22 Sinonasal Anatomy & Embryology with Radiology Correlates Flashcards
Describe the septum and the turbinates.
Describe the septum and the turbinates.
The nasal septum is the midline partition that separates the left and right sides of the nasal cavity. It is made of the quadrangular cartilage, perpendicular plate of the ethmoid bone, vomer, and maxillary crest. There are three paired turbinates, or concha, on each side. The middle and superior turbinates are part of the ethmoid bone, whereas the inferior turbinate is its own bone.
Define the paranasal sinuses.
Define the paranasal sinuses.
The paranasal sinuses are pneumatized areas of the facial and skull base bones. They communicate with the nasal cavity through small ostia, allowing air exchange and drainage of secreted mucus.
What epithelium lines the paranasal sinuses?
What epithelium lines the paranasal sinuses?
The sinuses are lined by pseudostratified ciliated columnar or respiratory epithelium. The cilia beat in a coordinated fashion to transport mucus from the point of its secretion in the sinus toward its natural ostium. From there, the cilia within the nasal cavity move the secretions toward the nasopharynx.
What is the function of the paranasal sinuses?
What is the function of the paranasal sinuses?
The short answer is that the function is unknown. A number of theories exist about the possible function of the sinuses, including lightening of the skull, enhancing vocal resonance, absorption of mechanical force during trauma in order to protect the eyes and brain, and production of or reservoir for nitric oxide, a postulated aerocrine substance that may regulate pulmonary function. All of these theories have evidence for and against them.
Where is the maxillary sinus located?
Where is the maxillary sinus located?
The maxillary sinus is located within the body of the maxilla. Medially it is bounded by the lateral nasal wall, superiorly by the floor of the orbit (containing the infraorbital nerve and artery), posteriorly by the pterygopalatine and infratemporal fossae, and inferiorly by the alveolar process and hard palate. The maxillary tooth roots commonly reach to the floor of the maxillary sinus (Figure 22-1).
Figure text:
1 Coronal computed tomography (CT) scan image in a bone window algorithm showing pneumatization in the head of the middle turbinate (*), also called a concha bullosa. Infraorbital ethmoid air cells (Haller cells) are seen as pneumatized air cells off the inferior orbital floor (arrow). This can narrow the drainage of the maxillary sinus (M). The lateral wall of the ethmoid cavity is the lamina papyracea (LP). The olfactory cleft and lateral lamella of the cribriform plate (LLCP) is depicted. Note the relationship of the LLCP with the insertion of the basal lamella of the middle turbinate, as well as the fovea ethmoidalis (F) laterally. The LLCP is commonly asymmetric. This asymmetric anatomic variation should be recognized on presurgical planning to prevent iatrogenic cerebrospinal fluid leaks. The ethmoid bulla is seen adjacent to the LP (+).
Where are the ethmoid sinuses located?
Where are the ethmoid sinuses located?
The ethmoid sinuses form a honeycomb-like series of cells medial to the orbits and inferior to the anterior cranial base. They are functionally divided into the anterior and posterior ethmoid cells by a portion of the middle turbinate called the basal lamella.
- Anterior cells are bounded medially by the middle turbinate and drain into the middle meatus.
- Posterior ethmoid cells are bounded medially by the superior turbinate and drain into the superior meatus.
The ethmoid cells are bounded laterally by the lamina papyracea of the orbit. Posterior to the posterior ethmoid cells is the sphenoid bone containing the sphenoid sinus. The nasal cavity is inferior to the ethmoid air cells and the frontal bone is superior. As the ethmoid cells form embryologically, they expand into the frontal bone superiorly and make shallow depressions in it, called fovea ethmoidales. The frontal bone abuts the cribriform plate of the ethmoid medially and a small portion of the cribriform plate sits superior to the ethmoid cells. This area tends to be very thin and easily punctured during sinus surgery, which can lead to a cerebrospinal fluid leak.
Where is the sphenoid sinus located?
Where is the sphenoid sinus located?
The sphenoid sinus pneumatizes the sphenoid bone and is posterior to the ethmoid sinus. The sella turcica and pituitary gland lie superior to the sphenoid sinus. Within the lateral wall of the sphenoid sinus is the venous cavernous sinus, containing the internal carotid artery. The optic nerve also lies within the lateral wall of the sphenoid sinus. Posterior to the sphenoid sinus is the posterior cranial fossa (Figure 22-2). The sphenoid sinus can pneumatize laterally into the pterygoid region of the sphenoid and thus lie inferior to the temporal lobes of the brain.
Figure text:
Coronal computed tomography (CT) scan in a bone window algorithm showing a right sphenoethmoidal air cell (Onodi cell) which is located superior and lateral to the sphenoid sinus (S). The optic nerve (ON) and carotid artery (C) are seen as bony protrusions in the sphenoethmoidal air cell (O) rather than the sphenoid sinus. The vidian nerve (VN) and the maxillary division of the trigeminal nerve (V2) can be seen inferior and laterally.
Where is the frontal sinus located?
Where is the frontal sinus located?
The frontal sinuses are air spaces within the frontal bones. The frontal bone thus has an anterior and posterior wall. The anterior wall lies deep to the forehead skin. The frontal lobes of the brain lie posterior to the frontal sinus. Inferiorly the frontal sinuses lie adjacent to the orbits laterally and the anterior ethmoid sinuses medially.
At what point during gestation do the sinuses begin to develop?
At what point during gestation do the sinuses begin to develop?
The sinuses begin to form in the third fetal month but only the ethmoid and maxillary sinuses are present at birth. They form as evaginations from the developing nasal cavity that invade into the surrounding bones.
Do the sinuses continue to develop postnatally?
Do the sinuses continue to develop postnatally?
Yes. The maxillary sinus continues to grow in size as the face grows overall. The maxillary sinus enlarges significantly again after eruption of the permanent dentition. The ethmoid sinuses continue to develop postnatally until about age 12. The frontal sinus pneumatizes slowly postnatally, rarely reaching any significant size during the first decade of life. Thereafter, it rapidly pneumatizes into the frontal bone reaching its final size near the end of the second decade of life. Likewise, the sphenoid sinus develops little until about age 7, after which it rapidly pneumatizes and reaches its final size during adolescence (Figure 22-3).
Figure text:
Coronal representation of the development of the frontal and maxillary sinus. The frontal sinus begins to develop at the age of 4 years and does not fully mature until after the age of 12 years. The newborn (N) has a small maxillary sinus that continues to expand in a lateral inferior direction, reaching adult pneumatization after 12 years of age.
How are the sinuses evaluated radiographically?
How are the sinuses evaluated radiographically?
The advent of high-resolution thin cut multiplanar computed tomography (CT) has dramatically improved the assessment of the complex anatomy of the paranasal sinuses. Early CTs used direct acquisition of coronal and axial images. Direct acquisition in the axial plane with reconstruction in the coronal and sagittal planes is now commonplace. Such triplanar imaging allows for study of complex anatomic relationships throughout the paranasal sinuses and cranial base. Of the three views, the coronal images can be considered the most useful because they closely resemble the surgeons’ endoscopic surgical view. Inflammation of the sinuses is seen on CT as thickening of the mucoperiosteum of the paranasal sinuses.
Plain radiographs of the sinuses are rarely used due to the lack of anatomic detail seen with CT imaging. MRIs can augment CTs by providing soft tissue analysis, as when secretions cannot be differentiated from a neoplasm. Due to the lack of bony detail, they are not commonly used for standard sinus evaluations.
What is the osteomeatal unit and what structures make up this area?
What is the osteomeatal unit and what structures make up this area?
The osteomeatal unit (OMU) is a functional anatomic area within the middle meatus comprised of:
- Ethmoid bulla
- Uncinate process
- Ethmoid infundibulum
- Hiatus semilunaris
The OMU is the common drainage pathway of the anterior ethmoid and maxillary sinuses. Depending on the superior attachment of the uncinate process, it may also drain the frontal sinus. Inflammation within the OMU may lead to obstruction of and inflammation within these draining sinuses.
What is the ethmoid bulla?
What is the ethmoid bulla?
The ethmoid bulla is the most consistent and typically largest anterior ethmoid cell. Its lateral wall is the lamina papyracea. It usually has a rounded shape anteriorly, running parallel to the uncinate process (see Figure 22-1, the + sign).
What is an uncinate process?
What is an uncinate process?
The term uncinate process means “hook-shaped” bone. It is a crescent- or hook-shaped fold of bone that sweeps from superior to posterior just anterior to the ethmoid bulla within the anterior ethmoid sinuses. The uncinate process and anterior face of the bulla tend to run parallel to each other, forming a small gap called the hiatus semilunaris. The uncinate process is attached to the lateral wall of the nose and has a free edge posteriorly. It therefore forms a trough-shaped space that runs from superior to posterior within the anterior ethmoid sinuses. This space is called the ethmoid infundibulum.
What is the difference between the hiatus semilunaris and the ethmoid infundibulum?
What is the difference between the hiatus semilunaris and the ethmoid infundibulum?
The hiatus semilunaris is a two-dimensional gap (hiatus means “gap”) between the ethmoid bulla and the uncinate process.
The ethmoid infundibulum is a three-dimensional trough between the uncinate process and lateral nasal wall/lamina papyracea. Surgically, the ethmoid infundibulum can be accessed through the hiatus semilunaris. In other words, the trough is reached through the semilunar gap.
What is the agger nasi?
What is the agger nasi?
The term agger nasi means “nasal mound” and refers to the area in the lateral wall of the nasal cavity that projects medially, just superior to the middle turbinate’s anterior superior attachment. It is commonly pneumatized, forming an agger nasi cell (Figure 22-4).
Figure Text:
Computed tomography (CT) images in bone window algorithms demonstrating types of frontal cells (Kuhn Classification I-IV): A, Type I cell directly above the agger nasi cell (*). B, Type II cell, C, Type III Kuhn cell. The coronal CT imaging shows bilateral Kuhn Type III frontal air cells. D, Type IV Kuhn frontal cell is isolated within the left frontal sinus.
What variations are seen in the anatomy of the ethmoid sinuses?
What variations are seen in the anatomy of the ethmoid sinuses?
Infraorbital ethmoid air cells (Haller cells) may be present laterally within the ethmoid sinus, adjacent to the inferior orbital floor and at the medial extent of the roof of the maxillary sinus. These cells are important to identify because they have the potential to narrow the ethmoid infundibulum and maxillary sinus drainage. The coronal CT is the best view for diagnosing these air cells (see Figure 22-1).
The term concha bullosa is used to describe pneumatization of the middle turbinate. A concha bullosa of the middle turbinate can narrow the OMU by compressing the uncinate process laterally (see Figure 22-1).
19 What variations are seen in the anatomy of the sphenoid sinus?
Sphenoethmoidal cells (Onodi cells) are posterior ethmoid cells that pneumatize into the sphenoid bone. This cell can extend superiorly, posterior and laterally and therefore have an intimate relationship with the optic nerve and carotid artery in its lateral wall. The sphenoethmoidal cell is best visualized on the coronal CT views with the appearance of a horizontal split of the sphenoid sinus. However, the coronal, sagittal, and axial views should be reviewed to clarify if the origin of the cell is from the posterior ethmoids rather than the sphenoid, which is medial and inferior (see Figure 22-2).
What variations are seen in the anatomy of the sphenoid sinus?
What variations are seen in the anatomy of the sphenoid sinus?
Sphenoethmoidal cells (Onodi cells) are posterior ethmoid cells that pneumatize into the sphenoid bone. This cell can extend superiorly, posterior and laterally and therefore have an intimate relationship with the optic nerve and carotid artery in its lateral wall. The sphenoethmoidal cell is best visualized on the coronal CT views with the appearance of a horizontal split of the sphenoid sinus. However, the coronal, sagittal, and axial views should be reviewed to clarify if the origin of the cell is from the posterior ethmoids rather than the sphenoid, which is medial and inferior (see Figure 22-2).
