[1450] Muscularis Mucosae vs. Muscularis Propria in Gallbladder, Cystic Duct and Common Bile Duct: Smoothelin and Desmin Immunohistochemical Study

K Raparia, QJ Zhai, MR Schwartz, L Peters, SS Shen, AG Ayala, JY Ro. The Methodist Hospital, Houston, TX

Background: The muscle layer in the gallbladder, cystic duct and common bile duct is not well defined and it is still unresolved whether it is muscularis mucosae or muscularis propria. Smoothelin is a novel smooth muscle-specific contractile protein expressed only by fully differentiated smooth muscle cells in the muscularis propria, and not by proliferative or noncontractile smooth muscle cells in muscularis mucosae. In this study, we attempt to characterize the property of muscle layers in gallbladder, cystic and common bile ducts by immunohistochemistry using desmin and smoothelin.
Design: Formalin-fixed paraffin-embedded sections of the gallbladder (15 cases), cystic duct (11 cases) and common bile duct (10 cases) were stained for smoothelin (1:100; Abcam Inc, Cambridge, MA) and desmin (1: 200; Dako, Carpinteria, CA). Staining intensity was evaluated as weak and strong. The staining pattern score was evaluated as follows: 0 or negative 5%; +1 or focal=5% to 10% positivity; +2 or moderate=11% to 50% positivity; and +3 or diffuse >50% muscle cells positivity.
Results: With desmin, strong and diffuse (+3) staining was observed in all gallbladders (15/15, 100%) highlighting one continuous layer of muscle. In contrast, the muscle layer was discontinuous and interrupted in all cystic ducts and in most of the common bile ducts highlighted by the desmin stain. Smoothelin intensely stained (more than 2+) muscle fibers in the gallbladder wall similar to that observed with desmin staining (10/15, 67%). In contrast, the common bile duct predominantly had absent or weak and focal immunostaining (0 or 1+ staining) with smoothelin (7/10, 70%) with only a few cases (3/10, 30%) having 2+ staining. Cystic ducts also showed absent or weak and focal immunostaining with smoothelin with 5 of 11 cases (44%) showing 2+ immunostaining with smoothelin.
Conclusions: 1) In the gallbladder, the continuos muscle layer appears to be muscularis propria and no muscularis mucosa is present. 2) In cystic and common bile ducts only attenuated and incomplete muscle layer is present, suggesting no or limited contractile function. 2) Differentiating these anatomic muscle structures may be important for the pathologic staging of carcinoma in these organs.
Category: Liver & Pancreas

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 245, Wednesday Morning