Various epithelial types modify the general features of the colposcopic appearance described above. In the normal cervix, glycogen-containing squamous epithelium, which is present during reproductive life, is thick and multilayered and acts as an effective filter, imparting a pink to reddish appearance when viewed colposcopically. The columnar epithelium is thin, contains mucus, and is highly translucent, resulting in a dense red colposcopic appearance. Within the bounds of the transformation zone, defined as the area in the columnar epithelium where a new squamous (metaplastic) epithelium forms, will be found metaplastic epithelium at various stages of development. It may be thinner than the normal squamous epithelium, devoid of glycogen, and appear reddish. Very rapidly regenerating epithelium, as seen in immature squamous metaplastic tissue, may adopt an opaque appearance. Abnormal epithelium contains the CIN stages, some of which will be precancerous. It differs from normal epithelium in that it is more cellular, with a higher nuclear content. The result is an opaque appearance, which has sometimes been described as deep red mixed with a dirty gray of whitish discoloration.

The atrophic or postmenopausal, or indeed the prepubertal, squamous epithelium is thinner than normal squamous epithelium and devoid of glycogen. The stromal blood supply is reduced and, as seen later, is characterized by a pale red colposcopic appearance.

When inflammatory infiltration occurs within the stroma, the resultant colposcopic appearance of the epithelium may be altered. The result may be a grayish white or yellowish appearance, dependent purely upon the degree of stromal inflammatory infiltration.

This is determined by the surface shape and by the variations in thickness of the epithelium. The surface shape can be either smooth or papillary. Columnar epithelium, for example, is represented colposcopically as grape-like villi that, when pronounced, become conglomerated into the so-called columnar ectopy.

Vascular patterns also become evident through the surface, as will be discussed later (Chapter 6). The capillaries may shine through the epithelium, either appearing as red dots on a white or opaque background, giving rise to so-called punctation, or arborizing within the stromal papillary ridges that subdivide the surface epithelium and thereby forming discrete fields, the so-called mosaic epithelium.

An addition to the colposcopic image may occur when white patches, which can be seen by the unaided eye, appear on the surface epithelium. This so-called leukoplakia is due to a thick keratin covering that may overlie both histologic normal and abnormal epithelium.

The combination of variable degrees of epithelial maturity, alterations in surface contour, and in blood vessel patterns, as described above, results in variation in the appearance of both normal and abnormal epithelia. There is no single appearance which can be called pathognomonic, especially for the abnormal epithelium; these changes therefore allow grading systems to be adopted. This helps in the identification of lesions that are insignificant or significant in respect of management; the former with minimal neoplastic potential, where invasion is years away (if it ever occurs), and the latter with a neoplastic potential with a high malignant potential. This grading system will be described later in Chapter 6, together with the Reid colposcopic index (see Table 6.2) and the recently described Swede score (see Table 6.4).

The colposcope is a microscope providing illuminated magnification that allows the cervix to be viewed at between six- and 40-fold magnification. Originally developed by Hinselmann in the 1920s, it has gained popularity in the last five decades in Western Europe and North and South America.

The colposcope lens has a focal length ranging between 200 and 300 mm; this establishes a comfortable working distance for the observer. Occasionally, the objective can be less, i.e., 125 mm; this is used predominantly when the saline method of colposcopy, a technique to demonstrate the vascular patterns within the surface epithelium, is employed.

In the acetic acid technique, strengths of between 3% and 5% acetic acid are used; the solution is applied with either a cotton ball or spray. The acetic acid causes the tissues, especially the columnar and abnormal epithelia, to become edematous. Abnormal (atypical) epithelium adopts a white or opaque appearance, as described previously, which is then quite easy to distinguish from the normal epithelium, which appears pink. The acetic acid seems to act by causing the coagulation of epithelial and stromal cytokeratins in a reversible event.

There also seems to be swelling of the tissues with an increase in the keratin filament proteins in the epithelium, which stain white with acetic acid. These keratin filament proteins, called cytokeratin, seem to be increased in association with cellular edema caused by acetic acid in this type of epithelium. There are 20 different cytokeratin polypeptides, but it is cytokeratin 10 which is believed to be an essential requirement for the formation of the so-called acetowhite epithelial change.

Normally functioning squamous epithelial cells contain glycogen storage, which can be stained mahogany brown with Lugol’s iodine. Normal columnar cells do not contain enough glycogen storage and appear paler after application of iodine solution. Similarly transformation zones with precancerous or cancerous lesion contain very little or no glycogen. These areas appear pale yellow following application of Lugol’s iodine.

Application of Lugol’s iodine is not essential, but it is an important part of colposcopic examination. It is especially helpful to clearly delineate the abnormal area prior to any treatment. Vaginal lesions can be better identified with an iodine test then with an acetic acid test.

HPV and human immunodeficiency virus (HIV) are associated with serious genital tract pathology. This has made it imperative that the decontamination of any equipment used in the colposcopy clinic is 100% reliable. Before the choice of instruments is made, one of the parameters which must be assessed is the ease with which decontamination may be accomplished. The hazard to the patient arises from the flora of the vagina and contamination with blood or serum. Although bacteria are easily dealt with largely by cleaning, the hazards posed by the blood-borne viruses (hepatitis A and C, and HIV) and the local viral pathogens (HPV and herpes simplex virus) are perhaps more emotive. It is now normal practice in most clinics in developed countries to use single-use sterilized equipment.

Otherwise the rules that should be followed are simple:

1. All equipment in contact with the patient must be cleanable, usually with hot water and detergent, to remove visible soil.
   
2. Once cleaned, it must be capable of undergoing a disinfecting process.
   
   
   
   1. This is preferably a moist heat process such as auto-claving.
      
   2. A second line approach is the use of a disinfectant with proven bacterial and virucidal properties, such as glutaraldehyde.

The local disinfection policies should be observed and local expert guidance sought. There is also value in using disposable instruments, especially vaginal speculi. However, this is an expensive exercise and there is no reason why, if the above decontamination procedures and principles are followed, concern should arise either in the patient or in the colposcopist.