Morphologic Analysis of Crista Galli Using Computed Tomography

J Rhinol 19(2), 2012 www.ksrhino.or.kr

Jong Jun Kim, MD1, Jae Hyeong Cho, MD1, Jae Won Choi, MD1, Hyun Woo Lim, MD1, Yong Jin Song, MD1, Soo-Jung Choi, MD2 and Nam-Kyung Yeo, MD1 1Department of Otolaryngology, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung, Korea 2Department of Radiology, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung, Korea

ABSTRACT Objective : We often observe the variation of Crista galli (CG) which lies in the midline above the cribriform plate on computed tomography (CT) scans. We investigated the variations in CG and the factors which affect its pneumatization. Materials and Methods : We analyzed the CT images of 818 chronic rhinosinusitis patients between July 2003 and July 2011. We investigated height, position relative to the cribriform plate, degree of pneumatization, and cell origin for the pneumatization in CG. We analyzed the relationship between several factors (age, sex, and position of CG) and pneumatization of CG. Results : The average height of CG was 17.98 mm. In 13.9% of subjects, the base of CG did not extend below the level of the cribriform plate. In 84.2%, CG extended less than 50% of its height below the cribriform plate. In 1.8%, CG extended more than 50% of its height below the cribriform plate. Pneumatization of CG was found in 12.2%. Except one, every pneumatization was connected with the frontal sinus. The rate of pneumatization was significantly different depending on age.Conclusion : Our study demonstrated that CG showed various morphology and pneumatizaiton. The pneumatization of CG was mainly originated from frontal sinus and related to aging. KEY WORDS : Crista galli · Computed tomography · Pneumatization · Ethmoid bone · Frontal sinus.

INTRODUCTION terior border, whereas its shorter thicker anterior border is joined to the frontal bone by 2 small alae, completing 4) Osteomeatal unit computed tomography (OMU CT) the margins of the foramen caecum. In the embryo, the scans frequently allow us not only to detect chronic rhi- ethmoidal cartilage consists of both a mesial mass(the me- nosinusitis (CRS) but also to decide the range of endo- sethmoid), which extends from the sphenoid to the tip of scopic sinus surgery (ESS) through the assessment of the the nasal process, and a pair of lateral masses developed extent and severity of disease. OMU CT scans provide the from the lateral nasal processes(the ectethmoid), lateral to important information about the anatomic variations of the olfactory sacs. The terminal portion of the mesial mass the paranasal sinuses. Several previous studies described persists as the cartilaginous nasal septum, whereas ossi- marked pneumatization of the ethmoid bone including the fication of the upper portion becomes the perpendicular Haller’s cells, agger nasi cells, concha bullosa, and Ono- plate and Crista galli. di’s cells.1-3) The morphologic variation of Crista galli is often ob- Crista galli is a large triangular process at the midline served on the preoperative OMU CT scans. Pneumatiza- on the superior surface of the cribriform plate anchors a tion of the Crista galli is one of the recognized incidental fold(falx cerebri) of dura mater in the cranial cavity. The findings on CT scans. Even though the pneumatization of falx cerebri attaches to its thin and slightly curved pos- Crista galli is not common, obstruction of the pneumatized Crista galli ostium may lead to chronic sinusitis and mu- Address correspondence and reprint requests to Nam-Kyung Yeo, De- 5) partment of Otorhinolaryngology, Gangneung Asan Hospital, University cocele formation within this structure. However, there is of Ulsan College of Medicine, 415, Bangdonglee, Sachunmyun, Gangne- a paucity of information concerning the anatomic charac- ung, 210-711, South Korea teristics of the Crista galli. The purpose of this study is to Tel: +82-33-610-3308, Fax: +82-33-610-4960 E-mail: [email protected] examine the morphologic variations of the Crista galli and Received for publication on April 4, 2012 the factors which affect its pneumatization. In order to ac- Accepted for publicatoin on July 18, 2012 complish this, we investigated axial and coronal CT scans

- 91 - 92 / J Rhinol 19(2), 2012 of the paranasal sinuses of 818 consecutive CRS patients. is located below the level of the cribriform plate. Type III—greater than 50% of the height of the Crista MATERIALS AND METHODS galli is located below the level of the cribriform plate. If the pneumatization of Crista galli was detected, an as- Subjects sessment was made as to whether the bony margins of the Crista galli were completely intact other than its caudal OMU CT scans were obtained from 1059 patients, who margin or there was an extension of either frontal sinus were diagnosed as CRS preoperatively at our institution or ethmoid complex into the Crista galli. In addition, we from July 1, 2003 through July 31, 2011. Patients with evaluated the existence of mucosal thickening extending previous histories of facial trauma, nasal surgery or sinus from adjacent frontal or ethmoid sinus into the pneuma- carcinoma were excluded from the investigation in order tized Crista galli. All scans were reviewed separately by to minimize the chance of acquired anatomic defects. Fi- one radiologist and one otolaryngologist. Any different nally, 818 consecutive axial and coronal CT scans of the opinions were resolved by consensus. paranasal sinuses were made to assess the height, the posi- Lastly, we also analyzed the relationship between other tion, the existence of pneumatization, and the connection factors (age, sex, and type of Crista galli) and the pneu- site of the pneumatization in the Crista galli. matization of Crista galli. The study was performed with the approval of the internal review board (number 2010- CT acquisition and images Analysis 051).

The OMU CT scans were retrospectively reviewed Statistical Analysis with the Picture Archiving and Communication System (PACS, Peta Vision, Asan Medical Center, Korea). CT Results were statistically analyzed using SPSS software examinations were performed with a 64 channel MDCT (version 12; SPSS Inc, Chicago, Illinois). Differences in (Lightspeed VCT, GE Healthcare, Milwaukee, USA; scan the rate of pneumatization of Crista galli depending on parameter, 120kVp, 250mAs; scan time, 1000msec; ma- age, sex, and type of Crista galli were analyzed by using trix size, 512x512) without contrast enhancement. The Chi square test. P values < 0.05 were considered statisti- patients were scanned in the supine position (gantry tilt, cally significant. about 21 degrees through anterior margin of frontal sinus and nostril), and coronary editing of 1-mm thick slices RESULTS from the front of the frontal sinus to the end of the sphenoid sinus was done. The CT scans were routinely evalu- Eight hundred eighteen sets of OMU CT scans were ated with a window width/level of 2000/265 HU for axial evaluated. The patient population was comprised of 512 scans and 2000/350 HU for coronal scans. men and 306 women, with a median age of 44.51 (range, The position of the Crista galli was evaluated according 7-91). Six hundred thirty-three patients (77.4%) had bilat- to Hajiioannou’ method6) The position of the Crista galli eral CRS and 185 patients (22.6%) had unilateral CRS. was categorized into three grades according to the loca- The average height of Crista galli was 17.98 ±3.7 mm. tion related to the cribriform plate (Fig. 1). Crista galli type I, in which the base of the Crista galli Type I—base of the Crista galli is located at the level of did not extend below the level of the cribriform plate, was the cribriform plate. found in 13.9% of subjects (114/818). Type II, the Crista Type II—less than 50% of the height of the Crista galli galli extended less than 50% of its height below the cribriform plate, was the most common position of Crista galli, which accounted for 84.2% of subjects (689/818). Type III, in which the Crista galli extended more than 50% of its height below the cribriform plate, was found in 1.8% of the CT scans (15/818). Pneumatization in Crista galli was found in 100 patients A B C (12.2%). There were 19 cases with only minimal pneuma- Fig. 1. Position of the Crista galli noted by relation to the cribri- tization and 81 cases with extensive pneumatization (Fig. form plate. Type I was regarded as when base of the Crista galli 2). Every pneumatization was connected with adjacent was at the level of the cribriform plate (A). Type II was less than paranasal sinuses. Except one case, every pneumatization 50% of the height of the Crista galli below the level of the cribriform plate (B). Type III was greater than 50% of the height of the was connected with the right (46 cases), left (38 cases) or Crista galli below the level of the cribriform plate (C). interseptal frontal sinus (15 cases) (Figs. 2, 3). Only one Kim et al : Variation of Crista Galli / 93

A B A B Fig. 5. Extension of the inflammatory disease into the pneumatized Crista galli. Axial (A) and coronal CT scans (B) of the paranasal sinuses in a 39-year-old man show thick mucosal thickening extending from the right frontal sinus into a well-pneumatized Crista galli (arrow).

Table 1. Rate of Pneumatization of Crista Galli. C D No. of Pneumatized Crista Galli / No. of Total % P- value Fig. 2. Pneumatization in Crista galli from frontal sinus. Coronal (A) and axial CT scans (B) of the paranasal sinuses in a 37-year- Age old man show the extensive pneumatization (arrow) of the Crista <18 years 2/73 2.7 0.01 galli from the left frontal sinus. The other coronal (C) and axial CT ≥ 18 years 98/745 13.2 scans (D) of the paranasal sinuses in a 54-year-old woman show minimal pneumatization (arrow) of the Crista galli from the right Sex Male 64/512 12.5 frontal sinus. 0.756 Female 36/306 11.8

Type of Crista galli TypeⅠ 10/114 8.8 TypeⅡ 88/689 12.8 0.415 TypeⅢ 2/15 13.3

A B C patient, who had bilateral undeveloped frontal sinuses, showed pneumatization of Crista galli connected to the right ethmoid sinus (Fig. 4). In 44 cases, inflammatory disease in a frontal sinus extended directly into the pneu- D E F matized Crista galli (Fig. 5). We analyzed the relationship between variable factors Fig. 3. Pneumatization in Crista galli from interseptal frontal sinus. Coronal (A, B, and C) and axial CT scans (D, E, and F) of the and pneumatization of Crista galli (Table 1). The age paranasal sinuses in a 45-year-old man show the typical pneu- was found to have an effect on the rate of pneumatiza- matization (arrow) of the Crista galli from the interseptal frontal tion of Crista galli (P=0.01). Among the 73 CT scans of sinus (star). patients under the age of 18, there were 2 cases of Crista galli pneumatization (2.7%). Among the 745 CT scans of patients with 18 and over the age of 18, there were 98 cases with pneumatization of the Crista galli (13.2%). In contrast, the rate of pneumatization was not affected by sex, or type of Crista galli. A B C DISCUSSION

Embryologically, the Crista galli is derived from the ethmoid bone. In the second fetal month, it is formed together with the central structures of the anterior skull D E F base and the perpendicular plate of the ethmoid bone by Fig. 4. Pneumatization in Crista galli from ethmoid sinus. Coronal the mesethmoidal cartilage which is derived from the pre- (A, B, and C) and axial CT scans (D, E, and F) of the paranasal 4) 6) sinuses in a 30-year-old woman show the pneumatization (white sphenoidal cartilage. Then, most ossification of the arrow) of the Crista galli from the ethmoid air cell (star). Bilateral cartilaginous Crista galli starts at approximately 2 months frontal sinuses were undeveloped (black arrow). of postnatal life, steadily increases in ossification to 14 94 / J Rhinol 19(2), 2012 months of age, and then slowly progresses until it finishes Crista galli pneumatization had the inflammatory mucosal by 24 months of age.7) For this reason, it had been tra- thickening extending from the frontal sinus. In addition, ditionally thought that aeration of the Crista galli would intraoperative damage to the pneumatized Crista galli can come from the ethmoid complex such as the frontal recess lead to skull base injury such as CSF leakage because and migrated ethmoid cells. Crista galli is a unit structure. Wingate et al. suggested However, recent studies demonstrated that pneumatiza- that the mucocele arising from the Crista galli was further tion of the Crista galli came primarily from the adjacent complicated by its intracranial extension.9) Therefore, it frontal sinuses by radiologic analysis.2) 4) Especially, Som is important to recognize this entity preoperatively and to et al. showed that there was 13% of Crista galli pneuma- differentiate it from an adjacent air cell to avoid extension tization from either the left or right frontal sinuses in 200 of surgery into the cranial vault. adult CT scans, and there were no cases of crista pneuma- To the best of our knowledge, this study is the first re- tization in the 132 CT scans of children 0–7 years of age.4) port to analyze the morphologic characteristics of Crista According to their suggestion, some Crista galli pneu- galli using computed tomography in Asian patients. Our matization would be present in the children if the pneu- findings are not surprising, because we showed the similar matizing cells were from the ethmoid complex, because position or pneumatization of Crista galli when compared the Crista galli is from the ethmoid bone and the ethmoid to the previous reports. However, we suggested another complexes are pneumatized at birth. evidence that the primary origin of pneumatization of the In the present study, we also demonstrated that pneu- Crista galli is from the frontal sinus according to the anal- matization of the Crista galli is generally from the frontal ysis of 818 CT scans. sinus. On the 818 OMU CT sca ns, all of crista pneumati- In conclusion, our study demonstrated that the Crista zation except one was connected with frontal sinus. Only galli showed various morphology and pneumatizaiton. one patient, who had bilateral undeveloped frontal sinus- The pneumatization of Crista galli was mainly extended es, showed the pneumatization of Crista galli connected from frontal sinus and related with aging. This finding to the right ethmoid sinus. Additionally, we showed that may have surgical implications when disease is present in there was statistically significant difference in the rate of the Crista galli. Crista galli pneumatization between children and adults groups. On the CT scans of the children and puberty pe- 저자역할(Author Contributions) riods adolescents (<18 years) whose frontal sinuses have 김종준, 여남경 은 본 연구에서 모든 자료에 접근할 수 있으며 자료의 not reached full size,8) we found 2.7% of Crista galli pneu- 완전성과 자료 분석의 정확성에 책임을 지고 있습니다. 연구 기획 : 여 matization. On the other hand, we had 13.2% of adults (≥ 남경. 자료 해석 및 분석 : 김종준, 최재원, 조재형, 임현우, 송용진, 최 18 years) with Crista galli pneumatization. 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