For educational and institutional use. This test bank is licensed for noncommercial, educational inhouse or online educational course use only in

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1 For educational and institutional use. This test bank is licensed for noncommercial, educational inhouse or online educational course use only in educational and corporate institutions. Any broadcast, duplication, circulation, public viewing, conference viewing or Internet posting of this product is strictly prohibited. Purchase of the product constitutes an agreement to these terms. In return for the licensed use, the Licensee hereby releases, and waives any and all claims and/or liabilities that may arise against ASRT as a result of the product and its licensing.

2 Sectional Anatomy Essentials Module 2: The Cranium and Facial Bones 1. Cranium and Facial Bones Welcome to Sectional Anatomy Module 2: The Cranium and Facial Bones. This module was written by Michael A. Manders, BS, R.R.A., R.T. (R), and Jeffrey D. Houston, MD. 2. License Agreement and Disclaimer 3. Objectives After completing this module, you will be able to: Name and locate the anatomical landmarks of the cranium. List and locate the paranasal sinuses and the skull foramina. Name the bones in the cranium and face. List the components of the temporomandibular joint, explain their function and their relationship to each other. Describe the structure and function of the ear. Identify the location and function of the facial muscles. List and locate the components of the eye. 4. Introduction Throughout the Sectional Anatomy Essentials series, we display most of the cross-sectional anatomy using multidetector computed tomography (CT) and magnetic resonance (MR) images to illustrate the three-dimensional relationship of the structures. Use the slider bar in this animation to scroll through the images. Because you can easily lose your frame of reference when viewing cross-sectional images, the location of the featured slice on many slides will be displayed on adjacent localizer images of the other 2 planes, like the image shown here. 5. Anatomical Landmarks For medical professionals learning about the cranium and facial bones, a good place to start is the anatomical landmarks used to locate and image the different parts of the cranium and face. These landmarks include the glabella, nasion, acanthion, mental point and the external auditory meatus, or the EAM. 6. Anatomical Landmarks The glabella is the small area just above the nose and between the eyebrows. In Latin, glabella means smooth, as this area is typically hairless. Just below the glabella, located directly between the eyes where the nasal bones meet the frontal bones of the cranium, you find the next anatomic landmark, the nasion. If you palpate up the bridge of the nose, the nasion is the depression you feel before reaching the level of the eyebrows. Below the tip of the nose, you can find the acanthion, which is the base of the anterior nasal spine. Moving inferiorly, you come to the mental point, which is the middle of the most distal portion of the chin. The last anatomical landmark to note is the external auditory meatus. This structure is the actual ear canal that can be seen from outside the patient.

3 7. Paranasal Sinuses The paranasal sinuses are air-filled cavities which are predominantly located in the anterior portion of the face. The exact biological function of these spaces is unknown, although there are multiple theories. One of the theories is that they protect the internal structures of the face from trauma by absorbing pressure in the same way that bubble wrap protects objects during shipping. Another thought is that they lighten the relative weight of the skull. The 4 cavities that make up the paranasal sinuses are the ethmoid, maxillary, sphenoid and frontal. We ll discuss each of these cavities in more detail later in this module. 8. Ostia The paranasal sinuses communicate with the nasal cavity via small pathways called ostia. The ostia allow mucus to drain, which is what happens when you have a runny nose. Sometimes, when you have allergies or a common cold for example, the linings of the ostia become inflamed and close off the pathways, causing the mucus to back up in the sinuses. Inflammation of the paranasal sinuses is a condition called sinusitis. 9. Ostia Look at the CT image on this slide. You can see an abnormal, completely opacified maxillary sinus and ostium on the patient s right side and a normal pneumatized maxillary sinus and patent ostium on the patient s left side. 10. Ethmoid Sinuses The ethmoid sinuses consist of multiple air pockets. The air pockets are located within the ethmoid bone, bilaterally between the eyes and posterior to the bridge of the nose. They are divided into 3 groups according to their position: anterior, middle and posterior. The anterior and middle ethmoid air cells drain into the middle nasal meatus, while the posterior ethmoid air cells drain into the superior nasal meatus. The ostiomeatal units are canals that guide mucus from the sinuses into the nose. 11. Ethmoid Sinuses If you look at the CT teaching scan, the ethmoid sinuses are best seen on slice 41, which is on this slide. 12. Maxillary Sinuses The maxillary sinuses are paired structures located just inferior to the orbits within the maxillas. Each maxillary sinus drains into the middle nasal meatus. Two facts are important to remember when studying the maxillary sinus. First, because only a thin bone separates the sinus from the orbit, a direct blow to the eye can break this bone, causing orbital structures to prolapse into the sinus and the area to fill with blood. Therefore, if a radiograph or a CT scan reveals asymmetric opacification of a maxillary sinus in a patient with a history of trauma to the eye, it s likely there s a fracture of the orbital floor. Second, keep in mind that the roots of multiple teeth are separated from the maxillary sinus by another thin bone. Therefore, sometimes maxillary sinusitis can present as dental pain. 13. Maxillary Sinuses The maxillary sinuses can be seen on a number of slices of the CT teaching scan. On this image, slice 28, the maxillary sinuses are labeled. Notice how easily they are seen on all 3 views.

4 14. Maxillary Sinuses As you scroll through this series of slices, watch the localizer images on the right-hand side to help you locate the maxillary sinuses. 15. Sphenoid Sinuses The sphenoid sinuses are typically paired. They are located posterior to the ethmoid sinuses and just inferior to the sella turcica, which we ll discuss later in this module. Each sphenoid sinus drains into the sphenoethmoidal recess, which then communicates with the superior nasal meatus. The sphenoid sinus serves as a route for neurosurgeons to access the pituitary gland through the nose, a procedure known as transsphenoidal surgery. The appearance of surgical packing material on an image can confuse novice technologists and resident physicians. For instance, when fat is used as a packing material it may later be mistaken for a fatty tumor if patient surgical history is not provided. 16. Sphenoid Sinuses Scroll through the slices in this animation to see the sphenoid sinuses. 17. Frontal Sinuses The frontal sinuses are located medially within the frontal bone at approximately the level of the roof of the orbit. Each frontal sinus drains into a middle nasal meatus. An interesting fact about the frontal sinuses is that they can considerably vary in size from person to person. 18. Frontal Sinuses Note the location of the frontal sinuses as you scroll through this portion of the CT teaching scan. 19. Paranasal Sinuses Anatomic Variants When talking about the paranasal sinuses, it s important to mention the anatomic variants of these structures. A case in which the sinus is missing all together is called an aplastic sinus. The overall size of each sinus cavity also can vary. The sinus may be smaller than normal, which is called a hypoplastic sinus. If the sinus is large or overly pneumatized, it is called hyperplastic. 20. Paranasal Sinuses Anatomic Variants Other common paranasal anatomic variants include concha bullosae, Onodi cells and Haller cells. A concha bullosa is an air cell within the middle turbinate and is a fairly common finding. Although typically asymptomatic, a large concha bullosa may obstruct a nearby sinus, leading to sinusitis. An Onodi cell is a posteriorly located ethmoid air cell, occurring extremely close to the optic nerve and sometimes the internal carotid artery. An Onodi cell is significant in that surgeons sometimes use the posterior ethmoid sinus to gain access to the sphenoid sinus. If the surgeon goes through an Onodi cell rather than the posterior ethmoid cell, the optic nerve may be damaged. A Haller cell is an extension of an ethmoid air cell into the inferomedial orbital floor. Although typically asymptomatic, it can become significant in much the same way as an Onodi cell. For example, an endoscopic surgeon who is unaware of a Haller cell may accidentally penetrate the orbit.

5 The last anatomic variant we ll discuss is the agger nasi cell. Agger means mound or heap in Latin. This structure is the anterior-most ethmoid air cell. It is located inferolateral to the frontal recess, the channel which communicates between the anterior ethmoid and frontal sinuses. The agger nasi cell is an important landmark for frontal sinus surgery because the roof of the cell is the floor of the frontal sinus. 21. Paranasal Sinus Imaging The primary imaging modality used to observe the paranasal sinuses is CT, with a patient scanned coronally in the prone position or in the supine hanging-head position. At some facilities, it s standard practice for the CT technologist to place a radiopaque marker on the patient s right cheek before the scan. As you now know, the paranasal sinuses are symmetric, so it may be impossible to differentiate the right from the left side if there is a technical or technologist error. Therefore, the placement of a radiopaque marker on the patient s right cheek confirms that the right side of the image is truly the right side of the patient. 22. Knowledge Check 23. Knowledge Check 24. Knowledge Check 25. Knowledge Check 26. Cranial Sutures The bones of the skull are bound together at joints called sutures to form the cranium. These joints are considered synarthroses, meaning that they allow for little to no movement. Special fibers called Sharpey fibers, named after the Scottish anatomist William Sharpey, hold the joints together. Sharpey fibers are bundles of cartilaginous threads forming connective tissue. 27. Cranial Sutures We ll discuss 4 primary sutures of the cranium: squamousal, coronal, sagittal and lambdoidal. 28. Cranial Sutures Reconstructed images may appear different depending on the software package used. These images were created using Vitrea 2 Software, a CT postprocessing program from Vital Images, a Toshiba Medical Systems Group company. In these images of the cranium, the various sutures appear as squiggly lines across the surface of the skull. Scroll through this animation to see the cranial sutures.

6 29. Cranial Sutures Scroll through this animation as we describe the cranial sutures. The squamosal suture is best demonstrated on a lateral view of the skull. It connects the superior temporal bone to the inferior parietal bone. The next suture is the coronal suture, which connects the posterior border of the frontal bone to the anterior border of the parietal bone. This suture is also best discerned on a lateral view of the skull. The sagittal suture connects the medial borders of each parietal bone and is best observed when viewing the skull from above. The lambdoidal suture connects the posterior borders of each parietal bone to the superior border of the occipital bone. It is best demonstrated from the side or the back. 30. The Fontanelles At birth, the cranium has 6 soft spots called fontanelles. The fontanelles are areas of an infant s head covered with a tough membrane instead of bone. The fontanelles allow the bones of the cranium to flex and thus permit a newborn to pass through the birth canal. The 2 largest fontanelles are the anterior fontanelle, which is located at the junction of the parietal bones and the frontal bone, and the posterior fontanelle, which is located at the junction of the parietal bones and the occipital bone. The anterior fontanelle typically closes at around 2 years of age, while the posterior fontanelle generally closes within the first several months of life. Two smaller fontanelles are located on each side of the skull: the sphenoidal fontanelles are found at the junction of the frontal, sphenoid, parietal and temporal bones, and the mastoid fontanelles are located at the intersection of the occipital, parietal and temporal bones. The fontanelles are of clinical significance in that they allow the cranial cavity to be imaged with sonography. Ultrasound imaging of the neonatal head can be very useful because it can detect abnormalities without exposing the pediatric patient to unnecessary radiation. 31. Shapes of the Skull Sutures are not fused at birth to allow for growth of the skull. Sometimes, sutures fuse prematurely, causing malformations of the skull as it grows. Archeologists originally developed the cephalic index to categorize human populations. Today, the index is commonly used to categorize the shape of the skull. The cephalic index is calculated by taking the maximum width of the head, multiplying that measurement by 100 and then dividing the product by the maximum length of the head. If the cephalic index is less than 75 in women and 75.9 in men, the individual is said to be dolichocephalic, or long-headed. This condition occurs when the sagittal suture fuses too soon. If the cephalic index is greater than 83 in women and 81.1 in men, the individual is said to be brachycephalic, or short-headed. This condition occurs when the frontal suture fuses too soon.

7 Some cultures purposely change the shapes of children s heads by different methods, including wrapping the skull with rope to elongate it or attaching a board to the head to flatten it. These changes are made for aesthetic reasons related to cultural beliefs. 32. Differentiating Sutures From Fractures With all the winding sutures running through the cranium, you may wonder how to differentiate between a suture and a fracture. The first difference is that a suture line has symmetric, wellcorticated borders, whereas an acute fracture does not. The exception is a diastatic fracture, which follows the suture line in newborns. In this case, although the suture has well-corticated borders, you can see that the suture is abnormally widened. A second characteristic differentiating a fracture from a suture is that a fracture typically is linear in orientation, while a suture is serpiginous, or winding. The third factor that can help distinguish a skull fracture from a suture is a thorough knowledge of where normal sutures are typically located. 33. Knowledge Check 34. Knowledge Check 35. Knowledge Check 36. Cranial Bones The cranium is the product of 8 bones that create a cavity for, and ultimately protect, the brain. The 8 bones are the occipital bone, 2 temporal bones, sphenoid bone, ethmoid bone, frontal bone and 2 parietal bones. These bones are held together by sutures, and each bone has specific structures that serve as attachment points and contribute to the function of the brain. Let s examine these bones and their specific structures. 37. Occipital Bone The occipital bone is located inferoposteriorly and makes up the posterior cranial fossa. The occipital bone is generally divided into 4 parts: the 2 lateral condyles, the basilar portion and the squamous portion. The 4 parts are divided by the foramen magnum, which is the passage for the medulla oblongata and spinal cord. 38. Occipital Bone Basilar Portion Anterior to the foramen magnum, the basilar portion articulates with the sphenoid bone by means of a thin plate of cartilage, which becomes ossified by approximately age 25. The very most anterior part of the basilar portion contains a shallow depression and slopes anterosuperiorly before connecting to the sphenoid bone. This part of the bone is called the clivus, which is Latin for slope. The clivus is important because it supports the pons. If you draw a line from the clivus posteriorly on a sagittal view, it should transect, or at least be tangential to, the dens. If not, there is an atlanto-occipital dislocation, which is often a fatal injury. Incidentally, the clivus contains more fat than other bones, giving it a unique appearance on T1-weighted magnetic resonance (MR) imaging.

8 39. Occipital Bone Squamous Portion The final part of the occipital bone is the squamous portion, which is located posterior to the foramen magnum. The internal surface of the squamous portion of the occipital bone is concave and divided into 4 fossae. The posterior 2 fossae accommodate the cerebrum, and the anterior hold the cerebellum. The fossae are divided by the cruciform eminence, which forms a cross. The junction of the 4 arms of the cruciform eminence form the internal occipital protuberance. The external surface of the squamous portion of the occipital bone is convex. If you palpate the upper posterior portion of your neck and move your fingers upward, you can feel a ridge of bone running transversely across the base of the skull. This ridge is the superior nuchal line. The external occipital protuberance is located in the middle of this ridge, at approximately the center of the external surface of the occipital bone. The peak of the external occipital protuberance is called the inion. 40. Occipital Bone Squamous Portion Because the squamous portion of the occipital bone is so large, it can be seen throughout most of the CT teaching scan. Scroll through this set of slices to see the structure. 41. Sphenoid Bone The sphenoid bone is located anterior to the basilar portion of the occipital bone. When looking at the shape of the sphenoid bone, many people think it resembles a bat or a butterfly. The sphenoid bone is divided into 3 parts: the body, the greater wings, and the lesser wings. 42. Sphenoid Bone Body The body of the sphenoid bone is cube-shaped and articulates posteriorly with the basilar portion of the occipital bone. The sphenoid sinuses are located within the body of the sphenoid bone, as is the sella turcica. The sella turcica, or Turkish saddle, is a deep indentation in the superior surface of the posterior portion of the body; it houses and protects the pituitary gland. The sella turcica is surrounded by 4 elevations: the tuberculum sellae anteriorly, the middle clinoid processes laterally and the dorsum sellae posteriorly. Arising from the superior borders of the dorsum sellae are the posterior clinoid processes. The body of the sphenoid articulates anteriorly with the cribriform plate of the ethmoid bone via a midline crest called the sphenoidal crest. 43. Sphenoid Bone Body Let s look at several images from the CT teaching scan. On slice 33 you can see the body of the sphenoid, the clivus and the basilar portion of the occipital bone. Slice 41 provides a view of the dorsum sellae. 44. Sphenoid Bone Body You can see the posterior clinoid processes on slice 42 and the tuberculum sellae on slice 43 of the CT teaching scan.

9 45. Sphenoid Bone Body The sella turcica is best seen on this sagittal slice 44 of the CT teaching scan. 46. Sphenoid Bone Greater Wings The paired greater wings of the sphenoid bone arise posteriorly from the lateral borders of the body. They extend upward, laterally and backward. Within the greater wings are foramina rotundum, foramina ovale and foramina spinosum. The superior surface of each greater wing makes up a portion of the middle cranial fossa. Posteriorly, the greater wings articulate with the temporal bones. Superiorly, they form joints with the parietal bones. Anteriorly, the greater wings articulate with the frontal bone. The greater wings also make up the posterior portion of the lateral wall of each orbit. 47. Sphenoid Bone Greater Wings You can see the greater wings of the sphenoid bone on slice 34 of the CT teaching scan. On this slice, also note the location of the foramen ovale and the foramen spinosum. 48. Sphenoid Bone Lesser Wings The lesser wings of the sphenoid also arise from the lateral borders of the body, anterior to the greater wings. The lesser wings contain the optic canals, anterior clinoid processes and superior orbital fissures. 49. Sphenoid Bone Lesser Wings The lesser wings are labeled on this image, which is slice 22 of the CT teaching scan. 50. Structures in the Lesser Wings This image is slice 23 of the CT teaching scan. On this slice, you can see the structures in the lesser wings including the optic canals, the anterior clinoid processes and the superior orbital fissures. 51. Ethmoid Bone The ethmoid bone has a cube-like shape and a spongy composition. It is located in the anterior cranial fossa. The ethmoid bone is generally divided into 4 parts: horizontal, vertical and the two lateral masses. 52. Ethmoid Bone Horizontal Part The horizontal part is called the cribriform plate and contains several foramina that convey the olfactory nerves. The cribriform plate articulates with the frontal bone. A small bony excrescence, or outgrowth, called the crista galli arises from the middle of the cribriform plate. The crista galli provides an attachment point for the falx cerebri that holds the brain within the anterior cranial fossa. 53. Ethmoid Bone Vertical Part The vertical part of the ethmoid bone is called the perpendicular plate. It is a thin bone that extends inferiorly and helps form the nasal septum. The posterior border of the perpendicular plate articulates superiorly with the sphenoidal crest and inferiorly with the vomer, which is an unpaired facial bone located behind the cartilage of the septum. The inferior border of the perpendicular plate is thicker than the rest of the plate and articulates with the nasal septal cartilage.

10 54. Ethmoid Bone Lateral Masses This image is slice 16 of the CT teaching scan. The lateral masses, or ethmoid labyrinth, make up the rest of the ethmoid bone and contain the ethmoid sinuses. Each of the paired ethmoid sinuses is composed of a variable number of air cells. Small, curled, scroll-like bone shelves extend medially from the lateral masses and are called the superior and middle nasal conchae, or turbinates. The superior nasal turbinates help protect the olfactory bulbs from direct contact with pressurized nasal airflow, and the middle turbinates do the same for the maxillary and ethmoid sinuses. An interesting fact is that the mucosa overlying the nasal turbinates cycles in thickness. This means that the mucosa covering the right nasal turbinates may appear thickened on 1 scan, but a scan performed only minutes later may show normal mucosal thickness on the right and thickened mucosa over the left nasal turbinates. The turbinates constantly cycle mucosa from 1 side to the other. The lateral wall of each lateral mass is called the lamina papyracea. This thin smooth bone makes up the medial border of the bony orbit. 55. Ethmoid Bone Lateral Masses The lateral masses of the ethmoid bone can be seen throughout the CT teaching scan. Scroll through these images. You can see how the superior and middle nasal turbinates appear on the different images. Note that the patient in this scan has a deviated septum. The bright line on the ridge of the nose should be straight but actually appears crooked and falls to the right side of the patient s nose. We ll talk more about deviated septums later in this module. 56. Knowledge Check 57. Knowledge Check 58. Knowledge Check 59. Frontal Bone The frontal bone is made up of 2 parts: the vertical and horizontal portions. We ll discuss each of these parts separately. 60. Frontal Bone Vertical Portion The vertical portion of the frontal bone, called the squamous portion, makes up the forehead region and contains the frontal sinuses. It extends superoposteriorly where it articulates with the parietal bones and inferoposteriorly where it articulates with the greater wings of the sphenoid bone. This image is slice 10 of the CT teaching scan. The vertical portion of the frontal bone and the frontal sinuses are labeled. If you look at the 2 localizer images on the right, you can see the level of the axial view.

11 61. Frontal Bone Horizontal Portion The horizontal portion of the frontal bone, or orbital plate, makes up the roof of the orbits and nasal cavity. This image is slice 10 of the CT teaching scan. Note the location of the horizontal portion of the frontal bone. 62. Frontal Bone The frontal bone is a large structure and can be seen throughout the majority of the CT teaching scan. As you scroll through the animation, watch the localizer images on the right-hand side. These views will help you recognize the size of the frontal bone. 63. Parietal Bones The paired parietal bones constitute the roof and sides of the cranial vault. The frontal border of each parietal bone articulates with the frontal bone at the coronal suture, and the occipital border articulates with the occipital bone at the lambdoidal suture. The squamous portion of each parietal bone articulates with the greater wing of the sphenoid anteriorly, the squamous portion of the temporal bone in the middle, and the mastoid part of the temporal bone posteriorly. Superiorly, the squamous portion of each parietal bone articulates with the squamous portion of the other parietal bone at the sagittal suture. Internally, along the sagittal suture, each parietal bone has shallow indentations that together form the sagittal sulcus; the sagittal sinus is located in the sagittal sulcus. The falx cerebri attaches to both sides of the sagittal sulcus. The most superior point along the sagittal suture is called the vertex and is the highest point of the cranium. 64. Parietal Bones Scroll through this animation to see the extent of the paired parietal bones. Keep in mind that the localizer images on the right-hand side show you the level of the axial image. 65. Temporal Bones The temporal bones are the final bones we ll discuss that constitute the cranial vault. Together with the sphenoid bone, the temporal bones form the middle cranial fossa. The paired temporal bones consist of 4 portions: squamous, tympanic, petrous and mastoid. 66. Temporal Bones Squamous Portion The squamous portion, also called the squama temporalis, is a smooth, thin piece of bone that extends superiorly to articulate with the squamous border of the parietal bone. The squamous portion is shown here on slice 8 of the CT teaching scan. Inferiorly, the squamous portion projects slightly anterior to and articulates with the greater wing of the sphenoid bone. 67. Temporal Bones Squamous Portion The zygomatic process of the temporal bone arises anteroinferiorly from the squamous portion. This process extends anteriorly until it articulates with the zygoma, completing what is called the zygomatic arch. We ll discuss the zygomatic arch shortly. 68. Temporal Bones Tympanic Portion The tympanic portion is located inferior to the squamous portion.

12 This image is slice 5 of the CT teaching scan. The anteroinferior surface of the tympanic portion forms the posterior border of the mandibular fossa; the posterosuperior surface creates the floor, anterior wall and part of the posterior wall of the external auditory meatus. The external auditory meatus, more commonly known as the ear canal, extends from the outer ear, or pinna, to where the canal narrows for the attachment of the tympanic membrane, a structure more commonly known as the eardrum. 69. Temporal Bones Tympanic Portion The tympanic portion and the external auditory meatus can be seen on these images. Scroll through this animation to see these structures. 70. Temporal Bones Petrous Portion The petrous portion has a pyramidal shape and extends anteromedially and slightly superiorly from the middle of the temporal bone. Wedged between the sphenoid and occipital bones, it is seen here on slices 6 and 8 of the CT teaching scan. The petrous portion contains the densest bone of the cranium to protect the fragile structures of the middle and inner ear; it is from this quality that the bone takes its name in Latin for rocky or stone-like. 71. Temporal Bones Petrous Portion Scroll through these images of the CT teaching scan to view the petrous portion. 72. Auditory Ossicles Directly medial to the tympanic membrane are the 3 smallest bones in the body the auditory ossicles. Traveling medially from the external ear, the first structure you come to is the malleus, which is commonly likened to a hammer, and attached to the tympanic membrane. When sound vibrations strike the tympanic membrane, they are transmitted through the malleus to the incus. The incus, which is frequently compared to an anvil, passes the vibrations to the stapes, the smallest bone in the body. The stapes is shaped like a stirrup and is attached to the fenestra ovalis, or oval window, which then transmits the sound vibrations to the vestibule of the inner ear. Three semicircular canals arise superiorly from the vestibule. Inferiorly, sound vibrations travel through a spiral-shaped, fluid-filled canal called the cochlea. At the center of the cochlea, the sound vibrations reach the organ of Corti, the primary sensory organ of hearing, where fluid vibrations act upon tiny cochlear hair cells to invoke neural signals. 73. Temporal Bones Mastoid Portion The mastoid portion of the temporal bone is posterior to the tympanic portion. The mastoid portion articulates superiorly with the parietal bone and posteriorly with the occipital bone. This part of the temporal bone contains 2 important structures: the mastoid process and the mastoid air cells. The mastoid process is a cone-shaped bony protuberance extending anteroinferiorly from the mastoid portion of the temporal bone. It provides an attachment point for many of the muscles of the neck, including the sternocleidomastoid, which we ll discuss in more depth in Module 5 of

13 the Sectional Anatomy series. This structure tends to be bigger in men because men typically have larger neck muscles and therefore need a larger attachment point. Within the mastoid process, there are multiple hollowed-out spaces filled with air called the mastoid air cells. These spaces are important clinically because middle ear infections often can spread to the mastoid air cells, a condition known as mastoiditis. Like the paranasal sinuses, the mastoid air cells can have anatomic variants, and the spaces can be diminutive or excessively pneumatized. 74. Knowledge Check 75. Cranial Foramina The cranium is primarily composed of solid bone, so blood vessels, nerves and other structures need a way in and out of the bone. These structures typically pass through the cranium via foramina. Foramen is Latin for hole or opening. There are many foramina throughout the cranium, but we ll focus on the following 12: the carotid canal, foramina of the cribriform plate, hypoglossal canal, internal auditory canal, jugular foramen, foramen lacerum, foramen magnum, optic foramen, foramen rotundum, foramen ovale, foramen spinosum and the superior orbital fissure. The foramina we ll discuss are paired structures except for the foramen magnum. We ve grouped the foramina according to the bones in which they re found. Understand that many different structures travel through each of the foramen. We ll just focus on the primary structures. 76. Temporal Bone Foramina The internal auditory canal, carotid canal and jugular foramen are found in the temporal bone. The internal auditory canal is located in the petrous portion of the temporal bone and contains the facial and vestibulocochlear nerves. The carotid canal is located posterior to the apex of the temporal bone and contains the internal carotid artery and the carotid plexus of nerves. The most posterior foramen of the temporal bone is the jugular foramen, which can be divided into 3 segments: anterior, intermediate and posterior. The anterior segment contains the inferior petrosal sinus. The intermediate segment contains the glossopharyngeal, vagus and accessory nerves. The posterior segment contains the sigmoid sinus, which extends into the internal jugular vein. 77. Carotid Canal and Jugular Foramen This image is slice 33 of the CT teaching scan. Both the carotid canal and the jugular foramen are labeled on this image. 78. Internal Auditory Canal The internal auditory canal is labeled on slice 35 of the CT teaching scan. 79. Imaging the Temporal Bones

14 The temporal bones are typically imaged with CT without intravenous contrast. Thin-section multiplanar reconstructions are used to permit visualization of the intricate and complex bony anatomy. MR imaging with and without intravenous contrast is routinely used to visualize the contents of the internal auditory canals and adjacent soft tissue structures. Modern pulse sequences, primarily balanced steady-state free precession techniques, with proprietary acronyms such as TrueFISP (Siemens) and FIESTA (General Electric), provide exquisite detail of the seventh and eighth cranial nerves. 80. Sphenoid Bone Foramina The sphenoid bone contains the optic foramen, superior orbital fissure, foramen rotundum, foramen ovale, foramen spinosum and foramen lacerum. Let s talk about each of these structures. 81. Sphenoid Bone Foramina Located anteriorly in the sphenoid bone, the optic foramen contains the optic nerve and ophthalmic artery. Moving posteriorly, you encounter the cleft-like superior orbital fissure, which carries divisions of the ophthalmic veins, divisions of the oculomotor nerve, the trochlear nerve, the abducens nerve, and branches of the ophthalmic nerve. Next, you find the foramen rotundum, which takes its name from the Latin word for round, and contains the maxillary nerve. Continuing posteriorly, you come to the foramen ovale, which you might have guessed is named after its oval shape, and contains the mandibular nerve. The next foramen is the foramen spinosum, which holds the meningeal branch of the mandibular nerve. Finally, the foramen lacerum is located at the base of the medial pterygoid plate. This foramen takes its name from Latin for its lacerated shape and holds the internal carotid artery after the artery exits the carotid canal. 82. Foramina of the Cribriform Plate The ethmoid bone contains the many tiny foramina of the cribriform plate, which transmit the olfactory nerve bundles to the nose. This structure is labeled here on axial slice 42 of the CT teaching scan. 83. Occipital Bone Foramina We ll discuss 2 foramina in the occipital bone: the foramen magnum and hypoglossal canal. The foramen magnum, which is Latin for large hole, is the largest foramen and allows the medulla oblongata to extend from the cranium. The hypoglossal canal is located along the posterior border of the foramen magnum and transmits the hypoglossal nerve. 84. Knowledge Check 85. Knowledge Check 86. Knowledge Check

15 87. Knowledge Check 88. Zygomatic Bone As we discussed earlier, the zygomatic arches arise from the lower squamous portions of the temporal bones. Anteriorly, they articulate with the temporal processes of the zygomatic bones. The zygomatic bone or zygoma makes up the cheekbone, along with parts of the floor and lateral borders of the orbit. Four processes arise from the zygoma: the frontosphenoidal, the orbital, the maxillary and the temporal. Let s discuss the location of each of these processes. 89. Zygomatic Bone Frontosphenoidal Process The frontosphenoidal process extends superiorly to articulate with the frontal bone. Along its medial border, the process also articulates with the sphenoid bone. The frontosphenoidal process is labeled on slice 47 of the CT teaching scan. 90. Zygomatic Bone Orbital Process The orbital process extends posteromedially and articulates superiorly with the frontal bone and posteriorly with both the greater wing of the sphenoid and the orbital surface of the maxilla. This is axial slice 42 of the CT teaching scan. Note the location of the orbital processes. 91. Zygomatic Bone Maxillary Process The maxillary process extends anteromedially and articulates with the maxilla. The maxillary processes are labeled on slice 30 of the CT teaching scan. 92. Zygomatic Bone Temporal Process Located posteriorly, the temporal process articulates with the zygomatic process of the temporal bone, creating the zygomatic arch. The temporal arch is labeled on slice 35 of the CT teaching scan. 93. Zygomatic Processes Let s review the 4 processes that arise from the zygoma. Remember that each of these structures is three-dimensional and cannot be seen exclusively on a single CT slice. For this example, we ve labeled the structures. 94. Maxillae The next pair of bones we ll discuss are the maxillae. The maxillae are fused medially below the nose. Arising superiorly from each maxilla is the frontal process, which articulates with the frontal bone. This image is axial slice 34 of the CT teaching scan. 95. Nasal and Lacrimal Bones Before going into further detail about the maxilla, we ll discuss the nasal and lacrimal bones. The nasal bones are located between the frontal processes of the maxillae and make up the bridge of the nose. Posterior to the nasal bones are the lacrimal bones. They make up a portion of the medial walls of the orbits and articulate with the maxillae. The articulation between each lacrimal bone and maxilla forms a canal called the lacrimal canal. When the eyes water, tears flow through this canal into the nasal cavity. This is why we sometimes get a runny nose when our eyes water.

16 96. Maxilla Body Returning to our discussion of the maxilla, as you move inferiorly from the frontal process of each maxilla, you find the body of the maxilla, which is the location of each maxillary sinus. The body of the maxilla is labeled on axial slice 25 of the CT teaching scan. 97. Maxilla Alveolar Process The alveolar process is inferior to the body of the maxilla and extends along the inferior border of each maxilla. Each alveolar process contains multiple depressions for the roots of the teeth. 98. Maxilla Palatine Process Extending posteriorly from each alveolar process is the palatine process of the maxilla. The palatine process forms the anterior three-quarters of the hard palate. In addition to the palatine process, you can see the body of the maxilla on this image, which is slice 25 of the CT teaching scan. 99. Maxillae We just discussed the following facial bone structures: the frontal process of the maxilla, the nasal bones, the lacrimal bones, the body of the maxilla, the alveolar process of the maxilla and the palatine process of the maxilla. Scroll through this animation to review the location of each of these structures Palatine Bone The horizontal portion of the L-shaped palatine bone articulates with the posterior border of the palatine process of the maxilla and forms the roof of the mouth. The vertical portion of the palatine bone, or perpendicular plate, creates the lateral wall of the nasal cavity Vomer The vomer extends superiorly from the superior surface of both the horizontal portion of the palatine bone and the palatine process of the maxilla. It creates the inferior portion of the bony nasal septum. Although the nasal septum is technically a midline structure, it is angulated to 1 side in many individuals. This condition is called a deviated septum. Recall from an earlier slide that the CT teaching scan shows a deviated septum. You can see that structure here as it relates to the vomer Inferior Nasal Conchae The last pair of bones that complete the nasal cavity are the inferior nasal conchae or turbinates. These small, curled, scroll-like bone shelves extend medially into the nasal cavity from each maxilla. There are air spaces inferior to each nasal concha, including the superior and middle conchae of the ethmoid bone. These spaces allow air to swirl around the conchae and become warmed and humidified. Each space, or meatus, is named for its associated conchae. In other words, there are the superior, middle and inferior meatuses Mandible The final bone that completes our discussion is the mandible, the largest of the facial bones. The mandible is labeled here on slice 4, but it can be seen on many of the slices of the CT teaching scan. The mandible is commonly divided into 5 parts: the body, the ramus, the angle, the coronoid process and the condyloid process.

17 104. Mandible Body The curved horizontal portion of the mandible, called the body, contains its own alveolar process along the superior border. Like the alveolar process of the maxilla, the body of the mandible has many depressions for the roots of the teeth Mandible Rami The rami arise at nearly right angles from the posterior portions of the body of the mandible. This angle is called the mandibular angle, which is labeled on both the axial and sagittal views of this image. The gonion is the most inferior, posterior, and lateral point of the mandibular angle and constitutes an anatomic landmark. Two processes extend from the most superior portion of each mandibular ramus. The most anterior of these processes is the coronoid process, which provides an attachment point for the temporalis muscle. The most posterior of the processes is the condyloid process, which sits in the mandibular fossa of the temporal bone and helps form the temporomandibular joint. We ll discuss the temporomandibular joint a little later. The depression between the coronoid and condyloid processes is called the mandibular notch Mandible This series of images provides a view of all 5 parts of the mandible. The images are labeled to help you become familiar with the location of these structures Mandible Now scroll through the series of images without the labels. How many of the facial bones and structures can you identify? 108. Knowledge Check 109. Knowledge Check 110. Teeth The teeth develop in the maxilla and mandible. Humans are diphyodonts, meaning that they have 2 sets of teeth. The first set is called the deciduous, or baby, teeth. There are 20 deciduous teeth in total, with 1 of each of the following types found in each quadrant of the mouth: central incisors, lateral incisors, canines, first molars and second molars. Between the ages of 6 and 12, the deciduous teeth are pushed out by the developing permanent teeth Teeth There are 32 permanent teeth: 16 arise from the maxilla and 16 arise from the mandible. Moving from midline laterally, the maxillary and mandibular teeth are the central incisor, lateral incisor, canine, first premolar, second premolar, first molar, second molar and third molar. The third molars are commonly referred to as the wisdom teeth and are sometimes removed if they cause problems with the other teeth. In about a third of the population, the third molars do not form at all. Although there are normally only 4 wisdom teeth, some people may have more than 4; these additional teeth are called supernumerary teeth.

18 112. Tooth Numbering System Dentists use a tooth numbering system to uniquely identify each tooth. The numbering system starts with the maxillary third molar on the right side, which is labeled as number 1. Working medially, the right maxillary second molar is number 2, the right maxillary first molar is number 3, the right maxillary second premolar is number 4, the right maxillary first premolar is number 5, the right maxillary canine is number 6, the right maxillary lateral incisor is number 7 and the right maxillary central incisor is number 8. The numbering continues in a clock-wise direction until all 32 teeth have been numbered Tooth Anatomy Each tooth comprises a crown and a root. The crown is the portion of the tooth visible above the gum line, and the root is the portion below the gum line. Structural parts of each tooth include the pulp, dentin, cementum and enamel. The pulp is the innermost portion of the tooth; it s composed of soft connective tissue containing blood vessels and nerves. Dentin is a porous substance that encloses the pulp and acts as a protective layer. The cementum is a bone-like layer that surrounds the root of the tooth and provides an attachment point for the periodontal ligaments that stabilize the tooth. The enamel is the hardest substance in the body and coats the outside of the crown Tooth Anatomy Teeth are typically imaged in the dentist s office but it is still useful for radiology professionals to have an understanding of the teeth. Dental professionals acquire selected periapical and bitewing intraoral images to assess teeth health. The U.S. Army initially developed extraoral panoramic x-ray imaging to demonstrate soldiers teeth on a single image. This technology turned out to be better suited for evaluating mandibular pathology than for assessing the teeth. Many facilities no longer have the equipment necessary to perform panoramic x-ray imaging, but CT with multiplanar reconstructions has filled the void Tooth Anatomy The enamel, pulp and dentin are labeled here. The image on this slide is a sagittal view of slice 55 of the CT teaching scan Temporomandibular Joints The paired temporomandibular joints, commonly called the TMJs, are anterior to the external auditory meatus. The image on this slide is a sagittal view of slice 68. The TMJ is a ginglymoarthrodial joint, meaning it is both a sliding and hinge-type joint that allows movement during mastication. The osseous components of each TMJ include the mandibular condyle, articular eminence and the mandibular fossa. The mandibular fossa is a recess in the temporal bone that receives the mandibular condyle Temporomandibular Joints Scroll through this animation as we describe the temporomandibular joints.

19 The majority of the time, the TMJ acts solely as a hinge joint. It s only when the mouth is opened widely that the mandibular condyle slides within the mandibular fossa, as seen on this slide. Located anterior to the mandibular fossa, the articular eminence is a raised portion of the temporal bone that serves as an attachment point for ligaments and protects against anterior dislocation of the mandible. A fibrous capsule surrounds the joint and attaches to the articular eminence, the neck of the mandibular condyle and to the articular disc Temporomandibular Ligament The lateral or temporomandibular ligament stabilizes the TMJ and prevents dislocations. This triangular-shaped ligament is composed of 2 stacked bands of tissue, one in front of the other, that arise from the zygomatic process of the temporal bone and the articular eminence to insert just inferior to the mandibular condyle. The TMJ ligament prevents posterior movement of both the articular disc and mandibular condyle. Scroll through this animation to see these structures TMJ Muscles Now that we ve covered the joint involved in mastication, let s touch on the muscles behind that movement. There are 4 primary muscles that move the mandible: the temporalis, masseter, medial pterygoid and lateral pterygoid. The temporal muscle or temporalis elevates the mandible; it originates from the temporal bone and inserts on the coronoid process of the mandible. The masseter muscle consists of superficial and deep portions, both of which originate from the zygomatic arch and attach to the lateral ramus of the mandible. The masseter also elevates the mandible. The function of the pterygoid muscles is to help open and close the jaw. The medial pterygoid muscle originates from the lateral pterygoid plate and inserts on the medial surface of the ramus and the angle of the mandible. The medial pterygoid muscle closes the jaw. The lateral pterygoid muscle has 2 heads. One head originates from the greater wing of the sphenoid and inserts onto the articular disc; the other head originates from the lateral surface of the lateral pterygoid plate and inserts under the condylar process of the mandible. The lateral pterygoid muscle opens the jaw Orbit In discussing the orbit, we ll focus on 2 primary parts: the bony orbit and the eye itself. The bony orbits are paired conical structures that protect the delicate structures of the eye. Each orbit consists of 3 cranial bones and 4 facial bones. The base of each orbit comprises the frontal bone superiorly, the zygoma and frontal bone laterally, the maxilla and zygoma bones inferiorly, and the frontal, lacrimal and maxilla bones medially. The wall of each orbit consists of the frontal bone and the lesser wing of the sphenoid bone superiorly; the zygoma and the greater wing of the sphenoid bone laterally; the maxilla, zygoma and palatine bone inferiorly; and the frontal process of the maxilla, lacrimal bone, ethmoid bone and a small part of the body of the sphenoid medially. The optic canal is at the apex, or point of the cone. As you might recall from our previous discussion, the optic canal contains the optic nerve and ophthalmic artery. Two other openings are present at the apex of the bony orbit: the superior and inferior orbital fissures. The bones of the orbits are routinely imaged using CT without intravenous contrast.

20 121. Orbit Scroll through the images to see the location of each of the orbit bones. The orbital bones are not labeled here. Can you identify all of the structures of the orbit? 122. Eye The orbital septum is created by the palpebral ligaments, a membranous sheet that extends from the eyelids to the orbital rims. The septum is commonly used in radiology as a reference point in describing the location of pathological processes, such as infection, because this structure marks the anterior margin of the orbit. Therefore, the term preseptal would imply the soft tissues overlying the orbit such as the eyelid and periorbital soft tissues, and postseptal would indicate the soft tissues actually within the orbit Globe The globe of the eye, also known as the bulbus oculi, is the eyeball itself, without the muscles and other appendages. The globe is divided into 2 compartments by the lens. The lens is a clear biconvex structure that adjusts the focus of the eye, much like a knob on a microscope. The lens is primarily made up of water and proteins Cataract As people age, the proteins of the eye can clump together and cloud the lens, obscuring vision. This common condition is known as a cataract. Following the surgical removal of the clouded lens, a plastic or acrylic replacement lens is put into place. Note the difference in appearance between a clouded lens, a normal lens and a lens replacement in these images Eye Anatomy As its name implies, the anterior compartment of the eye is located anterior to the lens. It is a small cavity filled with a liquid substance called the aqueous humor. The anterior compartment contains the cornea and iris. The cornea is the clear front part of the eye that refracts light to help the eye focus. The iris controls the size of the pupil. An individual s eye color is actually the color of the iris Globe Anatomy Posterior to the lens is the larger posterior compartment, which is filled with a jelly-like substance called vitreous humor. The retina surrounds the posterior compartment. The optics of the eye project images onto the retina, and then, through many chemical and electrical impulses, the retina sends these images to the brain Lacrimal Gland Many structures help the eye move, stay healthy and perform its job. The first of these structures that we ll discuss is the lacrimal gland. The lacrimal gland is located in the superolateral border of the orbit. The gland creates tears to lubricate and flush foreign debris from the eye. Compare the location of the lacrimal gland in this illustration to the labeled image, which is axial slice 43 of the CT teaching scan.