Anal colposcopic examination (anoscopy) is very important in defining the extent and features of lesions of anus, anal canal and perianal area. Colposcopy of the vulva seems to be invaluable aid in assesing the nature and the extent of external trauma. It may serve as a mean of an objective documentation when forensic evidence is needed, particularly when sexaul abuse of children is concerned.
The examination includes the same techniques as the examination of vulva. Firm lateral pressure on both buttocks may evert the anal canal to some degree, to reveal the abnormality. Traction on peri-anal skin also permits the examination on lower anal canal. Peri-anal skin and lower anal canal are first examined colposocpicaly before the application of 5% acetic acid. The field is soaked with 5% acetic acid which remain to act at least 2-3 minutes to mark eventually present lesions. If this procedure cause burning, warm water rinsing should immediately be applied.
If numerous white lesions are present anoscopy and proctoscopy should be performed. Using the proctoscope, views of the upper anal canal, the transition zone and low rectal mucosa are readily obtained. Proctoscopy combined with a standard colposcopic technique including the application of acetic acid may be very difficult. Day case anaesthesia may be considered if such an examination is not tolerable by the patient in the outpatient setting.
The boundaries of the peri-anal epithelium and the anal canal are poorly defined. Perianal skin is that which can readily be seen on parting the buttocks. Anal canal epithelium is defined as that epithelium above this level and is limited cephaloid by the rectal mucosa.
The normal peri-anal skin is unremarkable on colposcopy both before and after the application of acetic acid. The epithelium is heavily keratinized and responds to acetic acid only after prolonged soaking. Any changes present perianally may indicate the possible presence of similar lesions in the anal canal.
Anal canal may be involved either by the extension of VIN from perianal skin inwards to linea pectinea and then the lesions are in continuity with the perianal ones or anal mucosa can be affected isolately, without obvious connection with vulva and preineum. The colposcopy of the anal canal provide an excellent view of the anal cushions, the pectinate line and transition zone. Spraying acetic acid onto the upper anal canal cause the transition zone to become more opaque and, hence, more obvious. The transition zone is usually located slightly cephaloid to the pectinate line, although its position varies from one individual to another. The transition zone becomes more obvious if mucus from the lower rectum is removed via proctoscope using a cotton swab. Mucus in the anal canal or rectum may be misleading as it readily opacifies due to protein coagulation with the acetic acid. It is therefore essential to remove such mucus during the course of anal colposcopy in order to see clearly the underlying epithelium and its response to acetic acid. Immature normal squamous epithelium may show slight aceto-white change, necessitating careful interpretation of anal colposcopy in patients who have recently undergone any anal surgery or who have anal symptoms such as pruritus ani.
There are three distinct sites where the lesions can appear: perineum, anus and anal canal. Lesions affecting perineum and anal region are basically similar to those on the vulva. Many of them show pigmentation and hyperkeratosis.
Vascular changes usually seen on cervix (punctations and mosaic) are not frequent perianally but may be seen in anal canal.
In the anal canal, the dysplastic epithelium may appear hyperemic on examination prior to the application of acetic acid. After the application of acetic acid such areas become more obvious.
The colposcopic features of papillomavirus infection and dysplasia in the lower anal canal and peri-anal skin merge into each other. The colposcopic predictive distinction between pure non-condylomatous HPV infection and low-grade AIN (1-2) is less accurate than in the colposcopic assessment of the cervix. Biopsy of any white lesion or abnormal vascularity is necessary because anoscopy and proctoscopy are difficult. After biopsy majority of bleedings can be stopped by pressure of at least 3 minutes.
