Elektronenmikroskopische Untersuchungen am juxtaoralen Organ des Menschen

The juxta-oral organ of Chievitz (organum yuxtaorale) updated: Embryology, anatomy, function and pathology

BACKGROUND

The Chievitz's organ or juxta-oral organ is a mysterious bilateral structure, phylogenetically preserved, which develops from the mouth epithelium as an invagination that loses connection to it in the prenatal period. It is located laterally to the walls of the oral cavity in an imprecise anatomical location and receives abundant innervation from the buccal nerve. Structurally it consists of non-keratinizing squamous-like neuroepithelial cells surrounded by two layers of connective tissue with nerve fibers and different morphotypes of sensory corpuscles. Its function is completely unknown although based on its rich innervation it is assumed that works as a mechanoreceptor.

METHODS

We have performed immunohistochemistry for axonal and Schwann cells, and the putative mechanoproteins ASIC2, TRPV4 and Piezo2 in sections of fetal juxta-oral organ.

RESULTS

Intraparenchymatous nerve fibers and sensory corpuscles were observed as well as immunoreactivity for Piezo2 in both nerve fibers and epithelial parenchymatous cells.

CONCLUSIONS

We add indirect evidence that the juxtaoral organ is a mechanoreceptor because in addition to its dense innervation, the epithelial cells and sensory nerve fibers display immunoreactivity for the mechanogated ion channel Piezo2. Based on current knowledge, the functional and clinical importance of the juxta-oral organ should be further investigated.

Organogenesis of the juxta-oral organ in mice

The juxta-oral organ is a bilateral organ in the mammalian bucca. It consists of epithelial cords with surrounding mesenchyme. It develops from embryonic oral epithelium, but its macroscopic morphology in mice is less studied and seems to be very different from that of humans. The juxta-oral organ in mice extends more widely from the subcutaneous tissue of the mandible near the lateral fascia of the masseter to the submucosa of the soft palate. In this paper, we report that the mutant mouse allele Bmp7(lacZ) presented intense lacZ expression in the epithelial component of the juxta-oral organ in its homo- and heterozygous states. The main aims of this study were to show that this mutant mouse allele is suitable for observing macroscopic structure of the juxta-oral organ and to describe the development of this organ during embryonic and postnatal stages. Whole-mount beta-gal staining of this strain of mouse showed that the juxta-oral organ in mice appeared at E12.0 from oral epithelium and lost connection with it before E12.5. Then, the juxta-oral organ extended anteriorly to the lateral fascia of the masseter and posteriorly to the submucosal layer of the soft palate via the orbit. The mature juxta-oral organ had no connection to other epithelia such as those of the bucca and parotid duct. It persisted until adulthood and there seemed to be no tendency to regress. Transmission electron microscopy showed that each part of the juxta-oral organ was an epithelial cord surrounded by a basement membrane and mesenchymal tissue.

Morphogenesis of the juxtaoral organ in humans

The juxtaoral organ was studied using light microscopy in 55 human embryos and 90 fetuses at different stages of development. The juxtaoral organ arises from the epithelium at the bottom of the transverse opening of the primitive mouth during O'Rahilly stage 16 and becomes detached from the epithelium after O'Rahilly stage 18. The juxtaoral organ is innervated by the buccal nerve from O'Rahilly stage 20 onward, and its connective tissue capsule is clearly visible after week 11 of development. This study enabled us to describe three main periods of juxtaoral organ development: (1) the period of epithelial condensation and invagination, at O'Rahilly stages 16-17; (2) the period during which the juxtaoral organ becomes detached from the oral epithelium and is innervated, at O'Rahilly stages 18-23; and (3) the period during which the connective tissue capsule is formed, after week 11 of development. We also analysed the juxtaoral organ of five additional fetuses by immunohistochemistry with anti-NF-200 to verify their innervation. The results show that the juxtaoral organ may have a function in the mechanical activity of the region.

Intraoral tumor of Chievitz in a child

Juxtaoral organs known as organs of Chievitz are intramuscular embryonic structures found close to the angle of the mandible near the insertion of the pterygomandibular raphae. They are considered of neuroepithelial origin with no known function. We describe the first tumor of the organ of Chievitz which presented intraorally in a child. Immunohistochemically, the Chievitz nests showed positive reaction for vimentin, cytokeratins, and epithelial membrane antigen and ultrastructurally demonstrated cytoplasmic processes and intermediate filament bundles. These observations, together with light microscopic features, suggest that the epithelial nests of the organ of Chievitz are meningothelial rather than neuroepithelial.

The juxtaoral organ-a pitfall for pathologists

The first well-documented case in which the juxtaoral organ was identified in a surgical specimen removed because of oral cancer is reported. Recognition of this normal structure, the histological picture of which considerably resembles that of a mucoepidermoid carcinoma was crucial in determining the precise extent of the malignant process. Misinterpreting the JOO as cancer may lead to false prognoses or to unnecessarily extensive surgery. The differential diagnostic importance of orofacial epithelial structures localised perineurally is discussed.

Enzyme-histochemistry of the juxtaoral organ in man ("organ of Chievitz")

The activities of several enzymes - hydrolases, oxidoreductases and carbonic anhydrase - were demonstrated histochemically in the epithelial parenchyma of the human juxtaoral organ. Two characteristics enzyme-activity-patterns provided morphological distinction between two different forms of the juxtaoral organ, independently of the sex or age of the patient. Provisionally we have called them type I and type II. Type I showed a strong activity of alkaline phosphatase and carbonic anhydrase and low activity of non-specific esterases, whereas type II showed just the contrary. The enzyme activities in the epithelial parenchyma displayed obvious similarities to those of the duct cells of salivary glands but they were different from those of the oral mucosa studied. Only alkaline phosphatase of the enzymes demonstrated, showed activity in the epithelia of the juxtaoral organ but none in the oral mucosa or salivary glands. On account of the multiple nerve endings present, a receptor function is presumed for these, whereas the function of the epithelial parenchyma is still unknown.

Epithelial islands associated with mandibular nerves. Report of two cases in the walls of mandibular cysts

Epithelial islands in association with nerve fibers in the jaw bones have been reported previously. We describe two such cases and present evidence that the epithelial structures as observed in this study are odontogenic rests and not neuroepithelial organs. Regardless of origin, it should be recognized that these epithelial islands do not represent neural invasion by carcinoma.

Maxillary intraosseous neuroepithelial structures resembling those seen in the organ of Chievitz

Epithelial rests residing within nerve fibers coursing through histologically normal osseous marrow spaces are described. These structures appear to be identical to those found in the pterygomandibular space in a structure known as the organ of Chievitz. Their function is unknown, and yet it is hypothesized that they play a role in neurosensory mechanisms.