Endoscopic colorectal tattooing with carbon-based dyes is commonly employed in order to assist with later localization of the lesion. Although carbon is thought to be nontoxic, there usually is some ...inflammatory reaction with fibrosis and granuloma formation after tissue injection. The aim of this report is to alert to a possible underestimated, late consequence of colorectal carbon-based marker tattooing, namely pronounced fibrosis at the site of the injection that could lead to a blurring and misinterpretation of changes evaluated by radiological techniques. We describe a case of cT stage overestimation due to fibrosis of the rectal wall and perirectal fat, induced by carbon-based dye injection in a 66-year-old patient. In our case it was an overestimation of MR evaluation in the case of early invasive carcinoma. Although there have been some studies on tissue effect of carbon-based dyes, the possible scenario consequence of cancer stage overestimation due to fibrosis has not yet been described. Such a mistake could lead to inappropriate overtreatment. Clinicians must be aware of the possible consequences of dye injection and resultant overestimation of T stage of colorectal cancer. More histological studies concerning histological changes after carbon-based marker tattooing are needed to establish the extent of its significance.
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