St George's Gynaecological Oncology Website
St George's Gynaecological Oncology Website
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Cervical Screening
by
Thomas Ind
Consultant Gynaecological Surgeon
St George's & Royal Marsden Hospitals
Introduction
Cervical cancer is caused by some types of HPV virus (most importantly types 16, 18, 31, 33, 45) (refer to handout on cervical cancer). Prior to the development of cervical cancer histological pre-cancerous changes exist called CIN (Cervical Intraepithelial Neoplasia). The development from contact with HPV, HPV DNA getting into cells, the development of CIN, and progression to cancer takes many years. The whole basis of cervical screening in the UK is to detect CIN before it develops into cancer.
NHSCSP
The NHSCSP (National Health Service Cervical Screening Programme) is well recognised as being one of the best in the world. Attendance is over 80% with over 4 million smear tests reported every year. This has resulted in the number of deaths from cervical cancer in England and Wales falling to below 1000 every year. When you take into account the increasing incidence of sexual activity and early age of first sexual encounter then statistically we should have over 5000 deaths from cervical cancer if it were not for the screening programme.
The NHSCSP now offers a smear test at the age of 25; three yearly until 50 years; and five yearly from 50 years. Annual smear tests are performed for two years following treatment for CIN 1 and for ten years following treatment for CIN 2 or 3.
Age Group Frequency of Screening
25 First invitation
25 – 49 Three yearly
50 – 64 Five yearly
65+ Only those not screened from 50
or those with recent abnormal test
Smear test
When a biopsy of the cervix is taken, the full thickness of the tissue can be analysed by a histopathologist and CIN can be diagnosed (if present). When a smear is taken, only the top layer of cells can be analysed. Therefore, CIN cannot be diagnosed on a smear. However, changes in the top layer of cells can be analysed and these can be equated to CIN.
The terminology used for an abnormal cervical smear is Mild, Moderate, and Severe Dyskaryosis. These terms equate to the histopathological diagnoses of CIN 1 2 & 3. The smear test is a screening test (not a diagnostic test). It selects out a group of women to have a colposcopy and biopsy. It is about 60% accurate at predicting CIN but if repeated on a three yearly basis can prevent about 92% of all cervix cancers.
Incorrect smear results can occur from the incorrect taking of a smear, laboratory errors, and inaccurate reading. However, the technology is not 100% and even with good taking, preparation and interpretation the result can be incorrect. In the UK all negative and inadequate smears are reviewed by a second screener and all abnormal smears are reviewed by a consultant cytopathologist.
In the UK cervical screening is managed by the NHSCSP. Standards exist for smear takers and for cytologists examining the smears.
It is important for every medical student to know how to take a smear test. The newest method is with a cervical broom using liquid based cytology and this method will be described in detail. All students should practice this on the model provided by St George’s Hospital.
1 Prepare (before you meet the patient)
a. Label pot
b. Lay out instruments
i. Speculum (ensure that screw open and speculum warmed)
ii. Pot
iii. Broom
iv. Lubricant (should always be used irrespective possible effect on cytology)
2 When patient arrives
a. Introduce yourself
i. Name
ii. Position
b. Explain how the smear is going to be taken
3 Chaperone (for both men and women)
4 History (normally already taken)
5 Take verbal consent
6 Ask patient to undress (should occur in privacy without anyone watching)
7 Examine
a. Abdomen
b. Vaginal examination to locate position of cervix
8 Insert warm speculum with KY Jelly (direct insertion is OK; some prefer to insert at 45o and turn so horizontal – if so ensure only 45o so clitoris is not involved)
9 Open speculum and visualise the cervix
10 Apply broom
a. Middle portion should be in os
b. Outside portions should bend
c. Do five complete rotations of the broom
11 Place in liquid pot (10 firm dunks)*
12 Remove speculum ensuring vaginal wall not caught in blades
13 Cover patient and explain that the test is completed
14 Ensure that the form is correctly labelled and the pot is correctly labelled (check with patient)
* The method described is with the ThinPrep® technique. Surepath is another method of liquid based cytology and with this technique you must leave the brrom end in the liquid.
The older method of taking a smear was with a wooden spatula and slide. The wooden spatula would be turned 360o and pasted onto the slide before fixative was applied. This method is still being used in many GP surgeries until funding is found for the newer liquid based cytology which has less inadequate smears.
When taking a smear it is important to sample the transformation zone (where squamous ectocervical cells change to glandular endocervical cells). In some countries a smear is only considered adequate if both endo- & ecto- cervical cells are present. This is not the case in the UK but it is best practice to have both types of cells visible on a smear slide.
Abnormal Smears
The following are terms used to classify an abnormal smear according to NHSCSP Guidelines;
o Inadequate
o Borderline nuclear change – Squamous cell change
o Borderline nuclear change – Endocervical cell change
o Mild dyskaryosis
o Moderate dyskaryosis
o Severe dyskaryosis
o Possible invasion
o Glandular neoplasia
Inadequate smear
This means that there are not enough cells to make a diagnosis or that cervical cells are obscured by others (e.g. inflammatory or blood cells). A women should be referred to colposcopy after three consecutive inadequate smears.
Borderline smears
This is a smear where there are minor changes not amounting to mild dyskaryosis or atypical glandular cells (borderline nuclear change – squamous cell change or borderline nuclear change – endocervical cell change). Women should be referred to colposcopy after three consecutive borderline smears of squamous cell type and one of endocervical type.
Dyskaryosis
This can be mild, moderate, or severe. Over 75% of women with moderate and 85% of women with severe dyskaryosis have CIN 2 or 3 and are recommended colposcopy. The management of mild dyskaryosis is less clear. Dependant on which study is believed between 14 % and 60 % of women will have CIN 2 or 3. Cost benefit analysis supports colposcopy but as expertise are not universally available colposcopy is only recommended not compulsory. It is quite acceptable to repeat the smear in 3 – 6 months after a mildly dyskayotic smear and only referring if the second smear is abnormal.
Possible invasion
As a smear only takes the surface cells away it cannot diagnose invasion (cancer). However, some cytologic features strongly suggest invasion and in these circumstances colposcopy is recommended.
Glandular neoplasia
This denotes a possible abnormality in endocervical cells. Colposcopy is recommended as both preinvasive (precancer) and invasive (cancer) disease is possible).
Colposcopy
Colposcopy is an investigation for CIN. It involves examining a woman’s cervix through a specially designed microscope (colposcope). Cervical Intraepithelial Neoplasia (CIN) is diagnosed at biopsy. Acetic acid and Iodine are used as dyes. Acetic acid goes white with CIN and changes such as ‘mosiacism’ and ‘punctation’ can be seen with different levels of CIN. Iodine stains the cervix dark brown to black. Areas of CIN are light brown. Many things can cause false positive results on colposcpy stained with acetic acid or iodine alone and biopsy is recommended if abnormal areas are seen.
Treatment for CIN
The most common form of treatment for CIN is LLETZ (Large Loop Excision of the Transformation Zone). This is done in outpatients under local anaesthetic 85% of the time and involves the excision of about 1½ sugar lumps of tissue from the cervix using a fine wire loop and diathermy current. Other treatments include LASER cone biopsy (a cone of tissue is excised using a LASER); LASER ablation (a similar amount of tissue is ablated using LASER); LASER diathermy (a similar amount of tissue is ablated using diathermy); Cone biopsy (a cone of tissue is excised with a knife); NETZ (Needle Excision of the Transformation Zone – a cone of tissue is excised using a needle diathermy); and cold coagulation (100 degrees heat applied to cervix). Cryocautery (freezing of the cervix) does not cause an adequate depth of treatment and should not be used.
Confusion with terminology
A student should beware of terminology in American textbooks. Screening methods differ throughout te world and only UK books will give UK screening recommendations. Only books of less than a year old are likely to include the most recent recommendations. The ‘dysplasia’ is often used in the USA and equates to CIN and dyskarysis. The term LSIL and HSIL refer to Low & High grade Squamous Intraepithelial Lesions which correspond to CIN 1 and CIN 2 & 3 respectively. In the USA the term ASCUS (Atypical Squamous Cells of Uncertain Significance) equates to the UK cytological diagnosis of borderline nuclear change in squamous cells. The American term LEEP (Loop Electrical Excision Procedure) is equivalent to a LLETZ procedure.
Colposcopy certification
Most doctors who do colposcopy now hold the colposcopy certificate. This means that they attend a course every three years and submit an audit of their work every three years.
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