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Non-polypoid adenomas of the colon are associated with subjacent lymphoid nodules. An experimental study in rats
C A Rubio1, J Shetye, E Jaramillo
1Dept. of Pathology, Karolinska Institute, and Clinic of Gastroenterology and Hepatology, Karolinska Hospital, Stockholm, Sweden.
Background:
Subjacent lymphoid nodules (SLNs) have been found in 38% of non-polypoid colonic adenomas in humans. In the present work the presence of SLNs in experimentally induced colonic adenomas was investigated in rats.
Methods:
1,2-Dimethylhydrazine was injected subcutaneously in 290 Sprague-Dawley rats for 27 weeks.
Results:
An SLN was present in 28.6% of the 84 adenomas, in 8.4% of the 119 adenocarcinomas, and in 9.7% of the 31 small carcinomas without remnant adenomatous tissue. An SLN was found in 35.6% of the 59 non-polypoid neoplasias but only in 9.1% of the 175 polypoid (that is, exophytic) neoplasias. When only adenomas were considered, SLNs were present in 50.0% of the 34 non-polypoid adenomas but only in 14.0% of the 50 polypoid adenomas.
Conclusions:
Non-polypoid colonic adenomas evolve preferentially from the minimal fraction of the colonic mucosa that overlays the few existing lymphoid nodules in rats.