Squamous papilloma of the anal canal
22 March 2013 (online)
Squamous papillomas of the gastrointestinal tract are usually limited to the oral cavity , oropharynx , and the esophagus  ; squamous papilloma of the anal canal is a rare entity. We report a case of a squamous papilloma of the anal canal, initially suspected to be a fibroepithelial anal polyp.
An asymptomatic 60-year-old man underwent screening colonoscopy because of a strong family history of colonic polyps. Total colonoscopy was normal but retroflexion of the scope in the rectum revealed a 5-mm, sessile, nodular anal polyp ([Fig. 1]), which felt rigid when taking biopsy samples with cold forceps. Initially, a fibroepithelial anal polyp was suspected, but histopathological examination revealed fragments of mature squamous epithelium, which were of normal thickness and parakeratinized, without underlying fibrovascular stroma. Focally the lesion was slightly hypertrophic. The basal layer showed undulation, and regular polarity and cellular organization. Low mitotic activity was present in the basal and parabasal layers only, while the upper layers exhibited degenerative changes. A few binuclear cells were found. Some of the detached, smaller fragments resembled tips of fingerlike papillary projections. There were no signs of dysplasia or malignancy ([Fig. 2]). Human papilloma virus (HPV) was not detected in the biopsy samples using p16 immunostaining as a surrogate marker ([Fig. 3]). An index colonoscopy done at age 50 was completely normal. As the patient was asymptomatic, no endoscopic or surgical resection was carried out.
Squamous papilloma of the anal canal is a rare benign epithelial neoplasm that can be mistakenly suspected to be a fibroepithelial anal polyp. The tumor is characterized by papillomatous processes and covered by keratinized squamous epithelium . HPV negative lesions are also commonly regarded as ‘burned-out’ condylomas . It is important for colonoscopists to keep such lesions in mind when considering the differential diagnosis of an anal polyp.
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