Assessment of tumor infiltration depth in rectal cancer with transrectal sonography: caution is necessary.

PURPOSE: To assess the depth of infiltration of rectal cancer with transrectal ultrasound (US) (TRUS) and analyze interpretation errors. MATERIALS AND METHODS: Fifty-five consecutive patients with rectal cancer who underwent TRUS were prospectively studied. The effect of different patient inclusion criteria and US criteria was evaluated retrospectively. RESULTS: Extensive overstaging of T2 tumors, partially caused by inflammatory (desmoplastic) reaction or retraction of the muscularis propria, resulted in a specificity of only 24% for detection of perirectal infiltration. Sensitivity was 97%, and accuracy was 64%. Considerable variation in staging accuracy was observed when different patient selection criteria were used. Variation of US criteria improved differentiation between T2 and T3 tumors only slightly. CONCLUSION: The effect of different US criteria on differentiation of T2 and T3 tumors is limited. Spontaneous or iatrogenic inflammation is a major limiting factor. The accuracy of TRUS in staging rectal cancer is affected by patient inclusion criteria.