wire electrodes measured 0.2 mm in diameter. Conizations were performed by placing the loop perpendicularly to the cervix at either the 12 or 6 o'clock position with approximately a 3 mm margin around the atypical transformation zone, activating the cutting button on the handle of the probe, and allowing the wire to cut into the cervix to the desired depth. Next the loop was swept across the base of the tissue with very slight pressure while the cutting button was depressed, i.e., allowing the speed of the vaporization to determine the velocity of the sweep and subsequent finishing scoop action of the operator's hand.
A Lasersonics model 500 Z (Heraeus Lasersonics, Milpitas, Calif.) carbon dioxide laser rated at 60 W power and equipped with a micromanipulator was cou-
Volume 166 Number 2
Thermal tissue effects of electric loop and carbon dioxide laser 547
Fig. 3. A, Endocervical margin of loop electric excisional cone shows more extensive zone of thermal injury. Note vascular thrombosis and endocervical cleft distortion. (Original magnification x 100.) B, Detail of endocervical margin with 0.390 mm coagulation artifact. (Original magnification x 200.)
pled to a Zeiss OPM I-H colposcope. The 30 laser conizations were carried out with 40 W of power and a 0.5 mm spot according to methods previously described.' The endocervical margin was cut off with a superpulsed beam emitting 500 pulses/sec, 0.5 millisecond pulse width, with an average power of 23 W.
Results
Measurement of sections obtained from loop excisions revealed two zones of thermal injury at the ectocervical and endocervical margins (Table I): (1) a small zone of carbonization and tissue debris (Fig. 1) and (2) a larger zone of coagulation necrosis and vascular coagulation (Fig. 2). The latter could be easily defined from normal stromal tissue by its deeper pink color and its denser appearance (a secondary effect of desiccation). The range of total thermal injury was 0.91 to 0.300 mm with a mean of 0.187 mm.
The thermal injury zone was greater in both range and mean at the endocervical margin (Fig. 3). The range of thermal injury extended from 0.190 to 0.455 mm with a mean thermal injury zone of 0.295 mm.
Laser conization specimens demonstrated identical zones of thermal injury, i.e., carbonized zone and desiccation-coagulation zone. The ectocervical margins total from 0.091 to 0.210 mm with a mean zone of 0.164 mm. The endocervical margin's zone of thermal injury was smaller than those observed with the electric loop, ranging from 0.090 to 0.230 mm with a mean of 0.137 mm (Fig. 4). However, this small difference made
Fig. 4. Superpulsed laser endocervical margin measures 0.143 mm with small carbonization layer. (Original magnification x 100.)
no impact on the interpretation or adequacy of the margin.
The carbonized zones were virtually identical in both groups, measuring 0.013 to 0.026 mm.
Volume 166 Number 2
Thermal tissue effects of electric loop and carbon dioxide laser 547
Fig. 3. A, Endocervical margin of loop electric excisional cone shows more extensive zone of thermal injury. Note vascular thrombosis and endocervical cleft distortion. (Original magnification x 100.) B, Detail of endocervical margin with 0.390 mm coagulation artifact. (Original magnification x 200.)
pled to a Zeiss OPM I-H colposcope. The 30 laser conizations were carried out with 40 W of power and a 0.5 mm spot according to methods previously described.' The endocervical margin was cut off with a superpulsed beam emitting 500 pulses/sec, 0.5 millisecond pulse width, with an average power of 23 W.
Results
Measurement of sections obtained from loop excisions revealed two zones of thermal injury at the ectocervical and endocervical margins (Table I): (1) a small zone of carbonization and tissue debris (Fig. 1) and (2) a larger zone of coagulation necrosis and vascular coagulation (Fig. 2). The latter could be easily defined from normal stromal tissue by its deeper pink color and its denser appearance (a secondary effect of desiccation). The range of total thermal injury was 0.91 to 0.300 mm with a mean of 0.187 mm.
The thermal injury zone was greater in both range and mean at the endocervical margin (Fig. 3). The range of thermal injury extended from 0.190 to 0.455 mm with a mean thermal injury zone of 0.295 mm.
Laser conization specimens demonstrated identical zones of thermal injury, i.e., carbonized zone and desiccation-coagulation zone. The ectocervical margins total from 0.091 to 0.210 mm with a mean zone of 0.164 mm. The endocervical margin's zone of thermal injury was smaller than those observed with the electric loop, ranging from 0.090 to 0.230 mm with a mean of 0.137 mm (Fig. 4). However, this small difference made
Fig. 4. Superpulsed laser endocervical margin measures 0.143 mm with small carbonization layer. (Original magnification x 100.)
no impact on the interpretation or adequacy of the margin.
The carbonized zones were virtually identical in both groups, measuring 0.013 to 0.026 mm.
548 Baggish et al.
A major difference was noted in specimens taken with the electric loop measuring <5 mm deep. The zone of thermal injury in these instances was extensive, i.e., measuring up to 0.560 mm. The endocervical mucosa particulary showed extensive thermal artifact at the margin of resection. This degree of thermal injury was not produced with superpulsed laser beams, which again showed thermal injury measuring 0.090 mm to 0.230 mm.
Comment
Excisional cones obtained with high-frequency, lowvoltage, thin wire loops created wounds that were virtually identical to those obtained with the carbon dioxide laser. The zones of thermal injury were acceptably small and did not interfere with the histopathologic interpretation at either the ectocervical or endocervical margins. From this study the method of tissue ablation appears to be similar with either electric loop or laser modality, i.e., thermal energy creates temperatures exceeding 1000 C, resulting in vaporization of tissue. Lesser temperatures resulted in neighboring tissue undergoing desiccation and coagulation with resultant tissue distortion (thermal artifact). At the setting used in this study voltages between 200 and 500 were produced at the interface of the electrode (wire loop) and the tissue, creating electric arcs ideal for vaporization and associated with a low degree of coagulation. When voltage exceeded 500, more extensive coagulation was created with increased thermal artifact. Therefore the narrow band of 200 to 500 V is the acceptable range for electric excisional conization operations.
The laser wounds demonstrated in this study were obtained at power densities of approximately 16,000 W/cm2
• Less thermal damage was obtained at margins
February 1992 Am J Obstet Gynecol
where superpulsed beams were used because peak powers were extremely high (250 to 400 W) and pulsing allowed thermal relaxation of the tissues. With higher average superpulse powers, even less thermal i~ury might be anticipated, and over a large range of power settings, repetition rates, and pulse widths the zone of thermal injury in such instances would clearly vary directly with the duty cycle of the laser so long as that cycle remains <25%.
This study demonstrated that thin-loop high-frequency, low-voltage electric surgery and high-power density carbon dioxide laser produced similar wounds in excised human cervical tissue. The advantages of the electric thin loop relate to its simplicity and speed.
REFERENCES 1. Mor-Yosef S, Lopes A, Pearson S, Monaghan JM. Loop
GR. Colposcopic diagnosis and treatment of cervical dysplasia at a single clinic visit. Lancet 1990;2:229-31.
3. Luesley DM, Cullimore J, Redman CWE, et al. Loop diathermy excision of the cervical transformation zone in patients with abnormal cervical smears. BMJ 1990;300: 1690-2.
4. Prendeville W, Davis R, Berry PG. A low voltage diathermy loop for taking cervical biopsies: a qualitative comparison with punch biopsy forceps. Br J Obstet Gynaecol 1986;93:773-6.
5. Baggish MS, Dorsey J, Adelson M. A ten-year experience treating cervical intraepithelial neoplasia with the carbon dioxide laser. AM J Os STET GYNECOL 1989; 161 :60-8.
6. Baggish MS. A comparison between laser excisional conization and laser vaporization for the treatment of cervical intraepithelial neoplasia. AM J OSSTET GYNECOL 1986;155:39-44.
7. Baggish MS, Elbakry MM. Comparison of electronically superpulsed and continuous wave CO2 laser on the rat uterine horn. Fertil Steril1986;45:l20-7.
548 Baggish et al.
A major difference was noted in specimens taken with the electric loop measuring <5 mm deep. The zone of thermal injury in these instances was extensive, i.e., measuring up to 0.560 mm. The endocervical mucosa particulary showed extensive thermal artifact at the margin of resection. This degree of thermal injury was not produced with superpulsed laser beams, which again showed thermal injury measuring 0.090 mm to 0.230 mm.
Comment
Excisional cones obtained with high-frequency, lowvoltage, thin wire loops created wounds that were virtually identical to those obtained with the carbon dioxide laser. The zones of thermal injury were acceptably small and did not interfere with the histopathologic interpretation at either the ectocervical or endocervical margins. From this study the method of tissue ablation appears to be similar with either electric loop or laser modality, i.e., thermal energy creates temperatures exceeding 1000 C, resulting in vaporization of tissue. Lesser temperatures resulted in neighboring tissue undergoing desiccation and coagulation with resultant tissue distortion (thermal artifact). At the setting used in this study voltages between 200 and 500 were produced at the interface of the electrode (wire loop) and the tissue, creating electric arcs ideal for vaporization and associated with a low degree of coagulation. When voltage exceeded 500, more extensive coagulation was created with increased thermal artifact. Therefore the narrow band of 200 to 500 V is the acceptable range for electric excisional conization operations.
The laser wounds demonstrated in this study were obtained at power densities of approximately 16,000 W/cm2
• Less thermal damage was obtained at margins
February 1992 Am J Obstet Gynecol
where superpulsed beams were used because peak powers were extremely high (250 to 400 W) and pulsing allowed thermal relaxation of the tissues. With higher average superpulse powers, even less thermal i~ury might be anticipated, and over a large range of power settings, repetition rates, and pulse widths the zone of thermal injury in such instances would clearly vary directly with the duty cycle of the laser so long as that cycle remains <25%.
This study demonstrated that thin-loop high-frequency, low-voltage electric surgery and high-power density carbon dioxide laser produced similar wounds in excised human cervical tissue. The advantages of the electric thin loop relate to its simplicity and speed.
GR. Colposcopic diagnosis and treatment of cervical dysplasia at a single clinic visit. Lancet 1990;2:229-31.
3. Luesley DM, Cullimore], Redman CWE, et al. Loop diathermy excision of the cervical transformation zone in patients with abnormal cervical smears. BM] 1990;300: 1690-2.
4. Prendeville W, Davis R, Berry PG. A low voltage diathermy loop for taking cervical biopsies: a qualitative comparison with punch biopsy forceps. Br ] Obstet Gynaecol 1986;93:773-6.
5. Baggish MS, Dorsey], Adelson M. A ten-year experience treating cervical intraepithelial neoplasia with the carbon dioxide laser. AM] Os STET GYNECOL 1989; 161 :60-8.
6. Baggish MS. A comparison between laser excisional conization and laser vaporization for the treatment of cervical intraepithelial neoplasia. AM ] OSSTET GYNECOL 1986;155:39-44.
7. Baggish MS, Elbakry MM. Comparison of electronically superpulsed and continuous wave CO2 laser on the rat uterine horn. Fertil Steril1986;45:l20-7.
