Chronic sclerosing sialadenitis is a chronic (long-lasting) inflammatory condition affecting the salivary gland. Relatively rare in occurrence, this condition is benign, but presents as hard, indurated and enlarged masses that are clinically indistinguishable from salivary gland neoplasms or tumors. It is now regarded as a manifestation of IgG4-related disease.
 Involvement of the submandibular glands is also known as Küttner's tumor, named after Hermann Küttner (1870–1932), a German Oral and Maxillofacial Surgeon, who reported four cases of submandibular gland lesions for the first time in 1896.
 The inflammatory lesions in Küttner's tumor may occur on one side (unilateral) or both sides (bilateral), predominantly involving the submandibular gland, but is also known to occur in other major and minor salivary glands, including the parotid gland.
Overall, salivary gland tumors are relatively rare, with approximately 2.5–3 cases per 100,000 people per year seen in the Western world; however, salivary gland malignancies account for 3–5% of all head and neck cancers. However, salivary tumors show a great deal of morphological diversity, as well as variations in the nature of the lesion (malignant vs. benign):  approximately 20% to 25% of parotid tumors, 35% to 40% of submandibular tumors, and more than 90% of sublingual gland tumors are malignant. This situation underscores the diagnostic challenges in respect of Küttner's tumor; despite being benign, this condition mimics the clinical appearance of malignancy in the salivary gland.
 The swollen masses of Küttner's tumor are generally painful, and patients are advised surgical resection (known as 'sialadenectomy') of a part or whole of the glandular tissue upon suspicion of possible malignancy. It is only upon post-surgical histopathology of the excised mass that the diagnosis of Küttner's tumor is definitively made.
 The histopathological features that characterize Küttner's tumor include:
 The cause and pathogenesis of this chronic condition are not very well understood. Several factors have been postulated:
 This chronic condition is primarily observed in adult (40–70 years) patients. However, Küttner's tumor, with prominent immunopathological features, has been described in an 11-year-old boy in Brazil in 2012.
 Given the difficulties of a definitive pre-operative diagnosis, the clinical entity of Küttner's tumor has so far remained significantly under-reported and under-recognized. In recent times, armed with a better understanding of the occurrences and observable features of this condition, surgeons are increasingly depending upon pre-operative ultrasonography along with Fine-needle aspiration cytological (FNAC) examinations to make an accurate presumptive diagnosis, and according to one estimate, about 44% of patients undergoing submandibular resection are found to have this condition. In the ultrasonogram, Küttner's tumor is characterized by a diffuse, heterogeneous zone of echo-shadows. The FNAC finds cells greatly reduced in number (called 'paucicellularity') along with scattered tubular ducts against a backdrop of lymphoplasmacytic infiltration and fibrous depositions. There may be a reduced but moderate number of cells and ducts enveloped in fibrous sheaths, as well as fibrous proliferation of the gland's septa. The cytologic findings by themselves may not be specific, and the diagnosis requires adjunct consideration of both the ultrasonogram and clinical presentation. Application of magnetic resonance imaging (MRI) has been tried to non-invasively examine the morphological variations in Küttner's tumor and differentiate them from those seen in malignant tumors; while MRI findings of the affected tissue and the pattern of cellular infiltration may offer some diagnostic clues for this condition, so far the results have been inconclusive.
 Standard, and most effective, therapy to date is glandular sialadenectomy, which is associated with fairly low operative morbidity; however, in recent times, the administration of steroid (which can shrink the inflammatory lesion and is known to reduce serum IgG4 values) has been considered favorably, and may be useful in younger patients or those who refuse surgery.