Changes of HPV Infection

In cervical epithelia, all productive HPV infections commonly manifest themselves both cytologically and histologically through a distinctive cytopathic effect. The cell in which this is found has been termed the ‘koilocyte’ (Figure 10.3). This feature, first recognized more than 50 years ago, was given the term ‘koilocytotic atypia’ (some use koilocytic) as these cells histologically resembled those in skin warts. Some 20 years later it was recognized that this same cell type occurred in genital warts and was associated with both HPV infection and preinvasive squamous intraepithelial lesions.

The koilocyte is an intermediate cell that has a prominent cytoplasmic space around an atypical nucleus (Table 10.4; Figures 10.3–10.8). Due to an extensively marginated cytoplasm, the halo has a sharp edge. The cytoplasmic change is thought to be due to abundant expression of the HPV E1∧E4 fusion protein, which binds with cytoplasmic keratin. Even in the state where the nuclei are not overtly dysplastic by size criteria, they are still, nonetheless, irregular and hyperchromatic and, if near the surface, may show a wrinkled nuclear membrane. The nuclei, which lack nucleoli, are usually two to four times larger in nuclear area than those of the adjacent, nonballooned cells. Koilocytotic atypia, which under the Bethesda classification is considered a low-grade SIL, is the most common definite abnormality in cytologically screened women and is found in up to 4% of all cervical smears.

While the koilocyte is often described to be pathognomonic for HPV infection, perinuclear halos that mimic koilocytotic atypia may be caused by other infectious diseases and at times may be due to artifact. Epstein–Barr virus, when present in the cervix, may be associated with koilocytic change¹⁹ (although this may also be due to coinfection with HPV). Likewise, when the cytoplasmic halo is less than morphologically perfect, i.e., when the borders are smooth or when the nuclei have smooth borders, trichomoniasis may be a consideration. It is therefore important that the presence of a cytoplasmic halo is not overinterpreted as due to HPV infection. Rather, it is the combination of a well-defined halo plus definite nuclear atypia as defined previously that confers specificity to the morphologic findings. Other features associated with HPV infection include binucleation (Figure 10.4) and meganuclei. Both are found in the mid to superficial levels. Some investigators have suggested that the latter feature, or more severely pleomorphic koilocytes, is more associated with high-risk HPV types. However, since over 85% of cervical HPV infections are due to viruses from the high-risk group, this is not a practically useful concept and LSILs of the cervix cannot be reliably genotyped by morphology.

Nuclear Abnormalities

The defining hallmarks of SIL are its nuclear abnormalities. These include nuclei that are enlarged, pleomorphic (irregular in size and shape), and often have a wrinkled nuclear membrane. The chromatin is increased in amount (hyperchromasia) and irregularly clumped, often condensing along the inside of the nuclear membrane. Collectively, this constellation of features is described as ‘nuclear atypia.’ These changes may reflect the polyploid and/or aneuploid DNA content of the cells induced by the action of HPV E6 and E7 on host DNA synthesis and cell cycle checkpoints (see Chapter 9) and are important for the diagnosis of SIL. Neoplastic atypia is distinguished from reactive changes by the heterogeneity of the nuclear changes in SIL, contrasting with the relatively homogeneous changes in reactive atypia. It is of note that nucleoli are rare in preinvasive lesions, especially in smears, but are commonly seen in reactive atypia.

Cytologic atypia must always be interpreted within the local context of level in the epithelium, and by comparison with adjacent cells. It is common for the koilocytes of LSILs, which reflect HPV DNA amplification and viral propagation, to demonstrate bizarre nuclear pleomorphism in an irregular distribution. These are generally confined to the superficial layers, have classic perinuclear halos, and may be polynucleated. Clonal HSILs may contain koilocytes, but their more characteristic feature is an increased nuclear to cytoplasmic ratio which creates a basal-type appearance to cells high in the epithelium. This is in addition to the previously mentioned pleomorphism and chromatin changes, which are also present.

If a particular epithelium is extremely thin, it may be difficult to relate changes in cytology to position within the vertical height of the epithelium, thus confounding evaluation of maturation from base to surface. In this situation, the cytology alone may provide some clues as to grade, or the specimen may be regarded as ungradeable (or the grade undetermined/indeterminate).

Mitotic Activity

Mitotic activity is the histologic hallmark of cell proliferation. The conceptual distinction between a normal epithelium and SIL has much to do with the frequency, distribution, and type of mitotic activity. HSIL has a proliferative phenotype. Though LSIL is slightly more proliferative than normal epithelium, it does not display the same viral oncogene-driven proliferation as HSIL: this is related at least in part to the switch to productive HPV infection, which occurs in the suprabasal keratinocytes of low-grade lesions.

In normal epithelium, mitotic figures are rare and are restricted to the parabasal cells. In contrast, SIL shows an increased number of mitoses, and they may be present at any level in the epithelium. The frequency of mitoses in the epithelium increases from normal epithelium to LSIL to HSIL. Moreover, the density of mitotic figures in the superficial third of the epithelium increases with the degree of abnormality. Thus, vertical position in the epithelium at which mitotic figures are found is a useful diagnostic indicator when contemplating the grade of SIL. However, not all SILs show mitoses above the parabasal layer.

Mitotic activity above the basal layer, however, is not always by itself pathognomonic for SIL. A reactive or inflamed but otherwise normal differentiated epithelium may also have increased mitotic activity, but the mitotic figures are concentrated in the basal areas. More problematic are reactive changes in metaplastic squamous areas, such as an inflamed transformation zone, as these may have full thickness mitotic activity and fail to demonstrate the polarization of differentiation. The presence of reactive cytologic features lacking the particular chromatin condensation of SIL may assist in the distinction. Special stains for p16, which is positive in epithelia infected with high-risk HPV, may also be helpful in differentiating between reactive metaplasia and SIL.

Abnormal mitotic configurations, which reflect aneuploidy, are common in HSIL, where they account for between 15% and 30% of total mitoses, but rare in LSIL. HSIL associated with HPV type 16 infection has the highest number of mitoses and the most abnormal forms.20,21 The most common of these abnormal configurations is the lag-type mitosis, which is defined as a metaphase with nonattached chromatin in the area of the mitotic figure. The ‘three-group metaphase’ (Figure 10.9), which is where the main mass of the chromatin aligns along the equatorial plate and the nonattached condensed chromatin remains laterally at the two polar sites, has been found in 6% of CIN 1–2, 56% of CIN 3, and 93% of high-grade CIN lesions just adjacent to microinvasive carcinoma.^22,23 Two-group metaphases (displaced chromatin at only one polar site) may also be seen. Less common than either of these forms is the multipolar mitotic figure, either as a triaster (tripolar) (Figure 10.10) or as a more bizarre multipolar figure (Figure 10.11). Tripolar mitoses may reflect polyploidy, rather than aneuploidy, and thus may be seen in both HSIL and LSIL.

Differentiation, Maturation, and Stratification

‘Differentiation’ and ‘maturation’ are terms that, while having slightly different meanings, are often used synonymously and interchangeably in the cervix.

The proportion of epithelial cells showing differentiation is a useful indicator of the grade of SIL, although it must not be taken as the only criterion. For example, while SIL develops by a dysplastic process and may show little if any differentiation, it may be difficult to distinguish from an immature, but nondysplastic metaplastic squamous epithelium that also lacks any substantial degree of cytoplasmic differentiation. In this case, the distinguishing feature is the lack of nuclear atypia in the metaplastic process as well as much less evidence of mitotic activity. Nonetheless, distinction between the two conditions can be difficult and the presence of atypical changes in immature metaplastic squamous epithelium may indicate SIL, as shown by the presence of high-risk HPV types, high Ki-67 proliferation indices, p16 expression, and follow-up studies.24,25

As normal cells differentiate and mature and migrate toward the surface, stratification is observed. One means of assessing maturation is to look for a decreasing percentage of nuclear area to overall epithelial area, reflecting a decreasing nuclear to cytoplasmic ratio at increasingly more superficial levels of the epithelium. In smears, which sample superficial cell layers preferentially, this change in ratio is quite dramatic. In normal smears, the nucleus has undergone pyknosis by the time the cell reaches the surface, so that in the smear the nuclear to cytoplasmic ratio is quite low. With increasing grade of SIL, the individual cells have matured progressively less so that the amount of cytoplasm present, as well as its differentiation, is less. Thus, mildly dyskaryotic (a synonym of dysplasia used in cytologic terminology)/LSIL cells present in cervical smears/scrapes have ample cytoplasm with a well-defined polygonal squamous shape, and moderately dyskaryotic/HSIL-2 cells possess less cytoplasm and a less well-defined oval or elliptical squamous shape, whereas in severely dyskaryotic/HSIL-3 cells the rim of cytoplasm that encircles the nucleus is small. These features also occur in histopathologically defined lesions and, in SIL, the proportionally decreasing quantity of cytoplasm contributes far more to the increase in the nuclear to cytoplasmic ratio with increasing lesion grade than does the change in nuclear size. This is consistent with the persistence of nuclear abnormality throughout the epithelial thickness in all grades of SIL.

The presence of surface differentiation, which defined the difference between CIS and severe dysplasia, is poorly reproducible and of no biologic import, as mentioned previously. Thus, with the adoption of the CIN terminology and now with SIL terminology, the former class of squamous CIS is encompassed in CIN 3 and HSIL, respectively.

In smears, the Pap stain accentuates states of maturation. The color of staining, which results in either acidophilic (pink) or basophilic (blue-green) cytoplasm, usually corresponds to normal superficial and intermediate cell types, respectively. Although this helps to distinguish the various grades of SIL, it is not a reliable criterion, being influenced, for example, by stain quality control factors.

LSIL (Condyloma/CIN 1)

LSIL is a term that unifies entities previously referred to as condyloma acuminatum, ‘flat condyloma,’ and CIN 1. LSIL is the histopathologic presentation of productive episomal HPV propagation, essentially a field effect caused by viral activation in maturing squamous cells. Although a degree of nuclear maturation occurs, abnormal nuclei persist throughout the full thickness of the epithelium (if this were not so, a diagnosis by cytologic smear would not be possible; see earlier sections) (Figures 10.16–10.18). Mitotic figures, if present, are few in number and generally confined to the basal third of the epithelium. Abnormal mitosis forms are uncommon: these usually indicate aneuploidy and thus are more specific for the diagnosis of HSIL. Characteristic LSIL changes are concentrated in the upper part of the epithelium where productive episomal virus propagation in maturing squamous cells forms characteristic koilocytes. These koilocytotic nuclei can be wildly pleomorphic, and are among the largest nuclei seen in any kind of SIL. Upon integration of viral DNA into the genome of host cells, episomal propagation, and their koilocytotic phenotype, are diminished. Thus koilocytes are less common in HSIL (CIN 2 and 3), although they do still occur in these lesions, particularly where surface epithelial maturation is retained. LSILs, on occasion, may lie adjacent to high-grade lesions, or occasionally even adjacent to carcinomas. Sometimes this reflects progression of a single viral infection from an episomal to integrated phase across one epithelium, whereas in others it may be due to infection by multiple viral types.

In the past, much attention was paid to distinguishing isolated ‘koilocytosis’ from ‘dysplasia.’ These were pressing issues in a premolecular world where histologic–viral correlations were not yet available, and the functional significance of HPV infection was unknown. From a pathologist’s perspective, there was no objective gold standard to establish what was actually a koilocyte, or its diagnostic and clinical relationship to what had previously, and separately, been identified as a precancerous process (dysplasia). One solution was to diagnose HPV effects and dysplasia separately, so it was frequent to see a diagnosis of ‘koilocytotic change without dysplasia/CIN.’ Many of these ‘dysplasia-free’ koilocytes were overdiagnosed binucleate but otherwise normal-appearing nuclei in a glycogen-rich cell. This has been remedied by more specific criteria for histologic diagnosis of HPV-related koilocytes, which include nuclear size variation, wrinkled contours, and coarse chromatin as defined elsewhere. Other ‘dysplasia-free koilocytes’ described diagnoses separately applied to the superficial (koilocyte-containing) and basal (dysplasia) zones of one epithelium. This is no longer strictly necessary, as examination of all features of the epithelium must be considered in rendering a comprehensive diagnosis. Thus, using the diagnostic criteria described later, the distinction of whether an LSIL does or does not have a coexisting dysplasia is no longer clinically or scientifically significant. Rather, distinction of no-SIL from LSIL, and LSIL from HSIL are the key clinical management thresholds.

The basal area of the majority of LSILs lacks any notable architectural changes, more resembling the aligned uniform basal cells of a normal epithelium. When the basal area is affected, and this can be difficult to assess reliably in an inflamed or disoriented specimen, the pleomorphism is minimal, and confined to the deepest aspects. Usually the basal-most cells retain their alignment with the basement membrane in LSILs, a feature that changes with the clonal outgrowth of HSILs. LSILs lack the degree and extent of basal disorganization, which can be seen to creep upward in the epithelium of HSILs.

Several other features are found with low-grade lesions. Nuclei that are binucleate (Figure 10.4), or even sometimes multinucleate, are found in 95% of HPV infections.²⁶ Occasional cells may show individual cell keratinization (dyskeratosis) (Figures 10.19 and 10.20). In smears, LSIL (mildly dyskaryotic) cells have ample cytoplasm with a well-defined squamous shape (Figure 10.21). Anucleate and nucleate keratinized cells are commonly present in sheets or plaques with poorly defined cell borders.

On a cellular basis, the koilocyte in histologic specimens is usually distinctive although the number of cells with koilocytotic change ranges from few to many (Figure 10.22). Typically, the nucleus is 3–4 times enlarged in area compared to a normal intermediate cell, uniform in size and shape, and has a halo with smooth outer borders. HPV immunostains have shown that typical koilocytes usually react with antibodies to the HPV L1 group-specific capsid protein (Figures 10.23 and 10.24). Since capsid/virion production is a temporally controlled phenomenon linked to both differentiation and lesional age, which likely explains the variability in koilocyte number between lesions, not all cells containing HPV will necessarily stain. Cells less typical for koilocytes are less likely to stain. Because of the potential social stigma often attached to a smear or biopsy specimen that is diagnosed as harboring HPV, prudence dictates that no specimen should be diagnosed as LSIL unless the overall microscopic picture is distinctive.

If left untreated, most LSILs regress but laser vaporization or diathermy also easily eradicates them, although recurrence is common. Condylomata acuminata are a subtype of LSIL, so the patient with a cervical wart must have continued cytologic surveillance. Furthermore, histologic examination of LSIL should, of course, include an assessment of atypia throughout the epithelial thickness, as well as the surrounding epithelium. Sometimes a lesion with prominent superficial koilocytes suggestive of an LSIL contains cells that have sufficient atypia or basal changes to warrant a diagnosis of HSIL.

The Scant Endocervical Curettage

In the absence of any generally accepted criteria for what constitutes either an adequate or scant specimen, pathologists frequently encounter the problem of what language to use when reporting a curettage specimen where the diagnostic tissue is less than sufficient. This is also true for endometrial samples where only endocervical tissue is present. Many specimens, even with copious amounts of material, consist largely of mucus, which itself is not of diagnostic value. Often the only diagnostic cellular component present consists of little more than a few small strips of mucinous columnar epithelium devoid of any underlying stroma. To diagnose a specimen as ‘unsatisfactory’ would generally require that the clinician repeat a painful procedure. The recommended approach is to report endocervical curettages (ECCs) descriptively (mucus, mucinous columnar cells, fragments of endocervix, fragments of exocervix) and when necessary with the qualifiers ‘scant, rare, miniscule quantities of, etc.’ A typical example is ‘scant mucus and mucinous columnar epithelium.’ When the specimen consists of just a few exfoliated mucinous cells, some use the phraseology ‘rare exfoliated mucinous cells, inadequate (or insufficient or suboptimal) for further diagnosis,’ which serves as a trigger for the clinician to rethink the issue. A distinction should be made between strips of mucinous columnar cells and rare isolated exfoliated mucinous cells as the former likely reflects the curettage while the latter may represent little more than cells already exfoliated into the mucus. Although the ECC is primarily used to assess the extent of squamous neoplasia, it also helps in evaluating the presence or absence of glandular tumors and their precursors that may involve the endocervix.

Lesions Suspicious for, but Subdiagnostic of, SIL

Conceptually, this is the histologic equivalent of the cytologic diagnosis of atypical squamous cells of undetermined significance (ASCUS/borderline change). Since ASCUS/borderline change is a cytologic equivocation and a risk assessment rather than a biologic entity, there has been no formal translation to a histologic diagnostic entity. Rather, if features are present that raise the possibility of SIL (CIN) but this cannot be diagnosed, the findings should be described. Samples may be subdiagnostic because of adequacy (technical condition or abundance) or interpretive difficulties. Where appropriate, some indication of the basis of diagnostic uncertainty, and recommendation for clinical correlation and follow-up, can be made.

Basal Cell Hyperplasia

Basal cell hyperplasia shows regular replication of basal layers with nuclear enlargement. However, nuclear pleomorphism and hyperchromasia are absent. Differentiation is relatively normal in the upper half of the epithelium. While the significance of basal cell hyperplasia and its long-term implications are unknown, it may reflect the early stages of dysplasia occurring in the ‘original’ (native rather than metaplastic) squamous epithelium.

In some cases, the distinction between basal cell hyperplasia and HSIL (CIN 2-3) can be difficult to make. Cases exist where the basal and parabasal cells are remarkably abnormal, and yet the upper two-thirds of the epithelium is relatively normal (Figures 10.40 and 10.41). Emphasis on the upper layers leads to a diagnosis of basal cell hyperplasia, whereas emphasis on the basal layers leads to a diagnosis of HSIL (CIN 2-3). Ki-67 (MIB1) and p16 immunohistochemistry can be helpful in making the distinction, with Ki-67 highlighting the increased proliferation and p16 the presence of a high-risk HPV infection in HSIL.

Immature Squamous Metaplasia and Atypical Squamous Metaplasia

Squamous metaplasia is a physiologic process characterized by reserve cell hyperplasia, early squamous differentiation, variable polarity, and nuclear enlargement, any component of which may sometimes be quite exaggerated (see Chapter 8). Nuclear pleomorphism and hyperchromasia are absent, thus rendering to the epithelium an appearance of somewhat bland nuclei of uniform size and shape (the nuclei are typically round). During the time when metaplastic squamous cells develop, they may undermine and replace endocervical columnar cells. At times the nuclei can be enlarged and yet be relatively uniform, which elicits differences in diagnoses among pathologists as to whether the lesion represents immature squamous metaplasia or SIL, especially when columnar cells are present on the surface (Figure 10.42). HPV-associated features such as koilocytosis are rarely seen in immature metaplastic squamous epithelium, presumably as a result of the lack of differentiation.

It can be difficult to distinguish immature squamous metaplasia with minimal nuclear changes from SIL (CIN) (Table 10.5). Typically, immature metaplastic squamous cells have abundant cytoplasm and homogeneous round nuclei with fine speckled chromatin and a small nucleolus. The frequency of Ki-67 (MIB1)-reactive nuclei is low and the staining intensity minimal.²⁷ Cylindrical cells can occur intermingled with, or at the surface of, the immature cells and then are a strong diagnostic criterion, but are not always present. Whenever substantial nuclear pleomorphism is found, SIL (CIN) should be diagnosed even if columnar cells are present on the surface (Figure 10.43). Ki-67 staining is useful in resolving the differential diagnosis, as it is typically unremarkable in immature squamous metaplasia but appears at high density throughout the epithelium in SIL (CIN). Similarly, p16 is typically diffusely expressed in SIL (CIN) but absent or expressed only focally in immature metaplastic squamous epithelium.

Repair (Reactive Epithelial Changes)

Repair of the squamous epithelium is a condition that commonly mimics the features of SIL (CIN).²⁸ Unlike SIL (CIN), the stroma in repair is virtually always chronically and often floridly inflamed. The nuclei are uniform, with no or minimal pleomorphism. The chromatin is bland and evenly distributed. Nucleoli of ‘bull’s eye’ or macronucleolar appearance are often easily found (Figure 10.44). The epithelium in SIL (CIN) may be incidentally associated with an intensely inflamed stroma, but can be recognized by nuclei that are pleomorphic and commonly display coarse chromatin and mitoses.

Low Estrogen States and Atrophy

In low estrogen states (i.e., after menopause), and in high progesterone states (e.g. during pregnancy or as a result of progestogen therapy), the cervical squamous epithelium is usually thin and may be composed entirely of parabasal cells. While mild nuclear hyperchromasia is often seen, the nuclei are uniform in size and shape and a constant amount of cytoplasm surrounds most nuclei. Nuclear pleomorphism is absent. In some postmenopausal women, the cervix may exhibit a spectrum of epithelial alterations, including prominent perinuclear halos, nuclear hyperchromasia, some variation in nuclear size, and multinucleation. In one study, all cases showing these changes were negative for HPV by polymerase chain reaction (PCR) analysis.²⁹ Several features help to distinguish postmenopausal atrophy from the HPV-associated changes of SIL (CIN). They include less variation in nuclear size and staining intensity, more finely and evenly distributed nuclear chromatin, and greater uniformity of perinuclear halos in the former. Ki-67 (MIB1) expression can also be useful, as positive nuclei are typically limited to the lower layers. However, this must be interpreted with care as very thin epithelium may lack superficial cells and can mimic HSIL (CIN 2-3). However, correlation with HPV testing is important as many studies demonstrate a ‘bump’ in HPV prevalence in the postmenopausal age group. p16 immunostaining can be helpful as a surrogate marker of high-risk HPV infection in this situation as it is typically diffusely positive in SIL (CIN) but negative in atrophic epithelium. Hence, a combination of Ki-67 and p16 immunostaining may be particularly useful in this context.

Thin Epithelium

In an epithelium that has only a few layers of cells, it is commonly impossible to confidently diagnose the presence of SIL (CIN). There is often the concern that the epithelium is not naturally thin, and that some artifactual process is responsible for the removal of multiple superficial layers. In the absence of severe inflammation, SIL (CIN) should usually be diagnosed if there is cytologic atypia (Figure 10.45). Sometimes, the number of cell layers present is sufficient to diagnose SIL (CIN), or even probable HSIL (CIN 2-3), but further definition is precluded (Figure 10.46). It may be helpful to designate these lesions as SIL (CIN) of indeterminate grade (or ungradeable SIL (CIN)), using the cytologic features to indicate whether the lesion is likely to be low or high grade. Correlation with the Pap smear may be useful in this situation, as may immunostaining for Ki-67 and p16, as discussed previously for atrophic epithelium.

Invasive Squamous Cell Carcinoma

Not uncommonly, one of the most difficult entities to distinguish from HSIL (CIN 2-3) is invasive squamous cell carcinoma. This occurs most commonly if the biopsy is superficial and is devoid of an obvious stromal component. In such examples, the lesion appears as sheets of irregularly folded dysplastic epithelium lying on a thin basement membrane. The most appropriate diagnosis is that of ‘at least HSIL (CIN 2-3), cannot exclude invasion. In one study testing for cellular features that distinguish invasive and noninvasive disease, several histologic features found in the cone biopsy specimens were preferentially associated with invasive tumor.³⁰ These included giant bizarre cells that were irregular, hyperchromatic, and up to five times the size of a basal cell (67% vs 6%), large keratinized cells with distinct cell borders (87% vs 0%), keratin pearls (41% vs 0%), necrosis, often comedo-like (80% vs 8%), and neovascularized tumor cells close to the endothelial lining and lacking intervening connective tissue (57% vs 0%). In 74% of invasive carcinomas, a component of CIN 3 was present, of which 35% showed large keratinized cells or keratin pearls in the in situ components. This suggested that the presence of either feature in biopsy specimens showing CIN 3 might signify the presence of invasive lesions elsewhere in the cervical mucosa. In another study, several histologic features were associated with the presence of invasive disease: these included extensive and expansile involvement of endocervical crypts; and the presence of comedo-type necrosis in the center of involved crypts (see later).³¹

It is not unusual for the diagnosis of HSIL (CIN 2-3) to be correct, but for the results of hysterectomy to show the disease process to be more extensive than expected. Occasionally, the surface and the endocervical crypts are involved only by HSIL (CIN 2-3) in a biopsy, as suggested by a history of only HSIL (CIN 2-3) on smears (even when reviewed retrospectively) and the absence of any abnormality clinically. However, the hysterectomy specimen shows that the cervical wall harbors a small carcinoma or on occasion is permeated by a larger carcinoma (see Chapter 11).

Artifact

Fragmentation and thermal artifact in cone, loop electrosurgical excision procedure (LEEP) or loop excision of the transformation zone (LETZ) biopsy specimens are major problems affecting correct diagnosis.32,33 When specimens are fragmented into multiple small pieces, it is difficult, if not impossible, to evaluate margins. Thermal artifact, which is often caused by low-voltage techniques, results in an epithelium that appears smudged and uninterpretable. Cellular and nuclear details are lost (Figure 10.47). In a LEEP biopsy correctly done, the thermal artifact produces a very thin rim, usually a fraction of a millimeter wide, at the periphery of the specimen. The outermost layer, the carbonization zone, is usually quite thin. The coagulation zone is deeper and is significantly larger and more readily apparent. Unacceptable thermal artifact occurs when the coagulation zone is wide (Figure 10.48), resulting in extensive loss of cellular detail. A randomized controlled trial that evaluated pure cut versus traditional blending settings in large LETZs found no significant differences in thermal artifact. In the deep stroma, however, the blended setting had a thicker thermal artifact band (0.382 mm) than the pure cut setting (0.325 mm).³⁴

Stratified Mucin-Producing Intraepithelial Lesion

Some intraepithelial lesions show features intermediate between HSIL (CIN) and cervical adenocarcinoma in situ (AIS)(also termed high-grade cervical glandular intraepithelial neoplasia) (see Chapter 12). Where mucin-producing cells are admixed with non-mucin-producing cells in an atypical stratified intraepithelial lesion, the term stratified mucin-producing intraepithelial lesion or SMILE has been proposed.³⁵ This entity is uncommon³⁶ and when observed is best diagnosed as a histologic variant of cervical AIS: ‘cervical adenocarcinoma in situ, stratified mucin-producing intraepithelial type.’ In many cases features of ‘pure’ AIS are also present in the histologic slides.

Congenital Transformation Zone (See also Chapter 8)

Immature squamous epithelium may be present distal (caudal, vaginal) to the last endocervical gland (discussed later) in an anatomic position, peripheral to the transformation zone, which is normally occupied by native, mature squamous epithelium. Recognition of the appearance of this epithelium, which has been termed the ‘congenital transformation zone,’ is therefore important. Surface hyperkeratosis or parakeratosis is often present and this can produce a leukoplakic appearance colposcopically. Histologically, the typical features are a relative lack of epithelial maturation of squamous epithelium that has an irregular, dentate, contour. The lack of maturation raises the possibility of SIL (CIN) but cytologic atypia is absent. Specific recognition of this entity is important for colposcopy–histopathology correlation.

Miscellaneous Conditions

One of the more bizarre situations rarely encountered is when the cervix is treated for SIL (CIN), but the results of hysterectomy show the SIL (CIN) process involves more than the cervix. There are rare reported cases where hysterectomy and bilateral salpingo-oophorectomy performed to treat SIL (CIN) disclosed that the disease had extended to the endometrium and fallopian tubes, and there extensively replaced the normal glandular mucosa.37,38

p16

The cyclin-dependent kinase 2A inhibitor, p16^INK4, or simply p16, helps distinguish SIL (CIN) from reactive and atrophic lesions.³⁹ Since a retinoblastoma protein (pRb)-dependent negative feedback loop regulates p16 expression, continuous inactivation of pRb by high-risk (but not low-risk) HPV E7 results in increased p16 levels. Hence, increased p16 levels may reflect HPV-induced SIL (CIN) with deregulated E7 expression.⁴⁰ Marked overexpression of p16 protein, i.e., diffuse and strong immunostaining (Figure 10.49), is present in virtually all cervical squamous cell and adenocarcinomas, and high-grade squamous and glandular preinvasive lesions (HSIL (CIN) and AIS) infected by high-risk HPVs, e.g., types 16, 18, 31, 33, 52, and 58, in contrast to the weak/focal staining in lesions infected with HPV 6/11 or other low-risk HPVs.⁴¹ p16 overexpression is sensitive (84%) and specific (98%) for the detection of high-risk HPV.⁴² At low magnification, p16 staining facilitates finding a dysplastic area, especially if the epithelium is heavily infiltrated by leukocytes, as often occurs in SILs (CINs).³⁹ In addition, overexpressed p16 helps identify individual SIL cells in fluid-based cytologic smears.⁴³ This biomarker is particularly useful in the distinction between SIL (CIN) and reactive and atrophic epithelia, especially where the epithelium is thin (see earlier).

p16 positivity should not be used directly to grade SIL (CIN), a distinction that must be based upon the diagnostic appearance on H&E as outlined previously. This is because high-risk viruses infect some LSIL epithelia, and these will be p16 positive and should not be overdiagnosed as HSIL. A negative p16 result, however, can be used to rule out an HSIL where the differential diagnosis includes mimics such as atrophy or reactive change. Detailed discussion of the use of p16 is included in reference 6.

Ki-67

The expression of Ki-67 can also be used to support a diagnosis of SIL (CIN) as its expression signifies continued cellular proliferation and, if present beyond the parabasal cells, may indicate SIL (CIN). Used in conjunction with p16 immunostaining, it can help to distinguish between reactive and atrophic states and SIL (CIN).

ProExC

More recently, immunostaining using ProExC, which detects the combination of minichromosome maintenance (MCM) protein 2 (MCM2) and topoisomerase 2α (TOPO2α), has been suggested as an alternative biomarker for the diagnosis of SIL (CIN). This performs well in some studies⁴⁴ and there is some evidence that the combination of ProExC and p16 may be diagnostically useful.⁴⁵

HPV Typing

There is a large amount of literature addressing the role of HPV testing in cervical screening, particularly the triage of women with low-grade cervical cytologic abnormalities,⁴⁶ or during follow-up of patients with SIL (CIN),⁴⁷ but the role of HPV typing in the assessment of biopsy material is limited. The detection of HPV DNA by in situ hybridization can aid the identification of HPV-associated carcinomas, particularly adenocarcinomas, and in the distinction between cervical and endometrial adenocarcinomas.⁴⁸ However, its use in the assessment of SIL (CIN) is limited, particularly in view of the excellent performance of immunohistochemical biomarkers such as p16,^25,49 which are more easily implemented in a routine laboratory context.

Involvement of Endocervical Gland Crypts

Consideration of the involvement of endocervical gland crypts in addition to surface epithelium is important for patient management (Figures 10.50–10.52). The number and depth of involved crypts increases with the grade of SIL (CIN). In CIN 3 cone biopsy specimens, nearly 90% had involved crypts.⁵¹ The mean depth of involvement was 1.2 mm, but 5% extended deeper than 3 mm and some reached a depth of over 5.2 mm⁵² or even over 6 mm.

Extreme care must be taken not to mistake crypt involvement for invasive carcinoma. When HSIL (CIN 2-3) involves only a portion of the crypt, thus exposing some of the lining composed of mucinous columnar cells, the correct diagnosis is usually obvious. Difficulties arise when SIL (CIN) replaces the crypts in their entirety, especially in a biopsy specimen. In this instance the clue that the disease process is not invasive carcinoma, but HSIL (CIN 2-3) that involves a crypt, lies with its shape. Crypts that are involved have perimeters that are round to oblong and smooth, reflecting the fact that the normal crypt lining has been replaced. Sometimes the crypt diameter may be expanded. The stroma around the crypt is often inflamed, and may be edematous, complicating assessment of the epithelial–stromal interface. Tumor that is invasive usually has irregular and sharply angulated borders, and frequently exhibits features of increased squamous differentiation (e.g., increased cytoplasmic eosinophilia, reduced nuclear to cytoplasmic ratio, dyskeratosis) by comparison with the overlying or adjacent SIL (CIN).

Resection Margins

Not infrequently, LEEP, LETZ, or cone biopsy specimens disclose HSIL (CIN 2-3) that reaches the resection margins either on the surface or in involved endocervical crypts (Figure 10.53), both of which may confer an increased risk of residual disease. Residual CIN has been detected in 8–85% of women with positive margins on cone biopsy and in 0–55% of women with negative margins.⁵³ In a study of 782 women treated for CIN with large loop excision, 9% of margins were involved but, within 2 years, the treatment failure rate was 30%.⁵⁴ With uninvolved margins, 5% of these patients proved still to have residual disease. Endocervical glandular involvement, age exceeding 40 years, and the presence of satellite lesions were all identified as independent risk factors for the appearance of a subsequent lesion. Among a cohort of 390 patients, 22% had recurrent CIN or developed invasive carcinoma after cold knife conization with positive margins. Persistent or recurrent disease was more common in women with both ectocervical and endocervical margin involvement as opposed to singular ectocervical or endocervical positive margins.^55,56

In another study, if an ECC was positive for CIN, 65% had CIN 2–3 in a cone biopsy.⁵⁷ A retrospective study of 152 women who underwent ECC at the time of conization concluded that only the endocervical margin status predicted residual disease (and not ECC).⁵⁸

In one study where hysterectomy was performed soon after the cone biopsy, 61% of patients who had both involved margins and involved crypts had residual CIN: 29% of women with uninvolved margins and crypts also had residual CIN in the hysterectomy specimen.⁵⁹ In a second phase of the same investigation, women treated with cone biopsy alone were followed over a long period. Of women with both involved margins and involved crypts, 23% developed a subsequent recurrence, which compared to only 8% of women in whom both the margins and crypts were initially normal. The average time to the first recurrence was 2.2 years. In predicting recurrence, positive margins and involved crypts were each found to be independent prognostic factors with equal predictive value.

It is of note that margin status has been shown to be less sensitive than cytology or high-risk HPV testing in predicting post-treatment disease.60,61 In addition, a recent systematic review concluded that high-risk HPV testing had higher sensitivity than, but similar specificity to, cytology for the detection of post-treatment high-grade disease.⁴⁷

With the knowledge that the status of the endocervical margin can have a substantial effect on immediate therapy and later disease progression, a lively debate has ensued over the years about the wisdom of using frozen sections to examine cone biopsy specimens.⁶² The consensus has been that complete examination of specimens by frozen section is less thorough than if the specimen is first fixed in formalin and then carefully blocked. It is the common experience that cone specimens cut into 12 or more pieces not infrequently show only a small focus of high-grade disease, which would easily have been missed by frozen section examination. In the example shown, the entire focus of HSIL (CIN 3) was under 1 mm in total size (Figure 10.54). Frozen-section examination of large specimens is also time-consuming and expensive. However, in those institutions where frozen-section evaluation of the endocervical margins is performed routinely, the overall experience has been highly satisfactory.⁶³ A number of institution also report excellent correlation between the frozen sections and permanent sections in cases of CIN 3⁶⁴ and superficial invasive carcinoma.⁶⁵ Yet the artifacts and tissue loss at frozen section can compromise the evaluation of early invasion. Furthermore, rarely will the astute gynecologist need to alter the approach based on the finding of superficial invasion. Hence, frozen-section evaluation of conization is generally discouraged.

Invasive Disease

An obvious concern in the management of SIL (CIN) is to ensure that the therapy is not excessive for the degree of abnormality present. Conversely, it is important not to treat lesions inadequately and miss an occult carcinoma as a result. In a meta-analysis examining the use of various diagnostic techniques, both punch biopsy and cone biopsy with or without colposcopy missed significant numbers of invasive carcinomas (Table 10.6).⁵²

In one of the largest case series, 2.7% of 600 patients with CIN 3 had invasive carcinomas detected in a subsequent cone biopsy specimen.⁶⁶ Another 1% had microinvasive carcinomas. The major features identified in CIN 3 associated with carcinoma in another study were as follows:³¹

One study has shown that the mean size of CIN 3 lesions exhibiting microinvasion is seven times greater than CIN 3 lesions without invasion and 100-fold greater than CIN 1 lesions.⁶⁷ Several studies have shown that care must also be exercised to remove the entire lesion when locally destructive methods are used in the treatment of HSIL (CIN 2-3). In a multicenter retrospective study, the British Society for Colposcopy and Cervical Pathology identified 49 women who subsequently developed invasive carcinoma following therapy with laser vaporization, cold coagulation, diathermy, or cryosurgery.⁶⁸ Most of these tumors were ascribed to failure to recognize the early invasive disease at the time the patients were initially assessed. Fortunately, radical reoperation has been performed in such patients with low morbidity and excellent cure rates.⁶⁹

Regression

Practical data are difficult to find regarding the transit times from SIL (CIN) to invasive carcinoma. In one of the better older studies,⁷⁰ the median transit times for progression from mild, moderate, and severe dysplasia to CIS were 5 years (58 months), 3 years (38 months), and 1 year (12 months), respectively. The regression rate for the high-grade abnormality reverting to normal was 6%, a lower number than anticipated, attributed to the fact that biopsies were not taken. It was believed that removing even a small piece of tissue from a field of dysplasia materially altered the disease’s natural history. In contrast, others found higher regression rates:⁷¹ 50% of patients followed by cytology and biopsy experienced regression during the next 10 years. In the same interval, only 1.4% of all patients with dysplasia showed progression to CIS. In part the rates of progression and regression are related to the initial grade of the CIN, as shown by a meta-analysis of papers published since 1950 (Table 10.7).^72,73

In a more recent study based on a historical cohort of women whose Pap smear histories were recorded continuously between 1962 and 1980, and during which time CIN was managed conservatively, both CIN 1 and CIN 2 were more likely to regress (usually within 2 years) than to progress. The risk of progression from CIN 1 to CIN 3 or worse was only 1% per year, but the risk of progression from CIN 2 was 16% within 2 years and 25% within 5 years, in agreement with meta-analyses.⁷² Most of the excess risk for carcinomas developing from CIN 2 or 3 occurred within the first 2 years after the initial cervical abnormality was identified.⁷⁴

Two decades ago, it was generally assumed that progression through SIL (CIN) grades occurred incrementally, starting as LSIL (CIN 1) and over many years progressing through HSIL (CIN 2) to HSIL (CIN 3) before becoming invasive. However, this is not based on actual observations. The biopsies necessary to confirm the diagnoses on each occasion would destroy the tissue under study and colposcopic observations are insufficiently reliable to diagnostically render such a claim. Moreover, there are very rare reports of cases in which HSIL (CIN 2)and even LSIL (CIN 1) have apparently developed directly into invasive carcinoma, without reaching the stage of HSIL (CIN 3). It is possible that a small, very aggressive, newly formed clone of abnormal cells appearing in the deeper epithelium acquires sufficient molecular abnormality to drive the daughter cells to acquire invasive capacity so that these lesions immediately invade, bypassing HSIL (CIN 3). On the basis of such observations, some have argued for treating all patients who have SIL (CIN), irrespective of its grade, but this would lead to enormous overtreatment and has not been widely adopted. Also, it has never been fully established whether the lower grade SIL (CIN) lesions that appeared to progress rapidly to invasive disease had been adequately sampled.

Progression

The goal of early treatment is to prevent squamous cell carcinoma by eradicating preinvasive lesions. Cervical screening programs to detect SIL (CIN) by cytology and treat during the preinvasive phase are based on two assumptions: (1) a significant proportion of women with SIL (CIN) would eventually develop invasive carcinoma if not treated and (2) most invasive squamous cell carcinomas are preceded by a demonstrable intraepithelial phase. Despite the fact that cervical screening is the most effective cancer preventive program currently available, total eradication has not been obtained. There are numerous reasons why this hope has not been fully realized, including poor coverage by the screening programs of the population most at risk, poor quality of screening, and the possibility that some invasive carcinomas may not be preceded by a demonstrable preinvasive phase. Even so, a woman who has been screened even once during her lifetime will have a nearly sixfold lower incidence rate of cervical cancer (decreasing from about 34 to 4.2/100,000 women-years).⁷⁵

Several early studies provided insights into the relationship between SIL (CIN) and invasive carcinoma. One highly quoted study showed that 14% of 59 women whose CIS (now HSIL or CIN 3) remained untreated developed invasive carcinoma. It was later admitted that many of the original diagnoses were incorrect and that only 14 of the patients had acceptable CIS. Thus the percentage rose to 57%, i.e., 8 of 14 women developed invasive carcinoma over a period of 10 years. Later still, it was reported that 31 of these women had been followed for at least 12 years and that 22 (71%) of them had developed invasive disease.⁷⁶ Other reports from that time were similar.⁷⁷ Of 127 women with ‘epithelial atypia,’ 26% ultimately developed invasive carcinoma. In a fuller account of the same patients, it was admitted that only 67 had a recognizable abnormality still present at the end of the first year of follow-up. Of the 67 who remained in the series, two-thirds eventually developed invasive carcinoma. While the more recent amended rates are rarely quoted, they may well provide a more reliable indication of the malignant potential of SIL (CIN) than their earlier and more widely quoted figures. Most investigations have found that the time for progression from CIN 3 to occult invasive cancer takes between 5 and 25 years, with most series reporting times of over 10 years. Estimates of transit time from CIN to microinvasive/subclinical carcinoma are about 10 years with another 4–5 years elapsing until the tumor causes symptoms.⁷⁸

These estimates are in accord with the average ages when women develop SIL (CIN) (25–40 years), microinvasive carcinoma (43 years), stage 1 squamous cell carcinoma (48 years), and stage 4 squamous cell carcinoma (58 years) (Figure 10.55).

A common issue in evaluating the natural progression of SIL (CIN) is the effect introduced by both biopsy and conization. The former can theoretically affect the diseased tissues that remain in place, while conization certainly can ablate all tissues, removing the entire lesion or even the entire transformation zone. To overcome the difficulty that the method of diagnosis may interfere with the natural history of the disease, 52 women were traced who had positive smears diagnosed at least 2 years previously but had had neither biopsies nor any treatment.⁷⁹ Ten of these women (19%) developed invasive carcinoma, including some preclinical invasive carcinomas.

A notable study involved 948 women who had CIS diagnosed by histology, most of whom had cone biopsies.80,81 Of this group, 131 continued to have abnormal cytology, indicative of residual disease. No further treatment was given to these patients but they were followed closely. After 10 years 18% had developed invasive carcinoma, and after 20 years the number had risen to 36%. Of those whose cytology was normal after the initial treatment, 1.5% developed invasive carcinoma and 0.8% developed recurrent CIS. One explanation of the latter figures is that the propensity to develop new disease may remain where there is residual or new infection or other promoting factors (relative risk of 3.2). A retrospective study of 33 women revealed that the invasive carcinoma occurred within 5 and 10 years in 67% and 94% of women, respectively, after their CIN was treated.⁸²

The figures quoted for the progression from SIL (CIN) to invasive carcinoma thus vary widely, from 0.17% to 71%. Several difficulties exist in characterizing this relationship. First, all reliable methods for diagnosing SIL (CIN) involve the removal of tissue with the associated risk of interfering with the disease’s natural progression. Second and more importantly is an ethical consideration. Once it becomes apparent that there is a substantial risk of a woman developing invasive carcinoma from unattended SIL (CIN) it is unthinkable not to provide treatment. Because currently available methods to assess follow-up are destructive (biopsy), progression to cancer cannot be observed and therefore precise rates of progression from SIL (CIN) to invasive carcinoma are now virtually impossible to determine. Another factor to consider when evaluating follow-up studies, making certain conclusions difficult, is that the invasive or higher grade lesions may be unrelated to the original lesion, but caused by reinfection.

In examining the natural history of SIL (CIN) following conization, caution must be exercised in attributing the reappearance of an abnormality to the development of new disease. In one large study, 672 women were treated with conization for CIS and had resection margins free of tumor.⁶⁶ Of this group, 4% had abnormal smears detected within 3 months and 5% within 1 year, suggesting that the original tumor had never been fully resected. Another 2.5% developed abnormal smears during the ensuing 2–6 years. In general, the recurrence rate and time of recurrence correlated strongly with the presence or absence of initial disease at the resection margins (Table 10.8).⁶⁶

During the past several decades disquieting new trends have developed. Since the 1960s and the era of the ‘sexual revolution,’ the average age of SIL (CIN) development has fallen progressively to between 25 and 30 years of age and more recently even further. There is concern that the age when invasive carcinoma will develop is also dropping.

The second issue involves reports of young women developing invasive carcinoma of the cervix after recent prior negative cytology.26,83 Some of these lesions have been called rapidly progressive cancer, a condition discussed elsewhere (see Chapter 9). There are several explanations for these findings. Some of the smears were probably false negatives that would have been found to contain malignant cells or at least dyskaryotic/dysplastic cells on review. Others may have been genuine false negatives, in which either the cytologic sample was inadequate, the tumor was located high in the endocervical canal, or the tumor did not exfoliate cells and none were present in the smears.⁸⁴ However, it is impossible to escape the conclusion that at least some of these women had true progression from normal histology to invasive carcinoma. This has occurred in a short period between the collection of the smear and the diagnosis of the carcinoma, sometimes in less than a year. It seems reasonable to speculate that, although the mean time interval for the progression through SIL (CIN) to invasive carcinoma may be 10–15 years, a few women will fall at the two extremes of the distribution curve of the length of natural history. Some may have such a long natural history that progression to invasion will never occur in the course of their lifetime; these women would be categorized as nonprogressive. On the other hand, there may be those women at the other extreme, in whom the natural history of the disease runs a very rapid course, measured in months rather than years. These may be the patients described in the previous reports. Indeed, very rarely do women under age 20 develop rapidly lethal invasive cancer. This hypothesis presumes that one disease process is occurring and that the difference in the behavior in different women is the result of extreme variations in the length of the natural history of the same disease. Another suggestion for which there are only scant data is that certain HPV types associated with cervical cancer are intrinsically associated with more rapid progression. This may correlate with the finding that HPV type 18 is rarely detected in cases of HSIL (CIN 2-3), but commonly in cervical cancers that have metastasized.⁸⁵

Original Squamous Epithelium

Normal original squamous epithelium presents a uniform, relatively featureless appearance with a smooth surface contour, which does not become white after the application of acetic acid (Figures 10.56 and 10.57). The vessels are usually inconspicuous and are mostly of hairpin type, showing one ascending and one descending branch of very fine caliber, forming a small loop. If the surface epithelium is thin, it is sometimes possible to observe the whole loop by colposcopy. Generally only the tip of the loop is visible, so that these hairpin capillaries are usually seen as regularly and densely arranged small dots.

Columnar Epithelium

Normal columnar epithelium is easily recognized by its characteristic grape-like or villous appearance. Before application of acetic acid, the colposcopist will see that each columnar epithelial villus contains a fine capillary. As the villus is covered by no more than a single layer of columnar cells, the blood in the capillary gives columnar epithelium its typically red appearance. Following application of acetic acid, the villi often appear white and swollen and are more easily recognizable (Figure 10.58).

Squamous Metaplasia

The transformation zone in the cervix lies between the native/original squamous epithelium and the current squamocolumnar junction. It is normally covered at least in part by mature squamous metaplasia, but, at some earlier time, was covered by columnar epithelium. The new epithelium results from transformation of columnar to squamous epithelium, through the process of squamous metaplasia.

Mosaic and Punctation

These are both patterns of the small blood vessels that arise in the stromal plexus beneath the epithelium and pass into the epithelium surrounded by a very sparse stromal core (Figure 10.61). If the vessels branch and anastomose, forming a basket-like pattern around epithelial blocks, a mosaic pattern results (Figures 10.62 and 10.63). On the other hand, if the vessel travels toward the surface and then turns back again without branching, a punctate pattern will be seen (Figures 10.64 and 10.65). The two patterns often coexist on the same cervix. The degree of histologic abnormality that the epithelium shows may be roughly predicted by the intercapillary distance, the coarseness of the vessels, and the regularity of the pattern. The greater the intercapillary distance, the coarser the vessels and more irregular the pattern, the more severe the histologic grade of SIL (CIN) is likely to be. However, it is wrong to believe that colposcopy itself is capable of making a precise histologic diagnosis of an epithelial abnormality.¹⁴ The final diagnosis must always be histologic.

Acetowhite Epithelium

Application of aqueous acetic acid (3–5%) to the cervix causes a color change when SIL (CIN) (or some of the other changes listed earlier) is present. The acetic acid has the effect of making the abnormal epithelium appear white and opaque, whiter than it was before the application of the acetic acid and whiter than the normal epithelium after the application of acetic acid (Figures 10.66 and 10.67). The whiteness, usually referred to as ‘acetowhite epithelium,’ is related to the amount of nuclear material present.

Leukoplakia

Leukoplakia appears as a well-defined white area, often slightly raised and with a ‘waxy,’ shiny surface (Figure 10.68). It differs from acetowhite epithelium as it is white before acetic acid application and the acetic acid has no effect on its whiteness.

While the finding of leukoplakia indicates keratinized epithelium, the underlying features that enable the degree of abnormality to be assessed are masked by the keratin. Biopsy is therefore essential as the underlying pathology may range from otherwise normal epithelium with surface keratinization through keratinizing SIL (CIN) to invasive carcinoma.

Atypical Vessels

Atypical vessels indicate the possibility of a more advanced abnormality, perhaps early invasive carcinoma. These atypical vessels are basically punctate or mosaic patterns, but turn and run a short way parallel to the surface of the epithelium, forming commas, spirals, and irregular shapes (Figures 10.61 and 10.69).

Suspect Frank Invasive Carcinoma

This term refers to cases where a preclinical invasive carcinoma is present, usually larger than microinvasive carcinoma. The surface contour is irregular and nodular. There is intense acetowhiteness and coarse, bizarre, and irregular vessels (Figure 10.70).

Congenital Transformation Zone

In some patients, immature squamous epithelium is present peripheral to the transformation zone, producing an acetowhite epithelium that is nonglycogenated. These changes are primarily confined to the cervix, but in 4% of women they extend to involve the vagina, usually anteriorly and posteriorly.

This type of transformation zone may develop during intrauterine life, or later but prior to sexual activity, and is not associated with an increased risk of neoplastic change. It is colposcopically significant as it shares some features with SIL (CIN). The epithelium is acetowhite, has a fine mosaic pattern, and is either nonglycogenated or patchily and partially glycogenated. The histologic appearances were discussed previously and are illustrated in Chapter 8.

Other Colposcopic Findings