Electron microscopical observations on early sialoliths in a human submaxillary gland

Adenoid Cystic Carcinoma With Sialolithiasis of the Left Submandibular Gland: A Case Report and Literature Review

Adenoid cystic carcinoma is one of the most common salivary gland malignancies with poor long-term prognosis, but the coexistence of sialoliths is extraordinarily rare. In this article, we report a case of 30-year-old woman with a history of submandibular area swelling with intermittent pain increasing during mealtimes that had led her attending physician to diagnose a sialolith in the left submandibular gland on a radiograph 10 years before. However, the surgical specimen proved to be an adenoid cystic carcinoma accompanied with a sialolith. Histopathologically, the submandibular gland was displaced with a fibrous granulation tissue containing a small cribriform carcinoma invading the extracapsular region of the gland. We performed fluorescence in situ hybridization examination with an MYB-NFIB fusion probe of the lesion, with positive results. The patient underwent a supraomohyoid neck dissection as additional procedure because of the possibility of the extracapsular cancer nest remaining around the submandibular gland, but she remains well and disease free 11 years after the first operation.

On the structural diversity of sialoliths

Sialoliths from parotid and submaxillar glands have been characterized. Fractured and polished surfaces revealed an intrinsic structural diversity across the calculi sections. In general, the calculi presented highly mineralized amorphous-looking cores surrounded by concentric alternating mineralized and organic layers. The thickness of these layers decreased from the outer regions toward the center of the sialolith, illustrating a sequence of growth stages. Nevertheless, a significant variability could be detected among the specimens. In some cases, the calculi displayed multiple cores and lacked concentric laminated structures. In other instances, the specimens exhibited extensive regions of globular structures. In these cases, the globule diameter decreased across the radius toward the center of the sialoliths, and the globular structures tended to reorganize, forming bright and dark laminated layers surrounding the core. The participation of globular structures in the layer formation process points to morphogenetic mechanisms not previously described.

Microenvironmental adaptations in the parotid of ferret investigated by electron microscopy

Previous histochemical investigations suggested that the microenvironment in the parotid of ferret would foster microlithiasis because of a combination of pockets of inefficient secretion, brisk phagy and secretory material rich in calcium. We have undertaken the present ultrastructural investigation in an attempt to provide corroborative evidence. Parotids from four normal ferrets were examined by electron microscopy. Phagosomes in which there was cellular debris and occasionally secretory granules were present in acinar cells, which indicates crinophagy, and residual bodies were present in ductal cells. Atrophic parenchymal cells, degenerate parenchymal cells and apoptotic bodies were present. Cellular debris and secretory material were present in lumina, which indicates stagnation. The results indicate that removal of redundant secretory material and cells and low flow of saliva are features of the parotid of ferret and support the concept of pockets of inefficient secretory activity.

Distribution of kallikrein in striated duct cells of monkey submandibular glands

Although kallikrein has been localised in the striated duct cells of salivary glands, the manner in which it enters the saliva remains unclear. Here, immunocytochemistry was used at both the light- and electron-microscopic levels to localise kallikrein antigenicity. At the light-microscopic level, kallikrein was found at the apices of some, but not all duct cells. At the electron-microscopic level, it was found in small granules situated between the apical vacuoles and the luminal membrane. The kallikrein-containing granules underwent exocytosis at the cell apex.

The effects of obstruction and secretory stimulation on microlithiasis in salivary glands of cat: light and electron microscopy

Obstruction and increased secretory activity are considered to be important aetiological factors of salivary microlithiasis, which may itself be an aetiological factor of sialadenitis. However, there is a lack of substantial evidence for the importance of obstruction, and investigations on increased secretory activity used pathological doses of pharmacological agents. Therefore further investigation of these factors is essential. Feline parotid, submandibular and sublingual salivary glands, in which microliths occur normally as in man, were examined after ductal ligation to produce obstruction, electrical stimulation of the glandular nerves to produce increased secretory activity, or both. Microliths were detected in: 0 out of 38 untreated, 1 out of 55 ligated, 2 out of 17 stimulated and 2 out of 17 stimulated ligated submandibular glands; 6 out of 29 untreated, 7 out of 46 ligated, 3 out of 12 stimulated and 4 out of 14 stimulated ligated sublingual glands; and no parotid glands. The chi 2 test confirmed that the experimental procedures did not produce an increased occurrence of microliths. Microliths were detected in parenchymal cells, intercellularly in atrophic parenchyma, intraluminally, interstitially and in macrophages. The present investigation indicates that obstruction and increased secretory activity are not important aetiological factors of salivary microlithiasis.

Ultrastructural localization of microliths in salivary glands of cat

Although microliths occur in normal human salivary glands and may be an aetiological factor of sialadenitis, little is known of their natural history. In an attempt to remedy this, we investigated a large archival collection of normal and experimental feline parotid, submandibular and sublingual salivary glands. In submandibular and sublingual glands, microliths were detected ultrastructurally in: all types of acinar secretory cells; myoepithelial cells; ductal cells; lumina; intercellular spaces; basement membrane; stroma; macrophages; multinuclear giant cells; and neutrophils. Microliths were not detected ultrastructurally in parotid glands. Microliths appear to form in acinar cells during autophagy and in stagnant secretory material in lumina. Microliths appear to be removed by secretion in the saliva, discharge from cells laterally and basally, and engulfment by macrophages. There appears to be a turnover of microliths, which possibly is upset by secretory inactivity with a resulting accumulation that leads to localized obstruction and sialadenitis.

Microliths in normal salivary glands of cat investigated by light and electron microscopy

This investigation concerns the natural history of microlith in the salivary glands of cat. Microliths were detected in more sublingual than submandibular glands and were almost absent in the parotid. They were found intraparenchymally, intraluminally and interstitially, and ultrastructurally in phagosomes of acinar, ductal and myoepithelial cells, intermixed with the cytoplasm of degenerate acinar cells, and in intraparenchymal macrophages and a multinuclear giant cell. They appear to form in healthy acinar cells during autophagocytosis, and possibly to be discharged luminally, laterally or basally, and to form in the debris of degenerate cells intraparenchymally and intraluminally. They appear to be removed by expulsion in the saliva, scavenging macrophages, and possible eventual degradation in the parenchymal phagosomes. The greater occurrence of microliths in the sublingual gland may relate to a low level of secretory activity, and the near absence of microliths in the parotid to a low level of calcium. The feline salivary glands were found to be an outstanding model for the investigation of microlithiasis.

Analytical ultrastructural investigation of microliths in salivary glands of cat

Microliths in Araldite-embedded pieces of submandibular and sublingual glands of cat were stained in semithin sections by Methylene Blue and Azure II followed by Basic Fuchsin, and were examined in ultrathin sections by electron-microscopical X-ray microanalysis. Calcium and phosphorus were detected in substantial aggregates of crystals that were stained by Basic Fuchsin and appeared to be hydroxyapatite, but were not detected in granular material that was stained by Methylene Blue and Azure II and appeared to be organic. The polychromatic stain thus appears to be a useful indicator of calcified material. The majority of microliths in acini contained substantial aggregates of crystals, whereas the majority of those in ducts did not. This corresponds to the distribution of the glandular calcium, and suggests that microliths are variously enriched with calcium according to its local level.

The effect of sympathectomy on the occurrence of microliths in salivary glands of cat as studied by light and electron microscopy

Parasympathectomy is followed by a greatly increased occurrence of microliths in the feline submandibular gland, which appears to be because of secretory inactivity. The sympathetic nerves are also important in secretory processes, and so feline submandibular, sublingual and parotid glands subjected to postganglionic sympathectomy for periods from 1 day to 1 yr have now been investigated. Microliths were detected in two out of 28 sympathectomized submandibular glands and four out of 27 untreated glands, and in 10 out of 22 sympathectomized sublingual glands and seven out of 19 untreated glands. There were no significant differences between the occurrence of microliths in sympathectomized and untreated glands. Microliths were not detected in any of 29 sympathectomized and 30 untreated parotid glands. The appearance of the sympathectomized glands was similar to that of the untreated glands. The failure of sympathectomy to affect the occurrence of microliths or the appearance of the glands is possibly because of parasympathetic nerve impulses, which produce continuing secretory activity, and also the spontaneous secretion of the sublingual gland. The results support the concept that secretory inactivity is an aetiological factor of microlithiasis.

Increase of microliths in inactive salivary glands of cat

Secretory inactivity could be a factor in the formation of microliths, and so their occurrence in feline salivary glands after the secretory inactivity produced by parasympathectomy was investigated. Parasympathectomy was followed by a greatly increased occurrence of microliths in the submandibular salivary gland, but not in the parotid and sublingual, which may relate to residual secretory activity in these glands. This discovery suggests that secretory inactivity may indeed be a factor in the production of microliths in human salivary glands, and consequently of chronic sialadenitis and sialothiasis.

Ultrastructural and histochemical observations on microcalculi in chronic submandibular sialadenitis

A search for microcalculi was made in 14 cases of chronic submandibular sialadenitis. Microcalculi were found in all cases. They were within serous acinar cells and ductal cells, within lumina, and interstitially. They were stained variably by periodic-acid/Schiff and Alcian Blue at pH 2.5. Ultrastructural analytical examination showed them to consist of crystals containing calcium and phosphorus. The observations support the possibility that microcalculi form in autophagosomes, enter lumina and occasionally become impacted to produce sialolithiasis and sialadenitis.

Intraluminal crystalloids in malignant salivary gland tumors (electron microscopic and X-ray microanalytic studies)

The ultrastructural, X-ray microanalytical, histochemical and immunocytochemical features of intraluminal crystalloids found in adenocarcinomas of the parotid gland have been studied. The crystalloids, putatively derived from an abnormal crystalization of salivary duct proteins, are considerably different from the crystalloids found in normal parotid glands, pleomorphic adenomas, and sialocysts.

Salivary gland changes in disease

Ultrastructural alterations occurring in human salivary glands as a result of a variety of diseases are described. Major changes in these organs in cases of cystic fibrosis are probably the result of duct blockage, as indicated by study of chronically inflamed salivary glands. A new disease of salivary glands is reported in which parotid serous granules are distorted by bundles of fine filaments, which may be due to the untoward polymerization of a secretory protein, perhaps proline-rich protein. Finally, a clear-cell adenocarcinoma of palatine gland origin is described in which the nuclei display complex pseudoinclusions and the cytoplasm contains numerous herpes-type viruses.

Ultrastructural and histochemical observations on intracellular and luminal microcalculi in the feline sublingual salivary gland

As the genesis of salivary calculi in man has not been established, the fortuitous observation of microcalculi in sublingual glands of cats prompted this study. Microcalculi were seen occasionally within acinar cells and lumina and macrophages, and rarely interstitially. Microcalculi were stained with the periodic-acid/Schiff technique, and acid-phosphatase activity was associated with intracellular microcalculi. Intracellular microcalculi were seen ultrastructurally in acinar cells in membrane-bound vacuoles that also contained debris and sometimes what appeared to be secretory material. X-ray microanalysis showed the microcalculi to consist of crystals containing calcium and phosphorus. The observations suggest that the microcalculi form within autophagosomes in acinar cells by a precipitation of calcium and phosphorus present in degenerate material, and that the microcalculi eventually enter lumina, where they may be discharged in the saliva or retained and enlarge.

Scanning electron microscopic and X-ray microdiffractometeric studies on sialolith-crystals in human submandibular glands

The crystalline structures of 18 submandibular gland calculi were studied by radiomicrography , scanning electron microscope, and X-ray microdiffractometeric techniques. The following observations were made by SEM: Granular or globular structure was seen on the surface of all cases and pyramidal crystal in one case. In the inside, all showed lamellar pattern with amorphous nucleus in the center, and granular, plate-like and rhombohedral structures were also observed. X-ray microdiffractometeric analyses: Apatite was frequently observed in both outside and inside of the calculi. Whitlockite was next frequently detected and was seen more often in the inside. Brushite and weddellite were noted in the outside of calculi in one case each. Thus, it is suggested that brushite and weddellite were present in the front portion of calculus formation and then transformed into the more stable form e.g. apatite.

Weddellite in submandibular gland calculus

Scanning electron microscopy of a submandibular sialolith showed octahedral and dipyramidal crystals located at the surface layer of cortex. The crystal habits observed were consistent with those of a tetragonal crystal system. X-ray microdiffraction revealed the presence of weddellite. The origin of weddellite within the calculus remains to be determined.

Ultrastructural studies on the bleb formation in seal and rat submandibular gland striated ducts

For the present study Seal (Phoca vitulina) and rat submandibular gland striated ducts were investigated by electron microscopy. Both normal and stimulated animals (starved for 24 h and then fed 2 h before the tissues were removed) were examined. Basal invaginations of the cell membrane with areas heavily loaded with mitochondria were typical features of both animals. Secretory granules were especially numerous in the apical part of stimulated duct cells. The granules were separated from the luminal membrane of the cells by a condensed area called the spearating zone. Apical protrusions or blebs, which were frequently occurring in striated ducts of both animals, are interpreted as manifestations of apocrine secretion. It was concluded that this way of apocrine secretion is a fundamental function, since seals, which have salivary glands of a rather simple composition with acini which are functionally reduced, have retained the ability to form blebs.

Ultrastructural phosphatase cytochemistry of the intercalary ducts of the parotid and submandibular salivary glands of man

Cells of the intercalary ducts showed concentrations of secretory granules adjacent to the luminal plasma membrane. Evidence of thiamine-pyrophosphatase activity was seen in the Golgi apparatus and of acid-phosphatase activity in GERL-like structure, lysosomes and immature secretory granules. Adenosine-triphosphatase reaction-product was present along surfaces of myoepithelial cells and to a lesser extent along contiguous surfaces of duct cells. The findings indicate secretory activity in the intercalary duct cells.

The epithelium of the excretory duct of the human submandibular gland: a transmission and scanning electron microscopic study

The duct of the human submandibular gland (Wharton) is lined by a pseudostratified epithelium consisting of principal and basal cells. Scattered among them are a few goblet and ciliated cells. The principal cells are columnar in shape with many mitochondria, numerous dense bodies and a central nucleus with some indentations. Their apical cytoplasm shows a number of clear vesicles, some of which are reactive to silver and are extruded by exocytosis into the lumen. Other vesicles, which are unreactive, may represent the products of the absorption process. A mechanism of apocrine secretion is also observed in the principal cells. Thus, with regard to its functions, the duct of the human submandibular gland modifies the composition of saliva by adding a secretory component to it. This latter material is derived from the goblet cells but chiefly from merocrine (exocytosis) and apocrine secretion of principal cells.

Obstructive sialadenitis

The value of all the procedures which have been described for the investigation of disorders of the major salivary glands is discussed in so far as they aided the management of one bizarre case of obstructive submandibular sialadenitis. In particular an unusual indication for salivary gland scanning is also suggested.

Ultrastructure of salivary calculi

Twenty-one submandibular salivary calculi from 19 patients were examined with the light and electron microscope. Adjacent to the peripheral parts of the calculi metaplastic squamous epithelium or connective tissue was seen in close contact to the mineralized matrix. Disintegrated cellular substances from these tissue components were in some cases found to condense in a peripherally located zone of the salivary calculi. The morphology of the examined salivary calculi varied extensively not only within each calculus but also from one calculus to another. High and low incidence of crystals gave rise to the lamellated pattern. In some cases the crystals were so abundant as to five a dense homogeneous appearance. In the central parts of the calculi spheroid bodies of very low electron density with a size ranging from 1 to 100micrometer were found in an amorphous matrix. The origin of these structures is discussed. In the peripheral parts of some calculi osmiophilic spherical bodies with an electron microscopical appearance similar to lipid granules as well as bacteria of cocci or coliform type were found. Degenerated bacteria might in some cases contribute in forming part of the peripheral organic matrix.

The prevalence of consolidated salivary deposits in the small ducts of human submandibular glands

Deposits of apparently solid material were observed in the small salivary ducts in a series of non-diseased submandibular glands obtained from necropsies evenly divided by sex and adult age. The deposits were of granular or laminated structure. They were of mixed staining, the majority being predominantly eosinophilic. A small number of deposits were essentially wholly hematoxylinophilic and some of these were probably calcified. The prevalence of deposits, expressed as the number per unit sectional area, increased steadily with increasing age but was unrelated to sex. An apparently close correlation between intraductal salivary deposits and foci of obstructive adenitis in the same series of glands was shown to be mainly due to the common influence of age. The deposits probably form by precipitation of salivary glycoprotein, possibly because of parenchymal age changes. They may be related to early salivary lithogenesis but the statistical evidence of this study suggests that they are unlikely to be a major factor in the etiology of focal obstructive adenitis.

Ultrastructure of baboon parotid gland

The parotid gland of the olive baboon, Papio anubis, was examined by electron microscopy. The acini are all serous in nature, and consist of pyramidal cells with abundant secretory granules of varying size. These granules consist of a dense matrix in which a denser spherule or lenticular body is present. Granules linked by a short isthmus are observed in the apical cytoplasm, and granules in the process of discharging their contents to the acinar lumen may be connected to the luminal plasma membrane by a neck-like protrusion. Intercalated duct cells contain granules reminiscent of those found in the rat submandibular acinar cells. The striated ducts consist of tall cells interlocked in a complex fashion near their bases, with numerous vertically-oriented mitochondria lodged in their basal crenulations. Small vesicles whose contents vary in density are present in the apical cytoplasm as are large deposits of lipofuscin. The striated duct cells display a proclivity for ballooning into the duct lumen. Excretory ducts consist of simple to pseudostratified columnar epithelium, and lack basal striations or apical blebs.