Bilateral Aplasia of the Frontal, Sphenoid and Maxillary Sinuses and Unilateral Aplasia of the Ethmoid Air Cells

Abstract 
Background: Sporadic cases of sinus aplasia have been reported in the literature, but only a few cases of total aplasia of paranasal sinuses have been recorded. In this report, we aim to present a case of aplasia of all paranasal sinuses except for the right ethmoid sinus which was hypoplastic. 
Case Report: The patient was a 50-year-old female referred for obtaining Cone Beam Computed Tomography (CBCT) prior to dental implant placement. The patient was asymptomatic and did not have any complaints or discomforts associated with the craniofacial structures. CBCT views showed bilateral absence of paranasal sinuses. Only two ethmoid air cells were detected on the right side. 
Conclusion: This is the first case report for aplasia considering paranasal sinuses except for right ethmoid cells which were hypoplastic in Iranian population.
Keywords: Cone-beam computed tomography, Dental implants, Ethmoid sinus, Iran, Paranasal sinuses

Introduction
Paranasal sinuses are air-filled structures in the facial skeleton. They originate from evaginations from the nasal fossa into the surrounding bones during the third and fourth fetal months and tend to expand accompanying facial growth afterwards (1). Although functions of the paranasal sinuses are not clear, contributing to the vocal resonance, humidification and warming of the inspired air, thermal insulation and protection of the brain, lightening of the skull and facial bones and distribution of masticatory forces are considered as some of the roles for these air-filled cavities (2,3).
The exact causes of aplasia of the paranasal sinuses have not been completely understood yet. Each sinus enlarges in the medullary space of the representative bone. Developmental failures, infections, irradiation and hormonal disturbances can interfere with this process and result in hypoplasia or aplasia of sinuses (2,4). This report presents the first case in Iranian population, showing bilateral absence of paranasal sinuses with no signs of discomfort or syndromes. Only two ethmoid air cells were detected on the right side. 

Case Presentation
A 50-year-old Iranian woman attended School of Dentistry, Isfahan, Iran for dental implant treatment and was referred by the oral and maxillofacial surgeon for Cone Beam Computed Tomography (CBCT). Clinically, lack of malar prominence, maxillary deficiency and hypernasal speech were noted (Figure 1). The patient had no complaints of headache, hearing problems, nasal obstruction, nasal discharge, facial pressure and tiredness. She neither had any mastication problems nor a history of irradiation or trauma. The patient reported taking levothyroxine, hydroxychloroquine, diltiazem, aspirin, atorvastatin, nortriptyline, omeprazole, fluoxetine, prednisolone, and calcium, vitamin D, iron, and folic acid supplements. All laboratory tests were normal except inorganic phosphorus level which was slightly above the normal range. 
CBCT scans of both jaws were obtained by Galileos (Sirona Dental Systems GmbH, Bensheim, Germany) with exposure parameters of 85 kVp and 35 mAs, field of view of 15×15 cm and voxel size of 280 µm. Evaluation of coronal, axial and sagittal views revealed absence of pneumatization of the paranasal sinuses; although only two ethmoid air cells were noted on the right side. Nasal cavity, septum, conchae and lateral nasal wall appeared normal (Figure 2).
Clinical examination as well as paraclinical examinations ruled out presence of systemic diseases affecting body skeleton such as Paget’s disease, cretinism, thalassemia, or other syndromes. Genetic examination revealed a normal karyotype. There was no familial history of sinus agenesis. As the patient was asymptomatic, no further treatment option was required and the standard presurgical images for placement of dental implants were prepared.

Discussion
Development of paranasal sinuses can be adversely affected by conditions such as trauma, neonatal tumors, irradiation, hypothyroidism, primary ciliary dyskinesia, cystic fibrosis, infections, bone dysplasia and syndromes including Down syndrome, Apert syndrome, Crouzon syndrome, Treacher Collins syndrome, Schwartz-Lelek syndrome and Prader-Willi syndrome (2,4,5). Sinus aplasia is a rare phenomenon occurring more frequently in frontal and maxillary and seldom in sphenoid sinuses (6). Case reports of total aplasia of paranasal sinuses are extremely rare. Agenesis of the paranasal sinuses is an uncommon clinical condition that appears mainly in the frontal (12%) and maxillary (5-6%) sinuses (7,8) mostly unilaterally (9). In addition, unilateral absence of ethmoid sinus is reported as a rare case (10). Assiri et al demonstrated an incidence of bilateral frontal sinus aplasia of 3.3% among Saudi Arabian population; conversely, monolateral agenesia had an incidence of 5.12 and 1.33% for right and left sinus, respectively (11). In the same way, Jordanian population showed a prevalence of bilateral frontal sinus aplasia of 4.2% and unilateral frontal sinus aplasia of 6.6% (12). These results are slightly higher than that observed among Turkish population of 0.73 and 1.22% concerning bilateral and unilateral absence of the frontal sinuses, respectively (7).
Sinus aplasia may cause chronic headaches, facial fullness, nasal drip, and voice problems. However, patients may be asymptomatic, thus sinus aplasia can be an incidental finding detected by maxillofacial radiologists (13,14). Diagnosing aplasia or hypoplasia of paranasal sinuses can be important for a variety of reasons. Failure in development of paranasal sinuses can be a sign for underlying significant medical conditions. In addition, small or absent paranasal sinuses must be reported prior to any endoscopic sinus surgery or transsphenoidal hypophysectomy to prevent injuries to vital structures (15-17).
Bilateral paranasal sinus aplasia is an extremely rare condition and to our knowledge, there are few case reports of this anomaly: In 2012, Celebi et al presented a 35-year-old man with complaints of nasal obstruction and fullness of the face. He had a normal appearance without any associated disease or anomalies. Computed tomography (CT) revealed aplasia of all paranasal sinuses (4). In 2013, Korkmaz et al reported a 57-year-old female patient who complained of nasal stuffiness, frequent headaches and hearing loss during headache attacks. On CT examination, absence of all paranasal sinuses was noted (3). In 2013, Kandogan et al reported aplasia of maxillary, sphenoid and frontal sinuses and hypoplasia of both ethmoid sinuses in CT images of a 23-year-old male with complaints of nasal obstruction and headache (1). In 2015, Joshi et al reported a 15-year-old Hindu male patient with complaints of bilateral headache, facial fullness and postnasal discharge. Clinical examination showed lack of malar prominences. CT revealed aplasia of all paranasal sinuses (18). In 2017, Joshi et al reported a 7-year-old male child who was mentally disabled. Hypoplasia of cerebellar vermis, dilated IV ventricle and mega cistern magna were revealed in CT. He was diagnosed with Dandy-Walker malformation (6). Takaichi et al in 2020 presented a case of total aplasia of paranasal sinuses and multiple impacted teeth in a nonsyndromic 77-year-old male based on CT imaging and paraclinical examinations (19).
Our case presented the first case of aplasia of all paranasal sinuses, except for the right ethmoid sinus which was hypoplastic in Iranian population. The condition was diagnosed on CBCT images obtained for presurgical evaluation of alveolar bones for placement of dental implants. CBCT can be used effectively for diagnosing developmental abnormalities in the craniofacial skeleton (20-23).

Conflict of Interest
There was no conflict of interest for the authors in this study.