Colorectal cancer tumoral and nodal staging : Comparison between CT findings and pathological findings

Abstract

Background and Rationale : Colorectal cancer is a common malignancy of the gastrointestinal tract. In Thailand, colorectal cancer is the third most common cancer in males and fifth most common in females. Incidence rate of colorectal cancer has been rising in Thailand. Pathologic staging is the gold standard for colorectal cancer. However, it is followed by post-operative procedure. Computed tomography (CT) is noninvasive and preoperative assessment. Preoperative CT is useful for planning therapy by which local extension of the tumor into the adjacent organs or distant metastases are demonstrated. Differentiation between T2 and T3 colon cancer is important for consideration of chemotherapy.

Objective : To compare the multi-detected computed tomography (MDCT) of the whole abdomen for colorectal cancer staging correlated with pathologic staging including the accuracy of the staging of the tumor (T) and lymph nodes (N).

Research design : Retrospective descriptive study.

Setting : Department of Radiology, Faculty of Medicine, Chulalongkorn University and King Chulalongkorn Memorial Hospital.

Material and Methods : Abdominal MDCT scans of 178 patients with pathologic diagnosis of colorectal cancer were retrospectively reviewed from 1^st January 2007 to 31^st December 2009 at King Chulalongkorn Memorial Hospital.

Result : Agreement of CT for T staging is good with excellent interobserver agreement. The overall accuracy of correct T stage from CT scan was 75.84%. All overstaged CT scans with pathologic stage < T2 were pericolonic fat stranding due to mitoses, necrosis, mucin producing area, and desmoplastic reaction around the sheet of tumor from pathological reports. The causes of overstaging by CT scan with pathologic stage T3 were obliteration of fat plane of adjacent organs in 4 lesions, abutting peritoneum in 6 lesions, ascites in 1 lesion, and colonic perforation in 2 lesions. All cases of understaging by CT scan with pathologic stage T3 were no pericolonic fat stranding and 2 cases of understaging by CT scan with phathologic stage T4 were preserved fat plane between the mass and adjacent organs. The highest sensitivity, NPV and accuracy are stage T4 (86.4%, 97.8% and 89.9%, respectively). The highest specificity is stage T < 2 (92.3%). The highest PPV is stage T3 (90.3%). Agreement of CT for N staging is poor with good interobserver agreement. The overall accuracy of correct N stage from CT scan was 32.27%. The highest sensitivity is stage N0 (63.8%). The highest specificity, PPV and accuracy are stage N2 (99.1%, 83.3% and 64.6%, respectively). The highest NPV is stage N1(74.6%).

Conclusion : CT scan is useful in preoperative evaluation of colorectal cancer. In our study, colorectal cancer staging from CT scan is considered satisfactory for tumor staging, but too low to determine the nodal staging. The overall accuracy of correct T stage by CT scan was 75.84%.