in most mammals , the nasopalatine duct is responsible for the conduction of pheromones 
 from the mouth to the nasal cavity , thereby assisting in communication and 
 breeding . the duct generally 
 terminates in the floor of the nasal cavity near the vomeronasal organ . this organ is 
 part of the accessory olfactory system in mammals and is responsible for the capturing 
 of pheromones and neural communication with the central nervous system . the function of the vomeronasal organ in humans is contested , since the nasopalatine 
 duct can become blocked following birth . at times , the nasopalatine duct can remain patent , 
 maintaining communication between the oral cavity and nasal cavity . the vestigial form 
 of the nasopalatine duct in humans may cause problems , such as the development of a 
 nasopalatine duct cyst , which is the most frequent non - odontogenic cyst in the 
 maxilla . the development , function and persistence of the vomeronasal organ 
 and nasopalatine duct in animals has been the topic of studies . knowledge on 
 the development of the nasopalatine region and nasopalatine duct in humans is necessary 
 for understanding the morphology of this region and the establishment of theories that 
 may clarify the etiopathogenesis of lesions that occur in this anatomic region . a recent 
 published paper regarding histopathogenesis of a nasopalatine duct cyst suggests that 
 this lesion can be an inflammatory cyst , like a radicular cyst or a salivary duct 
 cyst - like mucocele . however , to our 
 understanding , the etiophatogenesis of this lesion remains unclear due to the reduced 
 number of articles published about it . the aims of the present study were to analyze the morphological aspects of the 
 nasopalatine region in human fetuses to determine the presence of the nasopalatine duct 
 and vomeronasal organ and describe the morphology of the incisive canal and 
 characteristics of the mucosa and submucosa , and correlating these characteristics with 
 the development of pathologies in the anterior region of the maxilla . five non identified fetuses were obtained from the anatomic bank of the oral 
 pathology sector of the authors ' university . the fetuses were submerged in a 10% 
 formalin solution ( synth , diadema , brazil ) . the inclusion criterion for the selection 
 of the fetuses was the absence of facial and palatine abnormalities , as observed 
 macroscopically . the five fetuses were decapitated and the heads were frozen at a temperature of -22c 
 for 24 hours . two sagittal cuts tangent to the wing of the nose were then performed 
 on the right and left sides with the aid of a circular electric saw ( bosch , so 
 paulo , brazil ) . on the sagittal cut the coronal cut passed through the pharynx and posterior region of the 
 soft palate . one axial cut began at the tip of the nose parallel to the base of the 
 skull base and the other at the lip commissures and oral cavity . these axial cuts 
 were performed from their points of origin to the coronal cut ( figure 1a ) . the resulting piece was made up of the anterior 
 region of the hard palate and the nasal cavity . this piece was submitted to 
 radiographic analysis with e041 occlusal , intra - oral film ( kodak , rochester , usa ) for 
 detection of the trajectory of the incisive canal ( figure 1b ) . cuts performed on head of fetus for histological processing in a. lateral 
 radiograph of final piece revealing trajectory of incisive canal in b 
 ( arrow ) the rectangular specimen was divided into three segments obtained through two 
 incisions . the first incision was made in the vestibular fornix and the second was 
 made between the soft and hard palate . thus , the first segment was comprised of the 
 upper lip and nose tip ; the second segment involved the hard palate ; and the third 
 segment was made up of the oropharynx and soft palate . due to the presence of bone 
 tissue , the second segment was demineralized in 12.5% ethylenediaminetetraacetic acid 
 ( dinmica qumica contempornea , so paulo , brazil ) for six weeks in a glass 
 recipient . the rest of the head was kept in a recipient containing a 10% formalin 
 solution . the second segment was submitted to routine histological procedures and embedded in a 
 single paraffin block . the segment was positioned for longitudinal histological cuts 
 parallel to the trajectory of the incisive canal ( located through radiographs ) . cuts 
 with 6-m thicknesses were performed and mounted on glass slides for microscopic 
 analysis . the pairs of slides were stained with methylene blue ( synth , diadema , 
 brazil ) and used to orient the pre - established cutting plane . the cuts were performed 
 up to the end of the incisive canal . from the pairs of slides , only the odd slides 
 were stained with hematoxylin - eosin ( he ) ( synth , diadema , brazil ) and cover slips 
 were placed over the specimens . the slides were examined under a light microscope ( carl zeiss , gottingen , germany ) . the following histological variables were analyzed : ( 1 ) shape and histological 
 aspects of the incisive canal ; ( 2 ) presence , shape and histological aspects of the 
 nasopalatine duct ; ( 3 ) location and histological aspects of the vomeronasal organ ; 
 and ( 4 ) histological aspects of the mucosa , submucosa and ossification of the 
 nasopalatine region . five non identified fetuses were obtained from the anatomic bank of the oral 
 pathology sector of the authors ' university . the fetuses were submerged in a 10% 
 formalin solution ( synth , diadema , brazil ) . the inclusion criterion for the selection 
 of the fetuses was the absence of facial and palatine abnormalities , as observed 
 macroscopically . the five fetuses were decapitated and the heads were frozen at a temperature of -22c 
 for 24 hours . two sagittal cuts tangent to the wing of the nose were then performed 
 on the right and left sides with the aid of a circular electric saw ( bosch , so 
 paulo , brazil ) . on the sagittal cut , three other cuts were performed - one coronal 
 and two axial . the coronal cut passed through the pharynx and posterior region of the 
 soft palate . one axial cut began at the tip of the nose parallel to the base of the 
 skull base and the other at the lip commissures and oral cavity . these axial cuts 
 were performed from their points of origin to the coronal cut ( figure 1a ) . the resulting piece was made up of the anterior 
 region of the hard palate and the nasal cavity . this piece was submitted to 
 radiographic analysis with e041 occlusal , intra - oral film ( kodak , rochester , usa ) for 
 detection of the trajectory of the incisive canal ( figure 1b ) . cuts performed on head of fetus for histological processing in a. lateral 
 radiograph of final piece revealing trajectory of incisive canal in b 
 ( arrow ) the rectangular specimen was divided into three segments obtained through two 
 incisions . the first incision was made in the vestibular fornix and the second was 
 made between the soft and hard palate . thus , the first segment was comprised of the 
 upper lip and nose tip ; the second segment involved the hard palate ; and the third 
 segment was made up of the oropharynx and soft palate . due to the presence of bone 
 tissue , the second segment was demineralized in 12.5% ethylenediaminetetraacetic acid 
 ( dinmica qumica contempornea , so paulo , brazil ) for six weeks in a glass 
 recipient . the rest of the head was kept in a recipient containing a 10% formalin 
 solution . the second segment was submitted to routine histological procedures and embedded in a 
 single paraffin block . the segment was positioned for longitudinal histological cuts 
 parallel to the trajectory of the incisive canal ( located through radiographs ) . cuts 
 with 6-m thicknesses were performed and mounted on glass slides for microscopic 
 analysis . the pairs of slides were stained with methylene blue ( synth , diadema , 
 brazil ) and used to orient the pre - established cutting plane . the cuts were performed 
 up to the end of the incisive canal . from the pairs of slides , only the odd slides 
 were stained with hematoxylin - eosin ( he ) ( synth , diadema , brazil ) and cover slips 
 were placed over the specimens . the slides were examined under a light microscope ( carl zeiss , gottingen , germany ) . the following histological variables were analyzed : ( 1 ) shape and histological 
 aspects of the incisive canal ; ( 2 ) presence , shape and histological aspects of the 
 nasopalatine duct ; ( 3 ) location and histological aspects of the vomeronasal organ ; 
 and ( 4 ) histological aspects of the mucosa , submucosa and ossification of the 
 nasopalatine region . it was not possible to determine the age and gender of one fetus 
 because only the head was available . the nasopalatine region exhibited similar histological aspects among the five 
 fetuses . on all longitudinal histological cuts , the oral cavity and nasal cavity were lined with 
 stratified parakeratinized squamous epithelial tissue and pseudo - stratified ciliate 
 columnar epithelial tissue with caliciform cells , respectively . between these 
 epithelial tissues , the presence of connective tissue and bone tissue in the process 
 of neoformation was evidenced in the premaxilla region . the nasal septum is in the 
 central portion of the premaxilla and made up of hyaline cartilage and 
 intra - membranous ossification , whereas ossification in the region of nasal conchae 
 was endochondral . tooth buds in the bell stage and delimited by the connective tissue 
 of the nasopalatine region were evidenced . the developmental stage of these tooth 
 buds was compatible with the age of the fetuses . the presence of cellular remnants of 
 the dental lamina that formed the gubernacular cord and the trajectory of the 
 incisive canal were also evidenced ( figure 2a ) . oral and nasal cavity showing stratified parakeratinized squamous epithelial 
 and pseudo - stratified ciliate columnar epithelial tissue . the nasal septum 
 in the central portion of the premaxilla and tooth buds in the bell stage . 
 bilateral vomeronasal organ ( arrows ) located alongside nasal septum ( a ) ; 
 vomeronasal organ and its constitution formed by tubular structure with 
 pseudo - stratified ciliate epithelium ; note associated blood vessels and nerves 
 ( b ) [ a : x1.25 magnification , hematoxylin & eosin ( he ) ; b : x3.2 
 magnification , he ) the incisive canal in the formation stage was observed in all specimens as an opening 
 delimited laterally by the periosteum and connecting the oral and nasal cavities . 
 near the nasal region , blood vessels , glands , nerves , 
 epithelial remains , remnants of the nasopalatine duct and a large quantity of fibers 
 were found within this canal in all the fetuses . y - shaped incisive canal and nasopalatine duct ( arrows ) opening into nasal 
 cavity ( x1.25 magnification , hematoxylin & eosin ) the nasopalatine duct is an epithelial structure with a heterogeneous pattern . in one 
 fetus , a bilateral nasopalatine duct was identified beginning at the floor of the 
 nasal cavity . the duct was completely patent on one side and partially patent on the 
 other ( figure 4 ) . structures similar to the 
 nasopalatine duct were observed in all the other fetuses , located along the incisive 
 canal . these structures had a larger diameter , similar to a cystic cavity ( figure 4 ) . the mucous glands were found near the 
 nasal mucosa , where their ducts opened . one patent nasopalatine duct was 
 islet - shaped , with mucous glands opening in its interior . persistent nasopalatine duct ( black arrow ) located in central portion of 
 incisive canal in a ( blue arrow ) . bilateral persistent nasopalatine duct ( black 
 arrows ) located in incisive canal in b [ a : x3.2 magnification , hematoxylin 
 & eosin ( he ) ; b : x1.25x magnification , he ] the vomeronasal organ is a bilateral epithelialized structure located alongside the 
 nasal septum above the incisive canal in all the fetuses . this organ is made up of a 
 tubular structure with a pseudostratified ciliate epithelium . the oral mucosa nearly always had a normal aspect and parakeratinized lining . in the 
 presence of horn cysts in the submucosa , the lining epithelium of the oral mucosa had 
 an atrophic pattern ( figure 5 ) . epithelial 
 remnants , microcysts , blood vessels , nerves and glands were found in the submucosa . the conjunctive tissue of the submucosa exhibited a moderately to highly fibrous 
 pattern . horn cyst ( blue arrow ) in region of submucosa and bilateral nasopalatine duct 
 entrance ( black arrows ) ( x3.2 magnification , hematoxylin & eosin ) it was not possible to determine the age and gender of one fetus 
 because only the head was available . the nasopalatine region exhibited similar histological aspects among the five 
 fetuses . on all longitudinal histological cuts , the oral cavity and nasal cavity were lined with 
 stratified parakeratinized squamous epithelial tissue and pseudo - stratified ciliate 
 columnar epithelial tissue with caliciform cells , respectively . between these 
 epithelial tissues , the presence of connective tissue and bone tissue in the process 
 of neoformation the nasal septum is in the 
 central portion of the premaxilla and made up of hyaline cartilage and 
 intra - membranous ossification , whereas ossification in the region of nasal conchae 
 was endochondral . tooth buds in the bell stage and delimited by the connective tissue 
 of the nasopalatine region were evidenced . the developmental stage of these tooth 
 buds was compatible with the age of the fetuses . the presence of cellular remnants of 
 the dental lamina that formed the gubernacular cord and the trajectory of the 
 incisive canal were also evidenced ( figure 2a ) .   oral and nasal cavity showing stratified parakeratinized squamous epithelial 
 and pseudo - stratified ciliate columnar epithelial tissue . the nasal septum 
 in the central portion of the premaxilla and tooth buds in the bell stage . 
 bilateral vomeronasal organ ( arrows ) located alongside nasal septum ( a ) ; 
 vomeronasal organ and its constitution formed by tubular structure with 
 pseudo - stratified ciliate epithelium ; note associated blood vessels and nerves 
 ( b ) [ a : x1.25 magnification , hematoxylin & eosin ( he ) ; b : x3.2 
 magnification , he ) the incisive canal in the formation stage was observed in all specimens as an opening 
 delimited laterally by the periosteum and connecting the oral and nasal cavities . 
 near the nasal region , blood vessels , glands , nerves , 
 epithelial remains , remnants of the nasopalatine duct and a large quantity of fibers 
 were found within this canal in all the fetuses . y - shaped incisive canal and nasopalatine duct ( arrows ) opening into nasal 
 cavity ( x1.25 magnification , hematoxylin & eosin ) the nasopalatine duct is an epithelial structure with a heterogeneous pattern . in one 
 fetus , a bilateral nasopalatine duct was identified beginning at the floor of the 
 nasal cavity . the duct was completely patent on one side and partially patent on the 
 other ( figure 4 ) . structures similar to the 
 nasopalatine duct were observed in all the other fetuses , located along the incisive 
 canal . these structures had a larger diameter , similar to a cystic cavity ( figure 4 ) . the mucous glands were found near the 
 nasal mucosa , where their ducts opened . one patent nasopalatine duct was 
 islet - shaped , with mucous glands opening in its interior . persistent nasopalatine duct ( black arrow ) located in central portion of 
 incisive canal in a ( blue arrow ) . bilateral persistent nasopalatine duct ( black 
 arrows ) located in incisive canal in b [ a : x3.2 magnification , hematoxylin 
 & eosin ( he ) ; b : x1.25x magnification , he ] the vomeronasal organ is a bilateral epithelialized structure located alongside the 
 nasal septum above the incisive canal in all the fetuses . this organ is made up of a 
 tubular structure with a pseudostratified ciliate epithelium . the oral mucosa nearly always had a normal aspect and parakeratinized lining . in the 
 presence of horn cysts in the submucosa , the lining epithelium of the oral mucosa had 
 an atrophic pattern ( figure 5 ) . epithelial 
 remnants , microcysts , blood vessels , nerves and glands were found in the submucosa . the conjunctive tissue of the submucosa exhibited a moderately to highly fibrous 
 pattern . horn cyst ( blue arrow ) in region of submucosa and bilateral nasopalatine duct 
 entrance ( black arrows ) ( x3.2 magnification , hematoxylin & eosin ) in the present study , the age of the fetuses ranged from 8.00 to 9.25 weeks of life , 
 which determined a homogeneous pattern in the morphological findings among the samples . another method described in the literature for determining the 
 age is based on the size of the central incisors . this method was not employed in the present study , since the 
 teeth must be individualized for the measurement of the incisors using calipers . variation in shape and occurrence was observed in our fetuses with regard to the 
 nasopalatine duct , which corroborates with clinical reports on the duct described in the 
 literature . this finding reveals an undefined behavior of 
 development and persistence of the nasopalatine duct in human fetuses . totally patent 
 and partially patent nasopalatine ducts and their remnants in the form of islets or 
 strings were observed . the presence of the nasopalatine duct or remnants of this duct 
 was observed in the interior of the incisive canal both in the portion near the incisive 
 papilla and near the nasal cavity . this suggests that the development of non - odontogenic 
 cysts in the anterior region of the maxilla has its etiology in the cellular remains of 
 the nasopalatine duct . the observation of epithelial remnants in the nasopalatine duct 
 near the incisive papilla in human fetuses suggests the possibility that incisive 
 papilla cysts originate from the embryological remains of the nasopalatine duct . this 
 brings into question the denomination of a cyst in the nasopalatine region as a 
 nasopalatine canal cyst , nasopalatine cyst or median palatine cyst . the nomenclature of these cysts should be based on etiophatogenesis 
 rather than anatomic location . based on the results of the present study , the correct 
 nomenclature would be a nasopalatine duct cyst , which corroborates with a number of 
 studies found in the literature . the nasopalatine duct should not be confused with the incisive canal , since the duct is 
 one of the structures present in the interior of the canal , as described in the present 
 study . this divergence in conceptualization may be caused by the fact that the duct is 
 sometimes obliterated in human adults . the authors of a recent study report two clinical cases of 
 " oronasal fistula of the incisive papilla " and state that duct is a 
 term used to define a tube formed by epithelial lines , characteristic of which is the 
 conduction of fluids . the authors 
 stress that the correct term for the anatomic structure should be 
 fistula rather than duct , since this structure may 
 not have the function of conducting fluids , making it obliterated . however , this 
 structure in the majority of mammals behaves as a duct and has the function of carrying 
 pheromones from the oral cavity to the nasal cavity 
 18,19 . in humans , this 
 structure is a holdover in the evolutional chain of the nasopalatine duct found in 
 animals and it is suggested that it be classified as a nasopalatine duct in humans as 
 well .   in nearly all human fetuses analyzed in the present study , the vomeronasal organ was 
 present bilaterally and was associated to the blood vessels and nerves . this suggests 
 that this organ may be responsible for capturing external signals , even in humans , 
 thereby placing into question whether it is truly a vestigial structure without function 
 in humans . a recent study has demonstrated that the vomeronasal organ may not be part of 
 the olfactory system , but rather an isolated structure . moreover , a comparative study using immunohistochemical 
 processing of the vomeronasal organ in humans , other primates and mammals that use this 
 organ for capturing pheromones suggest that the function of this organ is different in 
 these mammals when compared to humans and other primates . the presence of incisive canals was found in all the fetuses of the present study and 
 glands , nerves , remnants of the nasopalatine duct and a large quantity of fibers were 
 found in the interior of this canal . the incisor canals were bilateral and near the 
 nasal cavity in the shape of a y or u , as reported in previous studies . since the shape and histological 
 characteristics of the incisive canal exhibited a homogeneous pattern among the fetuses , 
 the possibility of lesions in this region originating from this anatomic structure can 
 be discarded . the oral mucosa , submucosa , ossification and dental structures did not exhibit 
 significant alterations from one fetus to another . however , an atrophic pattern was 
 observed in the oral mucosa in one fetus , in which a horn cyst was found in the 
 submucosa region . the persistence of this lesion may lead to the development of the cyst 
 in the newborn . this pathology is classified as bohn 's nodule , 
 epstein 's pearls or dental lamina cyst . these conditions are considered synonyms due to 
 their clinical - pathological characteristics and differ only with regard to the site of 
 occurrence . such alterations 
 appear within the first year of life and are resolved spontaneously without the need for 
 intervention . the present study allows the inference that the incisive canal , nasopalatine duct and 
 vomeronasal organ are distinct anatomic structures . moreover , the development of 
 nasopalatine duct cysts may be related to the persistent , totally patent or partially 
 patent forms of the nasopalatine duct and its cell remnants found in the interior of the 
 incisive canal .
the nasopalatine region is composed of structures such as the vomeronasal organ and 
 nasopalatine duct . the nasopalatine duct may provide the communication of the mouth 
 to the nasal cavity in human fetuses and can be obliterated in an adult human . 
 knowledge on the development of the nasopalatine region and nasopalatine duct in 
 humans 
 is necessary for understanding the morphology and etiopathogenesis of lesions 
 that occur in this region.objective:the aim of the present study was to describe the morphological aspects of the 
 nasopalatine region in human fetuses and correlate these aspects with the 
 development of pathologies in this region . 
 material and methods : five human fetuses with no facial or palatine abnormalities were used for the 
 acquisition of specimens from the nasopalatine region . 
 after demineralization , the 
 specimens were histologically processed . 
 histological cuts were stained with 
 methylene blue to orient the cutting plane and hematoxylin - eosin for the 
 descriptive histological analysis . 
 results : the age of the fetuses was 8.00 , 8.25 , 9.00 and 9.25 weeks , and it was not 
 possible to determine the age in the last one . the incisive canal was observed in 
 all specimens as an opening delimited laterally by the periosteum and connecting 
 oral and nasal cavity . 
 the nasopalatine duct is an epithelial structure with the 
 greatest morphological variation , with either unilateral or bilateral occurrence 
 and total patent , partial patent and islet forms . 
 the vomeronasal organ is a 
 bilateral epithelized structure located alongside the nasal septum above the 
 incisive canal in all the fetuses . 
 conclusions : the incisive canal , nasopalatine duct and vomeronasal organ are distinct anatomic 
 structures . 
 the development of nasopalatine duct cysts may occur in all forms of 
 the nasopalatine duct .