Histopathological correlates of abnormal pericolic fat on CT in the assessment of colorectal carcinoma.

The aim of this study was to assess the pathological significance of abnormal pericolic fat shown by CT in the context of colorectal carcinoma. CT and histopathological findings of 63 resected colorectal carcinomas were retrospectively reviewed. CT examinations were assessed by two observers for the presence or absence of abnormal pericolic fat (typically linear or nodular opacities) at tumour sites. Specimens were reviewed histopathologically for depth of tumour invasion, extramuscular tissue reaction, and number and largest size of tumour-involved and tumour-free lymph nodes. The sensitivity, specificity, positive predictive value and negative predictive value of pericolic fat in identifying extension of tumour infiltration beyond the muscle coat were 79% (42/53), 33% (2/6), 91% (42/46) and 15% (2/13), respectively. Despite these indicators of efficacy, the association between the presence of pericolic fat abnormality on CT and extramuscular extension of tumour (infiltration and/or nodal disease) or tissue reaction alone or in combination did not reach statistical significance (p>0.3 in all cases). Abnormal ("misty" or "mucky") pericolic fat in the assessment of colorectal cancer on CT is not a precise indicator of extramuscular extension of tumour, as it cannot clearly distinguish between tumour infiltration and tissue reaction beyond the muscle coat, or pericolic nodal involvement. However, it is a very helpful CT sign that may draw attention to the presence and site of a potential colonic abnormality.