[727] Lymph Node Yield and MRI Correlation of Pathological Lymph Nodes after Neoadjuvant Chemoradiation in Rectal Cancer: The Importance of Lymph Node Size

Paromita Roy, Aditi Chandra, Mousumi Kar, Indranil Mallick, Manas K Roy, Sudeep Banerjee, Divya Midha, Indu Arun, Susy S Kurian. Tata Medical Center, Kolkata, West Bengal, India

Background: Neoadjuvant chemoradiation (NACRT) is the current standard of care before surgery for rectal adenocarcinoma. Lymph node yield is reported to be poorer after NACRT and magnetic resonance imaging (MRI) is recognized to have only limited accuracy in identifying metastatic nodes. We aimed to perform a detailed analysis of the importance of the size of metastatic nodes in determining yiedl and identification on MRI.
Design: Pathological data from 21 patients who underwent conurrent radiotherapy and oral capecitabine followed by anterior or abdominoperineal resection were analyzed. The lymph node yield, size and invovement of each dissected node was documented. A radiologist blinded to the pathology was asked to scrutinize the post-NACRT MRI to detect metastatic nodes based on characteristics on T2 weighted and diffusion weighted images.
Results: A total of 310 nodes were dissected from 21 patients, with an average yield of 14.8 nodes / patient. Metastatic nodes (ypN+) were identified in 8/21 patients with a total of 32 positive nodes. The average size of dissected nodes was 2.8mm, with 286/310 (92%) nodes <=5mm and 263/310 (85%) nodes <=3mm. The average size of the nodes showing metastasis was 5 mm, and 21/32 (66%) nodes <=5 mm and 14/32 (44%) nodes <=3mm. The smallest metastatic node was 1mm in size. None of the positive nodes were >1cm in size. In our sample, MRI as a preoperative indicator of node positivity had only limited value with a sensitivity of 75%; specificity of 54%; positive predictive value of 50% and negative predictive value of 77%. In 2/2 patients with a false negative MRI all the pathological nodes were <= 5 mm. In 5/6 patients with false positive MRI reports there were at least 2 lymph nodes that were >4mm in size.
Conclusions: Lymph node yield after NACRT is not necessarily low if careful nodal examination is performed. Metastatic nodes after NACRT are often small in size and unless adequate sections of adipose tissue are submitted and diligently scrutinized, the identification of pathological nodes may be compromised. MRI is of limited value in predicting pathological nodal status after NACRT, and the lack of size correlation is likely to be an important cause.
Category: Gastrointestinal

Wednesday, March 6, 2013 9:30 AM

Poster Session V # 87, Wednesday Morning

 

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