Histologic diagnosis
Case 211
【Progress】
Preoperative needle biopsy was not conducted because of being afraid of tumor cell dissemination by procedure. He received surgical local resection of tumor without histological confirmation. Microscopic examination revealed adenoid cystic carcinoma.
【Discussion】
Salivary glands compose of a pair of parotid glands, a pair of submandibular glands, a sublingual gland and a number of minor glands. Saliva is mixed with mucin and serum. Parotid gland secretes more serum than submandibular gland, while a sublingual gland secretes least serum and more mucin. Although submandibular gland is smaller than parotid gland, submandibular gland secretes saliva most, approximately 65 to 70% of all saliva, followed by parotid gland, up to 30% and sublingual gland, 5% (1, 2, 3). Mucin makes food lubricate to swallow and forces bacteria to be caught and outflowed to stomach with strong acids, while serum contains antibody, pre-amylase enzyme and inorganic ions to defense against microorganism and to digest starch into smaller carbohydrates.
Microanatomy of salivary gland showed acinar cells which secrete serum or mucin, intercalated ducts which lead serum or mucin from acinar cells to striated ducts, striated ducts in which mucin and serum are mixed, and lead to excretory ducts. Parotid glans include many & long intercalated ducts and striated ducts, while sublingual glands own least intercalated ducts or striated ducts. Namely, mucin produced by acinar cells in sublingual ducts is secreted directory to excretory ducts.
In parotid glands, benign tumor occurs with incidence of approximately 80% and malignant tumor, approximately 20% (3). In submandibular glands, 50% of the tumors are benign or malignant (3). Meanwhile, in sublingual glands, malignant tumors occur in more than 90% (3). Benign tumors such as pleomorphic adenoma and Warthin tumor arise from intercalated ducts. Then, the occurrence incidence of benign tumor elevates in parotid glands abundant with intercalated duct, while it decreases in sublingual glands with least intercalated ducts. As a result, the tumors arisen from sublingual glands are malignant such as acinar adenocarcinoma from acinar cells, adenoid cystic carcinoma and mucoepidermoid carcinoma form excretory ducts.
When salivary gland tumors including pleomorphic adenoma (mixed tumor), adenolymphoma (Warthin tumor) and malignant tumors are encountered on MRI, MRI with diffusion & ADC values might be useful to differentiate them (4-6). It is reported that average ADC values calculated by b0 and b1000 are 0.74 for adenolymphoma, 0.95 for malignant tumors and 1.72 for pleomorphic adenoma (6). In our case, ADC value was 0.95 (Fig. 4), compatible with malignant tumor. Further, MRI showed sublingual tumor contained cystic component, implying adenoid cystic carcinoma rather than acinar cell carcinoma and mucoepidermoid carcinoma.
There are three diseases in sublingual glands: ranula, salivary stones and malignant tumors. Ranula is a pseudocyst leaked from sublingual glands. Salivary stones occur most in submandibular gland probably because of mucin saliva and tortuous duct. Sublingual duct is followed for more mucin saliva but short excretory duct. Salivary stones occur least in parotid gland for serous saliva.
【Summary】
We present a sixty five-year-old male for swollen floor in his oral cavity. Oral cavity findings displayed elastic-hard mass palpable in the left-sided floor. MRI with diffusion & ADC values are moderate high signal intensity and 0.95, respectively. It is borne in mind that there are three maladies in lingual glands: ranula, salivary stones and malignant tumors. Malignant tumors include mucoepidermoid carcinoma, adenoid cystic carcinoma and acinus adenocarcinoma. The incidence of malignant tumor in parotid gland, submandibular gland and sublingual gland is 20%, 50% and 95%, respectively. The benign tumors such as pleomorphic tumor and adenolymphoma arise from intercalated duct, while malignant tumors arise from acinar cell or excretory duct. Sublingual gland has least intercalated duct, implying it has no room for emerging benign tumor. ADC values of pleomorphic tumors, adenolymphoma and malignant tumors are 1.7, 0.75 and 0.95, respectively.
【References】
1.Ten Cate's Oral Histology, Nanci, Elsevier, 2013, page 255
2.Moore, Keith; et al. (2010). Clinically Oriented Anatomy, 5th Edition. Lippincott Williams and Wilkins. ISBN 978-0-7817-7525-0
3.Spiro RH. Salivary neoplasms: overview of a 35-year experience with 2,807 patients. Head Neck Surg 1986; 8: 177–84.
4.Assili S, et al. Dynamic contrast magnetic resonance imaging (DCE-MRI) and diffusion weighted MR imaging (DWI) for differentiation between benign and malignant salivary gland tumors. J Biomed Phys Eng 2015; 5: 157–68.
5.Hisatomi M, et al. Diagnostic value of dynamic contrast-enhanced MRI in the salivary gland tumors. Oral Oncol 2007; 43: 940–7.
6.Zheng N, et al. The diagnostic value of combining conventional, diffusion-weighted imaging and dynamic contrast-enhanced MRI for salivary gland tumors. Br J Radiol. 2018; 91: 20170707.
2020.11.11