the maxillary sinuses develop in the 3rd month of intrauterine life . at the time of the birth , the volume of the sinus is 6 - 8 mm . the volume of the maxillary antrum increases by 2 mm in the vertical and lateral dimensions and by 3 mm in the anteroposterior dimension yearly until the age of 8 years . at the age of 10 , the lower boundary of the maxillary sinus and the floor of the nasal cavity are on the same level . the incidence of maxillary sinus hypoplasia ranges between 1.5 and 10% , but some studies have reported less than this range . many of the patients with aplasia or hypoplasia of the maxillary sinus are asymptomatic and unaware of their conditions and it is identified on routine radiographs . however , some of the patients may suffer from chronic headaches , facial pain , and voice problems . maxillary sinus hypoplasia can lead to diagnostic problems , especially in conventional radiographs because it can be misdiagnosed as mucosal thickening in infectious disease or neoplasms involving the sinus . also , atelectasis of the sinus due to chronic sinusitis can be diagnosed as aplasia or hypoplasia of the sinus . computed tomography ( ct ) scanning and also cone beam computed tomography ( cbct ) and endoscopic examination of the sinus are the necessary diagnostic tools to detect the underlying abnormality . in this study , three cases with unilateral hypoplasia of the sinus , unilateral aplasia of the sinus , and bilateral aplasia of both maxillary sinuses are reported . a 68-year - old female was referred to the clinic of oral and maxillofacial radiology for cbct preparation , as pre - operative imaging for implant insertion in the maxilla . she looked healthy without any history of sinus disease such as headaches , nasal discharge , facial pain and voice abnormalities , hyposmia or anosmia , and purulent rhinorrhea . on physical examination , it was found that the right maxillary region was slightly depressed compared with the opposite side . she did not remember any history of infection or trauma in the right maxillary sinus . cbct was performed by a gallileos set ( sirona dental systems gmbh , bensheim , hessen , germany ) , and analyzed by sidexis - xg software with slices having an interval of 2 mm . evaluation of coronal and axial views revealed that the maxillary sinus of the right side was completely absent in all of the cuts . cbct : ( a ) coronal view shows absence of the right maxillary ; ( b ) axial view shows aplasia of the right maxillary sinus due to the lack of any symptoms , no additional treatment was done and the patient was informed about the sinus condition for possible future symptoms . a 20-year - old female was admitted to the clinic of radiology for cbct of the maxilla as pre - operative diagnostic imaging for implant insertion . she was completely healthy without any history of headaches , nasal discharge , facial pain , voice abnormalities , hyposmia or anosmia , and purulent rhinorrhea . also , she had no history of infection or trauma in the sinus areas . cbct was performed and evaluation of coronal and axial views revealed that all the left sinus dimensions were less than those of right sinus , and its dimensions seemed to be only equal to half of those of right sinus [ figure 2 ] . cbct : ( a ) coronal view shows the smaller size of left maxillary sinus ; ( b ) axial view shows the the smaller size of left maxillary sinus due to the lack of any symptoms , no additional treatment was done and the patient was informed about the sinus condition for possible future symptoms . a 12-year - old female was referred to the clinic of dentomaxillofacial radiology by her orthodontist for cbct of both mandible and maxilla . she suffered from chronic headaches , nasal discharges , and voice abnormality because of hypernasalism . on physical examination , cbct was performed and evaluation of coronal view revealed that the maxillary sinuses in both sides were absent in all slices , which was confirmed by the axial view as a bilateral aplasia of the maxillary sinuses [ figure 3 ] . cbct : ( a ) coronal view shows the bilateral absence of both maxillary sinuses ; ( b ) axial view shows the bilateral absence of both maxillary sinuses the patient was informed about the sinus condition and was refered to an otolaryngologist for further assessment . a 68-year - old female was referred to the clinic of oral and maxillofacial radiology for cbct preparation , as pre - operative imaging for implant insertion in the maxilla . she looked healthy without any history of sinus disease such as headaches , nasal discharge , facial pain and voice abnormalities , hyposmia or anosmia , and purulent rhinorrhea . on physical examination , it was found that the right maxillary region was slightly depressed compared with the opposite side . she did not remember any history of infection or trauma in the right maxillary sinus . cbct was performed by a gallileos set ( sirona dental systems gmbh , bensheim , hessen , germany ) , and analyzed by sidexis - xg software with slices having an interval of 2 mm . evaluation of coronal and axial views revealed that the maxillary sinus of the right side was completely absent in all of the cuts . cbct : ( a ) coronal view shows absence of the right maxillary ; ( b ) axial view shows aplasia of the right maxillary sinus due to the lack of any symptoms , no additional treatment was done and the patient was informed about the sinus condition for possible future symptoms . a 20-year - old female was admitted to the clinic of radiology for cbct of the maxilla as pre - operative diagnostic imaging for implant insertion . she was completely healthy without any history of headaches , nasal discharge , facial pain , voice abnormalities , hyposmia or anosmia , and purulent rhinorrhea . also , she had no history of infection or trauma in the sinus areas . cbct was performed and evaluation of coronal and axial views revealed that all the left sinus dimensions were less than those of right sinus , and its dimensions seemed to be only equal to half of those of right sinus [ figure 2 ] . cbct : ( a ) coronal view shows the smaller size of left maxillary sinus ; ( b ) axial view shows the the smaller size of left maxillary sinus due to the lack of any symptoms , no additional treatment was done and the patient was informed about the sinus condition for possible future symptoms . a 12-year - old female was referred to the clinic of dentomaxillofacial radiology by her orthodontist for cbct of both mandible and maxilla . she suffered from chronic headaches , nasal discharges , and voice abnormality because of hypernasalism . on physical examination , the scar of previous surgery was seen in the philtrom region . also , the maxillary sinus regions in both sides were depressed . cbct was performed and evaluation of coronal view revealed that the maxillary sinuses in both sides were absent in all slices , which was confirmed by the axial view as a bilateral aplasia of the maxillary sinuses [ figure 3 ] . cbct : ( a ) coronal view shows the bilateral absence of both maxillary sinuses ; ( b ) axial view shows the bilateral absence of both maxillary sinuses the patient was informed about the sinus condition and was refered to an otolaryngologist for further assessment . hypoplasia of maxillary sinus is less likely than of sphenoid and frontal sinuses , which can be acquired or congenital . some reasons have been mentioned as a cause of congenital hypoplasia or aplasia , such as : 
 arresting of the development because of infection , injuries , and irradiation.congenital first arch syndrome.developmental anomalies such as craniosynostosis , osteodysplasia , and down syndrome . also , some reasons are responsible for an acquired category of maxillary sinus hypoplasia , such as : 
 trauma with deformity due to fracture or surgery in the sinus region.thalassemia and cretinism.wegener's gralauloma ( inflammatory osteitis).neoplasms that cause osteitis . the sinus is fully developed with average dimensions of 34  33  25 mm . in case 3 , the patient was 12 years old , which was under the age of complete development of sinus . however , by this age , the dimensions of normal sinus must be at least at the level of middle turbinate . she had a history of cleft lip and palate that was a result of disturbance in the first arch development and the congenital first arch syndrome can be a cause of aplasia of the sinus . some of the putative roles that have been ascribed to the sinuses are as follows : air conditioning ( heating and humidification ) , acting as an air reservoir , ventilation , aiding in olfaction , reduction in weight of the cranium , addition of resonance to the voice , insulation of the cerebrum and orbits , and participation in the formation of the cranium . hypoplasia or aplasia of the maxillary sinus may cause symptoms such as headaches , facial pain , nasal discharge , and speaking voice problems . but the majority of patients are asymptomatic and unaware of their conditions . in this case series , two cases presented were asymptomatic , but case 3 had signs and symptoms of headaches , nasal discharge , and hypernasal speech . maxillary sinus opacification on plain radiographs can be diagnosed as a mucosal thickening of infectious disease , tumor , or aplasia of the sinus . cbct has the advantages of ct , in addition to requiring lower radiation dose , and is a good modality of diagnostic imaging in the evaluation of sinus conditions like aplasia or hypoplasia . radiological diagnosis of maxillary sinus hypoplasia and aplasia helps the otolaryngologists to differentiate that from chronic sinusitis and neoplasm . it is important to diagnose these abnormalities to prevent possible complications during endoscopic sinus surgery , such as causing potential harm to the orbit .
maxillary sinus aplasia and hypoplasia are rare conditions that can cause symptoms such as headaches and voice alteration . 
 the majority of patients are asymptomatic , but these conditions must be noticed for importance of differential diagnosis such as infection and neoplasms . 
 conventional radiographs could not differentiate between inflammatory mucosal thickening , neoplasm , and hypoplasia of the sinus . 
 computed tomography ( ct ) and also cone beam computed tomography ( cbct ) are the proper modalities to detect these conditions . in the present study , 
 cbct findings of three cases with maxillary sinus hypoplasia and aplasia are reported .