Asymmetry of the anterior ethmoidal artery in relation to the anterior skull base: a population-based study of 500 arteries.

OBJECTIVE: To analyze variability in the distance between the Anterior Ethmoidal Artery (AEA) and the anterior Skull Base (SB), as well as the frequency of lateral asymmetry in a Latin American population using computed tomography. METHODS: A total of 250 computed tomography scans of paranasal sinuses in coronal reconstruction (500 AEAs) were analyzed. After determining the image with the best anatomical view of the artery, the distance between its midpoint and the ethmoidal roof was measured, and the images were independently interpreted by 2 physicians. RESULTS: Of the 500 AEAs, 279 (55.8%) adhered to or passed through the SB at a distance of 0mm. A total of 221 AEAs (44.2%) were at some distance from the SB, of which 107 (48.4%) were on the right side, ranging from 1.18 to 6.75mm, and 114 (51.5%) were on the left side, ranging from 1.15 to 6.04mm. The overall mean distance between the AEA and SB was 1.22 (SD=1.57) mm, increasing to 2.77 (SD=1.14) when the arteries adhered to the SB were excluded. Seventy-six individuals (30.4%) had a lateral distance variation > 1mm. CONCLUSION: Our study includes the largest sample of AEA analyzed with computed tomography scans of paranasal sinuses. There was some distance between the AEA and SB in almost half the patients, and we found a high rate of lateral variability >1mm. LEVEL OF EVIDENCE: Level 3.

Analysis of sphenoid sinus and ethmoid sinus volume and asymmetry by sex: A 3D-CT study.

PURPOSE: To measure the volume of the sphenoid and ethmoid sinuses and to analyse the asymmetry index values by age/gender. METHODS: Three-dimensional (3D) Computed Tomography (CT) images of 150 individuals (75 females, 75 males) of both sexes between the ages of 18-75 were included in our study. Sphenoid and ethmoid sinus volumes were measured using the 3D Slicer software package on these images, and the asymmetry index was calculated. RESULTS: In our study, mean sphenoid sinus volume (female right: 4264.4 mm3, left: 3787.1 mm3; male right: 5201.1 mm3, left: 4818.2 mm3) and ethmoid sinus volume (female right: 3365.1 mm3, left: 3321.2 mm3; male right: 3440.9 mm3, left: 3459.5 mm3) were measured in males and females. Left sphenoid sinus values of males were statistically higher than females (p = 0.036). No statistically significant relationship existed between age, sinus volumes, and asymmetry index (p > 0.05). A statistically weak positive correlation existed between males' left sphenoid and ethmoid sinus volume (rho = 0.288; p = 0.012). There was no statistical relationship between asymmetry index in the whole group (p > 0.05). A statistically weak negative correlation was found between sphenoid and ethmoid sinus asymmetry index in males (rho=-0.352; p = 0.002). There was no statistical relationship between asymmetry index in females (p > 0.05). CONCLUSION: Knowing paranasal sinus morphology, morphometry, and asymmetry index value will be significant for preoperative and postoperative periods.

Severe unilateral refractory epistaxis arising from the septal branch of the anterior ethmoid artery.

KEY POINTS: The septal branch of the anterior ethmoid artery (sbAEA) is an underrecognized source of severe refractory epistaxis. Herein, we describe the presentation, predisposing factors, treatment strategies, and outcomes of a series of patients with this condition.

The Upper Attachment of the Uncinate Process and Anterior Ethmoidal Artery.

OBJECTIVE: Variations in the upper attachment of the uncinate process (UP) are important because they can affect frontal sinus drainage and change the morphology. Functional endoscopic sinus surgery (FESS) is the primary technique used to treat chronic medically refractory rhinosinusitis. Uncinectomy is the basis of FESS technique to obtain the best possible result from surgery. The anterior ethmoidal artery (AEA) enters the nasal cavity through the orbital medial wall (lamina papyracea) may also be affected by the upper attachment of the UP. The aim of this study was to investigate a possible link between UP variations and the course of the AEA. MATERIALS AND METHODS: This retrospective, computed tomography (CT)-based, anatomic study was conducted on 200 healthy adults (100 females and 100 males) by screening bilateral paranasal sinus images. The upper attachment of the UP was classified in 6 types (1-6) based on the Liu classification. The AEA was divided into 4 types (A-D) based on location: anterior to the frontal sinus (A), between the frontal sinus and the middle nasal turbinate (B), and anterior to the posterior ethmoidal cells (C and D). All the CT images were evaluated simultaneously by 2 anatomists and 1 radiologist. RESULTS: Of the total cases (200 right and 200 left side), 48.8% were type 1 UP attachment, 11.0% type 2, 12% type 3, 9% type 4, 18% type 5, and 1.2% type 6. The AEAs were classified as 12.2% type A, 71.8% type B, 15.2% type C, and 0.8% type D. CONCLUSION: The course of the AEA through the nasal cavity was observed to shift anteriorly from the ethmoidal bulla to the frontal sinus in patients with UP attached to the lamina papyracea and middle turbinate. Remarkably, the AEA always coursed anterior from the middle nasal turbinate line.

Examination of ethmoidal roof regarding Keros and Yenigun classifications in a Turkish population: a computerized tomography study.

PURPOSE: Understanding ethmoid roof morphology is crucial to prevent complications in endoscopic sinus surgery. This study aimed to evaluate the morphological properties of the ethmoidal roof regarding gender and age differences using Keros and Yenigun classifications on high-resolution computed tomography images. METHODS: We retrospectively analyzed 891 high-resolution computed tomography paranasal sinus study images and measured the depth of the cribriform plate in coronal sections and the anterior-posterior length in axial planes. The study retrospectively examined CT images of paranasal sinuses of patients living in the eastern Anatolian region of Turkey. RESULTS: In both Keros and Yenigun Classifications, the most common class was type 2, and the least common class was type 3. According to Keros et al.'s method, no significant difference was observed between men and women (p = 0.698). However, according to Yenigun et al., the average values of women in terms of the anterior-posterior distance of the ethmoid roof were significantly higher than men (p = 0.001). When examined according to age, a very low, negative correlation was revealed regarding Keros and Yenigun classifications (p = 0.047 and p < 0.001 retrospectively). According to Keros and Yenigun's classification, there was no significant difference between the left and right sides (p = 0.488 and p = 0.919, respectively). CONCLUSION: The morphological properties of the ethmoidal roof have importance to be considered for preoperative planning. Studying larger patient groups and meta-analyses that gather various research results about this subject might help better understand the ethmoidal roof morphology among populations.

A Consistent Endoscopic Landmark to Identify the Anterior Ethmoidal Artery.

OBJECTIVE: The anterior ethmoidal artery (AEA) is an important structure to identify during endoscopic sinus surgery. Although identification on imaging is easily taught, a consistent endoscopic landmark for the AEA, independent of anatomic ethmoid cell variation, is lacking, leaving many surgeons unclear about the exact location without dependence on navigation. Here, we describe a consistent endoscopic landmark, regardless of anatomical ethmoid variation. METHODS: We prospectively enrolled adult patients undergoing endoscopic surgery involving frontal and ethmoid sinuses in this observational study. The AEA landmark was defined simply as the septation or ridge one step back along the ethmoid skull base from the posterior table of the frontal sinus. The gold standard to calculate the sensitivity of our endoscopic landmark was an image-navigation system, registered to within 1.5 mm accuracy, locating the AEA within three planes. Both endoscopic and computerized tomography (CT) images of the pointer at the landmark were taken simultaneously. The concordance of endoscopic to navigation images was independently assessed by three blinded rhinologists. RESULTS: Forty patients were included in our study with 73 sides analyzed. Diagnoses included chronic rhinosinusitis without polyps (52.5%), with polyps (22.5%), recurrent acute sinusitis (15%), sinonasal tumors (7.5%), and odontogenic sinusitis (2.5%). The AEA was accurately identified using our endoscopic landmark in 97.3% of the cases (71/73). Of the two cases in which the AEA was not found within the landmark, the artery was located ≤1 mm posteriorly. CONCLUSION: We describe a consistent endoscopic landmark to identify the AEA, conserved across various clinical diagnoses and anatomic variations in sinus structure. LEVEL OF EVIDENCE: 3 Laryngoscope, 134:1096-1099, 2024.

Relation between anterior ethmoidal artery course on computed tomography and supraorbital ethmoid cell and Keros classification.

PURPOSE: The anterior ethmoidal artery (AEA) is an important risk area in endoscopic sinus surgery. This study aimed to evaluate the course of AEA according to the Keros classification and the presence of supraorbital ethmoid cell (SOEC) and to prevent possible complications by emphasizing the importance of preoperative paranasal computed tomography (CT) imaging. This approach will increase the effectiveness of endoscopic sinus surgery and improve patient safety. METHODS: The paranasal CT scan images of patients aged > 18 years between October 2020 and November 2021 from our center were retrospectively analyzed. The images were primarily evaluated in the coronal plane, and the sagittal and axial planes were utilized to evaluate variations in AEA regarding the skull base. Furthermore, the relation of AEA course with Keros classification and SOEC was evaluated. The study included 1000 patients aged 18-80 years (right and left, a total of 2000 samples). RESULTS: Grade 3 AEA was the most common regarding the skull base. Keros Type 2 was the most common classification. Overall, 48.7% patients had SOEC. The incidence of Grade 3 AEA was higher among patients with SOEC and a higher Keros classification compared with those without SOEC and a lower Keros classification. Furthermore, Keros Type 3 was the most associated with SOEC presence. CONCLUSION: Consistent with the literature, the probability of Grade 3 AEA in patients with high Keros classification and SOEC was significantly higher in our study. Therefore, we consider that preoperative imaging according to Keros classification and SOEC presence can predict AEA course and guide surgery.

Resection of Orbital Myxoma With Magnetic Resonance Imaging Evidence of Ethmoid Sinus Origin: Case Report and Review of 20 Patients in the Literature.

A 41-year-old woman showed a palpable mass at the superonasal orbital edge on the right side. Magnetic resonance imaging demonstrated a lobulated fluid-containing tubular mass which extended anteriorly to posteriorly along the medial orbital wall, nasal to the eyeball. She was followed once a year for 8 years until the age of 49 years when she decided to undergo surgical resection because of the enlarged mass. The lobulated large mass was resected and the pathology showed sparsely distributed spindle cells, positive for CD34, in alcian blue-positive mucous substances, indicative of myxoma. Postoperative magnetic resonance imaging showed residual lobulated tubular mass along the optic nerve on the medial side and superior to the eyeball. The residual orbital mass showed stable structure with more evident connection with the ethmoid sinus lesion, suggestive of the ethmoid origin, in 12 years until the age of 61 years. In the review of 20 patients with orbital myxomas in the literature, in addition to this case, roughly classified locations in the orbit were retrobulbar in 8 patients, on the lateral side of the orbit in 4, on the superior side in 6, on the medial side in 1 (this patient), and in the orbit with no specific description in 2. In pathological examinations, immunohistochemistry was not done in 8 patients, done but all negative in 2, and positive in 11 patients: nerve sheath myxoma was diagnosed in 3 patients based on positive S100 staining. Orbital myxoma is rare but considered in differential diagnosis of orbital masses.

Clinical and imaging features of ethmomaxillary sinus compared to Haller's cell.

PURPOSE: Understanding the anatomy of the paranasal sinuses and their variations is essential to achieving safe and effective endoscopic sinus surgery. The ethmomaxillary sinus (EMS) is a relatively under-researched anatomical variation. This study investigated the prevalence, clinical features, and effect of EMS on the maxillary sinus in comparison with Haller's cells. METHODS: Patients who visited the Rhinology Clinic at our hospital for rhinologic symptoms between January 2020 and December 2020. Computed tomography (CT) scans of paranasal sinuses were obtained at 1 mm-section thickness. Using CT scans, we investigated the clinical features of EMS, measured maxillary sinus volume, and analyzed the presence of maxillary sinusitis. RESULTS: EMS was observed in 26 of the 250 patients (10.4%). The male-to-female ratio was equal. The age ranged from 18 to 83 years (mean age, 56.3). Of the patients with EMS, 65.4% were unilateral and 34.6% were bilateral. The prevalence of Haller's cells was similar to that in EMS (10.8%). In the analysis of patients with unilateral EMS, the EMS side was found to have a significantly reduced maxillary sinus volume compared to the opposite side, whereas the difference was not significant in Haller's cells. There was no significant relationship between EMS or Haller's cells and maxillary sinusitis. CONCLUSIONS: EMS can significantly affect maxillary sinus volume. Therefore, surgeons should thoroughly review PNS CT scans before paranasal sinus surgery to determine the presence and features of EMS.

Anatomical landmarks for localisation of the anterior ethmoidal artery: a combined radiological and cadaveric (endoscopic) study.

PURPOSE: The anterior ethmoidal artery is a major surgical landmark that is susceptible to iatrogenic injury during surgery of the anterior ethmoidal sinus, frontal sinus, and skull base. The present study aimed to define the location of the anterior ethmoidal artery in relation to specific anatomical landmarks using radiological imaging and endoscopic dissection. METHODS: Eighty-six anterior ethmoidal arteries were assessed using computed tomography scans (bilateral analyses) and forty anterior ethmoidal arteries were assessed using cadaveric specimens (bilateral analyses). The skull base, anterior nasal spine, anterior axilla of the middle turbinate, and nasal axilla were morphometrically analysed to determine their reliability as anterior ethmoidal artery landmarks. RESULTS: Distances to the skull base, anterior nasal spine, and nasal axilla displayed statistically significant differences between sexes and sides (p < 0.05). All landmarks demonstrated excellent reliability as anatomical landmarks for the localisation of the anterior ethmoidal artery, radiologically and endoscopically (ICC values ranged from 0.94 to 0.99). CONCLUSION: The middle turbinate axilla was the most reliable landmark, due to the lack of statistically significant differences according to sex and laterality, and the high inter-rater agreement between measurements. Anatomical knowledge of variations and relationships observed in the present study can be applied to surgeries of the anterior ethmoidal sinus, frontal sinus, and skull base to improve localisation of the anterior ethmoidal artery, preoperatively and intraoperatively, and avoid iatrogenic injury of the vessel.

Supraorbital ethmoid cells (SOECs), anterior ethmoid artery notch and ethmoid roof relation in PNSCT.

OBJECTIVES: We investigated supraorbital ethmoid cell (SOEC) presence and types in paranasal sinus computed tomography (PNSCT). METHODS: The PNSCT images of 188 adult patients (93 males and 95 females) were evaluated as SOEC group (n = 87 sides), and non-SOEC group (n = 289 sides, control). In both groups, anterior ethmoid artery (AEA) notch-ethmoid roof distance and presence of AEA canal were evaluated. In the SOEC group, SOEC types (type 1 to 3) and SOEC angle are also examined. RESULTS: SOEC was detected in 87 sides (23.13 %). SOEC type 2 was the most detected type (71.3 %). AEA notch-ethmoid roof distance of the SOEC group was significantly higher than those in the non-SOEC group. AEA notch-ethmoid roof distance of the SOEC Type 3 group was significantly higher than SOEC Type 2 group. AEA notch-ethmoid roof distance was 3.74 ± 1.81 mm in the SOEC group and 0.68 ± 1.16 mm in the non-SOEC group. When SOEC types were considered, this distance was 5.29 ± 2.66 mm in type 3, 3.35 ± 1.35 mm in type 2 and 3.48 ± 0.92 mm in type 1. In higher SOEC types, SOEC angle; and AEA notch-ethmoid roof distance increased. CONCLUSION: In more pneumatized SOEC presence, SOEC angle increase, and AEA notch-ethmoid roof distance increases, AEA runs inferiorly in the ethmoid cells and freely below the skull base; and is more susceptible to injury. The surgeons should be more careful not to damage AEA in the FESS when detecting well-pneumatized SOECs (SOEC Type 3).

Radiological relationship of the ethmoid slit with the frontal sinus and the anterior ethmoidal artery and applications to the frontal sinus drillout.

PURPOSE: To compare two types of CT acquisition parameters: CT scan of the facial bone and CT scan of the sinuses, for studying the ethmoidal slit and its relationship with the frontal sinus and anterior ethmoidal artery. MATERIALS AND METHODS: Retrospective study of 145 scans of the sinuses and 79 of the facial bones performed between 2012 and 2016. On each scan, the visibility of the ethmoidal slits, their length, their distance from the ethmoidal artery, and their relationship with the anterior and posterior wall of the frontal sinus were studied. RESULTS: The ethmoidal slit was better visualized on CT scans of the facial bone (58.2%) than on those of the sinuses (43.1%) (p = 0.02). The distance between the anterior ethmoidal artery and the anterior part of the cribriform plate was 9.3 mm for CT scans of the facial bone and 8.4 mm for CT scans of the sinuses. The theoretical risk of damaging the glabellar soft tissue and that of damaging the meninges during a frontal sinusotomy was evaluated, respectively, at 9.6% and 26.1% for CT scans of the facial bone, and at 6.2% and 21.5% for sinus scans. CONCLUSIONS: CT scans of the facial bone are better than CT scans of the sinuses for identifying ethmoidal slits and their distance from the canal of the anterior ethmoidal artery. The identification of these elements is relevant for the surgeon during frontal sinus surgery and makes it possible to assess the risk of damaging the glabellar soft tissue or meninges. Performing a CT scan of the facial bone seems preferable to that of a CT scan of the sinuses in certain pathological situations, such as cerebrospinal rhinorrhea or revision surgeries of the frontal sinus.

Anterior ethmoid and frontal sinus drainage pathways: five patterns formed and defined by their bony walls.

PURPOSE: To perform endoscopic sinus surgery safely and effectively, surgeons need to visualize the complex anatomy of the anterior ethmoid and frontal sinus region. Because this anatomy is so variable and individualized, the foundation of understanding lies in identifying, following, and visualizing the drainage pathway patterns and anticipating possible variations. METHODS: We studied 100 sides (50 cases: 22 male, 28 female, aged 12-86, average age 46.5 years, ± 19.5) using computed tomography (CT) and multiplanar reconstruction (MPR) to identify and classify the drainage pathways leading to the frontal sinus and anterior ethmoidal cells. RESULTS: Analysis revealed five patterns of drainage pathways defined by their bony walls: between the uncinate process and the lamina papyracea [UP-LP]; between the uncinate process and the middle turbinate [UP-MT]; between the uncinate process and the accessory uncinate process [UP-UPa]; between the uncinate process and the basal lamella of the ethmoidal bulla [UP-BLEB]; and between the basal lamella of the ethmoidal bulla and the basal lamella of the middle turbinate [BLEB-BLMT]. In most cases, BLEB formed the posterior wall of the drainage pathway of the frontal sinus, indicating BLEB could be one of the most important landmarks for approaching the frontal sinus. CONCLUSIONS: As endoscopic sinus surgery depends on an understanding of this anatomy, this study may help surgeons to identify and follow the drainage pathways more accurately and safely through the anterior ethmoid to the frontal sinus.

Intraosseous Hemangioma of the Ethmoid Sinus.

Intraosseous hemangiomas, also referred to as bony hemangiomas, arising within the nasal cavity are exceedingly rare with only 2 cases arising in the ethmoid region. Despite their rarity, they are important to consider in a patient presenting with long-standing nasal congestion. While characteristic findings on computed tomography imaging may be observed, biopsy is diagnostic. En bloc resection using a transnasal endoscopic approach with or without preoperative embolization is the treatment of choice for intranasal intraosseous hemangiomas.

Computed tomography analysis of the anterior ethmoid genu of the frontal recess in non-diseased sinuses.

OBJECTIVE: Knowledge of anatomical variations of the frontal recess and frontal sinus and recognition of endoscopic landmarks are vital for safe and effective endoscopic sinus surgery. This study revisited an anatomical landmark in the frontal recess that could serve as a guide to the frontal sinus. METHOD: Prevalence of the anterior ethmoid genu, its morphology and its relationship with the frontal sinus drainage pathway was assessed. Computed tomography scans with multiplanar reconstruction were used to study non-diseased sinonasal complexes. RESULTS: The anterior ethmoidal genu was present in all 102 anatomical sides studied, independent of age, gender and race. Its position was within the frontal sinus drainage pathway, and the drainage pathway was medial to it in 98 of 102 cases. The anterior ethmoidal genu sometimes extended laterally and formed a recess bounded by the lamina papyracea laterally, by the uncinate process anteriorly and by the bulla ethmoidalis posteriorly. Distance of the anterior ethmoidal genu to frontal ostia can be determined by the height of the posterior wall of the agger nasi cell rather than its volume or other dimensions. CONCLUSION: This study confirmed that the anterior ethmoidal genu is a constant anatomical structure positioned within frontal sinus drainage pathway. The description of anterior ethmoidal genu found in this study explained the anatomical connection between the agger nasi cell, uncinate process and bulla ethmoidalis and its structural organisation.

Surgical Approach to Frontal and Ethmoid Sinus Osteomas: The Experience of 2 Metropolitan Italian Hospitals.

OBJECTIVES: The aim of this study was to report the surgical management experience of patients with osteomas of the frontal and ethmoid sinuses performed in 2 metropolitan Italian hospitals between 2012 and 2019. METHODS: A retrospective chart review of cases of frontal and ethmoid osteomas from the Ca' Granda Niguarda Hospital of Milan and the Policlinico Umberto I University Hospital of Rome was performed. All patients underwent preoperative computed tomography and, when orbital or intracranial extension was suspected, magnetic resonance imaging. Surgical treatment was performed according to Chiu classification. RESULTS: A total of 38 cases of frontal and ethmoid sinus osteomas were included in the study; 22 patients were men and 16 were women. The mean age at diagnosis was 49 years. Seven (18.4%) patients were treated using an open approach; 3 (7.9%) patients underwent open and endoscopic approach; the remaining 28 (73.7%) patients were treated with endoscopic approach. Seven (18.4%) patients had a cerebrospinal fluid leak intraoperatively and were treated with the placement of tissue graft through the defect. The mean follow-up time was 18 months; no recurrence was observed at 12-month follow-up. CONCLUSION: Osteomas of the frontal and ethmoid sinuses can be treated using different techniques, mostly endoscopically. The choice of surgical approach (endoscopic vs open) depends on the location and size of the osteoma, anatomical size, characteristic of the sinus, surgeon's experience, and available existing technical facilities. Cerebrospinal fluid leak is a possible complication of surgery.

Anatomical identification of supraseptal posterior ethmoid cells and its significance for endoscopic sinus surgery.

BACKGROUND: To investigate the anatomical imaging characteristics of supraseptal posterior ethmoid cells (SPEC). MATERIALS AND METHODS: Paranasal sinus computed tomography scans of 153 inpatients from February 2019 to September 2021 were reviewed, and the anatomical characteristics of SPEC in the scans were collected. RESULTS: Supraseptal posterior ethmoid cells are posterior ethmoid (PE) cells extending medially and superiorly to the posterior superior of the nasal septum and into the sphenoid body but not close to the optic canal. The SPEC, Onodi cell, and sphenoidal sinus (SS) may appear in the posterior superior of the nasal septum, but the occurrence rate of the SPEC (5.88%; 9/153 cases) was significantly lower than that of the SS (22.88%) and Onodi cell (21.57%). The anterior SPEC is adjacent to the cribriform plate, the perpendicular plate of the ethmoid bone and the posterior ethmoidal artery (PEA). The posterior SPEC is adjacent to the SS and PE (6/9 cases), the SS and Onodi cell (2/9 cases) or the PE only (1/9 cases). CONCLUSIONS: The SPEC is a rare pneumatization that occurs in the posterior superior area of the nasal septum. Care should be taken to protect the skull base, cribriform plate and PEA when opening the SPEC during endoscopic sinus surgery.

A Von Hippel-Lindau Disease-Associated Microcystic Adenoma of the Ethmoid Sinus Mimicking Metastatic Clear Cell Renal Cell Carcinoma.

ABSTRACT: A 38-year-old man with von Hippel-Lindau (VHL) disease and a history of renal cell carcinoma presented with a 2-month history of recurrent epistaxis. MRI revealed a microcystic tumor in the left ethmoid sinus with strong contrast enhancement. 18 F-FDG PET/CT showed FDG uptake (SUV max , 4.2) in the lesion. Under the suspicion of renal cell carcinoma metastasis, the patient underwent 2 surgical resections. However, based on the morphological and immunohistochemical findings, the patient was finally diagnosed with a VHL-associated microcystic adenoma of the ethmoid sinus, which is an extremely rare tumor that occurs in VHL disease.

[Anatomic variations in the ethmoid sinus in patients undergoing dacryocystorhinostomy at the Hassan II de Fès Medical Center (study of 215 patients)]. / Variations anatomiques du sinus ethmoïdal des patients opérés de dacryocystorhinostomie au centre hospitalier Hassan II de FES (étude de 215 patients).

INTRODUCTION: Although several studies have tried to identify the causes of failure of dacryocystorhinostomy (DCR) surgery, the ethmoid sinus remains an underestimated and little described source of failure. OBJECTIVE: To study anatomical relationship between the ethmoidal sinus, particularly the "Agger nasi" cell, with the lacrimal fossa in the North African population, little described in the literature. This study is based on the results of preoperative analysis of dacryo-computed tomography. PATIENTS AND METHODS: Analysis of preoperative computed tomography images of patients undergoing dacryocystorhinostomy over a 7-year period from January 2011 to December 2017. Anatomical relationships were studied according to the following classification: type I: No ethmoid cells located anteriorly to the posterior lacrimal crest on transverse images; type II: ethmoidal cells extending anteriorly to the posterior lacrimal crest, but not reaching the anterior edge of the lacrimal bone; Type III: ethmoidal cells located anterior to the lacrimal bone suture. RESULTS: Two hundred and fifteen preoperative computed tomography images were analyzed. The morphology of the ethmoid sinus was classified as type 1 in 33.5%, type 2 in 42.32% and type 3 in 24.18%. Computed tomography analysis was symmetrical in 87.5% and asymmetrical in 12.5%. CONCLUSION: During dacryocystorhinostomy, the surgeon must take into consideration type III, which can be present in 25% of cases. In the case of surgical failure, a dacryo-CT must be performed to rule out such anterior positioning of the ethmoid cells.