Pra Urusopone M.D. Radiologist at Department of Radiology, Lerdsin General Hospital

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1 16 π æπ åμâπ Delineation of Optic Nerve by Its Relationship with the Posterior Eithmoid and Sphenoid Sinuses According to Delano Classification Using Computed Tomography in Lerdsin General Hospital Pra Urusopone M.D. Radiologist at Department of Radiology, Lerdsin General Hospital ËÕß àõ Õ π Õß âπª μ (optic nerve) «æ π å À«à ß âπª μ posterior ethmoid sphenoid sinus μ àß Õß Delano â Õ å Õ æ «μõ å π ßæ π Õÿ ÿ æ.. ß æ å ßæ π «æ å 2014;39: πªí ÿ π ºà μ paranasal sinus â âõß (endoscopic sinus surgery) â âõ à ß æ àà Ë Ë ßæ π πõπ μ μà π ËÕß ºà μ π π È «Ë ß æ Õ à ß Ëß àõ Àâ Á μàõ âπª μ æ π Õß âπª μ π Ë 2 3 ßπ Èπ «æ π å Õß âπª μ posterior ethmoid sphenoid sinus ß «Õ à ß ºŸâ ß π ß â» æ ËÕÀ «æ π å À«à ß âπª μ posterior ethmoid sphenoid sinus â Õ å Õ æ «μõ å (CT scan) μ àß Õß Delano À «Ë Õß Ÿª Ÿ (bony variation) Ë ªìπªí à«ë Àâ Á μàõ âπª μ ËÕ æ â â» âõπà ß πºÿâªé«75 Ë CT scan Õß paranasal sinus À Õ facial bone (150 â ß) π à«ß Õπ ÿπ π æ.» Õπ π æ.» Ÿ Èß axial coronal plane àß π Õß âπª μ μ àß Õß Delano ªìπ 4 ÿà Ëßæ «à π Õß âπª μ Ëæ Ë ÿ Õ π Ë 1 âõ 76.0 (114 âπ) π Ë 2-4 æ âõ 9.3 (14 âπ) âõ 5.4 (8 âπ) âõ 9.3 (14 âπ) μ π Õß âπª μ Ë «Ë ßμàÕ Á Õ π Ë 2 3 Ëß» π Èæ âõ 14.6 à«πªí Ë ß à«õ à ßÕ Ëπ àπ protrusion of optic nerve, bony dehiscence of optic canal pneumatization of anterior clinoid process (ACP) æ âõ 4.0 âõ 10.7 âõ 12.0 (3 8 9 μ ) πõ π È ßæ Èß dehiscence of optic nerve à«pneumatized ACP πºÿâªé«3 ( âõ 4.0) 1 ªìπ âπª μ π Ë 2 â ß «Õ 1 ªìπ π Ë 1 â ß «Õ 1 ªìπ π Ë 3 ªìπ Èß 2 â ß π ËÕß Ë ºà μ paranasal sinus â âõß πõπ μ Ë ßæ π» ºŸâªÉ«μà æ Õ à ß Ëß ª π π Õß âπª μ ªí Ë ßÕ à ßÕ Ëπ àõπ ºà μ π Èπ ß ªìπ Ëß Ë ªìπÕ à ß π ªÑÕß π à Àâ «âõπ Ë ªìπÕ πμ μàõ âπ ª μ ßπ Èπ CT scan πºÿâªé«μà àõπ ºà μ ß à æ ß μà æ ËÕ ÕßÀ æ æ μà æ ËÕ ª π «ß ºπ ºà μ â«: âπª μ Posteior ethmoid sinus Sphenoid sinus Õ å Õ æ «μõ å

2 Vol. 39 No. 1 January-March Bulletin of the Department of Medical Services Abstract Endoscopic sinus surgery (ESS) is performed worldwide nowadays. Lerdsin General Hospital plans to have this operation performed in the near future. However there are risks associated with this surgery, particularly injury to optic nerve of Delano classification types 2 and 3. Complete preoperative evaluation of optic nerve and its proximity relationship to posterior ethmoid and sphenoid sinus is crucial for successful outcome. The objectives of this study were to delineate optic nerve as per its proximity relationship with the ethmoid and sphenoid sinuses according to Delano classification using CT scan and to determine the relative frequency of bony variations. Retrospective analysis of 150 optic nerves from 75 CT scans of paranasal sinuses or facial bones taken during June March 2014 was conducted. Images were reviewed in both coronal and axial planes. The results showed that the most frequent position of optic nerve (ON) according to Delano classification was type 1, i.e. a location close to posterior ethmoid sinus (PES) and sphenoid sinus (SS) without indentation of the wall, accounted for 114 nerves (76%). 41 nerves (9.3%) were found to indent the SS without contacting PES (type 2). The course of ON running through SS and close to both SS and PES (type 3 and 4) were observed in 8 (5.4%) and 14 nerves (9.3%) respectively. Optic nerve types which are prone to injury (type 2 and 3) were detected in 14.6% of patients. Other potential risk condition including protrusion of optic nerve, bony dehiscence and pneumatized anterior clinoid process (ACP) were detected in 3 (4.0%), 8 (10.7%) and 9 (12.0%) patients respectively. The concomitance of dehiscence and ACP pneumatization was seen in 3 patients (4%); the first case with optic nerve type 2 on the right side, the second case with optic nerve type 1 on the right side and the third one with optic nerves type 3 on both sides. As Lerdsin general hospitals plans to initiate endoscopic sinus surgery (ESS) in the future, evaluation of individual variations to configure the position of optic nerve and bony variation in the surgical area is essential for preoperative planning to prevent serious complication. Computed tomography of paranasal sinuses must be done not only to look for the pathology but also for the evaluation of bony variation in this complex anatomical region. Key words: Optic nerve type, posterior ethmoid sinus, sphenoid sinus, computed tomography Introduction Nowadays, endoscopic sinus surgery (ESS) is extremely used for the treatment of rhinonasal disease. This procedure will be performed in Lerdsin General hospital in the future. There may be complications from this surgery because of their complex anatomical region. Detailed knowledge of the anatomy of paranasal sinuses (PNS) and adjacent structures as well as their variations are crucial for preoperative planning in order to avoid unintentional complications. One of the serious complications is injury to optic nerve (ON). Thus a clear understanding of the relationship between the course of ON and sphenoid sinus (SS) and posterior ethmoid sinus (PES) is essential to prevent this complication. The relationship of them may be changed due to various degree of pneumatization of the mentioned PNS. Pneumatized SS can be too extensive to surround the anterior clinoid process (ACP),ON, foramen rotundum, vidian canal, pterygoid process or maxilloethmoid process. 1 Extensive pneumatization may predispose to ON injury especially the pneumatized PES behind the annulus tendinus communis where the ON is unprotected by surrounding extraoccular muscles, fatty tissue and periorbita. The objectives of this study are to delineate the precise relationship between the ON and PES and SS according to Delano classification using CT scan and to determine the relative frequency of variations in this relationship.

18 Material and Methods Retrospective review CT scan of PNS and facial bones of patients older than 16 years old from June 2013 to March 2014 were done.

All CT studies were performed using a 64 multislice CT equipment. (Somatom Definition AS Siemen) The technical parameter are shown in chart 1.

Filter Low/contrast B135 medium smooth Window 2500/800 All images were evaluated in both coronal and axial planes.

3 18 Material and Methods Retrospective review CT scan of PNS and facial bones of patients older than 16 years old from June 2013 to March 2014 were done. Seventy five patients (150 nerves) without prior trauma, serious rhinonasal infection or tumor were included in this study. There were fifty one males and twenty four females. All CT studies were performed using a 64 multislice CT equipment. (Somatom Definition AS Siemen) The technical parameter are shown in chart 1. Chart 1: Technical parameter of CT scan KV 120 mas 91 FOV 197 mm. Pitch 0.8 Slice thickness 2 mm. Filter Low/contrast B135 medium smooth Window 2500/800 All images were evaluated in both coronal and axial planes. Coronal CT scans were preferred for the detection of protrusion of the ON into SS, while the axial planes were better for detail of the complete course of the ON to PES and SS. Delano classified the relationship of the ON to SS and ES into four types. 2 Type 1: The nerve does not contact or impinge on either the SS or PES. (Fig. 1) Type 2: The nerve indents the SS without contacting the PES. (Fig. 2) Type 3: The nerve runs through the SS and it is surrounded by the pneumatized sinus for at least 50%. (Fig. 3) Type 4: The nerve courses close to both the SS and PES. (Fig. 4) Fig. 1 Optic nerve type 1 Fig. 2 Optic nerve type 2 Fig. 3 Optic nerve type 3

Vol. 39 No. 1 January-March 2014 19 Bulletin of the Department of Medical Services Protrusion of ON and bony dehiscence of the wall of ON was evaluated according to the criteria of Sirikci 3.

bony margins. (Fig. 5). Bony dehiscence was described as the absence of visible bone separating the sinus from the course of ON. (Fig. 6).

6 Dehiscence of right optic nerve type 4, left optic nerve type 1 Fig. 5 Fig.

4 Vol. 39 No. 1 January-March Bulletin of the Department of Medical Services Protrusion of ON and bony dehiscence of the wall of ON was evaluated according to the criteria of Sirikci 3. In coronal plane protrusion of the ON was determined as the presence of more than half the circumference of the concerned structures bulging into the sinus cavity with or without defects in their bony margins. (Fig. 5). Bony dehiscence was described as the absence of visible bone separating the sinus from the course of ON. (Fig. 6). Protrusion of ON and dehiscence of bony wall may coexist with pneumatized ACP which was also assessed in this study. (Fig. 7) Fig. 6 Dehiscence of right optic nerve type 4, left optic nerve type 1 Fig. 5 Fig. 4 Optic nerve type 4 Protrusion of right optic nerve with dehiscence and pneumatized bilateral anterior clinoid process Frequency of type of ON were calculated in percentage of overall incidence and according to gender and side. Prevalence of the protrusion of ON, dehiscence of bony wall and pnematization of ACP were shown according to gender. Comparison of previous studies were also reviewed. This study was approved by the Human Ethics Committee of Lerdsin General Hospital. Results A total one hundred and fifty nerves were evaluated in seventy five patients, fifty one males and twenty four females. The age range was between yrs. (mean age 40.9±2.2 yrs). Mean age of the male and female were 49.8±2.4 yrs. and 36.7±3.1 yrs. respectively. Overall incidence of the position of the ON according to Delano classification as shown in Table 1. Incidence of type of ON were also assessed according to gender as in Table 2 and according to the side of male and female patients as in Table 3.

5 20 Table 1 Number and percentage of the position of the optic nerve according to Delano classification Number of ON Percentage Type Type Type Type Total Protrusion of ON were seen in three patients (4.0%), two males and one female. They occurred in both sides of two patients who had ON type 2 and 3 respectively. (Table 4) Dehiscence of the bony wall was observed in eight patients (10.7%), six males and two females respectively. Among the six males, three dehiscence were found on the right, one on the left and two on bilateral sides. Two female patients had dehiscence Table 2 Number and percentage of type of optic nerve in male and female patients. Type Male Female Number of ON Percentage Number of ON Percentage Type Type Type Type Table 3 Number and percentage of type of optic nerve in male and female patients assessed according to the side. gender Number Right ON (%) Left ON (%) of patients Type 1 Type 2 Type 3 Type 4 Type 1 Type 2 Type 3 Type 4 male 51 39(76.5) 5(9.8) 3(5.9) 4(7.8) 40(78.4) 3(5.9) 2(3.9) 6(11.8) female 24 19(79.2) 2(8.3) 1(4.2) 2(8.3) 16(66.7) 4(16.7) 2(8.3) 2(8.3) Table 4 Number and percentage of protrusion of ON, dehiscence of the bony wall and pneumatized ACP in total seventy five patients. Type Right side Left side Bilateral sides total No. % No. % No. % No. % Protrusion ON Dehiscence bony wall Pneumatized ACP

6 Vol. 39 No. 1 January-March Bulletin of the Department of Medical Services on left and both sides respectively. (Table 5) Four dehiscence were seen in ON type 2, another three were seen on type 3, another two were seen on type 4 and the other one was seen ON type 1. Pneumatized ACP were seen in nine patients (12.0%), four males and five females. Two males showed pneumatized ACP at the right side (3.9%) and the others at the left side. For five females, the first three showed on the left side (12.5%), another two ones on the right side and both sides (4.2%). The concomitant presence of the dehiscence and ACP pneumatization was found in three patients (4.0%), two on the right side (2.7%) and one on both sides (1.3%). They were observed in ON Type 1, 2 and 3. The concomitant presence of the ON protrusion and ACP pneumatization was found in one patient (2 %) at both sides. It was observed in ON Type 3. DISCUSSION Damage of the optic nerve is one of the serious complication of ESS. The optic type 2 and 3 categories are regarded the most critical for the potential risk of injury as well as the protrusion of the optic canal into sphenoid and /or ethmoid sinuses. 4 In our study we found 14.6% of ON in type 2 and 3. (Table 6) However ON type 4 is more frequent than Table 5 Number and percentage of protrusion of ON, dehiscence of the bony wall and pneumatized ACP according to gender. Male (51) Female (24) Type Right Left Both Right Left Both No. % No. % No. % No. % No. % No. % Protrusion Of ON Dehiscence Of bony wall Pneumatized ACP Table 6 Comparison between studies of incidence of ON type from and our study. Study Number of ON Optic nerve Type 1 Type 2 Type 3 Type 4 Delano (76%) 44(15%) 19(6%) 9(3%) Heskova (55.9%) 10(14.7%) 16(23.5%) 4(5.9%) Our study (76%) 14(9.3%) 8(5.3%) 14(9.3%) As compared to other studies, percentage of ON type 1 found in our study is the same to Delano study.

7 22 Table 7 Percentage of protrusion of ON, dehiscence of bony wall and pneumatized anterior clinoid process from many studies. 4 Study Protrusion of ON (%) Dehiscence of bony wall (%) Pneumatized ACP (%) Delano 2 N/A 24 N/A Sirika Heskova Sapci 5 N/A Bademci N/A Unal Hewaidi Our study As shown in Table 7, there is the least frequency of protrusion of ON in this present study. others. Review of results of incidence of protrusion, dehiscence of bony wall and pneumatized ACP as shown in Table 7 CONCLUSION This study shows 14.6% of optic nerve type 2-3, the type which are prone to be injured during endoscopic sinus surgery. The percentage of protrusion of ON, dehiscence of bony wall and pneumatized anterior clinoid process, which are the predisposing factors to ON injury during surgical intervention are 4.0,10.7 and 12.0% respectively. (table 7) There is also concomitant between dehiscence of optic nerve and pneumatized ACP in 4.0%. These findings strongly insist that CT scan is still an ideal preoperative investigation to detect the position of optic nerve and bony variation in order to protect the complication and increase efficacy of endoscopic sinus surgery. References 1. Sirikci A, Bayazit YA, Bayram M, Mumbuc S, Gungor K, Kanlikama M. Variations of sphenoid and related structures. Eur Radiol 2000;10: DeLano MC, Fun FY, Zinreich SJ. Relationship of the optic nerve to the posterior paranasal sinuses: a CT anatomic study. AJNR Am J Neuroradiol 1996;17: Unal B, Bademci G, Bilgili YK, Batay F, Avci E. Risky anatomic variations of sphenoid sinus for surgery. Surg Radiol Anat 2006;28: Heskova G, Mellova Y, Holomanova A, Vybohova D, Kunertova L, Marcekova M, et al. Assessment of the relation of the optic nerve to the posterior ethmoid and sphenoid sinuses by computed tomography. Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub 2009; 153: Sapci T, Derin E, Almac S, Cumali R, Saydam B, Karavus M. The relationship between the sphenoid and posterior ethmoid sinuses and the optic nerves in Turkish patients. Rhinology 2004;42: Bademci G, Unal B. Surgical importance of neurovascular relationships of paranasal sinus region. Turkish Neurosurgery 2005;2: Hewaidi GH, Omami GM. Anatomic variation of sphenoid sinus and related structures in Libyan population: CT scan study. Libyan J Med 2005;3:

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