Surgical, . Radiolog¢ Anatomy

Surg Radioi Anat (1993) 15 : 181-185

Journal of Clinical Anatomy

© Springer-Verlag 1993

Radiological anatomy

Densitometric analysis of the paranasal sinuses

GM Sprinzl 1, WF Thumfart 2 and J Koebke 1 I Department of Anatomy tl and 2 Department of Otolaryngology, Head and Neck Surgery, University of Cologne, D-5000 K61n 41, Germany

Summary. The knowledge of weak points in the osseous structure of the skull is of great i m p o r t a n c e for endonasal operations. For this reason the anatomy of the skull is accurately described in serial sections. Serial sections of 1.5 mm thickness are evaluated by a computerized i m a g e a n a l y z i n g system, which allows qualitative as well as quantitative statements on the structure of the p a r a n a s a l sinuses and their neighbourhood. The bone density in the frontobasal area of the skull as well as of the ethmoid cells is presented separately. The anatomy of the sphenoid sinus is described by densitometric and gross techniques. Analyse densitom6trique des sinus paranasaux R 6 s u m 6 . La c o n n a i s s a n c e des points forts dans la structure osseuse du cr~me est d'une grande importance pour les interventions endona-

Correspondence to : GM Sprinzl

sales. Pour cette raison, l'anatomie du crfine est ddcrite avec prdcision sur des coupes s6rides. Les coupes s6ri6es de 1,5 mm d'6paisseur sont 6tudi6es par un systSme d'analyse d'images comput6ris6es, qui permet l'6tude h ta fois qualitative et quantitative de la structure des sinus paranasaux et de leur environnement. La densit~ osseuse dans l'aire fronto-basale du crfine et celle des cellules 6thmoidales sont prdsentdes sdpar6ment. L ' a n a t o m i e du sinus sphdno/dal est ddcrite ~t parfir de la tomodensitom6trie et de cette technique macroscopique.

Key words : Paranasal sinuses - Anatomy - - Densitometry - - Bone density measurement

Since the progress made in modern endoscopic sinus surgery by Mess e r k l i n g e r , S t a m m b e r g e r and Wigand, endoscopic operations have become a standard element of clinical practice [2-4, 8-10, 13-15]. In conducting endoscopic operations it is essential to have exact knowledge of the topographic ana-

tomy of the paranasal sinuses and their s u r r o u n d i n g structures. In addition to the difficulties presented by the complex anatomy involved, the operations are further complicated by the limited field of vision which endoscopic optics provides [1, 6]. For these reasons numerous authors have tried in recent years to describe and elucidate the complex morphology of the nasal cavity, due to the involvement of air spaces, blood-vessels and nerves as well as the close proximity to the frontal skull base [5, 7, 11]. This region requires a highly developed ability to think three-dimensionally. The aim of our research was not only to describe the anatomy of the nasal cavity exactly and to measure the size of the paranasal sinuses, but also to be able to make some qualitative statements about the structures of the paranasal sinuses and the frontal skull base. In our analysis we paid particular attention to the variations in bone density in the area of the frontal skull base and sphenoid sinus. We also observed the topographic relationship between the nasolacrimal canal and the maxillary sinus.

182

GM Sprinzl et al : Densitometric analysis of the paranasal sinuses Fig. 2a-h Densitometric image-sequence (diameter = 1.5 ram) of frontal skull base and maxillary sinus (t agger nasi cell, 2 clivus, 3 cribriform plate, 4 ethmoid cells, 5 frontal recess, 6 frontal sinus, 7 inferior concha, 8 maxillary sinus, 9 nasolacrimal canal, 10 Onodi's cell, ll optic nerve canal, 12 orbit, 13 pterygoid canal, t4 pterygopalatine tbssa, 15 sphenoid sinus)

Succession d'images densitom6triques (de 1,5 mm d'6paisseur) de la fosse crfinienne ant6rieure et du sinus maxillaire. 1 cellule de l'agger nasi ; 2 clivus ; 3 lame cribl~e ; 4 cellules 6thmoi'dales ; 5 r6cessus frontal ; 6 sinus frontal ; 7 cornet inf6rieur ; 8 sinus maxillaire ; 9 canal lacrymo-nasal ; 10 ceIlule d'Onodi ; 11 canal optique ; 12 orbite ; 13 canaI ptdrygo[dien ; 14 fosse pt~rygopalatine ; 15 sinus sph6noidal

Fig. 1 Drawing represent the median sectionplane

ReprEsentation du plan de section mddian

It was Leonardo da Vinci who was the first to represent cross-sections [15]. With the help of plastihated skull slices and their mdiotogic and d e n s i t o m e t r i c a n a l y s i s , extended insight to morphological structures is provided.

Material and m e t h o d s

After fixation in formalin, dehydration in ethanol and freeze substitution in acetone, a cadaver head was embedded in epoxy resin ([E6/EI2] method, G. v. Hagens, Heidelberg, Germany). The orientation of the specimen in the resin allowed sagittal sections. After curing of the specimen, the plastic block was sectio~ ned with a diamond-coated wiresaw (Well, Diamond-coated wiresaw, Mannheim, Germany) into 1.5 m m thick, parallel slices. The loss in section was less than 0.3 m m (Fig. 1). T h e slices were x - r a y e d and scanned with a computerized image analyzing system. Every slice was d i g i t i z e d with a C C D - c a m e r a , connected to a personal computer system. The data o b t a i n e d were c l e a n e d with special filters and balanced to references of an aluminium wedge. Every level of the alu-

m i n i u m w e d g e c o r r e s p o n d s to a certain colour. A low level (0.5 mm a l u m i n i u m ) c o r r e s p o n d s to the colour blue, a high level (2.0 m m aluminium) to the colour red. With this method not only qualitative, but also quantitative characteristics, e.g. bone density, can be analyzed. The images were photographed from the monitor of the personal computer with a reflex camera. The densitom e t r i c i m a g e s are p r e s e n t e d in sagittal plane in order to compare the images of the skull, as obtained by high-resolution computer tomographs to our own results. To illustrate this we h a v e c h o s e n s o m e slices, w h i c h will be discussed.

Results

Our results will be presented in two sections. The first will cover the structures in the area of the nasal cavity, the sphenoid sinus and the e t h m o i d cells (Fig. 2a-d). T h e second section will deal with the orbit, the nasolacrimat canal and the maxillary sinus (Fig. 2e-h). Figure 2a: This shows a sagittal s e c t i o n , w h i c h has b e e n t a k e n 0.5 mm from the median plane. The cribriform plate, the frontal sinus and the sphenoid sinus are clearly

visible. In the area of the anterior and posterior wall of the sphenoid sinus a bone density minimum can be identified. The cribriform plate presents itself as a very thin bony lamella. At the front of the cribriform plate is an o p e n i n g for the anterior ethmoidal artel3~ and nerve. Note the homogeneous bone density of the palate. F i g u r e 2b: Here the emphasis will be on the presentation of the sphenoid sinus, the cribrifonn plate, the clivus and the ethmoid cells. Again recognizable is the irregular bone density of the frontal skull base. Figure 2c: The slice was taken 6.0 mm lateral to the previous one. Noticeable is the low bone density in the area of the sphenoid sinus and the presentation of the agger nasi cell. Not only the frontal recess but also the inferior concha are presented. The roof of the anterior ethmold shows no regularity of bone density. Dehiscences in the anterior and the p o s t e r i o r regions of the sphenoid sinus are clearly recognizable. In this context the close topographic relationship between the

GM Sprinzl et at : Densitometric analysis of the paranasai sinuses

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184 s p h e n o i d sinus and the internal c a r o t i d a. m u s t be c o n s i d e r e d . Figure 2d: The anterior and the posterior wall of the frontal sinus show a v e r y high b o n e d e n s i t y . Remarkable are the good presentations of the ethmoid cells, especially the O n o d i cell, the s p h e n o i d sinus and the carotid artery canal. T h e d i s s e c t i o n p r e s e n t e d in Figure 3 demonstrates the peculiar anatomy of the structures just discussed. The r o o f and parts of the lateral wall of the sphenoid sinus have been removed. The internal carotid a., the optic n. and the occulomotor n. (which is often neglected) are visible. In dissecting the sphenoid sinus, especially its anterior wall, attention should be paid to the sphenopalatine artery. Figure 2e and f: In addition to

GM Sprinzl et al : Densitometricanalysis of the paranasal sinuses the frontal sinus the ethmoid cells stand out clearly. Here again the changing bone density at the frontal skull base can be observed. The floor of the frontal sinus shows a minimal bone density, The nasolacrimal canal, the optic nerve canal and the Onodi cell can be seen. Figure 2g: In this sagittal plane the orbit can distinguished clearly from the maxillary sinus. The pterygoid canal, the pterygopalatine fossa, the nasotacrimal canal and the final parts of the ethmoid cells are visible. Minimal bone density can be recognized in the inferior wall of the orbit. Note the in'egular bone density distribution in the anterior wall of the maxillary sinus. Figure 2h: The maxillary sinus is presented in its maximum extent. Again we see typical patterns of bone

density distribution. Observe the pterygopalatine fossa, the walls of the maxillary sinus, the nasolacrimal canal, the inferior orbital fissure and the infraorbital groove. In this area (the middle of the eye socket), the frontal sinus is separated from the orbit by a thin bony lamella.

Discussion

The study of bone density maps is essential to understand the osteologic anatomy and pathology of the skull. Ivleasurements of bone density allows us to illustrate weak points in the osseous pattern of the skull base. Furthermore, the high resolution of this method makes it possible to present small and fine osseous structures e.g. the e t h m o i d cells, the nasolacrimal canal, the posterior wall of the sphenoid sinus and the pterygoid canal. A three-dimensional reconstruction with our own data is possible. It is our intention to release a threedimensional reconstruction also with CT- or M R L d a t a . The ability to o b s e r v e structures f r o m v a r i o u s directions gives anatomists and ENT surgeons not only an insight into the skull anatomy, but also pre-operative information about the complex individual skull anatomy [16]. Using whole organ sections, we hope to be able to provide and to evaluate data, not only in the area of gross and osteologic anatomy, but also in the area of histology. Preliminary results of our research are very promising.

Acknowledgements. The authors would like Fig. 3

Lateral wall of the sphenoid sinus has been removed. The dissection demonstrates the carotid a. (triple arrow), the optic n. (double arrows) and the oculomotorn. (single arrow) La paroi lat4rale du sinus sphtnffdal a 6t6 enlevte, La dissection montre l'art~re carotide interne (fl~ches triples), te nerf optique (fl~ches doubles) et le neff oculomoteur(fl~che unique)

to thank W, Ebner for utilization of the diamond-coated wire-saw and his help during the cutting procedure. They are also grateful to Mrs. U. Koch and Mrs. C. OpfermannRngeler for producing the contact pictures and the drawing.

GM Sprinzl et al : Densitometric analysis of the paranasal sinuses

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Received March 26, 1993/Accepted in final form June 4, 1993