Skull Anatomy & Positioning PDF

Radiographic Procedures II Skull Part 2 – Cranial Anatomy & Positioning Jena Heflin, MBA, RT(R)
Skull Overview Consists of 22 separate bones – Cranial Bones (8) – Facial Bones (14) Four sutures connect the cranial bones – Coronal – Sagittal – Squamosal – Lambdoidal  Cranial Bones Calvaria Cranial...

Radiographic Procedures II Skull Part 2 – Cranial Anatomy & Positioning Jena Heflin, MBA, RT(R)
Skull Overview Consists of 22 separate bones – Cranial Bones (8) – Facial Bones (14) Four sutures connect the cranial bones – Coronal – Sagittal – Squamosal – Lambdoidal  Cranial Bones Calvaria Cranial Floor – Frontal – Occipital – Right Parietal – Left Parietal – Ethmoid – Sphenoid – Right Temporal – Left Temporal  1 Frontal Bone Divided into two portions: – Vertical Portion a.k.a. Squamous Portion & Frontal Squama Forms the forehead – Horizontal Portion a.k.a. Orbital Portion Forms the superior part of the orbit  Frontal Bone Supraorbital Groove (SOG) – Slight depression above each eyebrow – Marks the highest level of facial bone mass Supraorbital Margin (SOM) – Superior rim of the orbit Supercilliary Ridge (Arch) – Ridge of bone beneath each eyebrow  Frontal Bone Glabella – Smooth raised prominence between the eyebrows just above the bridge of the nose – Lies between the superciliary ridges Ethmoidal Notch – Ethmoid bone fits into notch Nasal Spine (a.k.a. Frontal Spine) – Found at the anterior end of the ethmoidal notch – Most superior part of the nasal septum  2 Frontal Bone – Anterior Aspect  Frontal Bone – Lateral Aspect  Frontal Bone – Inferior Aspect 3 Occipital Bone Consists of 4 parts – Squamous Portion (a.k.a. Squama) Saucer-shaped external surface – 2 Occipital Condyles Extend anteriorly, one on each side of the foramen magnum Articulate with the atlas (C1) to form the atlanto-occipital joint (only bony articulation between the skull and neck) – Basilar Portion Joins with the body of the sphenoid bone
Occipital Bone Foramen Magnum – Opening through which the spinal cord passes as it leaves the brain Jugular Foramen – Allows blood to drain from the brain via the internal jugular vein Hypoglossal Canals – Located on the ends of the occipital condyles

Occipital Bone – Internal Surface
 4 Occipital Bone – External Surface
 Occipital Bone – Lateral Aspect
 Parietal Bone Roughly square and convex in shape Form the sides of the cranium Form the posterior portion of the cranial roof Each parietal bone contains a parietal eminence – Corresponds with the width measurement of the skull
 5 Parietal Bone – External Surface
 Parietal Bone – Internal Surface
 Ethmoid Bone Small, cube-shaped bone Consists of: – Horizontal Plate – Vertical Plate – 2 Labyrinths Situated between the orbits
 6 Ethmoid Bone Horizontal Plate (a.k.a. Cribriform Plate) – Perforated by many foramina for transmission of olfactory nerves – Crista Galli Thick, conical process projecting superiorly from the cribriform plate Looks like a “rooster’s comb” Vertical Plate (a.k.a. Perpendicular Plate) – Thin, flat bone that projects inferiorly from the cribriform plate
Ethmoid Bone Labyrinths – Contain ethmoid sinuses (or air cells) – Walls form part of the medial orbit and the lateral nasal cavity – Two thin, scroll-shaped processes project inferiorly from each medial wall Superior Nasal Conchae (Turbinate) Middle Nasal Conchae (Turbinate)  Ethmoid Bone – Anterior Aspect 
7 Ethmoid Bone – Lateral Aspect  Superior Aspect  Sphenoid Bone Irregularly wedge-shaped bone Resembles a bat with its wings extended Situated in the base of the cranial floor Only bone to articulate with all remaining cranial bones Consists of: – Body 2 Lesser Wings 2 Greater Wings – 2 Pterygoid Processes  8 Sphenoid Bone Body of Sphenoid Bone – Contain 2 sphenoidal sinuses – Superior surface contains the sella turcica – Contains a carotid sulcus on either side of the sella turcica Internal Carotid Artery Cavernous Sinus  Sphenoid Bone Sella Turcica – Saddle-like depression that houses the pituitary gland – Lies in the MSP of the cranium – Located ¾ inch anterior and ¾ inch superior to the level of the EAM – Dorsum sellae – posterior boundary of sella turcica – Clivus Slanted area of bone posterior and inferior to dorsum sellae  Sphenoid Bone – Sella Turcica  9 Sphenoid Bone Lesser Wing – Triangular shaped, horizontal position – Project laterally from body of sphenoid – Posterior ends form the anterior clinoid processes – Optic canal Circular opening between the two roots of the anterior clinoid process  Sphenoid Bone Greater Wing – Form the sides of the body of sphenoid – Contain foramina rotundum, ovale, and spinosum Pterygoid Processes – Arise from the body and greater wings – Consists of a medial and lateral pterygoid laminae, which are fused together – Pterygoid Hamulus Elongated hook-like process on the inferior extremity of the medial lamina process  Sphenoid Bone – Superior Aspect  10 Sphenoid Bone – Oblique Aspect 
Temporal Bone Situated between the greater wings of the sphenoid bone and the occipital bone Consists of 4 main parts: – Squamous Portion – Tympanic Portion – Mastoid Portion – Petrous Portion  Temporal Bone Squamous Portion – Thin, upper portion – Most vulnerable portion of the skull to fracture – Zygomatic process – projects anteriorly to articulate with the zygomatic bone Tympanic Portion – Situated below the squamous portion – Forms most of the EAM (approx. ½ inch long) – Styloid Process – slender point of bone extending inferiorly  11 Temporal Bone Mastoid Portion – Mastoid Process – prominent portion Larger in males than in females Contain mastoid air cells, which start to develop after birth Number and size of mastoid air cells vary greatly Occasionally, they are absent altogether  Temporal Bone Petrous Portion – a.k.a Petrous Pyramid – Thickest, densest bone in the cranium – Contains organs for hearing and balance – Internal Auditory Meatus (IAM) Transmit the vestibulocochlear & facial nerves – Petrous Ridge Upper border of the petrous portion Same level as TEA  Temporal Bone – Lateral Aspect  12 Temporal Bone – Internal Surface  Temporal Bone – Coronal Section  Image Analysis Presentation of radiographs, pertinent anatomy, and positioning criteria  13 General Considerations 10 x 12 IRs 40-inch SID Use full lead apron for shielding Views taken on suspended respiration  PA Axial (Caldwell Method) Patient upright or supine CR angled 15° caudal (23° if using GML) – If no angle is used, petrous pyramids will fill the orbits Patient’s forehead and nose are resting on the bucky or table MSP & OML ⊥ to IR CR exits the nasion 
AP Axial (Caldwell Method) Patient upright or supine CR angled 15° cephalic (23° if using GML) – If no angle is used, petrous pyramids will fill the orbits MSP & OML ⊥ to IR CR enters the nasion  14 PA Axial (Caldwell Method) Structures Seen Petrous pyramids seen in the lower 1/3 of the orbits Orbits are equidistant from skull borders Symmetric petrous ridges *For AP Axial Caldwell Method, orbits will appear magnified  AP Axial (Towne Method) Patient supine CR angled 30° caudal (37° if using IOML) – You will need to remeasure SID due to tube angle & increase kVp by 5 MSP & OML ⊥ to IR CR enters 2 ½ inches above glabella and exits the foramen magnum, passing through the level of the EAM  AP Axial (Towne Method) Structures Seen Dorsum sellae is seen projected within the foramen magnum Symmetric petrous pyramids Demonstrates occipital bone and posterior portion of parietal bones  15 PA Axial (Haas Method) Patient supine with elbows flexed CR angled 25° cephalic – You will need to remeasure SID due to tube angle & increase kVp by 5 MSP & OML ⊥ to IR CR enters 1½ inches below the inion to exit 1½ inches superior to the nasion  PA Axial (Haas Method) Structures Seen Dorsum sellae is seen projected within the foramen magnum Symmetric petrous pyramids Demonstrates occipital bone and posterior portion of parietal bones  Lateral Projection Pt. positioned RAO or LAO; head is turned lateral (have pt. lie on the ear) MSP is // to IR IOML is ⊥ to the front edge of the IR IP is ⊥ to the IR CR enters about 2 inches above EAM  16 Lateral Projection Structures Seen Sella turcica is seen in profile Superimposed orbital roofs, greater wings of sphenoid, mastoid regions and TMJ’s No overlap of cervical spine by mandible  Submentovertical (SMV) Projection a.k.a. Schuller Method Pt. seated upright (supine is more difficult) Flex head back to place IOML // with the IR MSP is ⊥ to IR CR enters ⊥ to IOML, through sella turcica – At MSP between mandibular angles at a level ¾ inch anterior to EAM  Submentovertical (SMV) Projection Structures Seen Symmetric petrous pyramids Superimposition of mental protuberance over anterior frontal bone Demonstrates cranial base 
17 Cross-Table Lateral Projection Pt. supine with head in true AP position (no rotation) Elevate head on sponge to place head in the center of the IR Side of interest in contact with IR MSP is vertical and IP line is ⊥ to the IR CR enters horizontal and 2-inches superior to EAM Must rule out cervical injury before placing a sponge behind the patient’s head  Trauma AP/AP Axial Projection Pt. semisupine with head turned in true lateral Elevate head on sponge to place head in the center of the IR. Back of head against IR. MSP & OML ⊥ to the IR CR 0° or 15° cephalic CR enters at the nasion Must rule out cervical injury before placing a sponge behind the patient’s head  Hmmm… Critical Thinking WHAT WOULD YOU DO?  18 Situation A radiograph of an AP axial projection of the cranium reveals that the right petrous ridge is wider than the left side. Which specific positioning error is present on this radiograph? Choice A Choice B The skull is rotated to the right The skull is rotated to the left  Situation An AP axial (Towne) radiograph reveals that the foramen magnum appears closed. Which specific positioning error has occurred? Choice A Choice B The head is hyperextended The chin is tucked in too far  Situation A patient comes into the radiology department with a possible tumor of the pituitary gland. Which projection of the routine skull series will best demonstrate any bony involvement of the sella turcica? Correct Answer:  19 Assignment See course schedule for reading assignment Skull Worksheet – Section 1: Exercise 1 – 6 – Section 2: Exercise 2 Study Positioning Notes!!!  20