Gerald Langman, Abstract Co-Author: Nothing to Disclose

Ian Geh, Abstract Co-Author: Nothing to Disclose

Gamal Barsoum, Abstract Co-Author: Nothing to Disclose

Shuvro Himanish Roy-Choudhury MD, Presenter: Nothing to Disclose

Local lymph node staging in locally advanced rectal cancer is crucial as it dictates post operative adjuvant therapy for patients with positive nodes. Using size >5mm and MRI morphological criteria high accuracies have been reported, some with low histological lymph node yield. In a recent local study we found a lower accuracy of 60% for nodal staging. We therefore set out to find out the causes for this discrepancy by analysing the size and distribution of abnormal mesorectal nodes on histology

Between May 2007 and Jan 2009, 108 patients with resectable rectal cancer underwent total mesorectal excision. Of these, 35 (32%) patients had positive nodes. Mean age was 65 yrs (range 46-83) and 20 were males. An abdomino-perineal resection was performed in 8 and anterior resection in 27. The specimen was graded as Grade 1: 4, Grade 2: 12 and Grade 3: 19. Mean tumor length was 33mm (10-55 mm). Mean specimen length was 262 mm (100 - 470 mm), 33/35 patients were staged with MRI. None, short and long course pre-op chemoradiotherapy were given to 14, 13 and 8 patients respectively. All specimens were examined by a colorectal histopathologist using prescribed standards.

132 positive nodes were found in 35 patients. Mean node size was 4.5 mm (0.7 to 17.4 mm). Mean node yield was 38 (range 15-78). 81/132, 46/132 and 5/132 nodes were above, at and below the level of the tumor (p<0.05). Using a clock face 66/70 available nodes were located in the posterior half of the mesorectum (p<0.05). There were <3 nodes involved in 22 and >3 nodes involved in 13 patients. 90 (68%) positive nodes measured less than 5 mm. The mean diameter of the smallest and largest involved node was 3.5 mm (0.7-8.3 mm) and 6.6 mm (range 2.6-17.3 mm) respectively. In 11 (31%) patients, the largest involved node was < 5 mm. Of these 5 had one, 2 had two, 2 had three and 2 had >3 nodes involved. Six of these 11 patients had vascular invasion. MRI undercalled 8/11 of these patients.

Applying size criteria of 5mm to assess lymph node morphology will miss 31% patients with nodal spread in the setting of high histological nodal yield. Although the location of a node on MRI can be a useful predictor, alternative methods are desirable to improve accuracy of nodal staging in rectal cancer.

Thin section MRI needs to be supplemented by alternative techniques like USPIO or diffusion weighting to improve the accuracy.

Langman, G, Geh, I, Barsoum, G, Roy-Choudhury, S, Staging of Rectal Cancers: Assessing the Size and Distribution of Pathological Lymph Nodes in the Setting of High Histological Lymph Node Yield.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8007088.html