Skull Base Danger Zones in FESS

Skull Base Danger Zones in FESS Poster No.: C-2278 Congress: ECR 2014 Type: Educational Exhibit Authors: L. Renza Lozada, R. Carreño Gonzalez, G. Quintana Sanchez, 1 2 1 1 1 2 R. E. Figueroa ; Malaga/ES, Augusta, GE/US Keywords: Hyperplasia / Hypertrophy, Education and training, Structured reporting, Normal variants, Endoscopy, CT-High Resolution, Head and neck, Ear / Nose / Throat DOI: 10.1594/ecr2014/C-2278 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 37

Learning objectives To review the CT protocol and patient preparation pre-fess CT examination. To describe danger zones in skull base, emphasizing anatomic variants, which may predispose to major surgical complications. Background Functional endoscopic sinus surgery (FESS) has become the main technique for surgical management of refractory rhinosinusitis, improving sinus mucociliary clearance by removing diseased mucosa and bone that obstruct the sinus outflow tracts. One of the prerequisites for successful FESS is knowledge of the complex anatomy of the paranasal sinuses. The anatomy of the paranasal sinuses is variable and it is important to appreciate the clinical and surgical significance of these variations. Preoperative evaluation requires a proper CT protocol and a detailed report, with emphasis upon anatomic variants, which may predispose the patient to surgical complications or increase the surgical risks in the skull base. Patient preparation: The imaging goal should be to depict the underlying anatomic problem that is causing recurrent sinus disease. To achieve this goal, pre-fess CT examination should be performed after episodes of acute sinusitis have been treated. Decongestant intranasal drops should be administered prior to the examination in order to eliminate all reversible disease prior to their imaging studies. Clear anatomic landmarks and/or disease that persist in spite of treatment will dictate the site and extent of surgical intervention needed. CT Protocol: Unenhanced CT is performed using a multi-detector CT system covering the region from the top of the frontal sinuses to the hard palate and from the tip of the nose to the region just posterior to the mastoid air cells. The images are viewed in the coronal, sagittal, and axial planes in soft tissue and bone windows. (Fig 1). Main zones to evaluate for planning of FESS Page 2 of 37

1. The Ostiomeatal Complex (OMC): The OMC comprises the maxillary sinus ostium, the ethmoidal infundibulum, the bulla ethmoidalis, the uncinate process, the middle meatus and the hiatus semilunaris. It refers to the common drainage of the anterior sinuses. Diseased mucosa in the ethmoidal infundibulum impairs ventilation and drainage of the frontal, anterior ethmoid and maxillary sinuses. These structures are well visualized on coronal CT. (Fig 2). Fig. 2: Anatomy of the OMC References: Adapted from ELSEVIER.INC.-NETTERIMAGES.COM The Ethmoidal Infundibulum: The ethmoidal infundibulum is formed by these boundaries: anteriorly, the uncinate process; posteriorly, the anterior wall of the bulla ethmoidalis and laterally, the lamina papyracea. Medially it opens into the middle meatus through the hiatus semilunaris. The maxillary sinus ostium opens into the floor of the ethmoidal infundibulum. (Fig 3). Page 3 of 37

The Uncinate Process: The uncinate process is a thin, crescent-shaped bone. It is attached anteriorly to the lacrimal bone; inferiorly to the inferior turbinate; posteriorly it has a free margin; and superiorly the attachment is variable it may be attached to the anterior skull base, the lamina papyracea, or the middle turbinate. If the uncinate process inserts into the lamina papyracea, the ethmoidal infundibulum is closed superiorly (recessus terminals). In this situation, the frontal recess opens into the middle meatus medial to the ethmoidal infundibulum. If the uncinate process extends to the skull base or attaches to the middle turbinate, the frontal sinus opens into the ethmoid infundibulum. (Fig 3). Fig. 3: Coronal NECT shows the structures of the OMC and the Frontal Recess (F) References: Carlos Haya - Malaga/ES The Bulla Ethmoidalis Page 4 of 37

The bulla ethmoidalis is a prominent anterior ethmoid air cell and therefore a reliable anatomical landmark. The degree of pneumatization may vary since torus ethmoidalis to a giant bulla. (Fig 3-4). 2. The Frontal Recess: The frontal recess is the drainage pathway of the frontal sinus. The boundaries are: anteriorly, agger nasi cell; laterally, lamina papyracea and medially, middle turbinate. The frontal recess opens into the middle meatus or into the ethmoidal infundibulum. (Fig 3). 3. The Agger Nasi Cells: The agger nasi cell is the most anterior ethmoidal cell. On coronal CT, they appear inferior to frontal recess and lateral to the middle turbinate. Because of this intimate relationship, these cells form excellent surgical landmarks. (Fig 5-6). Fig. 6: Coronal CT shows Right Agger Nasi Cell (Arrow) References: Department of Radiology, Georgia Regents University, Augusta, GE/US Page 5 of 37

4. The Middle Turbinate and the basal lamella: The middle turbinate has variants that should be identified because they may be the cause of sinuses pathology and can difficult the endoscopic procedure. These are: concha bullosa, inter- lamellar cell of Grunwald and paradoxical middle turbinate. The basal lamella is the attachment of the middle turbinate to the lamina papyracea. The basal lamella divides the ethmoid cells into the anterior and posterior groups; the anterior group drains into the middle meatus while the posterior group drains into the superior meatus. 5. Posterior sinus group: Posterior Ethmoidal Sinuses and Sphenoid Sinuses: The posterior ethmoid sinuses are ethmoid air cells posterior to the basal lamella, which drain into the superior meatus. It is important to report the vertical distance from the superior margin of the maxillary sinus to the roof of the posterior ethmoid cells, to avoid inadvertent intracranial penetration during the procedure. The sphenoid sinus has a very variable pneumatization. Vital structures such as the carotid arteries, optic nerves, maxillary branches of the trigeminal nerves within the foramen rotundum, the Vidian canals and the cavernous sinuses are closely related to the sphenoid sinus. 6. The Onodi Cells: The onodi cells refers to a posterior ethmoid cell that extends lateral and superior to the sphenoid sinus and abuts the optic nerve. It is important to identify its due to there are increased chances of injury to the optic nerves (Fig 7). Page 6 of 37

Fig. 7: NECT A) Axial mucosal window B) Coronal soft tissue window C) Sagittal bone window. Demonstrated unilateral left-sided posterior Ethmoid Onodi Cell on top of the left sphenoid sinus adjacent to the left optic canal. References: Department of Radiology, Georgia Regents University, Augusta, GE/US 7. Haller Cells: Haller cells are created by ethmoidal pneumatization of the lamina papyracea medial to the natural ostium if the maxillary sinus. Large Haller cells could potentially impair drainage of the maxillary sinus. After a thorough evaluation of the main zones radiologist must pay attention to skull base danger zones that may predispose to iatrogenic damages. Images for this section: Page 7 of 37

Fig. 1 Page 8 of 37

Fig. 2: Anatomy of the OMC Page 9 of 37

Fig. 3: Coronal NECT shows the structures of the OMC and the Frontal Recess (F) Page 10 of 37

Fig. 4: Coronal NECT shows bilateral Bulla Ethmiodalis (B) Page 11 of 37

Fig. 5: Coronal CT shows left side Agger Nasi Cells (Arrows). Page 12 of 37

Fig. 6: Coronal CT shows Right Agger Nasi Cell (Arrow) Page 13 of 37

Findings and procedure details Surgical danger zones in the skull base: Frontal Recess and Anterior Ethmoidal Artery: The anterior ethmoidal artery arises from the ophthalmic artery in the orbit and pierces the lamina papyracea within the posterior wall of the frontal recess to penetrate the lateral lamella of the cribriform plate. Like anatomic variant the anterior ethmoidal artery may project within the frontal recess covered by a thin bony canal or dehiscent of bone cover, outlined only by mucosa. Best plane of evaluation: Coronal. Risk: Arterial hemorrhage, acute orbital bleed. Procedure: Exploration of the frontal recess. Fig 8, 9. Page 15 of 37

Fig. 9: Coronal CT shows dehiscence of the anterior ethmoidal arteries at the posterior margin of the corresponding left and right frontal recesses (Arrows). There is partial pneumatization of the vertical attachment of both middle turbinates and bilateral paradoxical middle turbinates. References: Department of Radiology, Georgia Regents University, Augusta, GE/US The Anterior Ethmoid sinus and Olfactory Fossa: The roof of the anterior ethmoid sinus is made up of the fovea ethmoidalis laterally and the lateral lamella of the cribriform bone medially. The lateral lamella defines the lateral margin of the olfactory fossa. Keros described three types of anterior skull-base configurations based on the length of the lateral lamella of the cribriform plate (Type I: less than 3mm, Type II: 3-7 mm, Type III: more than 7 mm). Deeper olfactory fossa has more damage risk during FESS. Best plane of evaluation: Coronal. Risk: Intracranial penetration and CSF leaks Procedure: Internal ethmoidectomy. Page 16 of 37

Fig 10, 11, 12 and 13. Fig. 13: Coronal NECT shows Olfactory Fossa Type III References: Carlos Haya - Malaga/ES Haller cells: Surgical resection of Haller cells requires a three-dimensional awareness of its relationship with the lamina papyracea and the orbit. The presence and specific location must be reported due to this cells are hidden from view by the uncinate process. Best plane of evaluation: Coronal. Risk: Orbital penetration. Procedure: Resection of Haller cells. The lamina papyracea: Page 17 of 37

The lamina papyracea has areas of focal dehiscence seen in 0.5% to 10% of the population. There is a reduction in the volume of orbital fat between the lamina papyracea and the medial rectus muscle in the posterior orbit. Therefore, there are increased chances of injury to the medial rectus muscle in cases of iatrogenic posterior orbital penetration secondary to posterior lamina papyracea defects. Best plane of evaluation: Axial and coronal. Risk: Orbital injury. Fig 14. Fig. 14: Axial CT soft tissue (A) and bone (B) windows show dehiscence of the right lamina Papyracea References: Carlos Haya - Malaga/ES Uncinate Process and Nasolacrimal Duct: Page 18 of 37

Dehiscent nasolacrimal duct or thin bone covering this duct and its proximity to the uncinate process should be reported to avoid uncinate incision or aggressive uncinectomy. Best plane of evaluation: Coronal. Risk: Nasolacrimal fistula or secondary nasolacrimal adhesions. Procedure: Uncinectomy. Fig 15. Onodi Cells and Optic Nerves: Onodi cells tend to expose the optic nerves submucosally along their superior lateral wall. Best plane of evaluation: Axial and coronal. Risk: Optic nerve injury. Procedure: Transethmoidal sphenoidotomy. Fig 16. Page 19 of 37

Fig. 16: A-B and C) Coronal and Axial NECT mucosal window show a right Onodi Cell at the superior lateral corner of the right sphenoid sinus, with dehiscence of the right optic nerve (red arrow). Also there is partial dehiscence of the left optic nerve in the left sphenoid sinus (green arrow). References: Department of Radiology, Georgia Regents University, Augusta, GE/US Sphenoid Sinus, Optic Nerves and Internal Carotid Arteries: Hyperpneumatization of the sphenoid sinus may produce areas of bone dehiscence, which could expose the optic nerve, the maxillary nerve (V2), or the internal carotid artery in submucosal position, leaving these structures vulnerable to iatrogenic damages. Best plane of evaluation: Axial and sagittal. Risk: Optic nerve, maxillary nerve or internal carotid artery injury. Fig 17, 18, 19 and 20. Page 20 of 37

Fig. 18: A) Axial CECT. Right Internal Carotid Artery dehiscent within hyperpneumatized sphnenoid sinus. B) A) Coronal CECT. Left Internal Carotid Artery dehiscent. C-D) Sagittal CECT Bone- Soft tissue window. Left Internal Carotid Artery dehiscent within hyperpneumatized sphnenoid sinus. References: Department of Radiology, Georgia Regents University, Augusta, GE/US Page 21 of 37

Fig. 19: A) Axial NECT bone window shows right optic nerve dehiscent and left optic nerve outlined by mucosa within the sphenoid sinus. B) Sagittal NECT bone window shows left optic nerve dehiscent C-D) Coronal NECT bone- soft tissue window show bilateral optic nerve dehiscent above de right and left sphenoid sinus. References: Department of Radiology, Georgia Regents University, Augusta, GE/US Images for this section: Page 22 of 37

Fig. 8: Picture shows the Anterior Ethmoidal Artery within the Frontal Recess Page 23 of 37

Fig. 10 Page 25 of 37

Fig. 11 Page 26 of 37

Fig. 12 Page 27 of 37

Fig. 13: Coronal NECT shows Olfactory Fossa Type III Page 28 of 37

Fig. 14: Axial CT soft tissue (A) and bone (B) windows show dehiscence of the right lamina Papyracea Page 29 of 37

Fig. 15 Page 30 of 37

Fig. 17: A-B) Coronal NECT bone window. Bilateral Internal Carotid Artery dehiscent within hyperpneumatized sphnenoid sinus. C) Coronal NECT soft tissue window D) Axial NECT bone window. Page 32 of 37

Fig. 20: Coronal NECT shows is hyperpneumatization of the sphenoidal sinuses with the foramen rotundum bulging into the sinuses (arrows). There is dehiscent right side maxillary nerve. Page 35 of 37

Conclusion 1. Pre-FESS CT should be realized with and adequate patient preparation and an optimal CT protocol. 2. The critical anatomical information provided by pre-fess CT has an impact on the surgical approach adopted by the surgeon and subsequently on the postoperative benefit to the patient. 3. FESS surgical technique requires high quality CT and expert report to minimize risks of major complications. Personal information References 1. John H. Krouse, Dewey A. Christmas, Powered Endoscopic Sinus Surgery. Williams & Wilkins; 1st edition (June 1997). 2. V. F. H. CHONG, Y. F. FAN, D. LAU* and D. S. SETHI.Pictorial Review Functional Endoscopic Sinus Surgery (FESS): What Radiologists Need to Know. Clinical Radiology(1998) 53, 650-658. 3. Beale TJ, Madani G, Morley SJ. Imaging of the paranasal sinuses and nasal cavity: normal anatomy and clinically relevant anatomical variants. Semin Ultrasound CT MR. 2009 Feb;30(1):2-16. 3. BJ. Bailey and JT. Johnson. Head and Neck Surgery - Otolaryngology. Lippincott Williams & Wilkins; 4th edition:2006. 3.Vaid S, Vaid N, Rawat S, Ahuja AT. An imaging checklist for pre-fess CT: framing a surgically relevant report. Clin.Radiol. 2011 May;66(5):459-70. Epub 2011 Feb 1. Page 36 of 37

4.Damm M, Quante G, Jungehuelsing M, Stennert E. Impact of functional endoscopic sinus surgery on symptoms and quality of life in chronic rhinosinusitis. Laryngoscope, Feb 2002; 112(2):310-5 5.Landsberg R, Friedman M. A computer-assisted anatomical study of the nasofrontal region. Laryngoscope, 2001; 111:2125-213 Maroldi R, Nicolai P. Imaging in Treatment Planning for Sinonasal Diseases. Berlin: Springer-Verlag: 2005. Page 37 of 37