Skull anatomy and positioning

skull anatomy and positioning radiology

1. DR. AMIT RAUNIYAR RESIDENT( 1 ST YEAR) RADIODIAGNOSIS & IMAGING NAMS SKULL ANATOMY AND RADIOLOGICAL POSITIONING

2. SKULL The skull is a bony structure that supports the face and forms a protective cavity for the brain. It is comprised of many bones, formed by intramembranous ossification, which are joined together by sutures (fibrous joints). The bones of the skull can be divided into two groups: those of the cranium (which can be subdivided the skullcap/ calvarium , and the cranial base) and those of the face .

3. The Cranium The cranium (also known as the neurocranium ), is formed by the superior aspect of the skull. It encloses and protects the brain, meninges and cerebral vasculature. Anatomically, the cranium can be subdivided into a  roof (known as the calvarium ), and a  base: Calvarium : Comprised of the frontal, occipital and two parietal bones. Cranial base:  Comprised of six bones – the frontal, sphenoid, ethmoid , occipital, parietal and temporal bones.

4. The human skull is generally considered to consist of twenty-two bones —eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the occipital bone , two temporal bones , two parietal bones , the sphenoid , ethmoid and frontal bones .

5. The facial skeleton (also known as the viscerocranium ) supports the soft tissues of the face. In essence, they determine our facial appearance. It consists of  14 individual bones, which fuse to house the orbits  of the eyes, nasal and oral cavities, as well as the sinuses. The frontal bone, typically a bone of the calvaria , is sometimes included as part of the facial skeleton.

6. CRANIAL(8)+FACIAL(14)=SKULL BONES(22)

7. The bones of the facial skeleton are the vomer , two nasal conchae , two nasal bones , two maxilla , the mandible , two palatine bones , two zygomatic bones , and two lacrimal bones

8. Coronal suture which fuses the frontal bone with the two parietal bones. Sagittal suture which fuses both parietal bones to each other. Lambdoid suture which fuses the occipital bone to the two parietal bones

9. Sutures of the Skull

10. FONTANELLE

11. In neonates, the incompletely fused suture joints give rise to membranous gaps between the bones, known as fontanelles . The two major fontanelles are the frontal fontanelle (located at the junction of the coronal and sagittal sutures) and the occipital fontanelle (located at the junction of the sagittal and lambdoid sutures).

12. The posterior fontanelle generally closes 2 to 3 months after birth; sphenoidal fontanelle around 6 months after birth; mastoid fontanelle closes next from 6 to 18 months after birth; and anterior fontanelle is generally the last to close between 18–24 months.

13. FOSSAE OF BRAIN

14. any of the three large depressions in the posterior, middle, and anterior aspects of the floor of the cranial cavity: a : the posterior one that is the largest and deepest of the three and lodges the cerebellum, pons , and medulla oblongata — called also posterior cranial fossa , posterior fossa b : the middle one that lodges the temporal lobes laterally and the hypothalamus medially — called also middle cranial fossa , middle fossa c : the anterior one that lodges the frontal lobes — called also anterior cranial fossa , anterior fossa

15. The pterion : a ‘H-shaped’ junction between temporal, parietal, frontal and sphenoid bones. The thinnest part of the skull. A fracture here can lacerate an underlying artery (the middle meningeal artery), resulting in a extradural haematoma . Anterior cranial fossa :  Depression of skull formed by frontal, ethmoid and sphenoid bones. Middle cranial fossa : Depression formed by sphenoid, temporal and parietal bones. Posterior cranial fossa : Depression formed by squamous and mastoid temporal bone, plus occipital bone.

16. SKULL ANTERIOR VIEW

17. Lateral Skull

18. PARANASAL SINUSES

19. SKULL TOPOGRAPHY

20. Landmarks Outer canthus of the eye : the point where the upper and lower eyelids meet laterally. Infra-orbital margin/point : the inferior rim of the orbit, with the point being located at its lowest point. Nasion : the articulation between the nasal and frontal bones. Glabella : a bony prominence found on the frontal bone immediately superior to the nasion . Vertex: the highest point of the skull in the median sagittal plane. External occipital protuberance ( inion ): a bony prominence found on the occipital bone, usually coincident with the median sagittal plane. External auditory meatus : the opening within the ear that leads into the external auditory canal.

21. Lines Inter-orbital (inter- pupillary ) line: joins the centre of the two orbits or the centre of the two pupils when the eyes are looking straight forward. Infra-orbital line: joints the two infra-orbital points. Anthropological baseline: passes from the infra-orbital point to the upper border of the external auditory meatus (also known as the Frankfurter line). Orbito-meatal base line (radiographic baseline): Extends from the outer canthus of the eye to the centre of the external auditory meatus . This line is angled approximately 10 degrees to the anthropological baseline.

22. Planes Median sagittal plane: divides the skull into right and left halves. Landmarks on this plane are the nasion anteriorly and the external occipital protuberance ( inion ) posteriorly . Coronal planes these are at right-angles to the median sagittal plane and divide the head into anterior and posterior parts. Anthropological plane: a horizontal plane containing the two anthropological baselines and the infra-orbital line. It is an example of an axial plane. Axial planes are parallel with this plane. Auricular plane: perpendicular to the anthropological plane. Passes through the centre of the two external auditory meatuses . It is an example of a coronal plane. The median sagittal , anthropological and coronal planes are mutually at right-angles.

23. POSITIONING CONSIDERATIONS Projections of the skull may be taken with the patient in the recumbent or erect position, depending on the patient's condition. Images can be obtained in the erect position with the use of a standard x-ray table in the vertical position or an upright Bucky.

24. PATIENT PREPARATION Ensure that all metal objects are removed from the patient, e.g. hair clips and hairpins. Bunches of hair often produce artefacts and thus should be untied. False teeth containing metal and metal dental bridges should be removed.

25. USEFUL ACCESSORIES

26. Every effort should be made to make the patient's body as comfortable as possible, Positioning aids such as sponges, sandbags, and pillows should be used if needed. Except in cases of severe trauma, respiration should be suspended during the exposure to help prevent blurring of the image caused by breathing movements of the thorax.

27. Exposure Factors The principal exposure factors for radiography of the skull include the following: Medium kV (65 to 85 kV film-based) (70 to 80 kV digital radiography [DR] and computed radiography [CR] Small focal spot <250 mA (if equipment allows) Short exposure time

28. Source to image receptor distance(SID) The minimum SID with the image receptor in the table or upright Bucky is 40 inches (100 cm).

29. Radiation Protection The best techniques for minimizing radiation exposure to the patient in skull radiography are to (1) use good collimation practices, (2) immobilize the head when necessary, minimizing repeats, and (3) center properly.

30. Gonadal shielding Generally, with accurate collimation, no detectable contribution to gonadal exposure occurs during radiography of the skull. However, lead shields should be used to reassure the patient.

31. Image receptor (IR) - the device that captures the radiographic image that exits the patient; film/screen cassettes and digital acquisition devices Central ray (CR) - the center-most portion of the x-ray beam emitted from the x-ray tube; has the least divergence Bucky surface A bucky is typically used for table or wall mounted x-ray systems and holds the x-ray cassette and grid. A bucky , is a device found underneath the exam table, a drawer like device that the cassette and grid is slid into before shooting x-ray.

32. Grids are placed between the patient and the X-ray film to reduce the scattered radiation and thus improve image contrast. They are made of parallel strips of lead with an interspace having an aluminum or organic spacer.

33. BASIC VIEWS LATERAL OCCIPITO FRONTAL / PA 0° PA- AXIAL 15° (CALDWELL) or PA axial 25° to 30° FRONTO OCCCIPITAL / AP VIEW AP-AXIAL (TOWNE)

34. Skull Series BASIC SPECIAL • Submentovertex (SMV) • PA axial (Haas method)

35. PA 0° The skull PA view is a non-angled PA radiograph of the skull. This view provides an overview of the entire skull rather than attempting to highlight any one region.

36. PA 0° Part Position Flex neck, aligning OML perpendicular to IR. Align midsagittal plane perpendicular to midline of table/Bucky to prevent head rotation and/or tilt (EAMs same distance from table/Bucky surface). centring point the beam is exiting at the nasion Rest patient's nose and forehead against table/Bucky surface. Center IR(Image receptor) to CR(central ray).

37. Technical factors posteroanterior projection collimation superior to the skin margins inferior to include the most inferior aspects of the skull lateral to include the skin margin orientation   portrait detector size 24 cm x 30 cm exposure 75-80 kVp 20-25 mAs SID 100 cm grid yes

38. Structures Shown : Frontal bone, crista galli , internal auditory canals, frontal and anterior ethmoid sinuses, petrous ridges, greater and lesser wings of sphenoid. Pathology demonstrated: Skull fractures (medial and lateral displacement)

39. PA AXIAL PROJECTION (Caldwell Method) The Caldwell view  is a caudally angled PA 15° CR or 25° to 30° CR radiograph of the skull, designed to better visualise the paranasal sinuses, especially the frontal sinus. Alternate 25° to 30°: An alternate projecion that allows better visualization of the superior orbital fissures , the foramen rotundum , and the inferior orbital rim

40. PA AXIAL PROJECTION (Caldwell Method) OML perpendicular to IR. Angle CR 15° caudad and Alternate with CR 25° to 30° caudad , OML forms 15 degree with horizontal central ray center to exit at nasion

41. Part Position Rest patient's nose and forehead against table/Bucky surface. Flex neck as needed to align OML perpendicular to IR. Align midsagittal plane perpendicular to midline of the grid or table/Bucky surface to prevent head rotation and/or tilt.

42. Structures Shown: Greater and lesser sphenoid wings, frontal bone, superior orbital fissures, frontal and anterior ethmoid sinuses, superior orbital margins, and crista galli are shown.

43. AP view The skull AP view  is a nonangled AP radiograph of the skull. This view provides an overview of the entire skull rather than attempting to highlight any one region. Position : supine OML perpendicular to Cassette(IR) the beam travels anterior to posterior (AP) direction, with 0° of angulation through the nasion . Central ray :perpendicular 5cm above nasion

44. AP PROJECTION

45. AP AXIAL(TOWNE) The Towne view  is an angled AP radiograph of the skull. AP AXIAL projection Position : prone/seated OML perpendicular to cassette(IR). For patients unable to flex their neck to this extent, align the IOML perpendicular to the IR.

46. Central Ray Angle CR 30° caudad to OML, or 37° caudad to IOML. (A 7° difference exists between the OML and the IOML.) Center at the midsagittal plane 2. inches (6.5 cm) above the glabella to pass through the foramen magnum at the level of the base of the occiput . Center IR to projected CR.

47. Advantages Occipital bone and posterior fossa space better evaluated than with a nonangulated AP view, which would have more skull base and facial bone overlap May be a useful additional view for evaluating skull fractures

48. Structures seen : Occipital bone, petrous pyramids, and foramen magnum are shown with the dorsum sellae and posterior clinoids visualized in the shadow of the foramen magnum.

49. Lateral view It is named according to the side of the head nearer to the image receptor. Central Ray Align CR perpendicular to IR. Center to a point 2.5 inches (5 cm) superior to EAM . IOML is perpendicular to cassette Pathology Demonstrated Skull fractures. A common general skull routine includes both right and left laterals.

50. Part Position Place the head in a true lateral position, with the side of interest closest to IR and the patient's body in a semiprone position as needed for comfort. Align midsagittal plane parallel to IR, ensuring no rotation or tilt. Align interpupillary line perpendicular to IR, ensuring no tilt of head .

51. Structures seen: Superimposed cranial halves with superior detail of the lateral cranium closest to the IR are demonstrated. The entire sella turcica , including anterior and posterior clinoids and dorsum sellae , is also shown. The sella turcica and clivus are demonstrated in profile.

52. Base Posterior Skull Measure: A-P at Glabella SID: 40” Bucky • Tube Angle: None but if patient cannot extend head back far enough to get inferior orbital meatal line perpendicular to horizontal CR tube angle may be needed

53. Patient is seated in a reclining chair. The chair is placed about 6” to 10” from Bucky. • Patient is asked to extend neck back until inferior orbital meatal line is parallel to film with top of skull touching the Bucky

54. Horizontal CR: EAM • Vertical CR: midsagittal • Center film to horizontal CR • Collimation: slightly less than film size or skin of skull • Breathing Instructions: suspended respiration • Make exposure

55. The entire skull is visualized. • The mandible and frontal region of skull are superimposed. • With a bright light, the zygomatic arches can usually be seen.

56. OTHER VIEWS

57. Schullers Projection The Schullers Projection can be used to evaluate the temporal mandibular joints and mastoid air cells and inner ear. Tube angle: 25 degrees caudal

58. Structures seen Mastoid air cells External auditory canal Tympanic cavity Temporomandibular joint

59. Waters Projection Sinus Measure: A-P at Glabella No tube angle

60. Patient is seated facing the Bucky. Get the chair as close to the Bucky as possible. Patient may spread legs to get chair as close as possible. May also be taken standing. • Mentomeatal line should be perpendicular to film with mouth closed.

61. Horizontal CR: exit through the base of nose or acantha . • Vertical CR: mid- sagittal • Center film to horizontal CR