Skull

RADIOGRAPHY OF THE SKULL

SKULL RADIOGRAPHIC ANATOMY

Skull As with other body parts, radiography of the skull requires a good understanding o all related anatomy. The anatomy o the skull is very complex, and specific attention to detail is required of the technologist.

The skull, or bony skeleton of the head, rests on the superior end o the vertebral column and is divided into two main sets o bones—8 cranial bones and 14 facial bones

CRANIAL BONES

The eight bones of the cranium are divided into the calvarium (skullcap) and the floor. Each of these two areas primarily consists o our bones.

Calvarium (Skullcap)

• Frontal
• Right parietal
• Left parietal
• Occipital

FLOOR

• Right temporal
• Left temporal
• Sphenoid
• Ethmoid

Joint of the cranium ( sutures)

Adult Cranium

The articulations or joints o the cranium are called sutures and are classified as fibrous joints. In an adult, these are immovable and there fore are synarthrodial-type joints.

sutures

INFANT

• Anterior Fontanel
• Posterior Fontanel
• Right sphenoid Fontanel
• Left sphenoid fontanel
• Right mastoid fontanel
• Left mastoid fontanel
• ADULT
• Bregma
• Lambda
• Right pterion
• Left pterion
• Right asterion

Left asterion

cranial Bones—PA Axial Caldwell Projection −15˚ caudad (Fig. 11.21) A. Supraorbital margin of the right orbit

• B. Crista galli of ethmoid
• C. Sagittal suture (posterior skull)
• D. Lambdoidal suture (posterior skull)

E. Petrous ridge

Cranial Bones—AP Axial Projection (Fig. 11.22)

• A. Dorsum sellae of sphenoid
• B. Posterior clinoid processes
• C. Petrous ridge or petrous pyramid
• D. Parietal bone
• E. Occipital bone

F. Foramen magnum

Cranial Bones—Lateral Projection (Fig. 11.23)

A. EAM

• B. Mastoid portion o temporal bone
• C. Occipital bone
• D. Lambdoidal suture

E. Clivus

• F. Dorsum sellae
• G. Posterior clinoid processes
• H. Anterior clinoid processes
• I. Vertex o cranium
• J. Coronal suture
• K. Frontal bone
• L. Orbital plates
• M. Cribriform plate

N. Sella turcica O. Body o sphenoid (sphenoid sinus) P. Petrous portion o temporal bone

Anatomy:

The skull is composed of 22 bones composing of the cranium (vault and base) and facial bones.

• It forms a protective covering of the brain.

The floor of the cranium is divided into anterior, middle and posterior cranial fossae.

Terminologies :

The radiography of the skull is carried out with reference to visible or palpable landmarks and recognized lines and planes of the skull.

Landmarks:

• Outer canthus of the eye: This is where the upper and lower eyelids meet laterally.
• Infra-orbital points: This is the lowest point of the inferior orbital margin.

Nasion: This is the infronto-nasal articulation.

Glabella: A bony prominence just above the nasion.

Vertex: this is the highest point of the skull in the Median sagittal plane.

External- occipital protuberance (inion): This is a bony prominence on the occipital bone.

External auditory meatus: This is the opening into the external Auditory canal.

Lines:

Interorbital (interpupillary) line: Is a line joining the center of two orbits or the center of two pupils when the eyes are looking straight forward. This is straight angles to the median sagittal plane.

Infraorbital line: This joins two infra-orbital points.

Anthropological base line: This passes from the infra-orbital point to the upper border of the external auditory meatus.

Skull

Auricular line: This line is perpendicular to anthropological base line and passing through the center of the external auditory meatus. It is in a coronal plane.

Orbito-meatal base line: This extends from the outer canthus of the eye to the center of the external auditory meatus. The line is about 10⁰ to the anthropological base line.

PLANES:

Median sagittal plane: Divides the skull into right and left halves. Landmarks of this plane are the nasion anteriorly and the external occipital protuberance (inion) posteriorly.

Orbito-meatal plane: This contains the two orbito-meatal basal lines and is of an angle of 10 degrees to the anthropological plane.

Anthropological plane(Frankfurter line): Is a horizontal plane containing the two anthropological basal lines and infra-orbital line.

Skull

Coronal planes: Are at right angles to the median sagittal plane and divide the head into an anterior part and posterior part.

Auricular plane: Is perpendicular to the anthropological plane and passes through the center of the two external auditory meatuses. It is one of the coronal planes.

Radiographic anatomy

Preparation of the Skull:

All radio-opaque materials should be removed when examining the skull. Materials such as ear-rings, hair grips, zip fasters, spectacles etc.

Preparation of the patient

Before undertaking skull radiography, the following specific considerations should be made:

• Ensure that all metal objects are removed from the patient, e.g. hair clips and hairpins.
• Bunches of hair often produce artifacts and thus should be untied.
• If the area of interest includes the mouth, then false teeth containing metal and metal dental bridges should be removed.
• The patient should be provided with a clear explanation of any movements and film positions associated with the normal operation of the skull unit.

Useful accessories

• The usefulness of foam pads as an aid to immobilization cannot be overstated. The photograph opposite shows a specially designed pad for skull radiography. It is available in a range of sizes to accommodate different age groups.
• Forty-five-degree triangular pads are extremely useful for immobilizing children. They can be held by the parent and support the head without the parent placing their hands in the primary beam.
• Individual side markers are essential for skull radiography, as the clip-type side markers are easily lost in the collimation, particularly when using a skull unit.
• Velcro straps are of great use when immobilizing a patient on a skull unit.

Positioning:

Accurate positioning of the skull is essential in order to produce a proper radiograph of a skull. Poor positioning may mislead the diagnosis desired.

CRANIUM

The examination of the skull is divided into the cranium and the facial bones.

A number of particular regions have their own specific techniques and these will be dealt with in turn.

When a patient is sent to the x-ray department with a request for the “skull” to be x-rayed, this normally refers to the cranium only.

Skull

Film: A 24 x 30 cms film is used for each view. Each film is placed longitudinally except for the lateral view when it is placed transversely.

• Routine views: -occipito-frontal
• -lateral
• Alternative views: -fronto-occipital
• 30⁰ fronto-occipital

Position terminology

Occipito-frontal

The patient lies prone on the x-ray table with his/her hands clasped beneath his/her chest so that the neck can be slightly flexed without too much strain.

The forehead and the nose rest on the table.

The head is adjusted so that the median sagittal plane and the radiographic base line are at 90⁰ to the film.

The median sagittal plane should be in the mid-line of the table.

Centre: – vertically, in the mid-line, 5 cms (2ins) below the radiographic base line.

The low centering point results in the up ward projection of much of the cranium vault above the dense petrous temporal bones.

In the correctly positioned film, the petrous temporal bones appear within the orbits. The cassette should be placed so that the upper border is 5 cms (2 ins) above the vertex.

Skull

Occipito-frontal (OF) projections can be employed with different degrees of beam angulation. The choice of projection will depend upon departmental protocol and the anatomy that needs to be demonstrated.

Position of patient and image receptor

This projection may be undertaken erect or in the prone position.

The erect projection will be described, as the prone projection may be uncomfortable for the patient and will usually only be undertaken in the absence of a vertical Bucky/image receptor.

• The patient is seated facing the erect Bucky/receptor so that the median sagittal plane is coincident with the midline of the image receptor and is also perpendicular to it.
• The neck is flexed so that orbito-meatal baseline is perpendicular to the image receptor. This can usually be achieved by ensuring the nose and forehead are in contact with the Bucky/receptor.
• Ensure the mid part of the frontal bone is positioned in the centre of the Bucky/receptor.
• The patient may place the palms of each hand either side of the head (out of the primary beam) for stability

Direction and location of the X-ray beam OF

• The collimated horizontal beam is directed perpendicular to the Bucky/receptor along the median sagittal plane.
• The beam collimation should include the vertex of the skull superiorly, the region immediately below the base of the occipital bone inferiorly and the lateral skin margins.

It is important to ensure the tube is centred to the centre of the Bucky receptor.

OF10°↓, OF15°↓, OF20°↓:

• The technique used for these three projections is similar to that employed for the OF except a caudal angulation is applied.

The degree of angulation will depend upon the technique, i.e. for an OF20↓ projection a 20° caudal angulation will be employed

• Ensure the collimated horizontal beam is always centred to the centre of the Bucky/image receptor after the tube angulation has been applied and not before.

Essential image characteristics

• All the cranial bones should be included within the image including the skin margins.
• It is important to ensure the skull is not rotated. This can be assessed by measuring the distance from a point in the midline of the skull to the lateral margin.

If this is the equidistant from both sides of the skull then it is not rotated.

Essential image characteristics (cont.) (Figs 8.11a–8.11c)

• The degree of beam angulation can be evaluated from an assessment of the position of the petrous ridges within the orbits:
• OF: the petrous ridges should be completely superimposed within the orbit with their upper borders coincident with the upper 1/3 of the orbit.
• OF10°↓: the petrous ridges appear in the middle 1/3 of the orbit
• OF15°↓: the petrous ridges appear in the lower 1/3 of the orbit.
• OF20°↓: the petrous ridges appear just below the inferior orbital margin.

Radiological considerations

• Asymmetry of projection of the squamo-parietal suture due to rotation increases the risk of it being mistaken for a fracture.
• As the beam angle increases, more of the orbital region is demonstrated. Thus the site of the suspected pathology should be considered when selecting the beam angle, e.g. an injury to the superior orbital region can be best evaluated with an OF20°↓ projection.

Common faults and solutions

• Rotation: ensure the patient has maintained their position immediately before the exposure is made.
• Incorrect beam angulation: NB: increased beam angulations will result in the petrous ridges appearing more inferiorly in the orbit.

If an OF20°↓ is undertaken and the petrous bones appear in the middle 1/3 of the orbit, then a greater angle should have been applied, in this case a further 10°.

Lateral erect (Figs 8.9a–8.9c)

This position may be used for a co-operative patient. Variations from the supine horizontal beam technique are noted below but all other imaging criteria remain the same.

Position of patient and image receptor

• The patient sits facing the erect Bucky/receptor and the head is then rotated such that the median sagittal plane is parallel to the Bucky/receptor and the interpupillary line is perpendicular to the Bucky/ receptor
• The shoulders may be rotated slightly to allow the correct position to be attained and the patient may grip the Bucky inferiorly for stability.
• Position the image receptor transversely such that its upper border is 5 cm above the vertex of the skull.
• A radiolucent pad may be placed under the chin/lower half of the face, for support.

Direction and location of the X-ray beam

• The X-ray tube should be centred to the Bucky/image receptor and the ‘tracking’ facility utilised if available.
• Adjust the height of the Bucky/tube so that the patient is comfortable (NB: do not decentre the tube from the Bucky at this point).
• Centre with a collimated horizontal beam midway between the glabella and the external occipital protuberance to a point approximately 5 cm superior and posterior to the EAM.

Common faults and solutions

• This is not an easy position for the patient to maintain.

Check the position of all planes immediately prior to the exposure; the patient may have moved.

Notes

• This projection can also be performed with the patient prone on a floating-top table with a collimated vertical beam.
• The projection may usefully be performed on babies in the supine position with the head rotated to either side.
• An air/fluid level in the sphenoid sinus (an indicator for a base of skull fracture) will not be visible if the patient is imaged with a collimated vertical central ray. This is not relevant in young babies, as the sinus is not fully developed.

Lateral:

• The patient lies semi-prone on the x-ray table.
• The affected side of the head is in contact with the table.
• The arm of the affected side rests along the table by the patient’s trunk.

The other arm is flexed and the hand rests on the table in front of the face.

The knee of the unaffected side is flexed and rest on the table.

The body is more relaxed in this position.

The head is adjusted to bring the sagittal plane parallel to the table and the interpupillary line perpendicular to the film.

A small radiolucent pad under the neck and chin may help to achieve this position.

Centre:- vertically, to a point mid-way between the glabella and the external occipital protuberance.

Fronto-occipital (Figs 8.12a–8.12c)

Fronto-occipital (FO) projections of the skull will demonstrate the same anatomy as OF projections.

The orbits and frontal bone however, will be magnified as they are positioned further from the image receptor. Such projections should only be undertaken when the patient cannot be moved and must be imaged supine.

These projections result in an increased radiation dose to the orbits and some loss of resolution of the anterior skull structures due to increased object-to-receptor distance.

Position of patient and image receptor

• The patient lies supine on the trolley (or X-ray table) with the posterior aspect of the skull resting on the image receptor/ gridded CR cassette.
• The head is adjusted to bring the median sagittal plane at right-angles to the image receptor and coincident with its midline. In this position the EAMs are equidistant from the image receptor to ensure no rotation.
• The orbito-meatal baseline should be perpendicular to the image receptor

Direction and location of the X-ray beam

• All angulations for FO projections are made cranially.
• The collimated vertical X-ray beam is directed perpendicular to the image receptor along the median sagittal plane.
• The collimated field should be set to include the vertex of the skull superiorly, the base of the occipital bone inferiorly and the lateral skin margins.

It is important to ensure that the tube is centered to the image receptor and ‘tracking’ applied if available.

FO10°↑, FO15°↑, FO20°↑:

• The technique used for these three projections is similar to that employed for the OF except cranial angulations are applied.

The degree of angulation will depend upon the projection required.

• Remember that the image receptor must be displaced superiorly to allow for the tube angulation, otherwise the area of interest will be projected off the image.

Common faults and solutions

• See OF projections.
• Remember increasing the degree of cranial angulation will project the petrous ridges more inferior in the orbits.

Occipito-frontal 20⁰ caudad

This is the second mostly used of view sometimes called the surveying view.

It does not show such a lucid surface of the cranium but gives better view of the orbits and particularly the wings of sphenoids.

The petrous bones are projected to the lower border of the orbit.

Position of the patient

The patient lies in the prone position like an ordinary O.F Centre:- in the mid-line above the external occipital protuberance to emerge through the nasion the tube angled 20⁰ caudad.

30⁰ fronto-occipital (Towne’s view)

• This is the best view for demonstrating the occipital bone.
• The patient lies supine on the x-ray table.

The median sagittal plane should be at right angles to the mid-line of the table.

The patient depressed his/her chin to bring the radiographic base line to 90⁰ to the table.

Half axial, fronto-occipital 30° caudal (Towne’s projection)

Position of patient and image receptor

• The patient lies supine on a trolley (or X-ray table) with the posterior aspect of the skull resting on an image receptor/ gridded CR cassette
• The head is adjusted to bring the median sagittal plane at right-angles to the image receptor and so that it is coincident with its midline.
• The orbito-meatal baseline should be perpendicular to the image receptor.

Direction and location of the X-ray beam

• The collimated vertical beam is angled caudally so it makes an angle of 30° to the orbito-meatal plane.
• To avoid irradiating the eyes the collimation is set to ensure the lower border is coincident with the superior-orbital margin and the upper border includes the skull vertex. Laterally the skin margins should also be included within the field.7
• The top of the receptor should be positioned adjacent to the vertex of the skull to ensure the beam angulation does not project the area of interest off the bottom of the image.

Essential image characteristics (Fig. 8.13b)

• The sella turcica of the sphenoid bone is projected to appear within the foramen magnum.
• The image must include all of the occipital bone and the posterior parts of the parietal bone and the lambdoidal suture should be clearly visualised.
• The skull should not be rotated. This can also be assessed by ensuring the sella turcica appears centrally in the foramen magnum.

Radiological considerations

• The foramen magnum should be clearly seen on this projection. The margins may be obscured by incorrect angulation, thus hiding serious fractures.
• The zygoma is well demonstrated on this projection and if fractured gives a clue to the presence of associated facial injury

Centre:- In the mid-line, 5 cms above the glabella, with the tube angled 30⁰ towards the feet.

Accident Technique

When the patient is brought to the x-ray department with head injuries, it is inadvisable to turn the patient’s head.

The patient should be examined in the supine position.

lateral

• The patient lies supine. The head is raised on a radiolucent pad.

A cassette and stationary grid are parallel to the sagittal plane.

The tube is turned so that the horizontal beam is at right angles to the cassette and grid.

As it is common for the cervical spine to be also injured in an accident involving the skull, the cassette should be placed so the upper cervical spine are included on the film.

Fronto-occipital

The patient remains supine .

The head is adjusted carefully to bring the sagittal plane and radiographic base line to 90⁰ to the film.

The x-ray tube is vertical and centered above the glabella.

the structure of skull and bone make it

Skull

The skull is made up of several bones that are fused together to form a protective structure around the brain and support the face. It has two main parts Cranial bones; These bones protect the brain.They are 8 cranial bones:

• Frontal bone: form the forehead and upper part of the eye socket.

Parietal bones(2): form the top and upper sides of the skull Occipital bone: form the back and the base of the skull and contain formen magnum where the spinal cord enter the skull.

Temporal bone (2): found below the parietal bones; They house structure of the ears.

Sphenoid Bones : found at the base of the skull in front of the temporal bones. Help form the eye socket.

Ethmoid bones: form part of nasal cavity and eye socket.

maxilla[2];upper jaws

• Mandible; lower jaws, the only movable bones of the skull
• Zygomatic bones; cheekbones
• Nasal bones; bridge of nose
• Palatine bones; forms the back of the hard plate
• Lacrimal bones; small bones forming party of the eye socket
• Inferior nasal conchae[2];party of the nasal cavity structure
• Vomer; form the part of nasal septum

2.Facial bones

Skull

These bones are joined together by sutures, which are immovable joints that fuse the bones tightly. This structure helps protect the brain and forms a rigid framework for the chewing, facial expression and other function

FUNCTIONS OF THE SKULL

• Protection of the brain
• Support for sensory organs
• Attachment of muscle
• Shape and structure of the head

Respiratory and airway function.

… The skulls complex structure plays a central role in protection delicate tissues and facilitating essential bodily function.