The article by H asegawa et al. aroused my interest and simultaneously raised the following question: Is sialolithiasis an acceptable underlying condition for adenoid cystic carcinoma (AdCC)? The authors understated in the abstract that ‘AdCC could arise in the background of chronic sialadenitis’ and also implied in the discussion that ‘This [hepatolithiasis is one of the important histopathogenetic backgrounds of cholangiocarcinomas] may also be the case for sialolithiasis in the salivary carcinogenesis.’
In concert with concepts of neoplasia in general, it is tempting to speculate that chronic inflammation may have a causative role in the development of a salivary gland tumour, but I would be interested to know on what basis H asegawa et al. considered submandibular duct lithiasis as ‘serious pathology’?
Chronic non-specific sialadenitis secondary to calculus is the most common obstructive disease and AdCC is the fourth most frequent epithelial malignancy of salivary gland origin . Nevertheless, almost all AdCC occur in the absence of clinical evidence of concurrent or previous sialolithiasis. It is well established that calculus most commonly develops in the submandibular gland, but AdCC more frequently affects the parotid and palatal minor glands, which are uncommon sites of duct lithiasis . If we accept their hypothesis, AdCC can occur either at relapse of calculus-associated obstructive sialadenitis or decades after its treatment; however, to my knowledge, there has been no formal description of this category in the literature. In addition, the complication of salivary gland carcinoma is extraordinarily rare in patients with autoimmune/sclerosing sialadenitis . From clear-cut clinical information, a 10-year history of calculi in the case reported by H asegawa et al. , by itself, is insufficient evidence of AdCC emerging in the setting of chronic sialadenitis. It must be kept in mind that AdCC grows very slowly and remains quiescent for years in most cases .
The consensus amongst pathology textbooks is that AdCC conceptually arises from the intraglandular intercalated duct . There are two exceptions of AdCC occurring in a main extraglandular excretory duct, both of which involved Stensen’s duct . To date, Wharton’s duct AdCC, either invasive or in situ , has not yet been described. Although incipient (limited to the central part of the gland), H asegawa et al. failed to trace origin of AdCC in the duct system that was chronically inflamed as a result of the presence of calculi. Moreover, microlithiasis was not recognizable in conjunction with carcinoma nests. When these findings are analysed and balanced against the above knowledgebase, there is little histologic evidence to show that AdCC supervenes on duct lithiasis. The fact that sialolithiasis, unlike cholelithiasis, seldom exhibits neoplastic/dysplastic changes in the duct epithelium lends further credence to this explanation .
There are a few reports on other types of epithelial tumour concomitant with sialolithiasis in the involved gland . Since epidemiologic data that epithelial salivary gland tumours are preceded by chronic obstructive sialadenitis is presently unavailable , care must be taken to ensure that neoplasm is secondary to inflammation . Very important from an aetiologic point of view is that predisposing factors for sialolith formation never initiate carcinogenesis. Bile exhibits a tumour-promoter activity, but saliva is well known to be anticarcinogenic per se . With regard to the neoplastic properties, sialolithiasis is essentially different from cholelithiasis. Taking into account all current knowledge, it is best to consider the reported coexisting lesions of AdCC and duct lithiasis as a coincidental occurrence probably due to higher incidences of both conditions in the submandibular gland .
Finally, are full radiographic examinations always necessary to rule out suspicion of malignancy during management of long-standing calculus? The answer is no. In practice, this ideal is difficult and even impossible for fortuitous diagnosis. Ironically speaking, excessive use of medical radiographs may place patients with ‘non-serious pathology’ at increased risk for the later development of salivary gland carcinoma .