[Rare case of supernumerary submandibular gland lobes forming a complex with the sublingual gland].

In the sublingual/submandibular gland complex (L/M complex hereafter), the submandibular gland process adjoins the sublingual gland. Therefore, it is speculated that the L/M complex in the fused state is due to excessive development of the submandibular gland process. However, we encountered a case of the L/M complex formed due to supernumerary glandular lobes (lobes A, B, and C) developing in the posterior 1/3 portion of the submandibular duct. Lobes A, B, and C showed the following macroscopic morphologies, constitutions, ducts, and histological morphologies. Lobe A was disc-shaped, and this lobe together with the major sublingual gland was wrapped with the minor sublingual gland. Lobe B was attached to lobe C, forming a cingulate lobe. Lobe B had an irregular shape and was attached to the superior area of lobe A, while lobe C was rod-shaped and attached to the posterior area of lobe B. The posterior area of lobe C was attached to the submandibular gland at the base of the submandibular duct. The excretory ducts of lobes A, B, and C joined, forming one duct, which joined the posterior 1/3 portion of the submandibular duct. The histological morphologies of lobes A, B, and C showed a predominance of serous cells over mucous cells, which was the same as the morphology of the submandibular gland. In this case, the L/M complex may have formed by the following mechanism. Supernumerary lobes A, B, and C of the submandibular gland formed in the posterior 1/3 portion of the submandibular duct, and lobe A together with the major sublingual gland was wrapped with the minor sublingual gland. Lobes B and C formed a cingulate lobe, and its posterior portion (posterior portion of lobe C) attached to the submandibular gland, resulting in a fused state.