eMedicine Specialties > Obstetrics and Gynecology > Gynecologic Surgery
Carbon Dioxide Laser Surgery for Cervical Dysplasia
Updated: Dec 5, 2007
Introduction
History of the Procedure
The key mechanisms of action of the laser were first discovered by Albert Einstein in the early 1900s. Initial results from the use of a carbon dioxide laser for the management of cervical dysplasia were less successful than anticipated initially because of an inability to determine penetration to an appropriate depth for reduction of recurrent disease. Not until 1978 did Anderson and Hartley emphasize the actual mechanics for the depth of cervical involvement.1 This task was further refined and shown to be both practical and efficacious by Jordan in 19852 and by Dorsey in 19793 , when the Greater Baltimore Medical Center published the first clinical experience with cervical conizations by carbon dioxide laser.
The carbon dioxide laser has been considered an effective modality for multiple tasks related to the treatment of cervical intraepithelial neoplasia (CIN), but most commonly for large lesions and for multifocal manifestations of human papilloma virus (HPV) disease. The use of this technology is limited in some areas because of healthcare provider and physician training experience and because of a lack of availability of equipment. Many hospitals require that specific credentials be obtained before using this modality, including documentation of didactic instruction and clinical supervision of initial procedures.
Problem
The US National Breast Cancer and Cervical Cancer Early Detection Program reports an overall rate of abnormal Papanicolaou test results of 3.8%, with specific rates for low-grade squamous lesions, high-grade squamous lesions, and squamous carcinoma of 2.9%, 0.8%, and 0.1%, respectively.4
In 2005, The US Centers for Disease Control and Prevention estimated that 20 million Americans are DNA positive for an anogenital type of HPV at any time. Almost half are sexually active adolescents or young adults aged 15-24 years. In the United States, 6.2 million individuals are estimated to become newly infected with HPV yearly.
CIN is a descriptive histologic term for squamous cervical abnormalities that are not malignant. CIN is subdivided into CIN types 1 (mild), 2 (moderate), or 3 (severe dysplasia). Histologically, the degrees of CIN (ie, 1, 2, or 3) correlate with the penetration of cellular abnormalities from the basal membrane to the surface. One-third penetration is mild, two-thirds penetration is moderate, and full-thickness penetration is severe.
The specific cytologic terminology has been revised since Dr. Papanicolaou's original classification in 1954. It has evolved from the descriptive terminology of 1968, to the terminology cited above as CIN in 1978, and finally culminating with the Bethesda System classification initially released in 1988 and revised in 2001. Those cytologic abnormalities most amenable to carbon dioxide laser therapy are now categorized as squamous intraepithelial lesions (SILs). In addition to these cytologic abnormalities of the cervix (ie, SILs), the treatment of squamous abnormalities and condyloma of the vagina and vulva are possible using the laser. Before performing an ablative or excisional procedure, cytologic abnormalities are evaluated by biopsy.
Optimal therapy for these problems is not confined to a single treatment algorithm, and several alternatives exist. Patient care must be individualized, and consideration must be given to age, parity, prior cervical cytologic abnormalities and treatments, plans for future childbearing, and the coexistent medical conditions of each patient. Carbon dioxide laser assists with conservative management of these cervical abnormalities.
Frequency
HPV infection has been demonstrated to be a highly significant risk determinant of cervical neoplasia. High-risk HPV types (ie, 16, 18, 31, 45) exhibit the strongest association with cervical malignancy. The presence of the virus alone may not be the sole cause of SILs or malignancy. Additional factors of importance include the following:
- HPV type, viral load, or simultaneous infection with multiple HPV types
- Duration of HPV infection
- Individual genetic predisposition
- Host and environmental factors
- Number of lifetime sexual partners
- Younger age at sexual debut
- Socioeconomic status and dietary factors
- Cigarette smoking
- Contraception
- Other sexually transmitted infections
Most women encounter HPV during their lifetime, and the cumulative prevalence rate is 25-60%.5 HPV infection may be present in women with normal cervical cytology, and most HPV types can cause mild or low-grade cervical cytologic abnormalities.6 As cytologic abnormalities become more severe (eg, high-grade SILs, moderate-to-severe dysplasia), a greater proportion of high-risk HPV types are identified.7
Terminology from the Bethesda System of cytologic evaluation of cervical cytology uses the term low-grade squamous intraepithelial lesion (LSIL) to refer to the cytological changes previously referred to as mild dysplasia, CIN 1, HPV effects, and koilo cytosis. In addition, the increased use of liquid-based cytology screening combined with this change in terminology has resulted in an increased number of Pap smears interpreted as LSIL. The median percentile reporting rate of LSIL in the United States was 2.4% for liquid-based specimens.
The terminology high-grade squamous intraepithelial lesion (HSIL), as defined by the Bethesda System, previously corresponded to the cytologic findings of moderate dysplasia, severe dysplasia, carcinoma in situ, CIN 2, 3. The rate of HSIL varies with age, being highest in women aged 20-29. The finding of HSIL is significant for findings associated with cervical disease and dysplasia, which may necessitate treatment. CIN 2, 3 or cervical cancer has been identified in 53-66% of women with HSIL cytologic results; 2% of women with HSIL were identified with invasive carcinoma.8
Until the development of the loop electrosurgical excision procedure (LEEP), the carbon dioxide laser represented the most versatile and effective tool available for treating cervical cytologic abnormalities. The advantages of carbon dioxide laser treatment include (1) a high cure rate, (2) the ability to treat multifocal or large lesions, (3) the ability to treat a range of cervical disorders by using ablative or excisional techniques, (4) excellent healing, (5) few complications, and (6) the ability to perform the procedure in an office or hospital setting. Disadvantages include (1) the availability of equipment, (2) the cost of purchasing new equipment, and (3) the availability of trained practitioners.
Etiology
The most likely etiology of squamous abnormalities of the cervix is infection with HPV, a double-stranded DNA tumor virus of the Papovaviridae family. The HPV has more than 100 subtypes and is present in more than 90% of preinvasive and invasive squamous neoplasms of the cervix. Serotypes associated with cervical squamous lesions may be designated as having a high or low risk for progression to malignancy.
Ultimate cure of the viral infection can only be achieved by the immune system of the human host because papillomaviruses are ubiquitous in higher vertebrates. Approximately 25 types of HPV infect the genital tract. Higher risk types, including types 16 and 18, are classified as such because of the gene products that bind to tumor suppressor portions of the host cells and cause their ultimate inactivation. Interactions of HPV with histocompatibility antigens may help explain why the same HPV type leads to invasive disease in one patient and not in another.
Treatment modalities, such as the carbon dioxide laser, destroy or excise infected cells, thus reducing the amount of infected tissue and, presumably, the host viral load. The subsequent healing process of the host stimulates viral combat at the surgical site.
Indications
Patients with abnormal cervical cytology findings must first be evaluated using colposcopy to help determine the location, extent, and severity of the clinical abnormalities. Colposcopically directed biopsies are indicated when, in the clinical opinion of the health care provider, CIN is present. Findings from one or more biopsy samples from the involved areas and findings from an endocervical curettage help document the location and histologic severity of the disease present.
The carbon dioxide laser has been used for ablating CIN or excising abnormal areas, including the transformation zone.
The carbon dioxide laser is customarily chosen over other ablative or excisional techniques when great precision is needed, particularly in situations involving large areas or when precise control over the depth of penetration is desired. Examples of procedures for which carbon dioxide laser is indicated include (1) ablation or excision of CIN in situations in which minimization of tissue destruction or removal is desired; (2) cervical treatment combined with treatment of dysplasia or condylomata or CIN on the vulvar, vaginal, perineal, or perirectal areas; and (3) multifocal cervical disease.
The carbon dioxide laser is used in conjunction with a microscope or colposcope. This allows precise application, which is one advantage of this treatment modality. Another advantage of the laser is hemostasis and minimal thermal necrosis (<100 µm) when properly set. In addition, the procedure time is brief, and the laser may be used in an office or outpatient setting with the patient under local anesthesia. The office setting also may be more economical than procedures performed in an outpatient setting.
Relevant Anatomy
HPV infects squamous and glandular cells of the cervix and squamous cells of the vagina and vulva. Evaluation of the cervix to detect abnormalities involves inspecting the cervix from the vaginal junction to the most cephalad extent of the visible endocervix. This, by definition, includes the transformation zone, the site where squamous and glandular cells meet and squamous metaplasia occurs. This area has the highest cell turnover and is by far the most common site for cytologic abnormalities.
The transformation zone is the histopathologic term used to describe the area of squamous metaplasia. This area is located between the mature columnar cells of the endocervix and the mature squamous cells of the external cervical portio. Although a sharp edge of demarcation is seen in many patients, in others, this transformation zone is an area of more gradual cellular change. The term metaplasia is defined as the transformation of one mature cell type to another. The location of the transformation zone is customarily on the external cervical surface or within the endocervical canal, and its position is determined by a number of factors, including inflammation, vaginal pH, or the presence of exogenous or endogenous hormones (eg, estrogen).
Contraindications
Contraindications to using the carbon dioxide laser for the treatment of CIN include (1) an inability to visualize the area to be treated because of anatomic considerations (eg, prolapsing lateral vaginal sidewall), (2) preoperative histology findings indicative of malignancy, and (3) inadequate physician training or experience. Laser ablation is contraindicated if the entire lesion is not visible, although excision procedures may be performed.
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References
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Further Reading
Keywords
CO2 laser surgery, laser surgery, cervical intraepithelial neoplasia, CIN, human papilloma virus, HPV, squamous cervical abnormality, squamous carcinoma, squamous cell cancer, squamous intraepithelial lesion, SIL, cervical neoplasia, cervical cancer, cervical malignancy, atypical squamous cells of undetermined significance, ASCUS, cervical atypia, squamous atypias
