Correlation of the ethmoid infundibulum to the medial orbital wall in maxillary sinus hypoplasia: "Infundibular lateralization" a diagnostic CT finding.

Abstract

In patients with chronic rhinosinusitis, the presence of maxillary sinus hypoplasia (MSH) may be obscured by extensive mucosal disease or nasal polyposis. Recognition of MSH and its effect on adjacent anatomic structures is of utmost clinical significance in endoscopic sinus surgery. Failure to recognize the impact that MSH has on the position of the ethmoid infundibulum relative to the medial orbital wall could lead to inadvertent damage to the wall during surger. We conducted a prospective study of 75 patients with clinically and endoscopically proven chronic rhinosinusitis to evaluate the prevalence of MSH. We found that MSH was present in 12 patients (16.0%); 7 of the 75 patients (9.3%) had bilateral disease, and 5 (6.7%) had unilateral disease. We then correlated the relationship of the ethmoid infundibulum to the medial orbital wall as determined by computed tomography in patients with and without MSH. We found that in most cases of MSH, the ethmoid infundibulum was displaced lateral to the medial wall of the orbit; the correlation between MSH status and displacement was statistically significant (p < 0.05). We propose the term " infundibular lateralization" to describe this consistent radiologic finding in MSH.

Introduction

Maxillary sinus hypoplasia (MSH) is a clinical entity well known to otolaryngologists and anatomists. (1,2) It sometimes mimics maxillary sinusitis. The association between MSH and anomalies of the uncinate process such as hypoplasia and aplasia has been described in previous studies. (1-3) Recognition of MSH and its associated anomalies is important in surgical planning for patients who are scheduled to undergo endoscopic sinus surgery because a failure to identify them could lead to iatrogenic damage to the orbital wall and other orbital complications. (3) Hypoplasia and aplasia of the maxillary sinus can usually be diagnosed on standard radiography; computed tomography (CT) is the modality of choice.

It has been reported in the literature that the maxillary ostium usually lies along the same vertical plane as the medial wall of the orbit. However, in patients with MSH, the ethmoid infundibulum is displaced laterally. As important as this knowledge is to surgeons who are planning an operative procedure on the sinuses, radiologists may neglect to transmit this key information. (4)

We conducted a study (1) to determine the prevalence of MSH in a population of patients with chronic rhinosinusitis and (2) to assess the correlation of the ethmoid infundibulum to the medial wall of the orbit as a radiologic finding in cases in which surgical landmarks are distorted because of extensive mucosal disease. To the best of our knowledge, no such study has heretofore been published.

Patients and methods

This prospective study was conducted over a 1-year period among patients in our ENT outpatient department who had been clinically and endoscopically diagnosed with chronic rhinosinusitis based on the criteria established by the Rhinosinusitis Task Force. (5) Patients with acute rhinosinusitis, clinically proven allergy, a gross nasal mass, a malignancy, extensive nasal polyposis, or a history of sinonasal surgeries (except antral washout) were not eligible for this study, nor were patients younger than 15 years. Ultimately, our study population was made up of 75 patients--42 males and 33 females, aged 15 to 45 years.

[FIGURE 1 OMITTED]

All patients underwent a detailed clinical and physical examination, nasal endoscopy with a 30[degrees], 2.7-mm rigid nasal endoscope, and coronal CT (Somatom DRH single-slice helical CT scanner; Siemens; Erlangen, Germany). Direct coronal positioning was done with the patient prone or supine and the chin extended (neck hyperextended). Images were 3 mm thick and were obtained in 3-mm increments. A bone algorithm was used for acquisition. Images were stored in a picture archiving and communication system (PACS). They were interpreted in bone windows by an ENT surgeon and a radiologist, who paid special attention to anatomic boundaries, anatomic variations, and the extent of mucosal disease. Visual examination of the CTs was conducted in accordance with the diagnostic criteria for MSH described by Geraghty and Dolan. (6)

The chi-square test was used for statistical analysis to test the associations between variables, and the p value was determined to test the significance of correlations. The frequency distributions of hypoplasia were determined by descriptive statistics.

Results

Of the 75 patients, 12 (16.0%) had MSH. Bilateral disease was identified in 7 of these patients (9.3% of the entire population) and unilateral disease in 5 (6.7%); of the 5 patients with unilateral disease, 2 (2.7% of the entire population) were affected on the right side and 3 (4.0%) on the left. In all, 9 right sinuses and 10 left sinuses were affected; expressed another way, 66 right maxillary sinuses and 65 left maxillary sinuses were normal.

Of the 19 affected sinuses, MSH was classified as mild (type I) in 14 (73.7%), significant (type II) in 4 (21.1%), and profound (type III) in 1 (5.3%) (figure 1).

On the side of all normal maxillary sinuses, the ethmoid infundibulum was in the same vertical plane as the medial wall of the orbit (table; figure 2, A). However, 17 of the 19 hypoplastic maxillary sinuses (89.5%) were associated with lateral displacement of the ethmoid infundibulum relative to the medial orbital wall--8 of the 9 hypoplastic right sinuses and 9 of the 10 hypoplastic left sinuses (figure 2, B). The correlation was statistically significant (p < 0.05).

Discussion

The maxillary sinus is the first of the paranasal sinuses to take form in the human fetus,v It develops during the fourth month of intrauterine life as a mucosal evagination in the center of the middle meatus. At birth, the cavity measures approximately 8.2 mm from anterior to posterior, 3.3 mm vertically, and 2.8 mm laterally. If development becomes arrested at any stage of intrauterine life, hypoplasia or aplasia occurs.

The reported prevalence of MSH varies to some degree. In the late 1970s, Karmody et al analyzed 750 radiographs and found bilateral hypoplasia on 54 images (7.2%), unilateral hypoplasia on 13 ( 1.7%), and aplasia on 3 (0.4%). (2) In more recent reports involving CT studies, prevalence was reported as 10.4, (1) 4.0, (6) and 17.5%. (8) All these earlier studies were retrospective. In our prospective study of 75 patients with chronic rhinosinusitis, the prevalence of bilateral and unilateral MSH was 9.3 and 6.7%, respectively.

The etiology of maxillary hypoplasia is unknown, and the process by which abnormal pneumatization occurs is not well understood. (1) It has been suggested that intrauterine developmental abnormalities and sinus infections during the first year of life are possibly responsible for the arrest or alteration of the pattern of maxillary sinus pneumatization. (3)

In hypoplasia and aplasia of the maxillary sinus, the floor and roof of the ipsilateral orbit are depressed. Depression of the orbital roof, which forms the floor of the frontal fossa, can also cause the brain to be caudally situated. (9) Geraghty and Dolan reported that the complete diagnostic criteria for MSH are (1) enlargement of the vertical orbit, (2) enlargement of the superior orbital fissure, (3) elevation of the canine fossa, (4) enlargement of the pterygopalatine fissure, and (5) lateralization of the infraorbital neurovascular canal. (6)

[FIGURE 2 OMITTED]

Bolger et al (1) proposed a three-part classification of MSH:

* Type I--mild. The uncinate process is normal, and the infundibular passage is well defined (figure 1, A). Varying degrees of mucosal thickening occur within the affected sinus.

* Type II--significant. The uncinate process is hypoplastic or absent, and the infundibular passage is ill defined or absent (figure 1, B). Total opacification of the affected sinus by soft-tissue density is seen on CT.

* Type III--profound. The uncinate process is absent, and the sinus is represented by only a shallow cleft in the lateral nasal wall (figure 1, C).

Bolger et al, in their study of 21 patients with MSH, found that 14 patients (66.7%) had type I MSH, 6 (28.6%) had type II, and 1 (4.8%) had type III. (1) In our study, type I MSH was noted in 14 of the 19 hypoplastic sinuses (73.7%), type II in 4 (21.1%), and type III in 1 patient (5.3%).

The presence of MSH frequently complicates surgical evaluation, For example, it may mimic chronic rhinosinusitis in patients who do not have rhinosinusitis. (10) A hypoplastic sinus is susceptible to mucus retention. Sometimes the presence of MSH is obscured by extensive mucosal disease or nasal polyposis. (11)

Meyers and Valvassori retrospectively reviewed 400 CTs obtained from patients who had undergone endoscopic sinus surgery. (4) They reported that in 4% of these cases, the medial wall of the orbit was lateral to the maxillary ostium as a result of MSH. In our study, 17 of 19 hypoplastic maxillary sinuses (89.5%) demonstrated lateral displacement of the ethmoid infundibulum relative to the medial orbital wall. This radiologic finding has not been previously reported.

In conclusion, MSH and its associated anomalies pose a surgical challenge to otolaryngologists who perform sinus surgery on patients with rhinosinusitis. Awareness of the anatomic consequences of MSH is vital in these circumstances--specifically, the lateral displacement of the ethmoid infundibulum in relation to the medial orbital wall. We propose that infundibular lateralization be included among the diagnostic radiologic findings in the assessment of the hypoplastic maxillary sinus.

References

(1.) Bolger WE, Woodruff WW Jr., Morehead J, Parsons DS. Maxillary sinus hypoplasia: Classification and description of associated uncinate process hypoplasia. Otolaryngol Head Neck Surg 1990; 103 (5 Pt 1):759-65.

(2.) Karmody CS, Carter B, Vincent ME. Developmental anomalies of the maxillary sinus. Trans Sect Otolaryngol Am Acad Ophthalmol Otolaryngol 1977;84(4 Pt 1):723-8.

(3.) Kapoor PK, Kumar BN, Watson SD. Maxillary sinus hypoplasia. J Laryngol Otol 2002:116(2):135-7.

(4.) Meyers RM, Valvassori G. Interpretation of anatomic variations of computed tomography scans of the sinuses: A surgeon's perspective. Laryngoscope 1998; 108(3):422-5.

(5.) Lanza DC, Kennedy DW. Adult rhinosinusitis defined. Otolaryngol Head Neck Surg 1997;117(3 Pt 2):S1-7.

(6.) Geraghty JJ, Dolan KD. Computed tomography of the hypoplastic maxillary sinus. Ann Otol Rhinol Laryngol 1989;98(11):916-18.

(7.) Clerico DM, Grabo DJ Jr. Maxillary sinus aplasia. Ann Otol Rhinol Laryngol 1997;106(9):799-800.

(8.) Milczuk HA, Dalley RW, Wessbacher FW, Richardson MA. Nasal and paranasal sinus anomalies in children with chronic sinusitis. Laryngoscope 1993;103(3):247-52.

(9.) Modic MT, Weinstein MA, Berlin AJ, Duchesneau PM. Maxillary sinus hypoplasia visualized with computed tomography. Radiology 1980;135(2):383-5.

(10.) Vinson RE Collette RE Maxillary sinus hypoplasia masquerading as chronic sinusitis. Postgrad Med 1991:89(4):189-90.

(11.) Salib RJ, Chaudri SA, Rockley TJ. Sinusitis in the hypoplastic maxillary antrum: The crucial role of radiology in diagnosis and management. J Laryngol Otol 2001:115(8):676-8.

Arif Ali, DLO, MS; Mary Kurien, DLO, MS; K.G. Selvaraj, PhD

From the Department of ENT (Dr. Ali and Dr. Kurien) and the Department of Biostatistics (Dr. Selvaraj), Christian Medical College and Hospital, Vellore, Tamitnadu, India.

Reprint requests: Dr. Mary Kurien, Department of ENT, Christian Medical College and Hospital, Vellore-632004, Tamilnadu, India. Phone: [phone] or 228-2098; fax: [phone] or 223-2103; e-mail: kurien_mary @ hotmail.com

Table. Correlation of the vertical plane of the ethmoid infundibulum
to the medial orbital wall according to MSH status

                          Infundibulum      Infundibulum
                          in line with       lateral to
Maxillary sinus         the orbital wall  the orbital wall    Total
CT findings                  n (%)             n (%)        (n = 75)

Right side
  Normal (n = 66)           66 (100)             0          66 (88.0)
  Hypoplastic (n = 9)       1 (11.1)          8 (88.9)      9 (12.0)

Left side
  Normal (n = 65)           65 (100)             0          65 (86.7)
  Hypoplastic (n = 10)      1 (10.0)          9 (90.0)      10 (13.3)