Standardization of Nodal Counting in the Obturator Fossa of Cadaveric Specimens
Authors: Beveridge Tyler S , Johnson Marjorie , Power Nicholas , Allman Brian L 
Published: November 2023

It is well accepted that the total number of lymph nodes removed during pelvic lymphadenectomy increases the accuracy of cancer staging, possibly improving the long‐term survival of patients. Because of this, the nodal count has been adopted as a measure of surgical performance; however, this presupposes that nodal counting is a reproducible and standardized process. At present, reported nodal counts are extremely variable, and inconsistency between institutions is common because of differing operational protocols. Furthermore, significant inter‐ and intra‐observer variability between pathologists at the same/similar institutions is common because it is not unanimously agreed whether non‐capsulated lymphoid aggregates (lymphatic nodules) should be considered in the total nodal count. Despite the disparate variations reported in the literature, it is our hypothesis that standardized lymphoid tissue counts can be achieved when evaluating: (1) the gross distribution of lymphatic elements (nodes and/or aggregations) within the tissue; (2) the number of capsulated nodes; and/or (3) the number of non‐capsulated lymphoid aggregations. To achieve this, we examined the distribution and number of all organized lymphatic elements present in the obturator fossa (bordered by the external iliac vein, superior; obturator nerve, inferior; pelvic brim and obturator internus, lateral; confluence of the common iliac vein, cranial; and the lymph node of Cloquet, caudal) of human cadavers with no known history of pelvic disease. Counts were obtained by gross evaluation of left (n=5) and right (n=5) obturator fossae tissue packets that had been removed en bloc and subjected to fat clearing with xylene. In order to confirm the gross identification of lymph nodes versus lymphoid aggregations, six samples were examined microscopically after being stained with Haematoxylin and Eosin (H&E) using standard histological protocols. Gross examination revealed the lymphatic elements were typically organized into three regions of the tissue packet: a small round collection at the cranial and caudal aspects, in addition to a large, elongated collection within the central portion. Despite a consistent topographic distribution, the total count (lymph nodes and lymphoid aggregations) demonstrate that the obturator fossa packet contains a varying number of lymphoid elements [overall mean = 7.1 ± 3.2; left mean = 8.8 ± 3.2; right mean = 5.4 ± 2.3], ranging from 3 to 13. Moreover, the number of lymphoid elements between sides was not correlated (r= −0.16; p>0.05). Standard H&E staining revealed four capsulated lymph nodes and two non‐capsulated lymphoid aggregations that were not distinguishable from one another by gross anatomic features. Given this result, additional histology will be completed on the remaining samples to quantify the number of lymph nodes versus lymphoid aggregations. Importantly, the present study has identified consistencies in the gross anatomical appearance of the lymphatic tissue within the obturator fossa despite inconsistent total nodal counts. Our future work is directed at gross and histological identification/differentiation of capsulated lymph nodes from non‐capsulated lymphoid aggregations present in the obturator fossa.Support or Funding InformationFrederick Banting and Charles Best Canada Graduate Scholarship Doctoral Awards (CGS‐D)