Computed tomography road map of the paranasal sinuses for treatment planning

Transcription

1 Computed tomography road map of the paranasal sinuses for treatment planning Poster No.: C-2607 Congress: ECR 2013 Type: Educational Exhibit Authors: N. Schembri, A. S. Gatt, D. Ellul, J. Brunton; Dundee/UK Keywords: Ear / Nose / Throat, CT, Normal variants, Diagnostic procedure, Structured reporting, Education and training DOI: /ecr2013/C-2607 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. Page 1 of 21

2 Learning objectives Computed tomography (CT) has superseded plain radiography in delineating bony anatomy. The role of CT in preoperative planning prior to functional endoscopic sinus surgery (FESS) has been well established. Complex anatomy and congenital anatomical variants of the paranasal sinuses impose an interpretation challenge to radiologists and intraoperative technical challenges to the surgeon. This poster aims to present a systematic approach utilising reformat CT reconstructions to discuss i. anatomy ii. clinically significant anatomical variants iii. terminology used in FESS with a view to encourage more accurate preoperative interpretation of normal and aberrant anatomy that plays a key role in the diagnosis and safe surgical management of these patients. Background What is FESS? Devised by Messerklinger & Stammberger in the 1980s & 1990s, FESS is a minimally invasive surgical procedure that offers access to nasal and sinus cavities facilitating the use of different instruments to identify & restore the proper drainage & ventilation relationships between the nose and sinus cavities. It relies on preservation and restoration of normal flow of mucosal secretions. Advantage Disadvantage Minimally invasive technique Proximity of the sinuses to the eyes, optic nerves, brain and internal carotid arteries Access to nasal cavity via nostrils Page 2 of 21

3 Indications for FESS Chronic sinusitis refractory to medical treatment is the main clinical indication, which includes: recurrent acute sinusitis nasal polyposis antrochoanal polyps sinus mucoceles Other uses include excision of selected tumours, CSF leak closure, orbital decompression (e.g. in Graves' ophthalmoplegia, optic nerve decompression), dacryocystorhinostomy, choanal atresia repair. What does the surgeon want to know? The surgeon relies on expert radiologist interpretation of CT of the paranasal sinuses such that imaging acts as a road-map of anatomy, highlighting normal variants, in particular hazardous ones, in order to prevent catastrophic complications. The radiologist's goal is to report on five key points: the extent of sinus opacification/disease opacification of sinus drainage pathways anatomical variants critical variants condition of surrounding soft tissues of the neck, brain and orbits Imaging findings OR Procedure details The following is a stepwise approach, starting at the external nares, to viewing the nasal cavity with cross-sectional imaging using 3D multiplanar reformats (MPR) of the paranasal sinuses acquired using a 64-slice multidetector CT scanner. st STEP 1 - NASAL SEPTUM - 1 structure encountered Normal Variant - Septal deviation may cause nasal cavity obstruction limiting endoscopic visualisation and access. Page 3 of 21

4 Implication - Patients may need pre-operative counselling for the need of septoplasty during FESS procedure. STEP 2 - FRONTAL/KUHN'S AIR CELLS The frontal air cells constitute the most complex of all the paranasal sinus drainage pathways. The frontal sinus drainage pathway (FSDP) has 2 compartments: superior and inferior. The latter is a narrow passageway formed by either the ethmoid infundibulum or the middle meatus depending on variable anatomical attachment of the uncinate process to the lamina papyracea or skull base. The frontal air cells constitute the superior compartment. They are divided into types I - IV according to their pattern of pneumatisation as per Bent et al (Figure 1). Type I - single cell above the agger nasi and inferior to frontal sinus floor Type II - this is a stack of air cells above the agger nasi, extending to inferior frontal sinus; it is the multiplicity of cells that distinguishes it from the Type I Type III - usually large, above agger nasi extending into frontal sinus Type IV - infrequent; isolated cells located within the frontal sinus Implication - They interfere with frontal recess drainage pathway if large. STEP 3 - BASAL LAMELLA of the MIDDLE TURBINATE This divides the anterior from the posterior ethmoid air cells and serves as a landmark for access to the posterior ethmoidal air cells. Normal Variants of the Middle Turbinate Concha bullosa (Figure 2) - common (15-45%) usually of little clinical significance. Paradoxical middle turbinate (Figure 3) - paradoxical lateral convexity may lead to obstruction of middle meatus. Implication - This has a critical attachment to the base of skull at the cribriform plate. It must also be preserved since it serves as a landmark for revision surgery. STEP 4 - UNCINATE PROCESS Page 4 of 21

5 The uncinate process (Figure 4) is part of the ethmoid bone and demonstrates variable anatomy. It serves as a landmark for the osteomeatal complex (OMC), lying just posterior to it. The osteomeatal complex is the confluence of the ethmoid bulla, maxiallary ostium laterally, uncinate process inferolaterally and the middle turbinate medially (Figure 5). The role of the uncinate process is that of facilitating drainage of the frontal recess. The uncinate process has a complex attachment: Anteriorly - to nasolacrimal apparatus Inferiorly - to inferior turbinate Posteriorly - it has a free margin Superiorly - its attachment is variable Variant insertion of its superior attachment is classified according to the criteria developed by Landsberg and Freidman (Figure 6). With usual anatomical configuration, removal of the uncinate process opens into the ethmoid infundibulum. Normal Variants - Lateral deviation of the uncinate process may cause narrowing of the hiatus semilunaris and infundibulum. Implication - There is a high risk of entry into the orbit if too lateral leading to surgical emphysema & risk of subsequent loss of vision. STEP 5 - ETHMOID AIR CELLS The ethmoid bulla is a reliable surgical landmark - it is the largest and most constant anterior ethmoid air cell. It is bound superiorly by the floor of the anterior cranial fossa and laterally by the lamina papyracea (Figure 7). Implication - (a) laterally - risk of penetration especially of a dehiscent lamina papyracea with risk of damaging orbital contents, (b) superiorly - penetration into floor of anterior cranial fossa. Normal Variants AGGER NASI CELL - consistent finding; it is the most anterior ethmoid air cell lying just anterior to attachment of middle turbinate and frontal recess (Figure 8). Implication - if large may cause medial displacement of the middle turbinate causing narrowing of the frontal recess. Page 5 of 21

6 HALLER CELL - infraorbital cell extending to floor of orbit (Figure 9). Implication - may cause narrowing of maxillary sinus ostium/ethmoid infundibulum. Posterior ethmoid air cells may have a variable relationship with the sphenoid sinus and may extend superiorly and laterally to sphenoid sinus. Implication - It is important to describe their relationship to the sphenoid sinus for accurate route mapping. ONODI CELL - posterior ethmoid air cell (5%) extending to the sphenoid sinus lying medial to the optic nerve (Figure 10). It displaces the sphenoid sinus medially and inferiorly. Implication - Potential damage to (a) the optic nerve (in 5%), and less commonly, (b) the internal carotid artery when attempts are made at endoscopy to enter the sphenoid sinus via what is thought to be the most posterior ethmoid cell rather than an Onodi cell. STEP 6 - SPHENOID SINUS Hazardous regional structures include: Internal carotid artery - most posterolateral structure; may also be dehiscent (Figure 11). Optic nerve- anteroposterior indentation in the roof - may be seen dehiscent in 4% (Figure 12). STEP 7 - CRIBRIFORM PLATE The keros classification describes the position of the cribriform plate relative to the fovea ethmoidalis (Figure 13): Keros I - 1-3mm Keros II - 3-7mm Keros III mm Implication - There is a higher risk of intracranial penetration with increasing depth and risk of damaging the anterior and/or posterior ethmoidal artery (Figure 14) as they cross the ethmoid sinus to enter the anterior cranial fossa via the cribriform plate back into the nasal cavity especially if dehiscent. Implications are worse in the case of a dehiscent anterior artery as compared with the posterior. Page 6 of 21

7 Images for this section: Fig. 1: Coronal section CT showing a type III frontal air cell (arrow) - this is usually large, situated above the agger nasi, extending into the frontal sinus. As depicted by this case, these cells can cause obstruction to frontal recess drainage. Page 7 of 21

8 Fig. 3: Coronal CT reformat of the paranasal sinuses at the level of the middle turbinate depicting a paradoxical left middle turbinate (dashed arrow). This particular case also demonstrates left uncinectomy and left maxillary antral polypoid sinus disease. A paradoxical middle turbinate can cause obstruction to the nasal cavity and middle meatus. Page 8 of 21

9 Fig. 4: Sagittal CT section of the nasal cavity demonstrating the paranasal drainage pathway. Page 9 of 21

10 Fig. 5: Coronal CT section demonstrating the uncinate process (UP) and maxillary antral ostium (MO), which form part of the osteomeatal complex (OMC). Page 10 of 21

11 Fig. 13: This coronal CT image depicts a Keros type II - 6mm descent of the cribriform plate (CP) from the fovea ethmoidalis (FE). There is a higher risk of intracranial penetration with increasing depth of the cribriform plate. Page 11 of 21

12 Fig. 12: Dehiscent right optic nerve (arrow) as demonstrated by coronal CT section. Page 12 of 21

13 Fig. 11: Dehiscent left internal carotid artery (arrow) as demonstrated on axial CT section of the middle cranial fossa. Page 13 of 21

14 Fig. 10: CT Sagittal and coronal CT section in the same patient showing ethmoidal air cell normal variants - Onodi air cell (arrow). Fig. 9: CT coronal section showing ethmoidal air cell normal variants - Haller cell. Page 14 of 21

15 Fig. 8: CT Sagittal section showing ethmoidal air cell normal variants - agger nasi (arrow). Page 15 of 21

16 Fig. 7: Sagittal CT demonstrating an ethmoid bulla (arrow) complicated by sinusitis and an effusion. The ethmoid bulla is bound superiorly by the floor of the anterior cranial fossa and laterally by the lamina papyracea. Page 16 of 21

17 Fig. 14: Axial CT section demonstrating a dehiscent left posterior ethmoidal artery (arrow). A low lying cribriform plate puts both the anterior and posterior ethmoidal arteries at risk as they cross the ethmoid sinus to enter the anterior cranial fossa via the cribriform plate back into the nasal cavity especially if dehiscent. Page 17 of 21

18 Fig. 6: Landsberg aand Friedman classification of superior uncinate process insertion. a) Type 1 - insertion into lamina papyracea, b) Type 2 - insertion into the posterior wall of the agger nasi cell, c) insertion into the lamina papyracea and junction of the middle turbinate with the cribriform plate, e) Type 5 - insertion into the skull base, f) Type 6 insertion into the middle turbinate. Page 18 of 21

19 Conclusion Major complications of FESS can be catastrophic. Detailed knowledge of normal and anomalous anatomy is essential for safe, successful sinus surgery. CT is the gold standard imaging modality in the preoperative diagnosis for FESS. Radiologists' familiarity with FESS technique & adopting a systematic approach is crucial to reviewing CT imaging for normal and variant anatomy of the paranasal sinuses. References Bent JP, Cuilty-Siller C, Kuhn FA. The frontal cell as a cause of frontal sinus obstruction. Am J Rhinol 1994; 8: Gonçalves FG, Jovem CL, Moura LO. Computed tomography of intra- and extramural ethmoid cells: iconographic essay. Radiol Bras Set/Out; 44(5): Amit ND Dwivedi, Kapil K Singha. CT of the Paranasal Sinuses: Normal Anatmoy, Variants and Pathology. Journal of Optoelectronics and Biomedical Materials 2010; 2(4): Cashman EC, MacMahon PJ, Smyth D. Computed tomography scans of paranasal sinuses before functional endoscopic sinus surgery. World J Radiol August 28; 3(8): Gotwald TF, Zinreich SJ, Corl F, Fishman EK. Three-Dimensional Volumetric Display of the Nasal Ostiomeatal Channels and Paranasal Sinuses. AJR January 2001; 176 (1): Daniels D et al. The Frontal Sinus Drainage Pathway and Related Structures. AJNR 2003; 24: Miranda, Christiana Maia Nobre Rocha de et al. Anatomical variations of paranasal sinuses at multislice computed tomography: what to look for.radiol Bras [online]. 2011; 44 (4): Turgut S, Ercan I, Sayin I, et al. The relationship between frontal sinusitis and localization of the frontal sinus outflow tract: a computer-assisted anatomical and clinical study. Arch Otolaryngol Head Neck Surg. 2005; 131: Page 19 of 21

20 Personal Information N. Schembri (corresponding author) Specialist Registrar Clinical Imaging Department Ninewells Hospital and Medical School Dundee DD1 9SY U.K. Tel: Bleep A.S. Gatt Specialist Registrar Clinical Imaging Department Ninewells Hospital and Medical School Dundee DD1 9SY U.K. D. Ellul Specialist Registrar Department of Otolaryngology Ninewells Hospital and Medical School Dundee DD1 9SY Page 20 of 21

21 U.K. J.N. Brunton Consultant Radiologist Clinical Imaging Department Ninewells Hospital and Medical School Dundee DD1 9SY U.K. Page 21 of 21