Clinical overview
Colposcopy is the magnified, illuminated examination of the cervix, vagina and vulva used to localise, characterise and biopsy the epithelial abnormalities that precede invasive cervical cancer. It is the diagnostic hinge of the cervical screening programme: screening (cytology or HPV testing) identifies who needs further assessment, but colposcopy decides what the lesion is and where to treat. For a South African registrar this is a high-volume, high-stakes skill. Cervical cancer is the commonest cancer in South African women and one of the leading causes of cancer death, driven by a high background prevalence of HIV — and HIV-positive women progress faster from high-grade lesions to invasive disease. The colposcopist therefore sits at the point where a treatable pre-invasive lesion is either caught and cured or missed and allowed to invade.
Running the clinic safely and competently means several distinct skills: set up and use the instrument, apply acetic acid and Lugol's iodine and interpret what they reveal, recognise the transformation zone and judge whether it is fully visible, grade an abnormality, take an adequate directed biopsy, decide between "see-and-treat" and biopsy-then-treat, and — most importantly — know when a colposcopic picture is sinister enough to mandate urgent referral for possible invasion rather than office treatment. The practical drill of the examination itself is the substance of this work. It pairs directly with CIN management, Cervical screening SA, CIN pathophysiology, HPV pathology and Cervical carcinogenesis.
Core knowledge
Figure F10.1 — Transformation zone = the safety decision: TZ types 1–3 and the hidden upper limit — if the upper limit/SCJ is hidden you cannot exclude canal disease; excision (not ablation) when high-risk or not fully visible.
The target: the transformation zone
Cervical neoplasia almost always arises in the transformation zone (TZ) — the band of metaplastic squamous epithelium between the original squamocolumnar junction (SCJ) and the new SCJ, where columnar endocervical epithelium has been progressively replaced by squamous epithelium. This immature metaplastic epithelium is uniquely vulnerable to HPV-driven transformation. Everything the colposcopist does is aimed at seeing this zone completely and assessing whether it harbours abnormality.
The position of the SCJ moves with hormonal status. In a young woman it usually lies on the ectocervix and the whole TZ is visible (an ectocervix picture). After the menopause, and with falling oestrogen, the SCJ retreats up the canal so that the TZ becomes partly or wholly endocervical and invisible to the naked eye. This single anatomical fact underlies the most important judgement in colposcopy: whether the examination is adequate (the whole TZ and the entire lesion are seen) or inadequate (the upper limit cannot be seen).
The TZ is classified into three types, which dictates how — and whether — a lesion can be treated in the office:
| TZ type | Squamocolumnar junction | Excision implication |
|---|---|---|
| Type 1 | Fully ectocervical, completely visible | Shallow ectocervical excision/ablation |
| Type 2 | Has an endocervical component, but fully visible (with manipulation) | Deeper excision, still visible margins |
| Type 3 | Endocervical component not fully visible | Cannot exclude canal disease; long cone/cylindrical excision, or refer |
The two stains and what they mean
Colposcopy relies on two contrast agents applied after a plain saline look:
- Acetic acid (3–5%) is the workhorse. It is thought to reversibly coagulate and dehydrate intracellular nuclear protein; epithelium with a high nuclear-to-cytoplasmic ratio (dysplastic, high-grade) turns dense, opaque white ("acetowhite") and is slow to fade. Low-grade change is thin, translucent and fades quickly. The colposcopist watches the speed of onset, density, persistence and margin of the acetowhite reaction — this dynamic is as informative as the static appearance.
- Lugol's iodine (Schiller's test) stains glycogen-rich mature squamous epithelium dark mahogany-brown. Dysplastic epithelium and columnar epithelium are glycogen-poor and stay pale yellow ("Schiller-positive" / iodine-negative). Lugol's is excellent for delineating lesion borders and for picking up vaginal (VaIN) extension, but it is non-specific (immature metaplasia and atrophic epithelium are also iodine-negative).
Grading systems
Two systems run in parallel: the colposcopic grading vocabulary and the pathology terminology it predicts.
- IFCPC 2011 terminology (International Federation for Cervical Pathology and Colposcopy) is the modern descriptive standard. It records: adequacy, SCJ visibility, TZ type; then grade 1 (minor) changes — thin acetowhite, fine mosaic, fine punctation, irregular/geographic borders — versus grade 2 (major) changes — dense acetowhite, rapidly appearing and slow to fade, coarse mosaic, coarse punctation, sharp borders, "inner border" sign, "ridge/cuffed gland openings"; then non-specific findings; then explicit features suspicious for invasion (atypical vessels, fragile bleeding, irregular surface, exophytic lesion, necrosis, ulceration).
- The older Reid Colposcopic Index (RCI) scores four features (margin, colour, vessels, iodine staining) 0–2 each to predict low- versus high-grade.