13674_C01.qxd 7/28/04 2:14 PM Page 1 1 Surgical Anatomy of the Paranasal Sinus M. PAIS CLEMENTE The paranasal sinus region is one of the most complex This chapter is divided into three sections: develop- areas of the human body and is consequently very diffi- mental anatomy, macroscopic anatomy, and endoscopic cult to study. The surgical anatomy of the nose and anatomy. A basic understanding of the embryogenesis of paranasal sinuses is published with great detail in most the nose and the paranasal sinuses facilitates compre- standard textbooks, but it is the purpose of this chapter hension of the complex and variable adult anatomy. In to describe those structures in a very clear and systematic addition, this comprehension is quite useful for an accu- presentation focused for the endoscopic sinus surgeon. rate evaluation of the various potential pathologies and A thorough knowledge of all anatomical structures their managements. Macroscopic description of the and variations combined with cadaveric dissections using nose and paranasal sinuses is presented through a dis- paranasal blocks is of utmost importance to perform cussion of the important structures of this complicated proper sinus surgery and to avoid complications. The region. A correlation with intricate endoscopic topo- complications seen with this surgery are commonly due graphical anatomy is discussed for a clear understanding to nonfamiliarity with the anatomical landmarks of the of the nasal cavity and its relationship to adjoining si- paranasal sinus during surgical dissection, which is con- nuses and danger areas. A three-dimensional anatomy is sequently performed beyond the safe limits of the sinus. complemented with schematic diagrams. The sinus surgeon must be able to orientate himself or herself while looking through optical instruments that Developmental Anatomy provide better illumination and a greater view of the del- icate structures of the nose and paranasal sinus. The sur- Nose Development geon must also develop a mental three-dimensional ana- tomical image, allowing himself or herself to know the The embryogenesis of the nose and paranasal sinuses is precise location, the relationships with vital structures, related to the regional embryology of the cranial-oral- and especially where the danger points lie. facial region. These primary events occur between the Besides clinical judgment and technical skills, a com- fourth and eighth weeks of fetal life. The first nasal petent surgeon must also be a good anatomist. To structures are initially identifiable in the 5 mm, 4-week- achieve these goals, it is wise to perform a reasonable old embryo.1,2 At this point, there are three developing number of surgical dissections on cadaveric specimens, facial projections that contribute to the formation of the attend several dissection courses, and participate in nose: the frontonasal process, the maxillary process, and many meetings. During the past years the author has or- the mandibular process. ganized international dissection courses on paranasal The frontonasal process is ectodermally derived, and sinus surgery with limited numbers of participants. This it develops independently over the forebrain giving rise is the best way to improve medical teaching, hospital to the forehead and the nasal olfactory placodes. A practice, and patient care. thickened plaque of ectoderm develops during the 1 13674_C01.qxd 7/28/04 2:14 PM Page 2 2 Sinus Surgery: Endoscopic and Microscopic Medial nasal Frontonasal process process Lateral nasal Nasal process placode Maxillary Buccopharyngeal process membrane Mandibular process Hyoid 1st arch pharyngeal groove 3rd Arch Cardiac bulge A Auditory vesicle 2nd branchial cleft Hyomandibular 3rd and 4th (1st branchial) cleft branchial clefts Maxillary process 1st cervical somite (myotome portion) Left optic vesicle 4th branchial arch Nasal placode 3rd branchial arch Hyoid (2nd branchial) arch Stomadeum Mandibular (1st branchial) arch Cardiac prominence B FIGURE 1–1 Embryo at 4 to 5 weeks. (A) Frontal view: Observe the branchial arch formation and the ruptured buccopharyngeal membrane. (B) Lateral view. fourth intrauterine week on each side of the ventral sur- of the nasal placode and the lateral nasal swelling at the face of this frontonasal elevation. Within a few days lateral side of the nasal placode.3 these thickenings become paired lateral nasal placodes Meanwhile, other outgrowths of mesenchymal origin (Fig. 1–1). Initially the placodes have a convex external called the maxillary processes grow ventrally from the surface, but the unequal forward growth of the fron- dorsal ends of the mandibular processes (first visceral) tonasal swelling (particularly the medial and lateral arch. These maxillary swellings are located at the infero- sides of the nasal placodes) will transform these surfaces lateral border of the placodes. These three swellings are into concave nasal grooves. These grooves are well devel- separated from each other by shallow depressions and oped when the embryo is 32 to 34 days old. They are sur- continue to grow forward and downward. As they do so, rounded by the medial nasal swelling at the medial side the epithelial linings of the medial and lateral nasal 13674_C01.qxd 7/28/04 2:14 PM Page 3 CHAPTER 1 Surgical Anatomy of the Paranasal Sinus 3 swellings fuse inferiorly, and the nasal grooves become pit. As the nasal pit deepens, it becomes the nasal sac. As blind-ending tubes or pits, called the nasal pits, that will the cavity enlarges, the posterior limiting membrane ultimately become the nares. The epithelium within the (initially the nasal fin) becomes the oronasal membrane. pits eventually develops neural processes that extend to- During the forward and downward growth of the vari- ward the brain to become the olfactory nerves. Thus, the ous facial swellings, each swelling also increases its di- development of the nasal pits is part of the cranial and mensions in a mediolateral direction. Thus, during the neural tube formation. transformation of the nasal groove into the primary The floor of each nasal pit is constituted by the fused nasal cavity, the furrows between maxillary and lateral medial and lateral nasal swellings and further anteriorly nasal swellings are increased, both on the external sur- by the fused medial nasal and maxillary swellings. The face and on the internal surface of the lateral wall of the epithelial lining in the contact plane is called the nasal primary nasal cavity. The early structures responsible for fin and is disrupted anteriorly by the outgrowth of the the development of the eyes are visible at 28 days. Ini- surrounding tissues. Posteriorly, this epithelial band per- tially, the early eyes are oriented laterally (80 degrees to sists for a short period of time in the floor of the nasal the neural axis), but during the next weeks the growth A B C 1 3 2 D E FIGURE 1–2 Developing face. (A) Fourth week. (B) Fourth eyes forward and toward the midline, the nose development, to fifth week. (C) Fifth to sixth week. (D) Sixth to seventh the sealing of the nasolacrimal groove (1), and the formation week. (E) Eighth to tenth week. Note the orientation of the of the upper lip (2) and the philtrum (3). 13674_C01.qxd 7/28/04 2:15 PM Page 4 4 Sinus Surgery: Endoscopic and Microscopic of the mesenchyme posterior to the eyes reorients the TABLE 1–1 Derivatives of Facial Components eyes forward toward the midline. The groove on the ex- ternal surface is transformed into the nasolacrimal duct Embryonic Part Facial Derivatives Skeletal Derivatives by the interposition of surface epithelium between the Frontonasal process Nasal bridge Nasal bones maxillary and lateral nasal swellings and by the loss of Median nasal Columella of nose Perpendicular plate contact between this epithelium and the surface epithe- process of the ethmoid bone lium. It is like an infolded epithelial transformation. Philtrum Vomer Lateral nasal process Sides and ala of The groove on the inside surface will develop into the nose inferior meatus of the nasal cavity. The nasolacrimal Maxillary process Major portion of Maxilla, zygoma, duct connects the eye to the internal nasal cavity inferior upper lip secondary palate Upper cheek to the attachment of the inferior turbinate. As the eye Mandibular process Lower lip, Mandible migrates from a lateral orientation relative to the devel- Lower cheek oping nose, the nasolacrimal duct assumes a more oblique rather than horizontal direction (Fig. 1–2). The rupture of the oronasal membrane in the 15 mm choana is the premaxilla (primitive palate). The external embryo takes place between days 42 and 44 in the poste- nares are widely separated by the remaining median rior floor of the nasal pit, transforming this blind- frontonasal process, which gradually reduces, bringing ending cavity into a primary nasal cavity that communi- the openings close together. cates with the primary oral cavity through the newly Simultaneously, other facial structures develop rapidly. formed opening, or primitive choana.1–3 Lack of disinte- The digestive tube is formed, and the cephalic opening gration of the oronasal membrane results in choanal of this tube, called the oral stoma, is found just caudal to atresia. The part of the roof of the mouth in front of the the level of the nasal pits. The branchial clefts and AB C D E F FIGURE 1–3 Development of the nose, mouth, and palate. (A–C) Formation of the nose, upper lip, and philtrum. (D–F) Differ- ent stages of palate formation and the separation of the nasal and oral cavities. 13674_C01.qxd 7/28/04 2:15 PM Page 5 CHAPTER 1 Surgical Anatomy of the Paranasal Sinus 5 arches form ventral to the eyes and caudal to the oral stoma. The maxillary process, derived from the first branchial arch with part of the medial nasal process, be- comes the upper jaw (Table 1–1). From days 45 to 48 formation of the secondary palate begins, due to the separation between the nasal cavity and the oral cavity.